Supplementary Calcium Restores Peanut (Arachis hypogaea) Growth and Photosynthetic Capacity Under Low Nocturnal Temperature

Microwave seed priming and ascorbic acid assisted phytoextraction of heavy metals from surgical industry effluents through spinach

The prevalence of inorganic pollutants in the environment, including heavy metals (HMs), necessitates a sustainable and cost-effective solution to mitigate their impacts on the environment and living organisms. The present research aimed to assess the phytoextraction capability of spinach (Spinach oleracea L.), under the combined effects of ascorbic acid (AA) and microwave (MW) irradiation amendments, cultivated using surgical processing wastewater. In a preliminary study, spinach seeds were exposed to MW radiations at 2.45 GHz for different durations (15, 30, 45, 60, and 90 seconds). Maximum germination was observed after the 30 seconds of radiation exposure. Healthy spinach seeds treated with MW radiations for 30 s were cultivated in the sand for two weeks, after which juvenile plants were transferred to a hydroponic system. Surgical industry wastewater in different concentrations (25 %, 50 %, 75 %, 100 %) and AA (10 mM) were provided to both MW-treated and untreated plants. The results revealed that MW-treatment significantly enhanced the plant growth, biomass, antioxidant enzyme activities and photosynthetic pigments, while untreated plants exhibited increased reactive oxygen species (ROS) and electrolyte leakage (EL) compared with their controls. The addition of AA to both MW-treated and untreated plants improved their antioxidative defense capacity under HMs-induced stress. MW-treated spinach plants, under AA application, demonstrated relatively higher concentrations and accumulation of HMs including lead (Pb), cadmium (Cd) and nickel (Ni). Specifically, MW-treated plants with AA amendment showed a significant increase in Pb concentration by 188 % in leaves, Cd by 98 %, and Ni by 102 % in roots. Additionally, the accumulation of Ni increased by 174 % in leaves, Cd by 168 % in roots, and Pb by 185 % in the stem of spinach plant tissues compared to MW-untreated plants. These findings suggested that combining AA with MW irradiation of seeds could be a beneficial strategy for increasing the phytoextraction of HMs from wastewater and improving overall plant health undergoing HMs stress.

Mitigating drought-induced oxidative stress in wheat (Triticum aestivum L.) through foliar application of sulfhydryl thiourea

Drought stress is a major abiotic stress affecting the performance of wheat (Triticum aestivum L.). The current study evaluated the effects of drought on wheat phenology, physiology, and biochemistry; and assessed the effectiveness of foliar-applied sulfhydryl thiourea to mitigate drought-induced oxidative stress. The treatments were: wheat varieties; V1 = Punjab-2011, V2 = Galaxy-2013, V3 = Ujala-2016, and V4 = Anaaj-2017, drought stress; D1 = control (80% field capacity [FC]) and D2 = drought stress (40% FC), at  the reproductive stage, and sulfhydryl thiourea (S) applications; S0 = control-no thiourea and S1 = foliar thiourea application @ 500 mg L-1. Results of this study indicated that growth parameters, including height, dry weight, leaf area index (LAI), leaf area duration (LAD), crop growth rate (CGR), net assimilation rate (NAR) were decreased under drought stress-40% FC, as compared to control-80% FC. Drought stress reduced the photosynthetic efficiency, water potential, transpiration rates, stomatal conductances, and relative water contents by 18, 17, 26, 29, and 55% in wheat varieties as compared to control. In addition, foliar chlorophyll a, and b contents were also lowered under drought stress in all wheat varieties due to an increase in malondialdehyde and electrolyte leakage. Interestingly, thiourea applications restored wheat growth and yield attributes by improving the production and activities of proline, antioxidants, and osmolytes under normal and drought stress as compared to control. Thiourea applications improved the osmolyte defense in wheat varieties as peroxidase, superoxide dismutase, catalase, proline, glycine betaine, and total phenolic were increased by 13, 20, 12, 17, 23, and 52%; while reducing the electrolyte leakage and malondialdehyde content by 49 and 32% as compared to control. Among the wheat varieties, Anaaj-2017 showed better resilience towards drought stress and also gave better response towards thiourea application based on morpho-physiological, biochemical, and yield attributes as compared to Punjab-2011, Galaxy-2013, and Ujala-2016. Eta-square values showed that thiourea applications, drought stress, and wheat varieties were key contributors to most of the parameters measured. In conclusion, the sulfhydryl thiourea applications improved the morpho-physiology, biochemical, and yield attributes of wheat varieties, thereby mitigating the adverse effects of drought.  Moving forward, detailed studies pertaining to the molecular and genetic mechanisms under sulfhydryl thiourea-induced drought stress tolerance are warranted.

