Shading Contributes to the Reduction of Stem Mechanical Strength by Decreasing Cell Wall Synthesis in Japonica Rice (Oryza sativa L.)

CsPAT1, a GRAS transcription factor, promotes lignin accumulation by antagonistic interacting with CsWRKY13 in tea plants

Lignin is an important component of plant cell walls and plays crucial roles in the essential agronomic traits of tea quality and tenderness. However, the molecular mechanisms underlying the regulation of lignin biosynthesis in tea plants remain unclear. CsWRKY13 acts as a negative regulator of lignin biosynthesis in tea plants. In this study, we identified a GRAS transcription factor, phytochrome A signal transduction 1 (CsPAT1), that interacts with CsWRKY13. Silencing CsPAT1 expression in tea plants and heterologous overexpression in Arabidopsis demonstrated that CsPAT1 positively regulates lignin accumulation. Further investigation revealed that CsWRKY13 directly binds to the promoters of CsPAL and CsC4H and suppresses transcription of CsPAL and CsC4H. CsPAT1 indirectly affects the promoter activities of CsPAL and CsC4H by interacting with CsWRKY13, thereby facilitating lignin biosynthesis in tea plants. Compared with the expression of CsWRKY13 alone, the co-expression of CsPAT1 and CsWRKY13 in Oryza sativa significantly increased lignin biosynthesis. Conversely, compared with the expression of CsPAT1 alone, the co-expression of CsPAT1 and CsWRKY13 in O. sativa significantly reduced lignin accumulation. These results demonstrated the antagonistic regulation of the lignin biosynthesis pathway by CsPAT1 and CsWRKY13. These findings improve our understanding of lignin biosynthesis mechanisms in tea plants and provide insights into the role of the GRAS transcription factor family in lignin accumulation.

Strong culm: a crucial trait for developing next-generation climate-resilient rice lines

Lodging, a phenomenon characterized by the bending or breaking of rice plants, poses substantial constraints on productivity, particularly during the harvesting phase in regions susceptible to strong winds. The rice strong culm trait is influenced by the intricate interplay of genetic, physiological, epigenetic, and environmental factors. Stem architecture, encompassing morphological and anatomical attributes, alongside the composition of both structural and non-structural carbohydrates, emerges as a critical determinant of lodging resistance. The adaptive response of the rice culm to various biotic and abiotic environmental factors further modulates the propensity for lodging. Advancements in next-generation sequencing technologies have expedited the genetic dissection of lodging resistance, enabling the identification of pertinent genes, quantitative trait loci, and novel alleles. Concurrently, contemporary breeding strategies, ranging from biparental approaches to more sophisticated methods such as multi-parent-based breeding, gene pyramiding, genomic selection, genome-wide association studies, and haplotype-based breeding, offer perspectives on the genetic underpinnings of culm strength. This review comprehensively delves into physiological attributes, culm histology, epigenetic determinants, and gene expression profiles associated with lodging resistance, with a specialized focus on leveraging next-generation sequencing for candidate gene discovery.

Blue light regulated lignin and cellulose content of soybean petioles and stems under low light intensity

To improve light harvest and plant structural support under low light intensity, it is useful to investigate the effects of different ratios of blue light on petiole and stem growth. Two true leaves of soybean seedlings were exposed to a total light intensity of 200μmolm-2 s-1 , presented as either white light or three levels of blue light (40μmolm-2 s-1 , 67μmolm-2 s-1 and 100μmolm-2 s-1 ) for 15days. Soybean petioles under the low blue light treatment upregulated expression of genes relating to lignin metabolism, enhancing lignin content compared with the white light treatment. The low blue light treatment had high petiole length, increased plant height and improved petiole strength arising from high lignin content, thus significantly increasing leaf dry weight relative to the white light treatment. Compared with white light, the treatment with the highest blue light ratio reduced plant height and enhanced plant support through increased cellulose and hemicellulose content in the stem. Under low light intensity, 20% blue light enhanced petiole length and strength to improve photosynthate biomass; whereas 50% blue light lowered plants' centre of gravity, preventing lodging and conserving carbohydrate allocation.

Impact of low light intensity on biomass partitioning and genetic diversity in a chickpea mapping population

With recent climatic changes, the reduced access to solar radiation has become an emerging threat to chickpeas' drought tolerance capacity under rainfed conditions. This study was conducted to assess, and understand the effects of reduced light intensity and quality on plant morphology, root development, and identifying resistant sources from a Sonali/PBA Slasher mapping population. We evaluated 180 genotypes, including recombinant inbred lines (RILs), parents, and commercial checks, using a split-block design with natural and low light treatments. Low light conditions, created by covering one of the two benches inside two growth chambers with a mosquito net, reduced natural light availability by approximately 70%. Light measurements encompassed photosynthetic photon flux density, as well as red, and far-red light readings taken at various stages of the experiment. The data, collected from plumule emergence to anthesis initiation, encompassed various indices relevant to root, shoot, and carbon gain (biomass). Statistical analysis examined variance, treatment effects, heritability, correlations, and principal components (PCs). Results demonstrated significant reductions in root biomass, shoot biomass, root/shoot ratio, and plant total dry biomass under suboptimal light conditions by 52.8%, 28.2%, 36.3%, and 38.4%, respectively. Plants also exhibited delayed progress, taking 9.2% longer to produce their first floral buds, and 19.2% longer to commence anthesis, accompanied by a 33.4% increase in internodal lengths. A significant genotype-by-environment interaction highlighted differing genotypic responses, particularly in traits with high heritability (> 77.0%), such as days to anthesis, days to first floral bud, plant height, and nodes per plant. These traits showed significant associations with drought tolerance indicators, like root, shoot, and plant total dry biomass. Genetic diversity, as depicted in a genotype-by-trait biplot, revealed contributions to PC1 and PC2 coefficients, allowing discrimination of low-light-tolerant RILs, such as 1_52, 1_73, 1_64, 1_245, 1_103, 1_248, and 1_269, with valuable variations in traits of interest. These RILs could be used to breed desirable chickpea cultivars for sustainable production under water-limited conditions. This study concludes that low light stress disrupts the balance between root and shoot morphology, diverting photosynthates to vegetative structures at the expense of root development. Our findings contribute to a better understanding of biomass partitioning under limited-light conditions, and inform breeding strategies for improved drought tolerance in chickpeas.

OsTCP19 coordinates inhibition of lignin biosynthesis and promotion of cellulose biosynthesis to modify lodging resistance in rice

Lignin and cellulose are two essential elements of plant secondary cell walls that shape the mechanical characteristics of the culm to prevent lodging. However, how the regulation of the lignin and cellulose composition is combined to achieve optimal mechanical characteristics is unclear. Here, we show that increasing OsTCP19 expression in rice coordinately repressed lignin biosynthesis and promoted cellulose biosynthesis, resulting in enhanced lodging resistance. In contrast, repression of OsTCP19 coordinately promoted lignin biosynthesis and inhibited cellulose biosynthesis, leading to greater susceptibility to lodging. We found that OsTCP19 binds to the promoters of both MYB108 and MYB103L to increase their expression, with the former being responsible for repressing lignin biosynthesis and the latter for promoting cellulose biosynthesis. Moreover, up-regulation of OsTCP19 in fibers improved grain yield and lodging resistance. Thus, our results identify the OsTCP19-OsMYB108/OsMYB103L module as a key regulator of lignin and cellulose production in rice, and open up the possibility for precisely manipulating lignin-cellulose composition to improve culm mechanical properties for lodging resistance.

