MultispeQ Beta: a tool for large-scale plant phenotyping connected to the open PhotosynQ network

Discovering novel genomic regions explaining adaptation of bread wheat to conservation agriculture through GWAS

To sustainably increase wheat yield to meet the growing world population's food demand in the face of climate change, Conservation Agriculture (CA) is a promising approach. Still, there is a lack of genomic studies investigating the genetic basis of crop adaptation to CA. To dissect the genetic architecture of 19 morpho-physiological traits that could be involved in the enhanced adaptation and performance of genotypes under CA, we performed GWAS to identify MTAs under four contrasting production regimes viz., conventional tillage timely sown (CTTS), conservation agriculture timely sown (CATS), conventional tillage late sown (CTLS) and conservation agriculture late sown (CALS) using an association panel of 183 advanced wheat breeding lines along with 5 checks. Traits like Phi2 (Quantum yield of photosystem II; CATS:0.37, CALS: 0.31), RC (Relative chlorophyll content; CATS:55.51, CALS: 54.47) and PS1 (Active photosystem I centers; CATS:2.45, CALS: 2.23) have higher mean values in CA compared to CT under both sowing times. GWAS identified 80 MTAs for the studied traits across four production environments. The phenotypic variation explained (PVE) by these QTNs ranged from 2.15 to 40.22%. Gene annotation provided highly informative SNPs associated with Phi2, NPQ (Quantum yield of non-photochemical quenching), PS1, and RC which were linked with genes that play crucial roles in the physiological adaptation under both CA and CT. A highly significant SNP AX94651261 (9.43% PVE) was identified to be associated with Phi2, while two SNP markers AX94730536 (30.90% PVE) and AX94683305 (16.99% PVE) were associated with NPQ. Identified QTNs upon validation can be used in marker-assisted breeding programs to develop CA adaptive genotypes.

Do Lignin Nanoparticles Pave the Way for a Sustainable Nanocircular Economy? Biostimulant Effect of Nanoscaled Lignin in Tomato Plants

Agriculture has a significant environmental impact and is simultaneously called to major challenges, such as responding to the need to develop more sustainable cropping systems with higher productivity. In this context, the present study aimed to obtain lignin nanoparticles (LNs) from pomace, a waste product of the olive oil chain, to be used as a nanobiostimulant in tomato plants. The biostimulant effect of this biopolymer is known, but its reduction to nanometer size can emphasize this property. Tomato plants were subjected to different LN dosages (25, 50, and 100 mg L-1) by foliar application, and inductive effects on photosynthetic machinery, aerial and root biomass production, and root morphology were observed. The treated plants showed increased efficiency in catching and using light, while they reduced the fraction dissipated as heat or potentially toxic to cells for the possibility of creating reactive oxygen species (ROS). Finally, this benefit was matched by increased pigment content and a stimulatory action on the content of nitrogen (NBI) and antioxidant substances such as flavonoids. In conclusion, the present study broadens the horizon of substances with biostimulant action by demonstrating the validity and efficacy of nanobiostimulants obtained from biological residues from the olive oil production chain.

Implementation of theoretical non-photochemical quenching (NPQ(T)) to investigate NPQ of chickpea under drought stress with High-throughput Phenotyping

Non-photochemical quenching (NPQ) is a protective mechanism for dissipating excess energy generated during photosynthesis in the form of heat. The accelerated relaxation of the NPQ in fluctuating light can lead to an increase in the yield and dry matter productivity of crops. Since the measurement of NPQ is time-consuming and requires specific light conditions, theoretical NPQ (NPQ(T)) was introduced for rapid estimation, which could be suitable for High-throughput Phenotyping. We investigated the potential of NPQ(T) to be used for testing plant genetic resources of chickpea under drought stress with non-invasive High-throughput Phenotyping complemented with yield traits. Besides a high correlation between the hundred-seed-weight and the Estimated Biovolume, significant differences were observed between the two types of chickpea desi and kabuli for Estimated Biovolume and NPQ(T). Desi was able to maintain the Estimated Biovolume significantly better under drought stress. One reason could be the effective dissipation of excess excitation energy in photosystem II, which can be efficiently measured as NPQ(T). Screening of plant genetic resources for photosynthetic performance could take pre-breeding to a higher level and can be implemented in a variety of studies, such as here with drought stress or under fluctuating light in a High-throughput Phenotyping manner using NPQ(T).

Integration of transcriptomics, metabolomics, and hormone analysis revealed the formation of lesion spots inhibited by GA and CTK was related to cell death and disease resistance in bread wheat (Triticum aestivum L.)

BACKGROUND

Wheat is one of the important grain crops in the world. The formation of lesion spots related to cell death is involved in disease resistance, whereas the regulatory pathway of lesion spot production and resistance mechanism to pathogens in wheat is largely unknown.

RESULTS

In this study, a pair of NILs (NIL-Lm5W and NIL-Lm5M) was constructed from the BC1F4 population by the wheat lesion mimic mutant MC21 and its wild genotype Chuannong 16. The formation of lesion spots in NIL-Lm5M significantly increased its resistance to stripe rust, and NIL-Lm5M showed superiour agronomic traits than NIL-Lm5W under stripe rust infection.Whereafter, the NILs were subjected to transcriptomic (stage N: no spots; stage S, only a few spots; and stage M, numerous spots), metabolomic (stage N and S), and hormone analysis (stage S), with samples taken from normal plants in the field. Transcriptomic analysis showed that the differentially expressed genes were enriched in plant-pathogen interaction, and defense-related genes were significantly upregulated following the formation of lesion spots. Metabolomic analysis showed that the differentially accumulated metabolites were enriched in energy metabolism, including amino acid metabolism, carbohydrate metabolism, and lipid metabolism. Correlation network diagrams of transcriptomic and metabolomic showed that they were both enriched in energy metabolism. Additionally, the contents of gibberellin A7, cis-Zeatin, and abscisic acid were decreased in leaves upon lesion spot formation, whereas the lesion spots in NIL-Lm5M leaves were restrained by spaying GA and cytokinin (CTK, trans-zeatin) in the field.

CONCLUSION

The formation of lesion spots can result in cell death and enhance strip rust resistance by protein degradation pathway and defense-related genes overexpression in wheat. Besides, the formation of lesion spots was significantly affected by GA and CTK. Altogether, these results may contribute to the understanding of lesion spot formation in wheat and laid a foundation for regulating the resistance mechanism to stripe rust.

Thermal imaging can reveal variation in stay-green functionality of wheat canopies under temperate conditions

Canopy temperature (CT) is often interpreted as representing leaf activity traits such as photosynthetic rates, gas exchange rates, or stomatal conductance. This interpretation is based on the observation that leaf activity traits correlate with transpiration which affects leaf temperature. Accordingly, CT measurements may provide a basis for high throughput assessments of the productivity of wheat canopies during early grain filling, which would allow distinguishing functional from dysfunctional stay-green. However, whereas the usefulness of CT as a fast surrogate measure of sustained vigor under soil drying is well established, its potential to quantify leaf activity traits under high-yielding conditions is less clear. To better understand sensitivity limits of CT measurements under high yielding conditions, we generated within-genotype variability in stay-green functionality by means of differential short-term pre-anthesis canopy shading that modified the sink:source balance. We quantified the effects of these modifications on stay-green properties through a combination of gold standard physiological measurements of leaf activity and newly developed methods for organ-level senescence monitoring based on timeseries of high-resolution imagery and deep-learning-based semantic image segmentation. In parallel, we monitored CT by means of a pole-mounted thermal camera that delivered continuous, ultra-high temporal resolution CT data. Our results show that differences in stay-green functionality translate into measurable differences in CT in the absence of major confounding factors. Differences amounted to approximately 0.8°C and 1.5°C for a very high-yielding source-limited genotype, and a medium-yielding sink-limited genotype, respectively. The gradual nature of the effects of shading on CT during the stay-green phase underscore the importance of a high measurement frequency and a time-integrated analysis of CT, whilst modest effect sizes confirm the importance of restricting screenings to a limited range of morphological and phenological diversity.

Morpho-physiological and yield traits for selection of drought tolerant Urochloa grass ecotypes

Drought has become more recurrent and causes a substantial decline in forage yields leading to strain on feed resources for livestock production. This has intensified the search for drought-tolerant forages to promote sustainable livestock production. The objective of this study was to identify drought-tolerant Urochloa grasses and to discern their morpho-physiological and yield traits to water stress as well as the relationship between these traits and indices of drought resistance. The results showed that the ecotypes, water regimes and their interaction significantly influenced all the studied morpho-physiological and yield traits. There was a significant decrease in plant height, number of leaves and tillers, dry matter yield, relative water content, photosystem II and efficiency of photosystem II with an increase in non-photochemical quenching. The principal component analysis revealed that the performance of Urochloa grass ecotypes was different under water sufficient (WS) and water deficit conditions. Drought tolerance indicators (mean productivity, geometric mean productivity, tolerance index and stress tolerance index) were most effective in identifying Urochloa ecotypes with high biomass production under both water deficient and WS conditions. Ecotypes K17, K7, Kisii, Busia and Kakamega were the most drought tolerant, Basilisk, K6, K10, K19 and Toledo were moderately tolerant whereas, CIAT6385, CIAT16449, K13, K5 and K9 were drought sensitive. The five drought-tolerant Urochloa ecotypes should be tested for sustainable biomass production under field conditions and used in breeding programmes to develop high-yielding drought-tolerant varieties.