Calcium enhanced the resistance against Phoma arachidicola by improving cell membrane stability and regulating reactive oxygen species metabolism in peanut

BACKGROUND

Peanut (Arachis hypogaea), a vital oil and food crop globally, is susceptible to web blotch which is a significant foliar disease caused by Phoma arachidicola Marasas Pauer&Boerema leading to substantial yield losses in peanut production. Calcium treatment has been found to enhance plant resistance against pathogens.

RESULTS

This study investigates the impact of exogenous calcium on peanut resistance to web blotch and explores its mechanisms. Greenhouse experiments revealed that exogenous calcium treatment effectively enhanced resistance to peanut web blotch. Specifically, amino acid calcium and sugar alcohol calcium solutions demonstrated the best induced resistance effects, achieving reduction rates of 61.54% and 60% in Baisha1016, and 53.94% and 50% in Luhua11, respectively. All exogenous calcium treatments reduced malondialdehyde (MDA) and relative electrical conductivity (REC) levels in peanut leaves, mitigating pathogen-induced cell membrane damage. Exogenous calcium supplementation led to elevated hydrogen peroxide (H2O2) content and superoxide anion (O2∙-) production in peanut leaves, facilitating the accumulation of reactive oxygen species (ROS) crucial for plant defense responses. Amino acid calcium and sugar alcohol calcium treatments significantly boosted activities of peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) in peanut leaves. Activation of these antioxidant enzymes effectively scavenged excess ROS, maintaining ROS balance and mitigating cellular damage.

CONCLUSIONS

In summary, exogenous calcium treatment triggered ROS production, which was subsequently eliminated by the activation of antioxidant enzymes, thereby reducing cell membrane damage and inducing defense responses against peanut web blotch.

Thiourea improves yield and quality traits of Brassica napus L. by upregulating the antioxidant defense system under high temperature stress

High temperature stress influences plant growth, seed yield, and fatty acid contents by causing oxidative damage. This study investigated the potential of thiourea (TU) to mitigate oxidative stress and restoring seed oil content and quality in canola. The study thoroughly examined three main factors: (i) growth conditions-control and high temperature stress (35 °C); (ii) TU supplementation (1000 mg/L)-including variations like having no TU, water application at the seedling stage, TU application at seedling stage (BBCH Scale-39), water spray at anthesis stage, and TU application at anthesis stage (BBCH Scale-60); (iii) and two canola genotypes, 45S42 and Hiola-401, were studied separately. High temperature stress reduced growth and tissue water content, as plant height and relative water contents were decreased by 26 and 36% in 45S42 and 27 and 42% Hiola-401, respectively, resulting in a substantial decrease in seed yield per plant by 36 and 38% in 45S42 and Hiola-401. Seed oil content and quality parameters were also negatively affected by high temperature stress as seed oil content was reduced by 32 and 35% in 45S42 and Hiola-401. High-temperature stress increased the plant stress indicators like malondialdehyde, H2O2 content, and electrolyte leakage; these indicators were increased in both canola genotypes as compared to control. Interestingly, TU supplementation restored plant performance, enhancing height, relative water content, foliar chlorophyll (SPAD value), and seed yield per plant by 21, 15, 30, and 28% in 45S42; 19, 13, 26, and 21% in Hiola-401, respectively, under high temperature stress as compared to control. In addition, seed quality, seed oil content, linoleic acid, and linolenic acid were improved by 16, 14, and 22% in 45S42, and 16, 11, and 23% in Hiola-401, as compared to control. The most significant improvements in canola seed yield per plant were observed when TU was applied at the anthesis stage. Additionally, the research highlighted that canola genotype 45S42 responded better to TU applications and exhibited greater resilience against high temperature stress compared to genotype Hiola-401. This interesting study revealed that TU supplementation, particularly at the anthesis stage, improved high temperature stress tolerance, seed oil content, and fatty acid profile in two canola genotypes.