Quantification of the Cumulative Shading Capacity in a Maize-Soybean Intercropping System Using an Unmanned Aerial Vehicle

In intercropping systems, higher crops block direct radiation, resulting in inevitable shading on the lower crops. Cumulative shading capacity (CSC), defined as the amount of direct radiation shaded by higher crops during a growth period, affects the light interception and radiation use efficiency of crops. Previous studies investigated the light interception and distribution of intercropping. However, how to directly quantify the CSC and its inter-row heterogeneity is still unclear. Considering the canopy height differences (Hms, obtained using an unmanned aerial vehicle) and solar position, we developed a shading capacity model (SCM) to quantify the shading on soybean in maize-soybean intercropping systems. Our results indicated that the southernmost row of soybean had the highest shading proportion, with variations observed among treatments composed of strip configurations and plant densities (ranging from 52.44% to 57.44%). The maximum overall CSC in our treatments reached 123.77 MJ m-2. There was a quantitative relationship between CSC and the soybean canopy height increment (y = 3.61 × 10-2×ln(x)+6.80 × 10-1, P < 0.001). Assuming that the growth status of maize and soybean was consistent under different planting directions and latitudes, we evaluated the effects of factors (i.e., canopy height difference, latitude, and planting direction) on shading to provide insights for optimizing intercropping planting patterns. The simulation showed that increasing canopy height differences and latitude led to increased shading, and the planting direction with the least shading was about 90° to 120° at the experimental site. The newly proposed SCM offers a quantitative approach for better understanding shading in intercropping systems.

Rice miR5504 regulates plant height by affecting cell proliferation and expansion

miRNAs play critical roles in the regulation of plant growth and development by cleaving mRNA or repressing transcription. In our previous study, miR5504 with unknown functions was captured by small RNA sequencing. Here, the function and characters of miR5504 were extensively analyzed using CRISPR/Cas9, overexpression strategy, Northern blot, cytological analysis, and transcriptomics analysis. We found that the dwarf phenotype of mir5504 mutants (mir5504-1 and mir5504-2) appeared on 35-day seedlings and became more apparent at the mature stage. The cytological results showed a substantial decrease in the vascular bundle number, cell number and cell length in the mir5504 mutant compared with NIP. In addition, we found that miR5504 regulated plant height by targeting LOC_Os08g16914. The results of RNA-seq revealed that numerous biological processes were mainly enriched, including DNA-binding transcription factor activity, transferase activity, regulation of transcription, metabolic process, and protein binding. Meanwhile, KEEG analysis showed that numerous proteins were associated with cellular processes and metabolism pathways. Taken together, miR5504 may be involved in the regulation of plant height by affecting cell expansion and division of internode in rice.

Physicochemical Properties and Tissue Structure of High Kernel Elongation Rice (Oryza sativa L.) Varieties as Affected by Heat Treatment

Heat treatment could affect the structure and properties of rice varieties. The present study was conducted in order to determine the effects of heat treatment on the physicochemical properties and tissue structure of Mahsuri Mutan, Basmati 370 and MR219 rice varieties. The three rice varieties were subjected to heat treatment (ageing) at 90 °C, using an oven, for 3 h. After the heat treatment, the samples were cooled at room temperature (25 °C) for 1 h. Physicochemical properties, such as alkali digestion value, water uptake ratio, solids in cooking water, high kernel elongation ratio and amylose contents, were determined. The procedure used in determining both apparent and absolute amylose involved measuring the iodine affinity of defatted whole starch. Ahigh-performance anion-exchange chromatograph was used to analyse branch chain length distribution of amylopectin quantitatively. The starch structure of the rice samples was observed under a scanning electron microscope. Data collected on physicochemical traits, heat treatment and control (ageing and non-ageing) were subjected to an analysis of variance using SAS software version 9.4. In this study, Mahsuri Mutan and Basmati 370 showed superior high kernel elongation as compared to their respective rice progenies. This study also found that heat treatment directly affected the increasingly high kernel elongation for both populations. The phenotypic correlation co-efficient indicated that there was a high positive correlation between high kernel elongation and water uptake ratio, implying that selection for water uptake ratio would increase the high kernel elongation characteristic. The heat treatment showed significant difference in all the physicochemical traits of the varieties studied. Heat treatment also affected the very long branch chains of starch, such as amylose. Observation under an electron microscope showed that the samples subjected to heat treatment had more cracks on the tissue structure compared to normal rice samples. The hexagon structure in Mahsuri Mutan produced a greater elongation effect on its kernel. The findings from this study could be useful to breeders in the selection and development of a new high kernel elongation rice variety.

Optimum nitrogen improved stem breaking resistance of intercropped soybean by modifying the stem anatomical structure and lignin metabolism

Excessive use of nitrogen fertilizers enhanced the stem lodging, leading to serious threats to environmental sustainability. As the maize-soybean intercropping system is eco-friendly, however, soybean micro-climate hinders soybean growth and caused lodging. Since the relationship between nitrogen and lodging resistance under the intercropping system is not widely studied. Therefore, a pot experiment was conducted with the application of different nitrogen concentrations referring to low nitrogen (LN) = 0 mg/kg, optimum nitrogen (OpN) = 100 mg/kg, and high nitrogen (HN) = 300 mg/kg. To evaluate the optimum nitrogen fertilization under the maize-soybean intercropping system, two soybean cultivars were selected Tianlong 1 (TL-1), (lodging resistant) and Chuandou 16 (CD-16), (lodging susceptible). The results revealed that under the intercropping system, the OpN concentration significantly improved the lodging resistance of soybean cultivars by reducing the plant height of TL-1 and CD-16 by 4 and 28% as compared to LN, respectively. Following OpN, the lodging resistance index for CD-16 was also increased by 67% and 59% under the respective cropping systems. In addition, we found that OpN concentration prompted the lignin biosynthesis by stimulating the enzymatic activities of lignin biosynthetic enzymes (PAL, 4CL, CAD, and POD), which was reflected at the transcriptional levels (GmPAL, GmPOD, GmCAD, Gm4CL), too. Henceforth, we proposed that optimum nitrogen fertilization boosts soybean stem lodging resistance by modulating the lignin metabolism in the maize-soybean intercropping system.

Bioengineering Techniques to Improve Nitrogen Transformation and Utilization: Implications for Nitrogen Use Efficiency and Future Sustainable Crop Production

Nitrogen (N) is crucial for plant growth and development, especially in physiological and biochemical processes such as component of different proteins, enzymes, nucleic acids, and plant growth regulators. Six categories, such as transporters, nitrate absorption, signal molecules, amino acid biosynthesis, transcription factors, and miscellaneous genes, broadly encompass the genes regulating NUE in various cereal crops. Herein, we outline detailed research on bioengineering modifications of N metabolism to improve the different crop yields and biomass. We emphasize effective and precise molecular approaches and technologies, including N transporters, transgenics, omics, etc., which are opening up fascinating opportunities for a complete analysis of the molecular elements that contribute to NUE. Moreover, the detection of various types of N compounds and associated signaling pathways within plant organs have been discussed. Finally, we highlight the broader impacts of increasing NUE in crops, crucial for better agricultural yield and in the greater context of global climate change.