Genotype-specific nonphotochemical quenching responses to nitrogen deficit are linked to chlorophyll a to b ratios

Non-photochemical quenching (NPQ) protects plants from photodamage caused by excess light energy. Substantial variation in NPQ has been reported among different genotypes of the same species. However, comparatively little is known about how environmental perturbations, including nutrient deficits, impact natural variation in NPQ kinetics. Here, we analyzed a natural variation in NPQ kinetics of a diversity panel of 225 maize (Zea mays L.) genotypes under nitrogen replete and nitrogen deficient field conditions. Individual maize genotypes from a diversity panel exhibited a range of changes in NPQ in response to low nitrogen. Replicated genotypes exhibited consistent responses across two field experiments conducted in different years. At the seedling and pre-flowering stages, a similar portion of the genotypes (∼33%) showed decrease, no-change or increase in NPQ under low nitrogen relative to control. Genotypes with increased NPQ under low nitrogen also showed greater reductions in dry biomass and photosynthesis than genotypes with stable NPQ when exposed to low nitrogen conditions. Maize genotypes where an increase in NPQ was observed under low nitrogen also exhibited a reduction in the ratio of chlorophyll a to chlorophyll b. Our results underline that since thermal dissipation of excess excitation energy measured via NPQ helps to balance the energy absorbed with energy utilized, the NPQ changes are the reflection of broader molecular and biochemical changes which occur under the stresses such as low soil fertility. Here, we have demonstrated that variation in NPQ kinetics resulted from genetic and environmental factors, are not independent of each other. Natural genetic variation controlling plastic responses of NPQ kinetics to environmental perturbation increases the likelihood it will be possible to optimize NPQ kinetics in crop plants for different environments.

Tomato and mini-cucumber tolerance to photoperiodic injury involves photorespiration and the engagement of nighttime cyclic electron flow from dynamic LEDs

Controlled environment agriculture (CEA) is critical for achieving year-round food security in many regions of the world. CEA is a resource-intensive endeavor, with lighting consuming a large fraction of the energy. To lessen the burden on the grid and save costs, an extended photoperiod strategy can take advantage of off-peak time-of-day options from utility suppliers. However, extending the photoperiod limits crop production morphologically and physiologically if pushed too long. Here, we present a continuous-light dynamic light-emitting diode (LED) strategy (involving changes in spectra, intensity, and timing), that overcomes these limitations. We focused on tomato, a well described photoperiodic injury-sensitive species, and mini-cucumber, a photoperiodic injury-tolerant species to first assess morphological responses under control (16-h photoperiod, unchanging spectrum), constant (24-h photoperiod, unchanging spectrum), and two variations of a dynamic LED strategy, dynamic 1 (16-h "day", 3-h "peak", 8-h "night" spectra) and dynamic 2 (20-h "day", 5-h "peak", 4-h "night" spectra). Next, we tested the hypothesis of photorespiration's involvement in photoperiodic injury by using a leaf gas exchange coupled with chlorophyll fluorescence protocol. We further explored Adenosine triphosphate (ATP): Nicotinamide adenine dinucleotide phosphate (NADPH) ratio supply/demand responses by probing photosynthetic electron flow and proton flow with the MultispeQ instrument. We found canopy architecture can be tuned by minor variations of the same dynamic LED strategy, and we highlight dynamic 1 as the optimal choice for both tomato and mini-cucumber as it improved biomass/architecture and first-yield, respectively. A central discovery was that dynamic 1 had a significantly higher level of photorespiration than control, for both species. Unexpectedly, photorespiration was comparable between species under the same treatments, except under constant. However, preliminary data on a fully tolerant tomato genotype grown under constant treatment upregulated photorespiration similar to mini-cucumber. These results suggest that photoperiodic injury tolerance involves a sustained higher level of photorespiration under extended photoperiods. Interestingly, diurnal MultispeQ measurements point to the importance of cyclic electron flow at subjective nighttime that may also partially explain why dynamic LED strategies mitigate photoperiodic injury. We propose an ontology of photoperiodic injury involving photorespiration, triose phosphate utilization, peroxisomal H2O2-catalase balance, and a circadian external coincidence model of sensitivity that initiates programmed cell death.

Exploring the mechanism of transformation in Acacia nilotica (Linn.) triggered by colchicine seed treatment

BACKGROUND

Acacia nilotica Linn. is a widely distributed tree known for its applications in post-harvest and medicinal horticulture. However, its seed-based growth is relatively slow. Seed is a vital component for the propagation of A. nilotica due to its cost-effectiveness, genetic diversity, and ease of handling. Colchicine, commonly used for polyploidy induction in plants, may act as a pollutant at elevated levels. Its optimal concentration for Acacia nilotica's improved growth and development has not yet been determined, and the precise mechanism underlying this phenomenon has not been established. Therefore, this study investigated the impact of optimized colchicine (0.07%) seed treatment on A. nilotica's morphological, anatomical, physiological, fluorescent, and biochemical attributes under controlled conditions, comparing it with a control.

RESULTS

Colchicine seed treatment significantly improved various plant attributes compared to control. This included increased shoot length (84.6%), root length (53.5%), shoot fresh weight (59.1%), root fresh weight (42.8%), shoot dry weight (51.5%), root dry weight (40%), fresh biomass (23.6%), stomatal size (35.9%), stomatal density (41.7%), stomatal index (51.2%), leaf thickness (11 times), leaf angle (2.4 times), photosynthetic rate (40%), water use efficiency (2.2 times), substomatal CO2 (36.6%), quantum yield of photosystem II (13.1%), proton flux (3.1 times), proton conductivity (2.3 times), linear electron flow (46.7%), enzymatic activities of catalase (25%), superoxide dismutase (33%), peroxidase (13.5%), and ascorbate peroxidase (28%), 2,2-diphenyl-1-picrylhydrazyl-radical scavenging activities(23%), total antioxidant capacity (59%), total phenolic (23%), and flavonoid content (37%) with less number of days to 80% germination (57.1%), transpiration rate (53.9%), stomatal conductance (67.1%), non-photochemical quenching (82.8%), non-regulatory energy dissipation (24.3%), and H2O2 (25%) and O-2 levels (30%).

CONCLUSION

These findings elucidate the intricate mechanism behind the morphological, anatomical, physiological, fluorescent, and biochemical transformative effects of colchicine seed treatment on Acacia nilotica Linn. and offer valuable insights for quick production of A. nilotica's plants with modification and enhancement from seeds through an eco-friendly approach.

Rejuvenating potato growth and yield in challenging semiarid and saline sandy Cholistan: harnessing PGPB-coated N and P application strategies

BACKGROUND

Potato serves as a major non-cereal food crop and income source for small-scale growers in Punjab, Pakistan. Unfortunately, improper fertilization practices have led to low crop yields, worsened by challenging environmental conditions and poor groundwater quality in the Cholistan region. To address this, we conducted an experiment to assess the impact of two fertilizer application approaches on potato cv. Barna using plant growth-promoting bacteria (PGPB) coated biofertilizers. The first approach, termed conventional fertilizer application (CFA), involved four split applications of PGPB-coated fertilizers at a rate of 100:75 kg acre-1 (N and P). The second, modified fertilizer application (MFA), employed nine split applications at a rate of 80:40 kg acre-1.

RESULTS

The MFA approach significantly improved various plant attributes compared to the CFA. This included increased plant height (28%), stem number (45%), leaf count (46%), leaf area index (36%), leaf thickness (three-folds), chlorophyll content (53%), quantum yield of photosystem II (45%), photosynthetically active radiations (56%), electrochromic shift (5.6%), proton flux (24.6%), proton conductivity (71%), linear electron flow (72%), photosynthetic rate (35%), water use efficiency (76%), and substomatal CO2 (two-folds), and lowered non-photochemical quenching (56%), non-regulatory energy dissipation (33%), transpiration rate (59%), and stomatal conductance (70%). Additionally, the MFA approach resulted in higher tuber production per plant (21%), average tuber weight (21.9%), tuber diameter (24.5%), total tuber yield (29.1%), marketable yield (22.7%), seed-grade yield (9%), specific gravity (9.6%), and soluble solids (7.1%). It also reduced undesirable factors like goli and downgrade yields by 57.6% and 98.8%, respectively. Furthermore, plants under the MFA approach exhibited enhanced nitrogen (27.8%) and phosphorus uptake (40.6%), with improved N (26.1%) and P uptake efficiency (43.7%) compared to the CFA approach.

CONCLUSION

The use of PGPB-coated N and P fertilizers with a higher number of splits at a lower rate significantly boosts potato production in the alkaline sandy soils of Cholistan.