Interaction of titanium dioxide nanoparticles with PVC-microplastics and chromium counteracts oxidative injuries in Trachyspermum ammi L. by modulating antioxidants and gene expression

The emergence of polyvinyl chloride (PVC) microplastics (MPs) as pollutants in agricultural soils is increasingly alarming, presenting significant toxic threats to soil ecosystems. Ajwain (Trachyspermum ammi L.), a plant of significant medicinal and culinary value, is increasingly subjected to environmental stressors that threaten its growth and productivity. This situation is particularly acute given the well-documented toxicity of chromium (Cr), which has been shown to adversely affect plant biomass and escalate risks to the productivity of such economically and therapeutically important species. The present study was conducted to investigate the individual effects of different levels of PVC-MPs (0, 2, and 4 mg L-1) and Cr (0, 150, and 300 mg kg-1) on various aspects of plant growth. Specifically, we examined growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress responses, antioxidant compound activity (both enzymatic and nonenzymatic), gene expression, sugar content, nutritional status, organic acid exudation, and Cr accumulation in different parts of Ajwain (Trachyspermum ammi L.) seedlings, which were also exposed to varying levels of titanium dioxide (TiO2) nanoparticles (NPs) (0, 25, and 50 µg mL-1). Results from the present study showed that the increasing levels of Cr and PVC-MPs in soils significantly decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants. Conversely, increasing levels of Cr and PVC-MPs in the soil increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation pattern in the roots of T. ammi seedlings. Interestingly, the application of TiO2-NPs counteracted the toxicity of Cr and PVC-MPs in T. ammi seedlings, leading to greater growth and biomass. This protective effect is facilitated by the NPs' ability to sequester reactive oxygen species, thereby reducing oxidative stress and lowering Cr concentrations in both the roots and shoots of the plants. Our research findings indicated that the application of TiO2-NPs has been shown to enhance the resilience of T. ammi seedlings to Cr and PVC-MPs toxicity, leading to not only improved biomass but also a healthier physiological state of the plants. This was demonstrated by a more balanced exudation of organic acids, which is a critical response mechanism to metal stress.

Exogenous Melatonin Promotes Cold Tolerance in Grape Seedlings: Physiological, Transcriptomic, and Functional Evidence

Melatonin (MEL) is an antioxidant molecule that enhances plant tolerance to environmental stress. However, the mechanisms by which MEL regulates cold signaling pathways in grapes under cold stress remain elusive. Here, we investigated the physiological and transcriptomic changes in grape seedlings treated with exogenous MEL to determine their protective role under cold stress. Results showed that 150 μM MEL effectively attenuated cold-induced cell damage by reducing reactive oxygen species (ROS) and preserving the chloroplast structure and function. MEL also inhibited tannin degradation, which contributed to its protective effect. Exogenous MEL promoted the synthesis of endogenous MEL, abscisic acid, auxin, and cytokinin while inhibiting gibberellin. Transcriptomic profiling revealed 776 differentially expressed transcripts in MEL-treated samples compared to controls. Functional analysis of a candidate hub gene, VvHSFA6b, showed that its overexpression in grape calli enhances cold tolerance by activating jasmonic acid synthesis pathway genes, promoting JA accumulation, and inhibiting JAZ-repressed transcription factors.

Physiological and Transcriptomic Analysis Reveals That Melatonin Alleviates Aluminum Toxicity in Alfalfa (Medicago sativa L.)