A Joint Transcriptomic and Metabolomic Analysis Reveals the Regulation of Shading on Lignin Biosynthesis in Asparagus

Asparagus belongs to the Liliaceae family and has important economic and pharmacological value. Lignin plays a crucial role in cell wall structural integrity, stem strength, water transport, mechanical support and plant resistance to pathogens. In this study, various biological methods were used to study the mechanism of shading on the asparagus lignin accumulation pathway. The physiological results showed that shading significantly reduced stem diameter and cell wall lignin content. Microstructure observation showed that shading reduced the number of vascular bundles and xylem area, resulting in decreased lignin content, and thus reducing the lignification of asparagus. Cinnamic acid, caffeic acid, ferulic acid and sinapyl alcohol are crucial intermediate metabolites in the process of lignin synthesis. Metabolomic profiling showed that shading significantly reduced the contents of cinnamic acid, caffeic acid, ferulic acid and sinapyl alcohol. Transcriptome profiling identified 37 differentially expressed genes related to lignin, including PAL, C4H, 4CL, CAD, CCR, POD, CCoAOMT, and F5H related enzyme activity regulation genes. The expression levels of POD, CCoAOMT, and CCR genes were significantly decreased under shading treatment, while the expression levels of CAD and F5H genes exhibited no significant difference with increased shading. The downregulation of POD, CCoAOMT genes and the decrease in CCR gene expression levels inhibited the activities of the corresponding enzymes under shading treatment, resulting in decreased downstream content of caffeic acid, ferulic acid, sinaperol, chlorogenic acid and coniferin. A significant decrease in upstream cinnamic acid content was observed with shading, which also led to decreased downstream metabolites and reduced asparagus lignin content. In this study, transcriptomic and metabolomic analysis revealed the key regulatory genes and metabolites of asparagus lignin under shading treatment. This study provides a reference for further understanding the mechanism of lignin biosynthesis and the interaction of related genes.

Effects of semi-deep water irrigation on hybrid indica rice lodging resistance

Recently, rice-aquatic animal integrated farming (RAAIF) has grown rapidly in China due to its favorable benefits and the lower application of pesticides and fertilizers. However, rice lodging occurs frequently under RAAIF, which restricts rice yield. We assumed that semi-deep water irrigation may cause weaker rice-lodging resistance since it is the most significant environmental factor for RAAIF that distinguishes it from rice monoculture. To investigate the response of rice stem lodging resistance to semi-deep water irrigation and its mechanism, three irrigation management modes, namely the typical high-yield irrigation model that is mainly based on swallow and wetting (CK), semi-deep water irrigation from the late tillering stage to the jointing stage (SDI1), and semi-deep water irrigation from the jointing stage to the middle grain-filling stage (SDI2), were conducted using three hybrid indica rice varieties: Shenliangyou136 (SLY136), Huiliangyousimiao (HLYSM), and Wanxiangyou982 (WXY982). Mechanics analysis indicated that the bending moment by the whole plant (WP) and the breaking strength (M) were both decreased by semi-deep water irrigation when compared with CK, while M presented a larger decreasing amplitude than WP, which induced the increased lodging index (LI) of rice, for all the tested varieties. SLY136 and HLYSM were affected more strongly by SDI1, whereas WXY982 was affected more strongly by SDI2. Significant weaker breaking force under two semi-deep water irrigation modes contributed to the decreased M relative to CK. Morphology results showed that semi-deep water irrigation reduced the thickness of mechanical tissues, sclerenchyma cells, and parenchyma cells; reduced the number of vascular bundles; and caused a looser arrangement, inducing the lower fullness of the rice basal internode. Decreased accumulation of lignin and cellulose was also linked to the weaker breaking force of the basal internode under semi-deep water irrigation, which was verified by correlation analysis. WXY982 had obvious lower structural carbohydrates content under semi-deep water irrigation than the other two varieties and thus showed worse breaking force and LI. In conclusion, the worse mechanical strength of the rice basal internode under semi-deep water irrigation was closely associated with weaker vascular bundle development and suppressed structural carbohydrate accumulation, and the decreasing degree of lodging resistance varied between rice varieties and semi-deep water irrigation periods.

Shading decreases lodging resistance of wheat under different planting densities by altering lignin monomer composition of stems

To clarify the influences of shading stress and planting density on the lignin monomer composition of wheat stems and their relationship with lodging resistance, Lodging resistant variety Shannong 23 (SN23) and lodging sensitive variety Shannong 16 (SN16) were grown during 2018-2019 and 2019-2020 growing seasons. The planting densities were 150 × 10⁴ plants ha^-1 (D1), 225 × 10⁴ plants ha^-1 (D2) and 300 × 10⁴ plants ha^-1 (D3). At the jointing stage, an artificial shading shed was used to simulate shading stress. Then the effects of shading on stem morphological characteristics, lignin monomer composition and lodging resistance of wheat under different planting densities were studied. Results indicate that shading at the jointing stage increased the length of basal internodes and the plant height and moved the height of center of gravity (CG) upward. Moreover, the stem diameter and the wall thickness decreased by 0.10-0.53 mm and 0.18-0.40 mm, respectively. The stem filling degree was reduced accordingly. As indicated by the correlation analysis and the stepwise regression analysis, shading-induced lodging mainly resulted from changes in the stem morphological characteristics and lignin accumulation. The influential magnitude of these factors was ordered as follows: stem filling degree, wall thickness, lignin content, contents and proportions of monomers S and H, and length of the second internode. The expression abundance of TaPAL, TaCOMT, TaCCR, and TaCAD declined in response to shading stress and high planting density. As a result, the distribution ratios of photosynthetic carbon sources to lignin monomers S, G and H were changed. The lignin content of stems on the day 42 after the jointing stage decreased by 18.48%. The monomer S content decreased, while the content and proportion of monomer H increased, thus weakening the breaking strength of wheat stems.

Effect of intermittent shade on nitrogen dynamics assessed by 15N trace isotopes, enzymatic activity and yield of Brassica napus L

Modern era of agriculture is concerned with the environmental influence on crop growth and development. Shading is one of the crucial factors affecting crop growth considerably, which has been neglected over the years. Therefore, a two-year field experiment was aimed to investigate the effects of shading at flowering (S1) and pod development (S2) stages on nitrogen (N) dynamics, carbohydrates and yield of rapeseed. Two rapeseed genotypes (Chuannong and Zhongyouza) were selected to evaluate the effects of shading on ¹⁵N trace isotopes, enzymatic activities, dry matter, nitrogen and carbohydrate distribution and their relationship with yield. The results demonstrated that both shading treatments disturbed the nitrogen accumulation and transportation at the maturity stage. It was found that shading induced the downregulation of the N mobilizing enzymes (NR, NiR, GS, and GOGAT) in leaves and pods at both developmental stages. Shading at both growth stages resulted in reduced dry matter of both varieties but only S2 exhibited the decline in pod shell and seeds dry weight in both years. Besides this, carbohydrates distribution toward economic organs was declined by S2 treatment and its substantial impact was also experienced in seed weight and seeds number per pod which ultimately decreased the yield in both genotypes. We also revealed that yield is positively correlated with dry matter, nitrogen content and carbohydrates transportation. In contrast to Chuannong, the Zhongyouza genotype performed relatively better under shade stress. Overall, it was noticed that shading at pod developmental stage considerable affected the transportation of N and carbohydrates which led to reduced rapeseed yield as compared to shading at flowering stage. Our study provides basic theoretical support for the management techniques of rapeseed grown under low light regions and revealed the critical growth stage which can be negatively impacted by low light.