New Perspective on the Use of α-Bisabolol for Weed Control

The indiscriminate use of synthetic herbicides reduces its effectiveness. Bioherbicides produced with metabolites emerge as an alternative to managing weeds. We aimed to analyze the phytotoxic potential of the essential oil of Vanillosmopsis arborea (EOVA) and the α-bisabolol molecule, its main component. We evaluated the effects of EOVA and α-bisabolol at different concentrations on the germination, growth, antioxidant metabolism, and photosynthesis of different species. EOVA and α-bisabolol showed promising phytotoxic effects on the germination and initial growth of the weed Senna occidentalis, inhibiting the activity of the antioxidant enzymes and increasing lipid peroxidation. α-Bisabolol reduced the weed seedling growth by inducing oxidative stress, which suggests a greater role in postemergence. Moreover, in the weed postemergence, both EOVA and α-bisabolol caused damage in the shoots, reduced the chlorophyll content, and increased lipid peroxidation besides reducing photosynthesis in S. occidentalis. Overall, we suggest the promising action of α-bisabolol and EOVA as bioherbicides for weed control.

Photoautotrophic cultivation of a Chlamydomonas reinhardtii mutant with zeaxanthin as the sole xanthophyll

BACKGROUND

Photosynthetic microalgae are known for their sustainable and eco-friendly potential to convert carbon dioxide into valuable products. Nevertheless, the challenge of self-shading due to high cell density has been identified as a drawback, hampering productivity in sustainable photoautotrophic mass cultivation. To address this issue, mutants with altered pigment composition have been proposed to allow a more efficient light diffusion but further study on the role of the different pigments is still needed to correctly engineer this process.

RESULTS

We here investigated the Chlamydomonas reinhardtii Δzl mutant with zeaxanthin as the sole xanthophyll. The Δzl mutant displayed altered pigment composition, characterized by lower chlorophyll content, higher chlorophyll a/b ratio, and lower chlorophyll/carotenoid ratio compared to the wild type (Wt). The Δzl mutant also exhibited a significant decrease in the light-harvesting complex II/Photosystem II ratio (LHCII/PSII) and the absence of trimeric LHCIIs. This significantly affects the organization and stability of PSII supercomplexes. Consequently, the estimated functional antenna size of PSII in the Δzl mutant was approximately 60% smaller compared to that of Wt, and reduced PSII activity was evident in this mutant. Notably, the Δzl mutant showed impaired non-photochemical quenching. However, the Δzl mutant compensated by exhibiting enhanced cyclic electron flow compared to Wt, seemingly offsetting the impaired PSII functionality. Consequently, the Δzl mutant achieved significantly higher cell densities than Wt under high-light conditions.

CONCLUSIONS

Our findings highlight significant changes in pigment content and pigment-protein complexes in the Δzl mutant compared to Wt, resulting in an advantage for high-density photoautotrophic cultivation. This advantage is attributed to the decreased chlorophyll content of the Δzl mutant, allowing better light penetration. In addition, the accumulated zeaxanthin in the mutant could serve as an antioxidant, offering protection against reactive oxygen species generated by chlorophylls.

Computer vision for plant pathology: A review with examples from cocoa agriculture

Plant pathogens can decimate crops and render the local cultivation of a species unprofitable. In extreme cases this has caused famine and economic collapse. Timing is vital in treating crop diseases, and the use of computer vision for precise disease detection and timing of pesticide application is gaining popularity. Computer vision can reduce labour costs, prevent misdiagnosis of disease, and prevent misapplication of pesticides. Pesticide misapplication is both financially costly and can exacerbate pesticide resistance and pollution. Here, we review the application and development of computer vision and machine learning methods for the detection of plant disease. This review goes beyond the scope of previous works to discuss important technical concepts and considerations when applying computer vision to plant pathology. We present new case studies on adapting standard computer vision methods and review techniques for acquiring training data, the use of diagnostic tools from biology, and the inspection of informative features. In addition to an in-depth discussion of convolutional neural networks (CNNs) and transformers, we also highlight the strengths of methods such as support vector machines and evolved neural networks. We discuss the benefits of carefully curating training data and consider situations where less computationally expensive techniques are advantageous. This includes a comparison of popular model architectures and a guide to their implementation.

Heat and salinity stress on the African eggplant F1 Djamba, a Kumba cultivar

Climate change is expected to increase soil salinity and heat-wave intensity, duration, and frequency. These stresses, often present in combination, threaten food security as most common crops do not tolerate them. The African eggplant (Solanum aethiopicum L.) is a nutritious traditional crop found in sub-Saharan Africa and adapted to local environments. Its wider use is, however, hindered by the lack of research on its tolerance. This project aimed to describe the effects of salinity (100 mM NaCl solution) combined with elevated temperatures (27/21°C, 37/31°C, and 42/36°C). High temperatures reduced leaf biomass while cell membrane stability was reduced by salinity. Chlorophyll levels were boosted by salinity only at the start of the stress with only the different temperatures significantly impacted the levels at the end of the experiment. Other fluorescence parameters such as maximum quantum yield and non-photochemical quenching were only affected by the temperature change. Total antioxidants were unchanged by either stress despite a decrease of phenols at the highest temperature. Leaf sodium concentration was highly increased by salinity but phosphorus and calcium were unchanged by this stress. These findings shed new light on the tolerance mechanisms of the African eggplant under salinity and heat. Further research on later developmental stages is needed to understand its potential in the field in areas affected by these abiotic stresses.

Precise colocalization of sorghum's major chilling tolerance locus with Tannin1 due to tight linkage drag rather than antagonistic pleiotropy

Chilling tolerance in crops can increase resilience through longer growing seasons, drought escape, and nitrogen use efficiency. In sorghum (Sorghum bicolor [L.] Moench), breeding for chilling tolerance has been stymied by coinheritance of the largest-effect chilling tolerance locus, qSbCT04.62, with the major gene underlying undesirable grain proanthocyanidins, WD40 transcriptional regulator Tannin1. To test if this coinheritance is due to antagonistic pleiotropy of Tannin1, we developed and studied near-isogenic lines (NILs) carrying chilling tolerant haplotypes at qCT04.62. Whole-genome sequencing of the NILs revealed introgressions spanning part of the qCT04.62 confidence interval, including the Tannin1 gene and an ortholog of Arabidopsis cold regulator CBF/DREB1G. Segregation pattern of grain tannin in NILs confirmed the presence of wildtype Tannin1 and the reconstitution of a functional MYB-bHLH-WD40 regulatory complex. Low-temperature germination did not differ between NILs, suggesting that Tannin1 does not modulate this component of chilling tolerance. Similarly, NILs did not differ in seedling growth rate under either of two contrasting controlled environment chilling scenarios. Finally, while the chilling tolerant parent line had notably different photosynthetic responses from the susceptible parent line - including greater non-photochemical quenching before, during, and after chilling - the NIL responses match the susceptible parent. Thus, our findings suggest that tight linkage drag, not pleiotropy, underlies the precise colocalization of Tan1 with qCT04.62 and the qCT04.62 quantitative trait nucleotide lies outside the NIL introgressions. Breaking linkage at this locus should advance chilling tolerance breeding in sorghum and the identification of a novel chilling tolerance regulator.

Phenotyping photosynthesis: yes we can

This article comments on:

Keller B, Soto J, Steier A, Portilla-Benavides AE, Raatz B, Studer B, Walter A, Muller O, Urban MO. 2024. Linking photosynthesis and yield reveals a strategy to improve light use efficiency in a climbing bean breeding population. Journal of Experimental Botany 75, 901–916.

Linking photosynthesis and yield reveals a strategy to improve light use efficiency in a climbing bean breeding population

Photosynthesis drives plant physiology, biomass accumulation, and yield. Photosynthetic efficiency, specifically the operating efficiency of PSII (Fq'/Fm'), is highly responsive to actual growth conditions, especially to fluctuating photosynthetic photon fluence rate (PPFR). Under field conditions, plants constantly balance energy uptake to optimize growth. The dynamic regulation complicates the quantification of cumulative photochemical energy uptake based on the intercepted solar energy, its transduction into biomass, and the identification of efficient breeding lines. Here, we show significant effects on biomass related to genetic variation in photosynthetic efficiency of 178 climbing bean (Phaseolus vulgaris L.) lines. Under fluctuating conditions, the Fq'/Fm' was monitored throughout the growing period using hand-held and automated chlorophyll fluorescence phenotyping. The seasonal response of Fq'/Fm' to PPFR (ResponseG:PPFR) achieved significant correlations with biomass and yield, ranging from 0.33 to 0.35 and from 0.22 to 0.31 in two glasshouse and three field trials, respectively. Phenomic yield prediction outperformed genomic predictions for new environments in four trials under different growing conditions. Investigating genetic control over photosynthesis, one single nucleotide polymorphism (Chr09_37766289_13052) on chromosome 9 was significantly associated with ResponseG:PPFR in proximity to a candidate gene controlling chloroplast thylakoid formation. In conclusion, photosynthetic screening facilitates and accelerates selection for high yield potential.

Radiation Hormesis in Barley Manifests as Changes in Growth Dynamics Coordinated with the Expression of PM19L-like, CML31-like, and AOS2-like

The stimulation of growth and development of crops using ionising radiation (radiation hormesis) has been reported by many research groups. However, specific genes contributing to the radiation stimulation of plant growth are largely unknown. In this work, we studied the impact of the low-dose γ-irradiation of barley seeds on the growth dynamics and gene expression of eight barley cultivars in a greenhouse experiment. Our findings confirmed that candidate genes of the radiation growth stimulation, previously established in barley seedlings (PM19L-like, CML31-like, and AOS2-like), are significant in radiation hormesis throughout ontogeny. In γ-stimulated cultivars, the expression of these genes was aligned with the growth dynamics, yield parameters, and physiological conditions of plants. We identified contrasting cultivars for future gene editing and found that the γ-stimulated cultivar possessed some specific abiotic stress-responsive elements in the promotors of candidate genes, possibly revealing a new level of radiation hormesis effect execution. These results can be used in creating new productive barley cultivars, ecological toxicology of radionuclides, and eustress biology studies.