Aluminum (Al) toxicity is the most common factor limiting the growth of alfalfa in acidic soil conditions. Melatonin (MT), a significant pleiotropic molecule present in both plants and animals, has shown promise in mitigating Al toxicity in various plant species. This study aims to elucidate the underlying mechanism by which melatonin alleviates Al toxicity in alfalfa through a combined physiological and transcriptomic analysis. The results reveal that the addition of 5 μM melatonin significantly increased alfalfa root length by 48% and fresh weight by 45.4% compared to aluminum treatment alone. Moreover, the 5 μM melatonin application partially restored the enlarged and irregular cell shape induced by aluminum treatment, resulting in a relatively compact arrangement of alfalfa root cells. Moreover, MT application reduces Al accumulation in alfalfa roots and shoots by 28.6% and 27.6%, respectively. Additionally, MT plays a crucial role in scavenging Al-induced excess H2O2 by enhancing the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), consequently reducing malondialdehyde (MDA) levels. More interestingly, the RNA-seq results reveal that MT application significantly upregulates the expression of xyloglucan endotransglucosylase/hydrolase (XTH) and carbon metabolism-related genes, including those involved in the glycolysis process, as well as sucrose and starch metabolism, suggesting that MT application may mitigate Al toxicity by facilitating the binding of Al to the cell walls, thereby reducing intracellular Al accumulation, and improving respiration and the content of sucrose and trehalose. Taken together, our study demonstrates that MT alleviates Al toxicity in alfalfa by reducing Al accumulation and restoring redox homeostasis. These RNA-seq results suggest that the alleviation of Al toxicity by MT may occur through its influence on cell wall composition and carbon metabolism. This research advances our understanding of the mechanisms underlying MT's effectiveness in mitigating Al toxicity, providing a clear direction for our future investigations into the underlying mechanisms by which MT alleviates Al toxicity in alfalfa.

Effect of Exogenous Calcium on Tolerance of Winter Wheat to Cold Stress during Stem Elongation Stage

Low-temperature stress during stem elongation is a major factor limiting wheat yield. While calcium (Ca2+) is known to enhance stress tolerance, it's potential as an alternative to cold priming and the underlying mechanisms in wheat remains unclear. The current study assessed the effects of exogenous Ca2+ and calcium inhibitors on wheat growth and related physiology mechanisms under low-temperature stress. The results revealed that exogenous Ca2+ increased photosynthesis and antioxidant capacity, lowered cell membrane damage, and ultimately enhanced tolerance to low-temperature stress during the stem elongation stage, compared with the non-exogenous Ca2+ treatment. Moreover, exogenous Ca2+ induced endogenous Ca2+ content and triggered the upregulation of Ca2+ signaling and cold-responsive related genes. This study highlights the significance of exogenous Ca2+ in enhancing stress tolerance and contributing to wheat yield improvement under low-temperature stress.

The physio-biochemical characterization reflected different calcium utilization efficiency between the sensitive and tolerant peanut accessions under calcium deficiency

Peanut yield in southern China is usually limited by calcium deficiency in soil. Most previous studies have found that small-seed varieties showed higher tolerance than large-seed varieties (e.g. Virginia type) under calcium deficiency, however, our preliminary research found that sensitive varieties also existed in small-seed counterparts. Few studies have been conducted to characterize low-calcium tolerance among small-seed germplasms with genetic diversity, and the differences in physiological characteristics between sensitive and tolerant varieties has not been reported yet. Thus, in order to better understand such differences, the current study firstly collected and characterized a diversity germplasm panel consisting of 50 small-seed peanut genotypes via a 2-year field trial, followed by the physiological characterization in sensitive (HN032) and tolerant (HN035) peanut genotypes under calcium deficiency. As a result, the adverse effects brought by calcium deficiency on calcium uptake and distribution in HN032 was much larger than HN035. In details, calcium uptake in the aboveground part (leaves and stems) was reduced by 16.17% and 33.66%, while in the underground part (roots and pods), it was reduced by 13.69% and 68.09% under calcium deficiency for HN035 and HN032, respectively; The calcium distribution rate in the pods of HN035 was 2.74 times higher than HN032. The utilization efficiency of calcium in the pods of HN035 was 1.68 and 1.37 times than that of HN032 under calcium deficiency and sufficiency, respectively. In addition, under calcium deficiency conditions, the activities of antioxidant enzymes SOD, POD, and CAT, as well as the MDA content, were significantly increased in the leaves of HN032, peanut yield was significantly reduced by 22.75%. However, there were no significant changes in the activities of antioxidant enzymes, MDA content, and peanut yield in HN035. Therefore, higher calcium absorption and utilization efficiency may be the key factors maintaining peanut yield in calcium-deficient conditions for tolerant genotypes. This study lays a solid foundation for selecting low-calcium tolerant varieties in future peanut breeding.