A Phytochrome B-PIF4-MYC2/MYC4 module inhibits secondary cell wall thickening in response to shaded light

Secondary cell walls (SCWs) in stem cells provide mechanical strength and structural support for growth. SCW thickening varies under different light conditions. Our previous study revealed that blue light enhances SCW thickening through the redundant function of MYC2 and MYC4 directed by CRYPTOCHROME1 (CRY1) signaling in fiber cells of the Arabidopsis inflorescence stem. In this study, we find that the Arabidopsis PHYTOCHROME B mutant phyB displays thinner SCWs in stem fibers, but thicker SCWs are deposited in the PHYTOCHROME INTERACTING FACTOR (PIF) quadruple mutant pif1pif3pif4pif5 (pifq). The shaded light condition with a low ratio of red to far-red light inhibits stem SCW thickening. PIF4 interacts with MYC2 and MYC4 to affect their localization in nuclei, and this interaction results in inhibition of the MYCs' transactivation activity on the NST1 promoter. Genetic evidence shows that regulation of SCW thickening by PIFs is dependent on MYC2/MYC4 function. Together, the results of this study reveal a PHYB-PIF4-MYC2/MYC4 module that inhibits SCW thickening in fiber cells of the Arabidopsis stem.

Use of ATR-FTIR spectroscopy for analysis of water deficit tolerance in Physalis peruviana L

Treatments that allow plants to better tolerate water deficit become essential, such as the application of chemical priming. In addition, it is essential to use analyses capable of measuring these effects at the biomolecular level, complementing the other physiological evaluations. In view of the above, this study aimed to evaluate the use of attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy for analyses of water deficit tolerance in Physalis peruviana plants. For this, samples of leaves, stems and roots of plants subjected to different pretreatments with proline (10 mM and 20 mM), sodium nitroprusside (SNP 25 μM and 50 μM) and H₂O as control, aiming at increasing tolerance to water deficit, were evaluated. The chemical agents used attenuated water deficit in P. peruviana plants, influencing phenotypic characterization and spectral analyses. Analysis of FTIR spectra indicates that different functional groups present in leaves, stems and roots were influenced by water deficit and priming treatments. Changes in lipid levels contributed to reducing water losses by increasing the thickness of cuticular wax. Accumulation of proteins and carbohydrates promoted osmoregulation and maintenance of the water status of plants. Thus, water deficit causes changes in the functional groups present in the organs of P. peruviana, and the ATR-FTIR technique is able to detect these biomolecular changes, helping in the selection of priming treatments to increase tolerance to water deficit.

Effect of Temperature and Radiation on Indica Rice Yield and Quality in Middle Rice Cropping System

Rice (Oryza sativa L.) is cultivated in a wide range of climatic conditions, thereby inducing great variations in the rice growth, yield and quality. However, the comprehensive effects of temperature and solar radiation under different ecological regions on the rice growth, yield and quality are not well understood, especially in a middle rice cropping system. The rice growth, yield- and quality-related traits were investigated under different ecological regions. Among different areas, the days before the heading stage and after the heading stage of six cultivars ranged from 80 to 120 and from 30 to 50. The gaps of the grain yield, head rice rate, chalky grain rate and chalkiness level were about 1.2-52.4%, 1.0-3.0%, 2.7-12.7% and 0.3-4.5%, respectively. This study demonstrated that in these regions, temperature is a limiting factor compared with radiation. Moreover, the rice growth, yield and quality were closely associated with daily air (DT), maximum (MaT), minimum (MiT) and effective accumulated temperatures (EAT). An excellent rice growth, a high grain yield and an excellent quality could be achieved if the EAT was higher than 1592 °C·d and the MiT was lower than 23.1 °C before the heading stage, and if the DT, MiT and MaT were lower than 25.7 °C, 22.0 °C and 30 °C after the heading stage, respectively. These findings served as an important reference for optimizing cultivar selection for a specific area and determining suitable areas for a certain variety.

Adaptive strategies of Scots pine under shade: Increase in lignin synthesis and ecotypic variation in defense-related gene expression

Shade is a stressful condition for plants characterized by low Red:Far-Red (R:FR) ratio. The northern latitudes in Sweden daily receive more hours of FR-enriched light (twilight) or shade-like conditions compared to southern forests during the growing season. Scots pine (Pinus sylvestris L.) is a shade-intolerant species. Yet, it is well adapted to this latitudinal variation in light, which is evident by a northward increase in FR requirement to maintain growth. Shade adversely affects plant growth; it makes the plant weak and, therefore, susceptible to pathogen attack. Lignin is involved in plant protection against pathogen invasion mainly by forming a physical barrier. We studied lignin synthesis and expression of defense-related genes (growth-defense trade-offs) under a low R:FR (shade) ratio in Scots pine. A higher number of immunity/defense-related genes were up-regulated in response to shade in northern populations compared to southern ones, which can be viewed as a local adaptation to light quality for optimal growth and survival. Light quality regulates lignin metabolism; light stimulates lignin synthesis, while shade causes a decrease in lignin synthesis in most angiosperms. In contrast, Scots pine shows an increase in lignin synthesis supported by the higher expression of a few key genes in the lignin biosynthetic pathway, a novel finding reported by our study. These findings can be applied to future breeding strategies in forestry to produce disease-resilient trees.

Enhanced lignin synthesis and ecotypic variation in defense-related gene expression in response to shade in Norway spruce

During the growth season, northern forests in Sweden daily receive more hours of far-red (FR)-enriched light or twilight (shade) as compared to southern forests. Norway spruce (shade-tolerant) are adapted to latitudinal variation in twilight characterized by a northward increase in FR requirement to maintain growth. Shade is a stressful condition that affects plant growth and increases plant's susceptibility to pathogen attack. Lignin plays a central role in plant defense and its metabolism is regulated by light wavelength composition (light quality). In the current work, we studied regulation of lignin synthesis and defense-related genes (growth-defense trade-offs) in response to shade in Norway spruce. In most angiosperms, light promotes lignin synthesis, whereas shade decreases lignin production leading to weaker stem, which may make plants more disease susceptible. In contrast, enhanced lignin synthesis was detected in response to shade in Norway spruce. We detected a higher number of immunity/defense-related genes up-regulated in northern populations as compared to south ones in response to shade. Enhanced lignin synthesis coupled with higher defense-related gene expression can be interpreted as an adaptive strategy for better survival in northern populations. Findings will contribute to ensuring deployment of well-adapted genetic material and identifying tree families with enhanced disease resistance.

Agronomic evaluation of shade tolerance of 16 spring Camelina sativa (L.) Crantz genotypes under different artificial shade levels using a modified membership function

Camelina [Camelina sativa (L.) Crantz] is currently gaining considerable attention as a potential oilseed feedstock for biofuel, oil and feed source, and bioproducts. Studies have shown the potential of using camelina in an intercropping system. However, there are no camelina genotypes evaluated or bred for shade tolerance. The objective of this study was to evaluate and determine the shade tolerance of sixteen spring camelina genotypes (growth stage: BBCH 103; the plants with 4-5 leaves) for intercropping systems. In this study, we simulated three different shade levels, including low (LST), medium (MST), and high shade treatments (HST; 15, 25, and 50% reduction of natural light intensity, respectively), and evaluated the photosynthetic and physiological parameters, seed production, and seed quality. The mean chlorophyll pigments, including the total chlorophyll and chlorophyll a and b across the 16 genotypes increased as shade level increased, while the chlorophyll fluorescence parameter F_v/F_m, chlorophyll a/b, leaf area, the number of silicles and branches plant^-1 decreased as shade level increased. The first day of anthesis and days of flowering duration of camelina treated with shade were significantly delayed and shortened, respectively, as shade increased. The shortened lifecycle and altered flowering phenology decreased camelina seed yield. Additionally, the shade under MST and HST reduced the seed oil content and unsaturated fatty acids, but not saturated fatty acids. The dendrograms constructed using the comprehensive tolerance membership values revealed that CamK9, CamC4, and 'SO-40' were the relatively shade-tolerant genotypes among the 16 camelina genotypes. These camelina genotypes can grow under the shade level up to a 25% reduction in natural light intensity producing a similar seed yield and seed oil quality, indicating the potential to intercrop with maize or other small grain crops. The present study provided the baseline information on the response of camelina genotypes to different shade levels, which would help in selecting or breeding shade-tolerant genotypes.