Photosynthetic mechanisms underlying NaCl-induced salinity tolerance in rice (Oryza sativa)

BACKGROUND

Salinity stress is an environmental constraint that normally develops concurrently under field conditions, resulting in drastic limitation of rice plant growth and grain productivity. The objective of this study was to explore the alleviating effects of NaCl pre-treatment on rice seedlings as well as the salt tolerance mechanisms by evaluating morph-physiological traits.

RESULTS

Variety Huanghuazhan, either soaked in distilled water or 25 mg/L Prohexadione calcium (Pro-Ca), were first hardened with varying concentrations of NaCl solutions (0 and 50 mM NaCl), and then subjected to varying degrees of salt stress (0 and 100 mM NaCl), indicated by S0, S1, S2 and S3, respectively. Growth analysis suggested that NaCl-pretreatment improved the root/shoot ratio in water-soaked rice plant at DAP 0. Data related to the reaction center density, photosynthetic electron transport efficiency, trapping efficiency were compared before (CK) using performance Index (PIabs). Compared to S2 (Pro-Ca-S2) treatment, PIabs did not show any difference with plants pre-treated with NaCl (S3 or Pro-Ca-S3). Rather than PIabs, significant difference was found in photosynthetic electron transport efficiency (ΨEo). The ΨEo value in Pro-S2 was significantly lowered as compared to Pro-S3 treatment at DAP 7, and the decrease rate was about 6.5%. Correlation analysis indicated leaf PIabs was weak correlated with plant biomass while the quantum yield for reduction of the PSI end electron acceptors, trapped energy flux per reaction center and PSII antenna size displayed strong positive correlation with biomass. Additional analysis revealed that 100 mM NaCl significantly reduced leaf linear electron flux under low-light conditions, regardless of whether seedlings had been pre-treated with 50 mM NaCl or not.

CONCLUSIONS

NaCl-induced salt tolerance was related to the robust photosynthetic machinery.

Effect of copper oxide and zinc oxide nanoparticles on photosynthesis and physiology of Raphanus sativus L. under salinity stress

The study evaluates the impact of two metal oxide nanoparticles: copper oxide (CuO) and zinc oxide (ZnO) on the growth and physiology of Raphanus sativus L. (radish) under salinity stress. Fifteen days old seedlings of R. sativus were subjected to different concentrations of salt stress (0 mM, 150 mM, and 300 mM NaCl) alone and in interaction with 100 mgL-1 metal oxide nanoparticle treatments (CuO and ZnO NPs via foliar spray) for 15 days. The results confirmed the severe effects of salinity stress on the growth and physiology of radish plants by decreasing nutrient uptake, leaf area, and photosystems photochemistry and by increasing proline accumulation, anthocyanin, flavonoids content, and antioxidant enzyme activities which is directly linked to increased oxidative stress. The foliar application of CuO and ZnO NPs alleviated the adverse effects of salt stress on radish plants, as indicated by improving these attributes. Foliar spray of ZnO NPs was found efficient in improving the leaf area, photosynthetic electron transport rate, the PSII quantum yield, proton conductance and mineral content in radish plants under NaCl stress. Besides, ZnO NPs decreased the NaCl-induced oxidative stress by declining proline, anthocyanin, and flavonoids contents and enzymatic activities such as superoxide dismutase (SOD), ascorbate peroxidase (APX) and guaiacol peroxidase (GOPX). Thus, our study revealed that ZnO NPs are more effective and have beneficial effects over CuO NPs in promoting growth and reducing the adverse effects of NaCl stress in radish plants.

Tools for Measuring Photosynthesis at Different Scales

Measurements of in vivo photosynthesis are powerful tools that probe the largest fluxes of carbon and energy in an illuminated leaf, but often the specific techniques used are so varied and specialized that it is difficult for researchers outside the field to select and perform the most useful assays for their research questions. The goal of this chapter is to provide a broad overview of the current tools available for the study of photosynthesis, both in vivo and in vitro, so as to provide a foundation for selecting appropriate techniques, many of which are presented in detail in subsequent chapters. This chapter will also organize current methods into a comparative framework and provide examples of how they have been applied to research questions of broad agronomical, ecological, or biological importance. This chapter closes with an argument that the future of in vivo measurements of photosynthesis lies in the ability to use multiple methods simultaneously and discusses the benefits of this approach to currently open physiological questions. This chapter, combined with the relevant methods chapters, could serve as a laboratory course in methods in photosynthesis research or as part of a more comprehensive laboratory course in general plant physiology methods.

Quinoa panicles contribute to carbon assimilation and are more tolerant to salt stress than leaves

Contribution of inflorescences to seed filling have attracted great attention given the resilience of this photosynthetic organ to stressful conditions. However, studies have been almost exclusively focused to small grain cereals. In this study, we aimed to explore these responses in quinoa, as a climate resilient seed crop of elevated economic and nutritious potential. We compared the physiological and metabolic performance of panicles and leaves of two quinoa cultivars growing under contrasting salinity levels. Plant growth, photosynthetic and transpiratory gas exchange and chlorophyll fluorescence were monitored in inflorescences and leaves throughout the experiment. At flowering stage, young and mature leaves and panicles were sampled for key metabolic markers related to carbon, nitrogen and secondary metabolisms. When subjected to salt stress, panicles showed attenuated declines on photosynthesis, water use, pigments, amino acids, and protein levels as compared to leaves. In fact, the assimilation rates, together with a high hexose content evidenced an active photosynthetic role of the panicle under optimal and salt stress conditions. Moreover, we also found significant genotypic variability for physiological and metabolic traits of panicles and leaves, which emphasizes the study of genotype-dependent stress responses at the whole plant level. We conclude that quinoa panicles are less affected by salt stress than leaves, which encourages further research and exploitation of this organ for crop improvement and stress resilience considering the high natural diversity.

Mitigating Salinity Stress in Quinoa (Chenopodium quinoa Willd.) with Biochar and Superabsorber Polymer Amendments

In agriculture, soil amendments are applied to improve soil quality by increasing the water retention capacity and regulating the pH and ion exchange. Our study was carried out to investigate the impact of a commercial biochar (Bc) and a superabsorbent polymer (SAP) on the physiological and biochemical processes and the growth performance of Chenopodium quinoa (variety ICBA-5) when exposed to high salinity. Plants were grown for 25 days under controlled greenhouse conditions in pots filled with a soil mixture with or without 3% Bc or 0.2% SAP by volume before the initiation of 27 days of growth in hypersaline conditions, following the addition of 300 mM NaCl. Without the Bc or soil amendments, multiple negative effects of hypersalinity were detected on photosynthetic CO2 assimilation (Anet minus 70%) and on the production of fresh matter from the whole plant, leaves, stems and roots (respectively, 55, 46, 64 and 66%). Moreover, increased generation of reactive oxygen species (ROS) was indicated by higher levels of MDA (plus 142%), antioxidant activities and high proline levels (plus 311%). In the pots treated with 300 mM NaCl, the amendments Bc or SAP improved the plant growth parameters, including fresh matter production (by 10 and 17%), an increased chlorophyll content by 9 and 13% and Anet in plants (by 98 and 115%). Both amendments (Bc and SAP) resulted in significant salinity mitigation effects, decreasing proline and malondialdehyde (MDA) levels whilst increasing both the activity of enzymatic antioxidants and non-enzymatic antioxidants that reduce the levels of ROS. This study confirms how soil amendments can help to improve plant performance and expand the productive range into saline areas.

Synthetic polyploid induction influences morphological, physiological, and photosynthetic characteristics in Melissa officinalis L

Melissa officinalis L., a well-known herb with diverse industrial and ethnopharmacological properties. Although, there has been a significant lack in the breeding attempts of this invaluable herb. This study aimed to enhance the agronomical traits of M. officinalis through in vitro polyploidization. Nodal segments were micropropagated and subjected to oryzalin treatment at concentrations of 20, 40, and 60 mM for 24 and 48 hours. Flow cytometry, chromosome counting, and stomatal characteristics were employed to confirm the ploidy level of the surviving plants. The survival rate of the treated explants decreased exponentially with increasing oryzalin concentration and duration. The highest polyploid induction rate (8%) was achieved with 40 mM oryzalin treatment for 24 hours. The induced tetraploid plants exhibited vigorous growth, characterized by longer shoots, larger leaves, and a higher leaf count. Chlorophyll content and fluorescence parameters elucidated disparities in photosynthetic performance between diploid and tetraploid genotypes. Tetraploid plants demonstrated a 75% increase in average essential oil yield, attributed to the significantly larger size of peltate trichomes. Analysis of essential oil composition in diploid and tetraploid plants indicated the presence of three major components: geranial, neral, and citronellal. While citronellal remained consistent, geranial and neral increased by 11.06% and 9.49%, respectively, in the tetraploid population. This effective methodology, utilizing oryzalin as an anti-mitotic agent for polyploid induction in M. officinalis, resulted in a polyploid genotype with superior morpho-physiological traits. The polyploid lemon balm generated through this method has the potential to meet commercial demands and contribute significantly to the improvement of lemon balm cultivation.

Reduced GSH Acts as a Metabolic Cue of OPDA Signaling in Coregulating Photosynthesis and Defense Activation under Stress

12-oxo-phytodienoic acid (OPDA) is a primary precursor of jasmonates, able to trigger autonomous signaling cascades that activate and fine-tune plant defense responses, as well as growth and development. However, its mechanism of actions remains largely elusive. Here we describe a dual-function messenger of OPDA signaling, reduced glutathione (GSH), that cross-regulates photosynthesis machinery and stress protection/adaptation in concert, optimizing plant plasticity and survival potential. Under stress conditions, the rapid induction of OPDA production stimulates GSH accumulation in the chloroplasts, and in turn leads to protein S-glutathionylation in modulating the structure and function of redox-sensitive enzymes such as 2-cysteine (Cys) peroxiredoxin A (2CPA), a recycler in the water-water cycle. GSH exchanges thiol-disulfides with the resolving CysR175, while donating an electron (e-, H+) to the peroxidatic CysP53, of 2CPA, which revives its reductase activity and fosters peroxide detoxification in photosynthesis. The electron flow protects photosynthetic processes (decreased total non-photochemical quenching, NPQ(T)) and maintains its efficiency (increased photosystem II quantum yield, ΦII). On the other hand, GSH also prompts retrograde signaling from the chloroplasts to the nucleus in adjusting OPDA-responsive gene expressions such as Glutathione S-Transferase 6 (GST6) and GST8, and actuating defense responses against various ecological constraints such as salinity, excess oxidants and light, as well as mechanical wounding. We thus propose that OPDA regulates a unique metabolic switch that interfaces light and defense signaling, where it links cellular and environmental cues to a multitude of plant physiological, e.g., growth, development, recovery, and acclimation, processes.

Identification of quantitative trait loci for drought tolerance in Bukoba/Kijivu Andean mapping population of common bean

KEY MESSAGE

Quantitative Trait Loci "hotspots" for drought tolerance were identified on chromosomes Pv06, Pv07 and Pv10 of common bean. Drought is a major production constraint of common bean (Phaseolus vulgaris L.) worldwide. The objective of this study was to identify the Quantitative Trait Loci (QTL) for drought tolerance in an Andean population of Recombinant Inbred Lines (RILs). A total of 155 F5:7 RILs derived from a cross between Kijivu (drought tolerant) and Bukoba (drought susceptible) were evaluated for drought tolerance in field and pot experiments. Four field experiments were conducted at three locations in Zambia in 2020 and 2021. All field trials were conducted in the dry season under irrigation. The 155 RILs were genotyped with 11,292 SNPs, and composite interval mapping was conducted to identify QTL for drought tolerance. Seed yield for Kijivu under drought stress was consistently higher than for Bukoba across all four field trials. A total of 60 QTL were identified for morphological, agronomic, and physiological traits under drought stress and non-stress conditions. However, the majority of these QTL were specific to drought stress. QTL "hotspots" for drought tolerance were identified on chromosomes Pv06, Pv07, and Pv10. Extensive co-localizations for agronomic and morpho-physiological traits under drought stress were observed at the three drought-tolerance QTL hotspots. Additionally, these three QTL hotspots overlapped with previously identified QTL for drought tolerance, while several others identified QTL are novel. The three identified QTL hotspots could be used in future marker-assisted selection for drought tolerance in common bean.

Influence of Increase in Phosphorus Supply on Agronomic, Phenological, and Physiological Performance of Two Common Bean Breeding Lines Grown in Acidic Soil under High Temperature Stress Conditions

Many common bean (Phaseolus vulgaris L.) plants cultivated in areas of the world with acidic soils exhibit difficulties adapting to low phosphorus (P) availability, along with aluminum (Al) toxicity, causing yield loss. The objective of this study was to evaluate the influence of an increase in P supply level on the agronomic, phenological, and physiological performance of two common bean breeding lines grown in acidic soil, with low fertility and under high temperature conditions, in a screenhouse. A randomized complete block (RCB) design was used under a factorial arrangement (five levels of P × 2 genotypes) for a total of 10 treatments with four replications. The factors considered in the experiment were: (i) five P supply levels (kg ha-1): four levels of P0, P15, P30, and P45 through the application of rock phosphate (RP), and one P level supplied through the application of organic matter (PSOM) corresponding to 25 kg P ha-1 (P25); and (ii) two advanced bean lines (BFS 10 and SEF10). Both bean lines were grown under the combined stress conditions of high temperatures (day and night maximum temperatures of 42.5 °C/31.1 °C, respectively) and acidic soil. By increasing the supply of P, a significant effect was found, indicating an increase in the growth and development of different vegetative organs, as well as physiological efficiency in photosynthesis and photosynthate remobilization, which resulted in higher grain yield in both bean lines evaluated (BFS 10 and SEF10). The adaptive responses of the two bean lines were found to be related to phenological adjustments (days to flowering and physiological maturity; stomatal development), as well as to heat dissipation strategies in the form of heat (NPQ) or unregulated energy (qN) that contributed to greater agronomic performance. We found that, to some extent, increased P supply alleviated the negative effects of high temperature on the growth and development of the reproductive organs of bean lines. Both bean lines (BFS 10 and SEF 10) showed adaptive attributes suited to the combined stress conditions of high temperature and acidic soil, and these two lines can serve as useful parents in a bean breeding program to develop multiple stress tolerant cultivars.

Exploration of chlorophyll fluorescence characteristics gene regulatory in rice (Oryza sativa L.): a genome-wide association study

Chlorophyll content and fluorescence parameters are crucial indicators to evaluate the light use efficiency in rice; however, the correlations among these parameters and the underlying genetic mechanisms remain poorly understood. Here, to clarify these issues, we conducted a genome-wide association study (GWAS) on 225 rice accessions. In the phenotypic and Mendelian randomization (MR) analysis, a weak negative correlation was observed between the chlorophyll content and actual quantum yield of photosystem II (Φ I I ). The phenotypic diversity observed in SPAD, N P Q t , Φ N P Q , and F v / F m among accessions was affected by genetic background. Furthermore, the GWAS identified 78 SNPs and 17 candidate genes significantly associated with SPAD, N P Q t , Φ I I , Φ N P Q , q L and q P . Combining GWAS on 225 rice accessions with transcriptome analysis of two varieties exhibiting distinct fluorescence characteristics revealed two potential candidate genes (Os03g0583000 from Φ I I & q P traits and Os06g0587200 from N P Q t trait), which are respectively associated with peroxisomes, and protein kinase catalytic domains might involve in regulating the chlorophyll content and chlorophyll fluorescence. This study provides novel insights into the correlation among chlorophyll content and fluorescence parameters and the genetic mechanisms in rice, and offers valuable information for the breeding of rice with enhanced photosynthetic efficiency.

Toward commercial applications of LED and laser-induced fluorescence techniques for food identity, quality, and safety monitoring: A review

The assessment of food safety and quality is a matter of paramount importance, especially considering the challenges posed by climate change. Convenient, eco-friendly, and non-destructive techniques have attracted extensive attention in the food industry because they can retain food safety and quality. Fluorescence radiation, the process by which fluorophore emits light upon the absorption of ultraviolet or visible light, offers the advantages of high sensitivity and selectivity. The use of excitation-emission matrix (EEM) has been extensively explored in the food industry, but on-site detection of EEMs remain a challenge. To address this limitation, laser-induced fluorescence (LIF) and light emitting diode-induced fluorescence (LED-IF) have been implemented in many cases to facilitate the transition of fluorescence measurements from the laboratory to commercial applications. This review provides an overview of the application of commercially available LIF/LED-IF devices for non-destructive food measurement and recent studies that focus on the development of LIF/LED-IF devices for commercial applications. These studies were categorized into two stages: the preliminary exploration stage, which emphasizes the selection of an appropriate excitation wavelength based on the combination of EEM and chemometrics, and the pre-application stage, where experiments were conducted on scouting with specific excitation wavelength. Although commercially available devices have emerged in many research fields, only a limited number have been reported for use in the food industry. Future studies should focus on enhancing the diversity of test samples and parameters that can be measured by a single device, exploring the application of LIF techniques for detecting low-concentration substances in food, investigating more quantitative approaches, and developing embedded computing devices.

Recurrent allopolyploidizations diversify ecophysiological traits in marsh orchids (Dactylorhiza majalis s.l.)