Foliar Application of NH4 +/NO3 - Ratios Enhance the Lodging Resistance of Soybean Stem by Regulating the Physiological and Biochemical Mechanisms Under Shade Conditions

Shading is one of the most chronic restrains which can lead to the lodging of intercropped plants. In order to increase the soybean stem lodging resistance, a 2-year field trial was conducted to evaluate the impact of different ratios and concentrations of NH₄ ⁺/NO₃ ^- on the morpho-physiological and biochemical characteristics of soybean stem under shade conditions. The total 5 ratios of NH₄ ⁺/NO₃ ^- were applied as follows: T0 = 0/0 (control), T1 = 0/100 (higher ratio), T2 = 25/75 (optimum), T3 = 50/50 (optimum), and T4 = 75/25 (higher ratio) as a nitrogen source. Our findings displayed that the T2 (25/75) and T3 (50/50) treatments alleviated the shading stress by improving the photosynthetic activity, biomass accumulation, carbohydrates contents, and lignin related enzymes (POD, CAD, and 4Cl) which led to improvement in stem lodging resistance. The correlation analysis (p ≤ 0.05, p ≤ 0.01) revealed the strong relationship between lodging resistance index and stem diameter, stem strength, lignin content, photosynthesis, and lignin related enzymes (POD, CAD, and 4CL) evidencing the strong contribution of lignin and its related enzymes in the improvement of lodging resistance of soybean stem under shade conditions. Collectively, we concluded that optimum NH₄ ⁺/NO₃ ^- ratios (T2 and T3) can boost up the lodging resistance of soybean stem under shade stress.

Integrated Expression Analysis of Small RNA, Degradome and Microarray Reveals Complex Regulatory Action of miRNA during Prolonged Shade in Swarnaprabha Rice

Prolonged shade during the reproductive stage can result in significant yield losses in rice. For this study, we elucidated the role of microRNAs in prolonged-shade tolerance (~20 days of shade) in a shade-tolerant rice variety, Swarnaprabha (SP), in its reproductive stage using small RNA and degradome sequencing with expression analysis using microarray and qRT-PCR. This study demonstrates that miRNA (miR) regulation for shade-tolerance predominately comprises the deactivation of the miR itself, leading to the upregulation of their targets. Up- and downregulated differentially expressed miRs (DEms) presented drastic differences in the category of targets based on the function and pathway in which they are involved. Moreover, neutrally regulated and uniquely expressed miRs also contributed to the shade-tolerance response by altering the differential expression of their targets, probably due to their differential binding affinities. The upregulated DEms mostly targeted the cell wall, membrane, cytoskeleton, and cellulose synthesis-related transcripts, and the downregulated DEms targeted the transcripts of photosynthesis, carbon and sugar metabolism, energy metabolism, and amino acid and protein metabolism. We identified 16 miRNAs with 21 target pairs, whose actions may significantly contribute to the shade-tolerance phenotype and sustainable yield of SP. The most notable among these were found to be miR5493-OsSLAC and miR5144-OsLOG1 for enhanced panicle size, miR5493-OsBRITTLE1-1 for grain formation, miR6245-OsCsIF9 for decreased stem mechanical strength, miR5487-OsGns9 and miR168b-OsCP1 for better pollen development, and miR172b-OsbHLH153 for hyponasty under shade.

Cryptochrome-mediated blue-light signal contributes to lignin biosynthesis in stone cells in pear fruit

Light environment is an indispensable factor that regulates multitudinous developmental processes during the whole life cycle of plants, including fruit development. Stone cells which negatively influence pear fruit quality because of their strongly lignified cell wall are also affected by light, however, how light qualities influence lignin biosynthesis in pear remains unclear. Here, the calli of European pear (Pyrus communis L.) treated with different lights were used to explore the changes in phenotype, lignin content, and H₂O₂ content, coupled with RNA-Seq and quantitative real-time PCR (qRT-PCR) to investigate the possible regulation pathway of light on lignin biosynthesis in stone cells. Results showed that blue light increased the expression of lignin structure genes and promoted lignin accumulation. Besides, four blue light receptors cryptochromes (CRYs) were identified in white pear, named PbCRY1a (Pbr024556.1), PbCRY1b (Pbr001636.3), PbCRY2a (Pbr023037.1), and PbCRY2b (Pbr002655.4). qRT-PCR analysis showed that PbCRY1a is highly expressed in cultivars with a high content of stone cells. Furthermore, the molecular function of PbCRY1a on stone cell formation in pear fruit was demonstrated by genetic transformation of pear calli and Agrobacterium-mediated transient overexpression in pear fruitlets. Co-expression network analyses with RNA-seq data showed that 8 MYB and 5 NAC genes were classified into different co-expression clusters with lignin biosynthesis genes under blue light conditions. These results indicate that CRY-mediated blue-light signal plays an important role in cell wall lignification and promotes the formation of stone cells in pear by regulating downstream genes.

Risk Assessment of the Chiral Fungicide Triticonazole: Enantioselective Effects, Toxicity, and Fate

The enantioselective toxicity of triticonazole (TRZ) to non-target organisms, the effect on wheat growth and quality, and the environmental fate of TRZ were investigated systematically in this study. The acute toxicity of S-TRZ to non-target aquatic and terrestrial organisms was greater than that of rac-TRZ and R-TRZ. The S-enantiomer significantly inhibited the growth and lodging resistance of wheat. S- and R-TRZ not only reduced the grain yield but also inhibited the activities of ADP-glucose pyrophosphorylase (AGPase) and starch synthase. The results of homology modeling and molecular docking further showed that the inhibition of AGPase activity by the two enantiomers hindered the accumulation of starch. By contrast, the racemate promoted the growth and development of wheat and improved grain quality. And the half-lives of the racemate in stems, grains, leaves, and soils were shorter than those of the enantiomers. The results of risk quotient (RQ) values showed that the application of TRZ enantiomers during wheat planting would bring a higher potential dietary risk to Chinese consumers. In comprehensive consideration of these results, the application of the racemate may be safer and more reasonable at the flowering stage of wheat.

Beyond the PAR spectra: impact of light quality on the germination, flowering, and metabolite content of Stevia rebaudiana (Bertoni)

BACKGROUND

Stevia rebaudiana is a high value crop due to the strong commercial demand for its metabolites (steviol glycosides) but has limited geographical cultivation range. In non-native environments with different daylength and light quality, Stevia has low germination rates and early flowering resulting in lower biomass and poor yield of the desired metabolites. In this study, artificial lighting with light-emitting diodes (LEDs) was used to determine if different light quality within and outside of the photosynthetically active radiation (PAR) range can be used to improve germination rates and yields for production of steviol glycosides for the herbal supplement and food industry.

RESULTS

Plants treated with red and blue light at an intensity of 130 μmol m^-2  s^-1 supplemented with 5% of UV-A light under a 16-h photoperiod produced the most desirable overall results with a high rate of germination, low percentage of early flowering, and high yields of dry leaf, stevioside and rebaudioside A, 175 days after planting.

CONCLUSION

While red and blue light combinations are effective for plant growth, the use of supplemental non-PAR irradiation of UV-A wavelength significantly and desirably delayed flowering, enhanced germination, biomass, rebaudioside A and stevioside yields, while supplemental green light improved yield of biomass and rebaudioside A, but not stevioside. Overall, the combination of red, blue and UV-A light resulted in the best overall productivity for Stevia rebaudiana. © 2021 Society of Chemical Industry.

Variety-specific transcript accumulation during reproductive stage in drought-stressed rice

The divergence of natural stress tolerance mechanisms between species is an intriguing phenomenon. To study it in rice, a comparative transcriptome analysis was carried out in 'heading' stage tissue (flag leaf, panicles and roots) of Nagina 22 (N22; drought-tolerant) and IR64 (drought-sensitive) plants subjected to field drought. Interestingly, N22 showed almost double the number of differentially expressed genes (DEGs) than IR64. Many DEGs colocalized within drought-related QTLs responsible for grain yield and drought tolerance and also associated with drought tolerance and critical drought-related plant traits such as leaf rolling, trehalose content, sucrose and cellulose content. Besides, co-expression analysis of the DEGs revealed several 'hub' genes known to actively regulate drought stress response. Strikingly, 1366 DEGs, including 21 'hub' genes, showed a distinct opposite regulation in the two rice varieties under similar drought conditions. Annotation of these variety-specific DEGs (VS-DEGs) revealed that they are distributed in various biological pathways. Furthermore, 103 VS-DEGs were found to physically interact with over 1300 genes, including 32 that physically interact with other VS-DEGs as well. The promoter region of these genes has sequence variations among the two rice varieties, which might be in part responsible for their unique expression pattern.

Enhancement of Lodging Resistance and Lignin Content by Application of Organic Carbon and Silicon Fertilization in Brassica napus L

This study was aimed to investigate the effects of organic carbon and silicon fertilizers on the lodging resistance, yield, and economic performance of rapeseed. Two cultivars, namely Jayou (lodging-resistant) and Chuannongyou (lodging-susceptible), were selected to evaluate the effects of various fertilizer treatments on rapeseed culm morphology, lignin accumulation, and their relationships with their lodging resistance indices. The results showed that both organic carbon and silicon fertilizer applications increased the plant height, basal stem diameter, internode plumpness, and bending strength of rapeseed in both the studied years. The bending strength was significantly and positively correlated with the lodging resistance index and lignin content. It was found that both organic carbon and silicon fertilizers had improved the activities of lignin biosynthesis enzymes (phenylalanine ammonia-lyase, 4-coumarate:CoA ligase, cinnamyl alcohol dehydrogenase, and peroxiredoxins) and their related genes to increase lignin accumulation in the culm, which ultimately improved the lodging resistance. At the same time, the thickness of the stem cortex, vascular bundle area, and xylem area was increased, and the stem strength was improved. The effect of silicon fertilizer was better than that of organic carbon fertilizer, but there was no significant difference with the mixed application of silicon fertilizer and organic carbon fertilizer. Similarly, silicon fertilizer increased the number of pods, significantly increased the yield, and improved the economic benefit, while organic carbon fertilizer had no significant effect on the yield. Therefore, we believe that organic carbon and silicon fertilizer can improve the lodging resistance of rape stems by improving the lignin accumulation and the mechanical tissue structure. Still, the effect of silicon fertilizer is the best. Considering the economic benefits, adding silicon fertilizer can obtain more net income than the mixed application of silicon fertilizer and organic carbon fertilizer.

Molecular signatures of local adaptation to light in Norway spruce

MAIN CONCLUSION

Transcriptomic and exome capture analysis reveal an adaptive cline for shade tolerance in Norway spruce. Genes involved in the lignin pathway and immunity seem to play a potential role in contributing towards local adaptation to light. The study of natural variation is an efficient method to elucidate how plants adapt to local climatic conditions, a key process for the evolution of a species. Norway spruce is a shade-tolerant conifer in which the requirement of far-red light for growth increases latitudinally northwards. The objective of the study is to characterize the genetic control of local adaptation to light enriched in far-red in Norway spruce, motivated by a latitudinal gradient for the Red:Far-red (R:FR) ratio to which Norway spruce has been proven to be genetically adapted. We have established the genomic signatures of local adaptation by conducting transcriptomic (total RNA-sequencing) and genomic analyses (exome capture), for the identification of genes differentially regulated along the cline. RNA-sequencing revealed 274 differentially expressed genes in response to SHADE (low R:FR light), between the southern and northern natural populations in Sweden. Exome capture included analysis of a uniquely large data set (1654 trees) that revealed missense variations in coding regions of nine differentially expressed candidate genes, which followed a latitudinal cline in allele and genotype frequencies. These genes included five transcription factors involved in vital processes like bud-set/bud-flush, lignin pathway, and cold acclimation and other genes that take part in cell-wall remodeling, secondary cell-wall thickening, response to starvation, and immunity. Based on these results, we suggest that the northern populations might not only be able to adjust their growing season in response to low R:FR light, but they may also be better adapted towards disease resistance by up-regulation of the lignin pathway that is linked to immunity. This forms a concrete basis for local adaptation to light quality in Norway spruce, one of the most economically important conifer tree species in Sweden.

Genotypic Variation of Endophytic Nitrogen-Fixing Activity and Bacterial Flora in Rice Stem Based on Sugar Content

Enhancement of the nitrogen-fixing ability of endophytic bacteria in rice is expected to result in improved nitrogen use under low-nitrogen conditions. Endophytic nitrogen-fixing bacteria require a large amount of energy to fix atmospheric nitrogen. However, it is unknown which carbon source and bacteria would affect nitrogen-fixing activity in rice. Therefore, this study examined genotypic variations in the nitrogen-fixing ability of rice plant stem as affected by non-structural carbohydrates and endophytic bacterial flora in field-grown rice. In the field experiments, six varieties and 10 genotypes of rice were grown in 2017 and 2018 to compare the acetylene reduction activity (nitrogen-fixing activity) and non-structural carbohydrates (glucose, sucrose, and starch) concentration in their stems at the heading stage. For the bacterial flora analysis, two genes were amplified using a primer set of 16S rRNA and nitrogenase (NifH) gene-specific primers. Next, acetylene reduction activity was correlated with sugar concentration among genotypes in both years, suggesting that the levels of soluble sugars influenced stem nitrogen-fixing activity. Bacterial flora analysis also suggested the presence of common and genotype-specific bacterial flora in both 16S rRNA and nifH genes. Similarly, bacteria classified as rhizobia, such as Bradyrhizobium sp. (Alphaproteobacteria) and Paraburkholderia sp. (Betaproteobacteria), were highly abundant in all rice genotypes, suggesting that these bacteria make major contributions to the nitrogen fixation process in rice stems. Gammaproteobacteria were more abundant in CG14 as well, which showed the highest acetylene reduction activity and sugar concentration among genotypes and is also proposed to contribute to the higher amount of nitrogen-fixing activity.