Whole-genome duplication has shaped the evolution of angiosperms and other organisms, and is important for many crops. Structural reorganization of chromosomes and repatterning of gene expression are frequently observed in allopolyploids, with physiological and ecological consequences. Recurrent origins from different parental populations are widespread among polyploids, resulting in an array of lineages that provide excellent models to uncover mechanisms of adaptation to divergent environments in early phases of polyploid evolution. We integrate here transcriptomic and ecophysiological comparative studies to show that sibling allopolyploid marsh orchid species (Dactylorhiza, Orchidaceae) occur in different habitats (low nutrient fens vs. meadows with mesic soils) and are characterized by a complex suite of intertwined, pronounced ecophysiological differences between them. We uncover distinct features in leaf elemental chemistry, light-harvesting, photoprotection, nutrient transport and stomata activity of the two sibling allopolyploids, which appear to match their specific ecologies, in particular soil chemistry differences at their native sites. We argue that the phenotypic divergence between the sibling allopolyploids has a clear genetic basis, generating ecological barriers that maintain distinct, independent lineages, despite pervasive interspecific gene flow. This suggests that recurrent origins of polyploids bring about a long-term potential to trigger and maintain functional and ecological diversity in marsh orchids and other groups.

Foliar Selenium Application to Reduce the Induced-Drought Stress Effects in Coffee Seedlings: Induced Priming or Alleviation Effect?

This study aimed to investigate the role of Se supply in improving osmotic stress tolerance in coffee seedlings while also evaluating the best timing for Se application. Five times of Se foliar application were assessed during induced osmotic stress with PEG-6000 using the day of imposing stress as a default, plus two control treatments: with osmotic stress and without Se, and without osmotic stress and Se. Results demonstrated that osmotic stress (OS) promoted mild stress in the coffee plants (ψw from -1.5MPa to -2.5 MPa). Control plants under stress showed seven and five times lower activity of the enzymes GR and SOD compared with the non-stressed ones, and OS was found to further induce starch degradation, which was potentialized by the Se foliar supply. The seedlings that received foliar Se application 8 days before the stress exhibited higher CAT, APX, and SOD than the absolute control (-OS-Se)-771.1%, 356.3%, and 266.5% higher, respectively. In conclusion, previous Se foliar spray is more effective than the Se supply after OS to overcome the adverse condition. On the other hand, the post-stress application seems to impose extra stress on the plants, leading them to reduce their water potential.

Acclimation strategies of the green alga Chlorella vulgaris to different light regimes revealed by physiological and comparative proteomic analyses

Acclimation to different light regimes is at the basis of survival for photosynthetic organisms, regardless of their evolutionary origin. Previous research efforts largely focused on acclimation events occurring at the level of the photosynthetic apparatus and often highlighted species-specific mechanisms. Here, we investigated the consequences of acclimation to different irradiances in Chlorella vulgaris, a green alga that is one of the most promising species for industrial application, focusing on both photosynthetic and mitochondrial activities. Moreover, proteomic analysis of cells acclimated to high light (HL) or low light (LL) allowed identification of the main targets of acclimation in terms of differentially expressed proteins. The results obtained demonstrate photosynthetic adaptation to HL versus LL that was only partially consistent with previous findings in Chlamydomonas reinhardtii, a model organism for green algae, but in many cases similar to vascular plant acclimation events. Increased mitochondrial respiration measured in HL-acclimated cells mainly relied on alternative oxidative pathway dissipating the excessive reducing power produced due to enhanced carbon flow. Finally, proteins involved in cell metabolism, intracellular transport, gene expression, and signaling-including a heliorhodopsin homolog-were identified as strongly differentially expressed in HL versus LL, suggesting their key roles in acclimation to different light regimes.

Early-Stage Detection of Biotic and Abiotic Stress on Plants by Chlorophyll Fluorescence Imaging Analysis

Most agricultural land, as a result of climate change, experiences severe stress that significantly reduces agricultural yields. Crop sensing by imaging techniques allows early-stage detection of biotic or abiotic stress to avoid damage and significant yield losses. Among the top certified imaging techniques for plant stress detection is chlorophyll a fluorescence imaging, which can evaluate spatiotemporal leaf changes, permitting the pre-symptomatic monitoring of plant physiological status long before any visible symptoms develop, allowing for high-throughput assessment. Here, we review different examples of how chlorophyll a fluorescence imaging analysis can be used to evaluate biotic and abiotic stress. Chlorophyll a is able to detect biotic stress as early as 15 min after Spodoptera exigua feeding, or 30 min after Botrytis cinerea application on tomato plants, or on the onset of water-deficit stress, and thus has potential for early stress detection. Chlorophyll fluorescence (ChlF) analysis is a rapid, non-invasive, easy to perform, low-cost, and highly sensitive method that can estimate photosynthetic performance and detect the influence of diverse stresses on plants. In terms of ChlF parameters, the fraction of open photosystem II (PSII) reaction centers (qp) can be used for early stress detection, since it has been found in many recent studies to be the most accurate and appropriate indicator for ChlF-based screening of the impact of environmental stress on plants.

A genotype × environment experiment reveals contrasting response strategies to drought between populations of a keystone species (Artemisia tridentata; Asteraceae)

Western North America has been experiencing persistent drought exacerbated by climate change for over two decades. This extreme climate event is a clear threat to native plant communities. Artemisia tridentata is a keystone shrub species in western North America and is threatened by climate change, urbanization, and wildfire. A drought Genotype × Environment (G × E) experiment was conducted to assess phenotypic plasticity and differential gene expression in A. tridentata. The G × E experiment was performed on diploid A. tridentata seedlings from two populations (one from Idaho, USA and one from Utah, USA), which experience differing levels of drought stress during the summer months. Photosynthetic data, leaf temperature, and gene expression levels were compared between treatments and populations. The Utah population maintained higher photosynthetic rates and photosynthetic efficiency than the Idaho population under drought stress. The Utah population also exhibited far greater transcriptional plasticity than the Idaho population and expressed genes of response pathways distinct from those of the Idaho population. Populations of A. tridentata differ greatly in their drought response pathways, likely due to differences in response pathways that have evolved under distinct climatic regimes. Epigenetic processes likely contribute to the observed differences between the populations.

Systems-level proteomics and metabolomics reveals the diel molecular landscape of diverse kale cultivars

Kale is a group of diverse Brassicaceae species that are nutritious leafy greens consumed for their abundance of vitamins and micronutrients. Typified by their curly, serrated and/or wavy leaves, kale varieties have been primarily defined based on their leaf morphology and geographic origin, despite having complex genetic backgrounds. Kale is a very promising crop for vertical farming due to its high nutritional content; however, being a non-model organism, foundational, systems-level analyses of kale are lacking. Previous studies in kale have shown that time-of-day harvesting can affect its nutritional composition. Therefore, to gain a systems-level diel understanding of kale across its wide-ranging and diverse genetic landscape, we selected nine publicly available and commercially grown kale cultivars for growth under near-sunlight LED light conditions ideal for vertical farming. We then analyzed changes in morphology, growth and nutrition using a combination of plant phenotyping, proteomics and metabolomics. As the diel molecular activities of plants drive their daily growth and development, ultimately determining their productivity as a crop, we harvested kale leaf tissue at both end-of-day (ED) and end-of-night (EN) time-points for all molecular analyses. Our results reveal that diel proteome and metabolome signatures divide the selected kale cultivars into two groups defined by their amino acid and sugar content, along with significant proteome differences involving carbon and nitrogen metabolism, mRNA splicing, protein translation and light harvesting. Together, our multi-cultivar, multi-omic analysis provides new insights into the molecular underpinnings of the diel growth and development landscape of kale, advancing our fundamental understanding of this nutritious leafy green super-food for horticulture/vertical farming applications.

Faster induction of photosynthesis increases biomass and grain yield in glasshouse-grown transgenic Sorghum bicolor overexpressing Rieske FeS

Sorghum is one of the most important crops providing food and feed in many of the world's harsher environments. Sorghum utilizes the C₄ pathway of photosynthesis in which a biochemical carbon-concentrating mechanism results in high CO₂ assimilation rates. Overexpressing the Rieske FeS subunit of the Cytochrome b₆ f complex was previously shown to increase the rate of photosynthetic electron transport and stimulate CO₂ assimilation in the model C₄ plant Setaria viridis. To test whether productivity of C₄ crops could be improved by Rieske overexpression, we created transgenic Sorghum bicolor Tx430 plants with increased Rieske content. The transgenic plants showed no marked changes in abundances of other photosynthetic proteins or chlorophyll content. The steady-state rates of electron transport and CO₂ assimilation did not differ between the plants with increased Rieske abundance and control plants, suggesting that Cytochrome b₆ f is not the only factor limiting electron transport in sorghum at high light and high CO₂ . However, faster responses of non-photochemical quenching as well as an elevated quantum yield of Photosystem II and an increased CO₂ assimilation rate were observed from the plants overexpressing Rieske during the photosynthetic induction, a process of activation of photosynthesis upon the dark-light transition. As a consequence, sorghum with increased Rieske content produced more biomass and grain when grown in glasshouse conditions. Our results indicate that increasing Rieske content has potential to boost productivity of sorghum and other C₄ crops by improving the efficiency of light utilization and conversion to biomass through the faster induction of photosynthesis.