Agro-Techniques for Lodging Stress Management in Maize-Soybean Intercropping System-A Review

Lodging is one of the most chronic restraints of the maize-soybean intercropping system, which causes a serious threat to agriculture development and sustainability. In the maize-soybean intercropping system, shade is a major causative agent that is triggered by the higher stem length of a maize plant. Many morphological and anatomical characteristics are involved in the lodging phenomenon, along with the chemical configuration of the stem. Due to maize shading, soybean stem evolves the shade avoidance response and resulting in the stem elongation that leads to severe lodging stress. However, the major agro-techniques that are required to explore the lodging stress in the maize-soybean intercropping system for sustainable agriculture have not been precisely elucidated yet. Therefore, the present review is tempted to compare the conceptual insights with preceding published researches and proposed the important techniques which could be applied to overcome the devastating effects of lodging. We further explored that, lodging stress management is dependent on multiple approaches such as agronomical, chemical and genetics which could be helpful to reduce the lodging threats in the maize-soybean intercropping system. Nonetheless, many queries needed to explicate the complex phenomenon of lodging. Henceforth, the agronomists, physiologists, molecular actors and breeders require further exploration to fix this challenging problem.

Exploring feature selection of St John's wort grown under different light spectra using 1 H-NMR spectroscopy

INTRODUCTION

Nuclear magnetic resonance (NMR) spectroscopy combined with multivariate statistical analysis can provide tools to help detect differences in plant chemistry when grown under varying conditions. Hypericum perforatum, or Saint John's wort, plants are a suitable model to explore methods of discrimination between early stage plants grown in different conditions.

OBJECTIVES

The purpose of this work was to develop a method for identifying differences in chemical profiles between young Hypericum perforatum plants grown under different lighting conditions.

MATERIAL AND METHODS

Cuttings were grown for 3 weeks under different light conditions. Plant extracts were prepared in MeOD-d₄ and analysed by ¹ H-NMR. A multivariate analysis method of the NMR data was developed in an effort to determine variations in chemical profiles.

RESULTS

The method identified specific metabolites as drivers of difference between the plants grown under different light conditions. STOCSY (statistical total correlation spectroscopy) and quantification of highlighted metabolites supported the findings of the multivariate analysis. Glutamine, sucrose and fructose were found to be chemical markers of light quality in this study.

CONCLUSION

NMR metabolomics using a medium field instrument could find differences in plant chemistry when grown in different conditions. This method could easily be extended to benchtop instruments and be used for crop monitoring and growth condition optimisation.

How does nitrogen shape plant architecture?

Plant nitrogen (N), acquired mainly in the form of nitrate and ammonium from soil, dominates growth and development, and high-yield crop production relies heavily on N fertilization. The mechanisms of root adaptation to altered supply of N forms and concentrations have been well characterized and reviewed, while reports concerning the effects of N on the architecture of vegetative and reproductive organs are limited and are widely dispersed in the literature. In this review, we summarize the nitrate and amino acid regulation of shoot branching, flowering, and panicle development, as well as the N regulation of cell division and expansion in shaping plant architecture, mainly in cereal crops. The basic regulatory steps involving the control of plant architecture by the N supply are auxin-, cytokinin-, and strigolactone-controlled cell division in shoot apical meristem and gibberellin-controlled inverse regulation of shoot height and tillering. In addition, transport of amino acids has been shown to be involved in the control of shoot branching. The N supply may alter the timing and duration of the transition from the vegetative to the reproductive growth phase, which in turn may affect cereal crop architecture, particularly the structure of panicles for grain yield. Thus, proper manipulation of N-regulated architecture can increase crop yield and N use efficiency.

Effects of lignin, cellulose, hemicellulose, sucrose and monosaccharide carbohydrates on soybean physical stem strength and yield in intercropping

Soybean (Glycine max L.) has been extensively cultivated in maize-soybean relay intercropping systems in southwest China. However, during the early co-growth period, soybean seedlings suffer from severe shading by maize resulting in lodging and significant yield reduction. The purpose of the present research was to investigate the reasons behind severe lodging and yield loss. Therefore, four different soybean genotypes (B3, B15, B23, and B24) having different agronomic characteristics were cultivated in intercropping and monocropping planting patterns. The results showed that under different planting patterns, the stem resistance varied among genotypes (P < 0.01). The lodging resistance index of B3, B15, B23, and B24 genotypes was 70.9%, 60.5%, 65.2%, and 57.4%, respectively, under intercropping, among which the B24 genotype was less affected by the shade environment as there was little decrease in the lodging resistance index of this genotype under intercropping. The lignin content of B23 and B24 was significantly higher than that of B3 and B15 under both planting patterns. Under intercropping, the hemicellulose content of B23 and B24 stems was significantly higher than that of B3 and B15. Compared to the monocropping, the content of mannose in the structural carbohydrate of soybean stems was decreased in all genotypes except B23, but the difference was not significant. The content of xylose in the structural carbohydrate of soybean stems was significantly higher than that in B3 and B15. Mannose content showed no significant difference among genotypes. The arabinose content of B24 was significantly higher than that of B3, B15, and B23. The effective pod number, seed number per plant, seed weight per plant and yield of soybean plants were significantly decreased under intercropping. Conclusively, manipulation of structural and nonstructural carbohydrate rich soybean genotypes in intercropping systems could alleviate the yield loss due to lodging.

Optimized nitrogen management enhances lodging resistance of rice and its morpho-anatomical, mechanical, and molecular mechanisms

Increasing evidence shows that improved nitrogen management can enhance lodging resistance and lower internodes play a key role in the lodging resistance of rice. However, little is known about the cellular and molecular mechanisms underlying the enhanced lodging resistance under improved nitrogen management. In the present study, two rice varieties, with contrasting lodging resistance, were grown under optimized N management (OPT) and farmers’ fertilizer practices. Under OPT, the lower internodes of both cultivars were shorter but the upper internodes were longer, while both culm diameter and wall thickness of lower internodes were dramatically increased. Microscopic examination showed that the culm wall of lower internodes under OPT contained more sclerenchyma cells beneath epidermis and vascular bundle sheath. The genome-wide gene expression profiling revealed that transcription of genes encoding cell wall loosening factors was down-regulated while transcription of genes participating in lignin and starch synthesis was up-regulated under OPT, resulting in inhibition of longitudinal growth, promotion in transverse growth of lower internodes and enhancement of lodging resistance. This is the first comprehensive report on the morpho-anatomical, mechanical, and molecular mechanisms of lodging resistance of rice under optimized N management.

Improving Lodging Resistance: Using Wheat and Rice as Classical Examples

One of the most chronic constraints to crop production is the grain yield reduction near the crop harvest stage by lodging worldwide. This is more prevalent in cereal crops, particularly in wheat and rice. Major factors associated with lodging involve morphological and anatomical traits along with the chemical composition of the stem. These traits have built up the remarkable relationship in wheat and rice genotypes either prone to lodging or displaying lodging resistance. In this review, we have made a comparison of our conceptual perceptions with foregoing published reports and proposed the fundamental controlling techniques that could be practiced to control the devastating effects of lodging stress. The management of lodging stress is, however, reliant on chemical, agronomical, and genetic factors that are reducing the risk of lodging threat in wheat and rice. But, still, there are many questions remain to be answered to elucidate the complex lodging phenomenon, so agronomists, breeders, physiologists, and molecular biologists require further investigation to address this challenging problem.

Shade tolerance in Swarnaprabha rice is associated with higher rate of panicle emergence and positively regulated by genes of ethylene and cytokinin pathway

This study identifies characteristics of seedling, mature plant phenotypes, changes at genetic and genomic level associated with Swarnaprabha (SP) rice grown under prolonged shade and compared with Nagina 22 (N22). Coleoptile length under low red/far-red was intermediate between that in dark and red light in a 7-days growth frame. Whereas, highest rootlet number was discriminating in seedlings grown for 28 days in hydroponics. In shade, SP and N22 both showed several tolerant mature plant phenotypes, except the panicle length, yield per plant and % grain filling, which were higher in SP. Percentage decrease in yield / plant in shade showed significant positive correlation with increase in NDVI, decrease in panicle length and % grain filling (p ≤ 0.01). Rate of panicle emergence in shade was higher in SP than N22. Expression patterns of PHYTOCHROME INTERACTING FACTOR LIKE-13 and PHYTOCHROME B were contrasting in SP and N22 seedlings under continuous red or red/far-red. Microarray analysis revealed the up-regulation of most of the ethylene and cytokinin pathway genes in shade grown panicles of SP. Significant up-regulation of ETHYLENE RESPONSE ELEMENT BINDING PROTEIN-2, MOTHER OF FLOWERING TIME 1, and SHORT PANICLE1 genes in shade grown panicles of SP could explain its sustainable higher yield in shade.

Selenium reduces cadmium uptake into rice suspension cells by regulating the expression of lignin synthesis and cadmium-related genes

Although previous studies have indicated that selenium (Se) can reduce cadmium (Cd) uptake into rice, the mechanism at the cellular level has not been reported. Here, rice suspension cells exposed to Cd treatment in the presence or absence of Se were characterized. Compared with treatment with alone, pretreatment with Se increased the proportion of live cells by 83.1%. The levels of reactive oxygen species and mitochondrial membrane potential in the Se-pretreated rice cells were decreased by 86.6% and 76.0%, respectively. In addition, non-invasive micro-test technology suggested that the mean values of Cd²⁺ influx decreased significantly in the Se-pretreated rice cells in a concentration-dependent manner. The results of inductively coupled plasma-mass spectrometry (ICP-MS) showed that 67.4%-78.8% Cd accumulated onto the cell walls of the pretreated-Se rice cells. The addition of Se increased the lignin content and thickness of the cell walls, leading to an improved mechanical force of the cell walls, as determined by atomic force microscopy (AFM). Furthermore, Se pretreatment decreased the expression of genes involved in Cd uptake (OsNramp5) and transport (OsLCT1) but activated the expression of genes involved in Cd transport into vacuoles (OsHMA3) and lignin synthesis (OsPAL, OsCoMT and Os4CL3). These results indicated that supplying Se alleviates Cd toxicity by regulating the express of lignin synthesis and Cd-related genes. The present findings provide new insights on a plausible explanation of the Se-reduced Cd uptake into rice.

Application of paclobutrazol: a strategy for inducing lodging resistance of wheat through mediation of plant height, stem physical strength, and lignin biosynthesis

Lodging is a major constraint contributing to poor grain yield and quality of wheat (Triticum aestivum L.) worldwide. The use of plant growth regulators is becoming a foremost agro-chemical approach for minimizing the risk of lodging in cereal crops. The present study was conducted to examine the effects of the paclobutrazol application on culm physical strength, lignin content, and lodging resistance of wheat. Wheat seeds were soaked in paclobutrazol at the concentrations of 0 (CK, as control), 200 (PB1), 300 (PB2), and 400 (PB3) mg L^-1. Our results showed that paclobutrazol resulted in a dose-dependent decrease of plant height, internode length, and center of gravity height. Paclobutrazol treatments evidently increased the culm diameter, culm filling degree, and wall thickness of basal internodes, resulting in greater stalk-breaking strength and lodging resistance index (CLRI), where their maximum values were obtained with PB1 treatment. In addition, the activities of lignin-related enzymes were improved by paclobutrazol, particularly at low concentration, which increased the lignin accumulation of the basal internodes of wheat, subsequently improving the capability of stalk lodging resistance. Moreover, the correlation analysis revealed significant correlations between stem diameter, culm filling degree, and lignin with stalk bending strength and CLRI. The paclobutrazol concentration ≥ 300 mg L^-1 (PB2 and PB3 treatments) showed inhibitive effects on various culm morphological traits. These results suggest that not only the plant height, but also the lignin contents and physical strength of internodes are closely related with the lodging resistance of wheat, and reduction in plant height along with improved culm morphological characteristics and higher lignin accumulation in basal internodes could effectively relieve the risk of lodging.

Blue Light Regulates Secondary Cell Wall Thickening via MYC2/MYC4 Activation of the NST1-Directed Transcriptional Network in Arabidopsis

Secondary cell walls (SCWs) are formed in some specific types of plant cells, providing plants with mechanical strength. During plant growth and development, formation of secondary cell walls is regulated by various developmental and environmental signals. The underlying molecular mechanisms are poorly understood. In this study, we analyzed the blue light receptor cryptochrome1 (cry1) mutant of Arabidopsis thaliana for its SCW phenotypes. During inflorescence stem growth, SCW thickening in the vasculature was significantly affected by blue light. cry1 plants displayed a decline of SCW thickening in fiber cells, while CRY1 overexpression led to enhanced SCW formation. Transcriptome analysis indicated that the reduced SCW thickening was associated with repression of the NST1-directed transcription regulatory networks. Further analyses revealed that the expression of MYC2/MYC4 that is induced by blue light activates the transcriptional network underlying SCW thickening. The activation is caused by direct binding of MYC2/MYC4 to the NST1 promoter. This study demonstrates that SCW thickening in fiber cells is regulated by a blue light signal that is mediated through MYC2/MYC4 activation of NST1-directed SCW formation in Arabidopsis.

Exploiting SPL genes to improve maize plant architecture tailored for high-density planting

Maize (Zea mays ssp. mays) is an agronomically important crop and also a classical genetic model for studying the regulation of plant architecture formation, which is a critical determinant of grain yield. Since the 1930s, increasing planting density has been a major contributing factor to the >7-fold increase in maize grain yield per unit land area in the USA, which is accompanied by breeding and utilization of cultivars characterized by high-density-tolerant plant architecture, including decreased ear height, lodging resistance, more upright leaves, reduced tassel branch number, and reduced anthesis-silking interval (ASI). Recent studies demonstrated that phytochrome-mediated red/far-red light signaling pathway and the miR156/SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) regulatory module co-ordinately regulate the shade avoidance response and diverse aspects of plant architecture in responding to shading in Arabidopsis. The maize genome contains 30 ZmSPL genes, and 18 of them are predicted as direct targets of zma-miR156s. Accumulating evidence indicates that ZmSPL genes play important roles in regulating maize flowering time, plant/ear height, tilling, leaf angle, tassel and ear architecture, and grain size and shape. Finally, we discuss ways to exploit maize SPL genes and downstream targets for improving maize plant architecture tailored for high-density planting.

Shade Inhibits Leaf Size by Controlling Cell Proliferation and Enlargement in Soybean

To gain more insight into the physiological function of shade and how shade affects leaf size, we investigated the growth, leaf anatomical structure, hormones and genes expressions in soybean. Soybean seeds were sown in plastic pots and were allowed to germinate and grow for 30 days under shade or full sunlight conditions. Shade treated plants showed significantly increase on stem length and petiole length, and decrease on stem diameters, shoot biomass and its partition to leaf also were significantly lower than that in full sunlight. Smaller and thinner on shade treated leaves than corresponding leaves on full sunlight plants. The decreased leaf size caused by shade was largely attributable to cell proliferation in young leaves and both cell proliferation and enlargement in old leaves. Shade induced the expression of a set of genes related to cell proliferation and/or enlargement, but depended on the developmental stage of leaf. Shade significantly increased the auxin and gibberellin content, and significantly decreased the cytokinin content in young, middle and old leaves. Taken together, these results indicated that shade inhibited leaf size by controlling cell proliferation and enlargement, auxin, gibberellin and cytokinin may play important roles in this process.