DNA methylation levels of TaP5CS and TaBADH are associated with enhanced tolerance to PEG-induced drought stress triggered by drought priming in wheat

Drought priming is a promising strategy to enhance tolerance to recurred drought in wheat. However, the underlying mechanisms of priming-induced tolerance are far from clear. Here, three different priming intensities (P1D, P2D, P3D) and two varieties with different sensitivities to drought priming were used to investigate the effects and mechanisms of drought priming. Results showed light (P1D) or moderate (P2D) drought priming intensity induced positive effects for the drought sensitive variety (YM16), while high (P3D) priming intensity brought a negative impact on the plant drought resistant. For drought insensitive one (XM33), light priming intensity had no significant effect on tolerance to drought, while moderate or high intensity showed better priming effects. Moderate priming induced higher leaf water potential and also the osmolytes levels. Consistent with the proline and betaine, the related synthetic enzymatic activities, as well as the expression of TaP5CS and TaBADH were higher in P2D in YM16 and P3D in XM33. The contents of proline and betaine showed a positive correlation with activities of SOD, CAT, GR, AsA, and GSH contents, and a negative correlation with O₂^.-, H₂O₂, and MDA contents. Further analysis revealed CG demethylation of ATG-proximal regions in the promoter of TaP5CS and TaBADH were involved in promoting the synthesis of proline and betaine in primed plants. Collectively, these findings demonstrate drought priming effect was variety independent but depended on the priming severity, and demethylation of TaP5CS and TaBADH involved in the accumulation of osmolytes which contribute to the enhanced drought tolerance induced by priming.

Red pigments in autumn leaves of Norway maple do not offer significant photoprotection but coincide with stress symptoms

The reasons behind autumn colors, a striking manifestation of anthocyanin synthesis in plants, are poorly understood. Usually, not all leaves of an anthocyanic plant turn red or only a part of the leaf blade turns red. In the present study, we compared green, red and yellow sections of senescing Norway maple leaves, asking if red pigments offer photoprotection, and if so, whether the protection benefits the senescing tree. Green and senescing maple leaves were illuminated with strong white, green or red light in the absence or presence of lincomycin which blocks photosystem II (PSII) repair. Irrespective of the presence of anthocyanins, senescing leaves showed weaker capacity to repair PSII than green leaves. Furthermore, the rate of photoinhibition of PSII did not significantly differ between red and yellow sections of senescing maple leaves. We also followed pigment contents and photosynthetic reactions in individual leaves, from the end of summer until abscission of the leaf. In maple, red pigments accumulated only during late senescence, but light reactions stayed active until most of the chlorophyll had been degraded. PSII activity was found to be lower and non-photochemical quenching higher in red leaf sections, compared with yellow sections of senescing leaves. Red leaf sections were also thicker. We suggest that the primary function of anthocyanin synthesis is not to protect senescing leaves from excess light but to dispose of carbohydrates. This would relieve photosynthetic control, allowing the light reactions to produce energy for nutrient translocation at the last phase of autumn senescence when carbon skeletons are no longer needed.

The impact of growth at elevated [CO2] on stomatal anatomy and behavior differs between wheat species and cultivars

The ability of plants to respond to changes in the environment is crucial to their survival and reproductive success. The impact of increasing the atmospheric CO2 concentration (a[CO2]), mediated by behavioral and developmental responses of stomata, on crop performance remains a concern under all climate change scenarios, with potential impacts on future food security. To identify possible beneficial traits that could be exploited for future breeding, phenotypic variation in morphological traits including stomatal size and density, as well as physiological responses and, critically, the effect of growth [CO2] on these traits, was assessed in six wheat relative accessions (including Aegilops tauschii, Triticum turgidum ssp. Dicoccoides, and T. turgidum ssp. dicoccon) and five elite bread wheat T. aestivum cultivars. Exploiting a range of different species and ploidy, we identified key differences in photosynthetic capacity between elite hexaploid wheat and wheat relatives. We also report differences in the speed of stomatal responses which were found to be faster in wheat relatives than in elite cultivars, a trait that could be useful for enhanced photosynthetic carbon gain and water use efficiency. Furthermore, these traits do not all appear to be influenced by elevated [CO2], and determining the underlying genetics will be critical for future breeding programmes.

Application of Indole-Alkaloid Harmaline Induces Physical Damage to Photosystem II Antenna Complexes in Adult Plants of Arabidopsis thaliana (L.) Heynh

Finding herbicides with new and multiple modes of action is a solution to stop the increase in resistant weed species. Harmaline, a natural alkaloid with proven phytotoxic potential, was tested on Arabidopsis adult plants by watering and spraying; watering resulted as the more effective treatment. Harmaline altered several photosynthetic parameters, reducing the efficiency of the light- (Φ_II) and dark-adapted (F_v/F_m) PSII, suggesting physical damages in photosystem II, although dissipation of the energy in excess under the form of heat was not compromised as demonstrated by the significant increase in Φ_NPQ. Metabolomic alterations, such as osmoprotectant accumulation and reduction in sugars' content, also indicate a reduction of photosynthetic efficiency and suggest early senescence and water status alteration induced by harmaline. Data suggest that harmaline might be considered a new phytotoxic molecule interesting for further studies.

Data-Independent Acquisition Proteomics Reveals the Effects of Red and Blue Light on the Growth and Development of Moso Bamboo (Phyllostachys edulis) Seedlings

Moso bamboo is a rapidly growing species with significant economic, social, and cultural value. Transplanting moso bamboo container seedlings for afforestation has become a cost-effective method. The growth and development of the seedlings is greatly affected by the quality of light, including light morphogenesis, photosynthesis, and secondary metabolite production. Therefore, studies on the effects of specific light wavelengths on the physiology and proteome of moso bamboo seedlings are crucial. In this study, moso bamboo seedlings were germinated in darkness and then exposed to blue and red light conditions for 14 days. The effects of these light treatments on seedling growth and development were observed and compared through proteomics analysis. Results showed that moso bamboo has higher chlorophyll content and photosynthetic efficiency under blue light, while it displays longer internode and root length, more dry weight, and higher cellulose content under red light. Proteomics analysis reveals that these changes under red light are likely caused by the increased content of cellulase CSEA, specifically expressed cell wall synthetic proteins, and up-regulated auxin transporter ABCB19 in red light. Additionally, blue light is found to promote the expression of proteins constituting photosystem II, such as PsbP and PsbQ, more than red light. These findings provide new insights into the growth and development of moso bamboo seedlings regulated by different light qualities.

Microalgae from Nordic collections demonstrate biostimulant effect by enhancing plant growth and photosynthetic performance

We investigated the biostimulant potential of six microalgal species from Nordic collections extracted with two different procedures: thermal hydrolysis with a weak solution of sulfuric acid accompanied by ultrasonication and bead-milling with aqueous extraction followed by centrifugation. To this aim, we designed a phenotyping pipeline consisting of a root growth assay in the model plant Arabidopsis thaliana, complemented with greenhouse experiments to evaluate lettuce yield (Lactuca sativa L. cv. Finstar) and photosynthetic performance. The best-performing hydrolyzed extracts stimulated Arabidopsis root elongation by 8%-13% and lettuce yield by 12%-15%. The in situ measured photosynthetic performance of lettuce was upregulated in the efficient extracts: PSII quantum yield increased by 26%-34%, and thylakoid proton flux increase was in the range of 34%-60%. In contrast, aqueous extracts acquired by bead-milling showed high dependence on biomass concentration in the extract and an overall plant growth enhancement was not attained in any of the applied dosages. Our results indicate that hydrolysis of the biomass can be a decisive factor for rendering effective plant biostimulants from microalgae.

Design and Implementation of a Low-Cost Chlorophyll Content Meter

Chlorophyll meters are portable devices used to assess and improve plants' nitrogen management and to help farmers in the determination of the health condition of plants through leaf greenness measurements. These optical electronic instruments can provide an assessment of chlorophyll content by measuring the light passing through a leaf or by measuring the light radiation reflected from its surface. However, independently of the main principle of operation and use (e.g., absorbance vs. reflectance measurements), commercial chlorophyll meters usually cost hundreds or even thousands of euros, making them inaccessible to growers and ordinary citizens who are interested in self-cultivation, farmers, crop researchers, and communities lacking resources in general. A low-cost chlorophyll meter based on light-to-voltage measurements of the remaining light after two LED light emissions through a leaf is designed, constructed, evaluated, and compared against two well-known commercial chlorophyll meters, the SPAD-502 and the atLeaf CHL Plus. Initial tests of the proposed device on lemon tree leaves and on young Brussels sprouts plant leaves revealed promising results compared to the commercial instruments. The coefficient of determination, R2, was estimated to be 0.9767 for the SPAD-502 and 0.9898 for the atLeaf-meter in lemon tree leaves samples compared to the proposed device, while for the Brussels sprouts plant, R2 was estimated to be 0.9506 and 0.9624, respectively. Further tests conducted as a preliminary evaluation of the proposed device are also presented.

Increased sedoheptulose-1,7-bisphosphatase content in Setaria viridis does not affect C4 photosynthesis

Sedoheptulose-1,7-bisphosphatase (SBPase) is one of the rate-limiting enzymes of the Calvin cycle, and increasing the abundance of SBPase in C3 plants provides higher photosynthetic rates and stimulates biomass and yield. C4 plants usually have higher photosynthetic rates because they operate a biochemical CO2-concentrating mechanism between mesophyll and bundle sheath cells. In the C4 system, SBPase and other enzymes of the Calvin cycle are localized to the bundle sheath cells. Here we tested what effect increasing abundance of SBPase would have on C4 photosynthesis. Using green foxtail millet (Setaria viridis), a model C4 plant of NADP-ME subtype, we created transgenic plants with 1.5 to 3.2 times higher SBPase content compared to wild-type plants. Transcripts of the transgene were found predominantly in the bundle sheaths suggesting the correct cellular localization of the protein. The abundance of ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit was not affected in transgenic plants overexpressing SBPase, and neither was leaf chlorophyll content or photosynthetic electron transport parameters. We found no association between SBPase content in S. viridis and saturating rates of CO2 assimilation. Moreover, a detailed analysis of CO2 assimilation rates at different CO2 partial pressures, irradiances, and leaf temperatures showed no improvement of photosynthesis in plants overexpressing SBPase. We discuss the potential implications of these results for understanding the role of SBPase in regulation of C4 photosynthesis.

The Geomagnetic Field (GMF) Is Required for Lima Bean Photosynthesis and Reactive Oxygen Species Production

Plants evolved in the presence of the Earth's magnetic field (or geomagnetic field, GMF). Variations in MF intensity and inclination are perceived by plants as an abiotic stress condition with responses at the genomic and metabolic level, with changes in growth and developmental processes. The reduction of GMF to near null magnetic field (NNMF) values by the use of a triaxial Helmholtz coils system was used to evaluate the requirement of the GMF for Lima bean (Phaseolus lunatus L.) photosynthesis and reactive oxygen species (ROS) production. The leaf area, stomatal density, chloroplast ultrastructure and some biochemical parameters including leaf carbohydrate, total carbon, protein content and δ¹³C were affected by NNMF conditions, as were the chlorophyll and carotenoid levels. RubisCO activity and content were also reduced in NNMF. The GMF was required for the reaction center's efficiency and for the reduction of quinones. NNMF conditions downregulated the expression of the MagR homologs PlIScA2 and PlcpIScA, implying a connection between magnetoreception and photosynthetic efficiency. Finally, we showed that the GMF induced a higher expression of genes involved in ROS production, with increased contents of both H₂O₂ and other peroxides. Our results show that, in Lima bean, the GMF is required for photosynthesis and that PlIScA2 and PlcpIScA may play a role in the modulation of MF-dependent responses of photosynthesis and plant oxidative stress.

Particle films improve photosynthesis of citrus trees under excess irradiance by reducing leaf temperature

High irradiance and increased air temperature during extreme weather conditions affect tree crops and impact the yield and quality of fruits. Moreover, flowering and fruit set of Citrus are likely impaired by UV radiation and/or reduced carbon assimilation, which increase reactive oxygen species production and damage the leaf photosynthetic apparatus. Particle coating films sprayed on leaves have been offered as a way to minimize crop losses due to the climate change scenario, even though the extent of leaf protection is not characterized. We evaluated the use of two protective films on the oxidative stress and leaf photosynthesis of sweet orange trees exposed to varying daylight levels. Trees were maintained under full sun light, sprayed or not (control) with kaolin or calcium carbonate, and under reduced irradiance using either aluminum shade cloth 50% or anti-UV transparent plastic. Kaolin or calcium carbonate reflected 20%-30% of the incident light on the leaf surface compared to leaves not sprayed and under full sunlight. Leaves with coating exhibited improved CO₂ assimilation and photosystem II efficiency, and lower leaf temperatures over time. In addition, the coating protected leaves against excess irradiance due to dissipation of excess energy into the photosynthetic apparatus (NPQt). Nonenzymatic mechanisms for UV protection, such as carotenoids, were higher in full sun control plants than in leaf-coated plants. Comparable responses were observed on trees maintained covered either by the cloth or the plastic film. Finally, we conclude that the use of suspension particles mitigates the harmful effects of excess UV irradiance and temperature in sweet orange trees.

Floral hemp (Cannabis sativa L.) responses to nitrogen fertilization under field conditions in the high desert

While most studies on floral hemp (Cannabis sativa L.) concur that additions of nitrogen (N) increase plant growth, the performance of floral hemp is heavily influenced by environmental conditions, management and cultivar selection. In regions with a short growing season, the availability of soil N may determine plant developmental rates, final inflorescence biomass and cannabinoid concentrations, but no studies have addressed this for field-grown hemp under high-desert conditions. This field study evaluated the effect of no supplemental N and N fertilization at 90 kg ha-1 on three hemp cultivars (Berry Blossom, Red Bordeaux, and Tahoe Cinco) in Northern Nevada. N increased plant height, canopy cover, stem diameter and shoot biomass, but other physiological parameters were dependent on cultivar. For instance, inflorescence biomass and inflorescence-to-shoot ratio in Red Bordeaux was not affected by N fertilization. Similarly, cannabinoid concentrations were affected by timing of harvest and cultivar but not by N treatment. We evaluated the use of a SPAD meter for ease of determining leaf N deficiency, and correlations with leaf chlorophyll content showed that the SPAD meter was a reliable tool in two cultivars but not in Tahoe Cinco. N treatment increased overall CBD yield, which was driven by increases in inflorescence biomass. Tahoe Cinco was the best CBD yielding cultivar, as it maintained a high inflorescence-to-shoot ratio regardless of N treatment. Our study suggests that even though hemp may have a positive response to soil N management, adjustments based on genotype by environment interaction should be aimed at maximizing cannabinoid yield either by increasing biomass and/or CBD concentrations as long as THC levels are within the permissible <0.3% for U.S. industrial hemp cultivation.

Contributions of phenotypic integration, plasticity and genetic adaptation to adaptive capacity relating to drought in Banksia marginata (Proteaceae)

The frequency and intensity of drought events are predicted to increase because of climate change, threatening biodiversity and terrestrial ecosystems in many parts of the world. Drought has already led to declines in functionally important tree species, which are documented in dieback events, shifts in species distributions, local extinctions, and compromised ecosystem function. Understanding whether tree species possess the capacity to adapt to future drought conditions is a major conservation challenge. In this study, we assess the capacity of a functionally important plant species from south-eastern Australia (Banksia marginata, Proteaceae) to adapt to water-limited environments. A water-manipulated common garden experiment was used to test for phenotypic plasticity and genetic adaptation in seedlings sourced from seven provenances of contrasting climate-origins (wet and dry). We found evidence of local adaptation relating to plant growth investment strategies with populations from drier climate-origins showing greater growth in well-watered conditions. The results also revealed that environment drives variation in physiological (stomatal conductance, predawn and midday water potential) and structural traits (wood density, leaf dry matter content). Finally, these results indicate that traits are coordinated to optimize conservation of water under water-limited conditions and that trait coordination (phenotypic integration) does not constrain phenotypic plasticity. Overall, this study provides evidence for adaptive capacity relating to drought conditions in B. marginata, and a basis for predicting the response to climate change in this functionally important plant species.

Foliar cytokinins or brassinosteroids applications influence the rice plant acclimatization to combined heat stress

The effect of different foliar sprays numbers of cytokinins - (CK) and brassinosteroids - (BR) on the physiological, biochemical, and panicle parameters of rice plants subjected to combined heat stress (high day/night temperatures) were studied in three different experiments. The treatments established for the first (E1) and second (E2) experiments were the following: i) absolute control, ii) stress control, iii) heat stress + one foliar spray of CK, iv) heat stress + two foliar sprays of CK, v) heat stress + three foliar sprays of CK, vi) heat stress + one foliar spray of BR, vii) heat stress + two foliar sprays of BR, or viii) heat stress + three foliar sprays of BR. For the third experiment (E3), the treatments were the following: i) absolute control, ii) stress control, iii) heat stress + three foliar applications of CK, iv) heat stress + three foliar applications of BR. Rice-stressed plants and sprayed with three foliar sprays of CK or BR had a better stomatal conductance in E1 and E2 compared to their heat-stressed control. The relative tolerance index suggests that three CK or BR applications helped to mitigate the combined heat stress in both experiments. The foliar CK or BR applications at the flowering and grain-filling stages in rice-stressed plants increased Fv/Fm ratio and panicle characteristics (number of filled spikelets and the percentage of panicle blanking in E3). In conclusion, foliar applications of BR or CK can be considered an agronomic strategy to help improve the negative effect of combined heat stress conditions on the physiological behavior of rice plants during different phenological stages.

Environmental stress - what can we learn from chlorophyll a fluorescence analysis in woody plants? A review

Chlorophyll a fluorescence (ChF) signal analysis has become a widely used and rapid, non-invasive technique to study the photosynthetic process under stress conditions. It monitors plant responses to various environmental factors affecting plants under experimental and field conditions. Thus, it enables extensive research in ecology and benefits forestry, agriculture, horticulture, and arboriculture. Woody plants, especially trees, as organisms with a considerable life span, have a different life strategy than herbaceous plants and show more complex responses to stress. The range of changes in photosynthetic efficiency of trees depends on their age, ontogeny, species-specific characteristics, and acclimation ability. This review compiles the results of the most commonly used ChF techniques at the foliar scale. We describe the results of experimental studies to identify stress factors that affect photosynthetic efficiency and analyse the experience of assessing tree vigour in natural and human-modified environments. We discuss both the circumstances under which ChF can be successfully used to assess woody plant health and the ChF parameters that can be useful in field research. Finally, we summarise the advantages and limitations of the ChF method in research on trees, shrubs, and woody vines.