Exogenous calcium: Its mechanisms and research advances involved in plant stress tolerance

Abiotic stresses are various environmental factors that inhibit a normal plant growth and limit the crop productivity. Plant scientists have been attempting for a long time to understand how plants respond to these stresses and find an effective and feasible solution in mitigating their adverse impacts. Exogenous calcium ion as an essential element for the plant growth, development and reproduction has proven to be effective in alleviating plant stresses through enhancing its resistance or tolerance against them. With a comprehensive review of most recent advances and the analysis by VOSviewer in the researches on this focus of "exogenous calcium" and "stress" for last decade, this paper summarizes the mechanisms of exogenous calcium that are involved in plant defensive responses to abiotic stresses and classifies them accordingly into six categories: I) stabilization of cell walls and membranes; II) regulation of Na⁺ and K⁺ ratios; III) regulation of hormone levels in plants; IV) maintenance of photosynthesis; V) regulation of plant respiratory metabolism and improvement of root activities; and VI) induction of gene expressions and protein transcriptions for the stress resistance. Also, the progress and advances from the updated researches on exogenous calcium to alleviate seven abiotic stresses such as drought, flooding, salinity, high temperature, low temperature, heavy metals, and acid rain are outlined. Finally, the future research perspectives in agricultural production are discussed.

Adaptation of protein phosphatases in Oryza sativa and Cucumis sativus to microcystins

Microcystins (MCs) in irrigation water could inhibit crop growth and yield. Protein phosphatases (PPs) play an important role in regulating physiological mechanisms in plants to adapt abiotic stresses. To clarify the adaptation mechanism in plants to MCs stress, we compared PPs in rice and cucumber leaves by analyzing PPs total activity, protein phosphatase-2A (PP2A) activity and expression, as well as related growth and gas exchange parameters. After 7-day exposure of MCs (5 ~ 100 µg/L) and 7-day recovery without MCs, rice showed higher tolerance to MCs by analyzing dry weight and gas exchange parameters. Both crops may regulate PPs activity to adapt MCs stress by increasing the expression of genes encoding PPs. Among them, PP2A activity in two crops showed more sensitivity to MCs than total PPs activity. In addition, the higher expressions of PP2A catalytic and regulatory subunits and lower decrease PP2A activity were observed in rice leaves compared to cucumber. All results suggest that the expression levels of PP2A subunits could play a role in maintaining the activity of PP2A to regulating plant tolerance to MCs stress.

Ecology and management of the invasive land snail Bulimulus bonariensis (Rafinesque, 1833) (Stylommatophora: Bulimulidae) in row crops

Solutions for managing the growing populations of the snail Bulimulus bonariensis (Rafinesque, 1833) in row crops, notably peanut (Arachis hypogaea L.), are urgently needed in the United States. This species has become a concern to the economy and food security for infesting commercial crops in U.S. southern states. In the present study, sampling, trapping, and management strategies were investigated to support a management program for B. bonariensis in row crops. In addition, the preference of B. bonariensis for species of row crops and weeds, used as a shelter, and snail dispersal capacity were documented. The results indicated that the ideal tools for monitoring and capturing snails are beat cloth and cardboard trap, respectively. Metaldehyde 4% bait produced effective control. Tillage was tested as an alternative cultural management tactic and produced the most promising outcomes in lowering snail populations. According to snail ecological studies, peanut and soybean are the preferred crops used as shelter over cotton and corn. Among eight common winter-growing weeds, the favored non-crop host plants are cutleaf primrose (Oenothera laciniata) and dandelion (Taraxacum officinale). The snail field population tends to increase as early spring temperatures rise, with more snails becoming trapped in warm, humid conditions but not through heavy precipitation. This study provides ecology information on B. bonariensis and validates tactics to manage this invasive species in row crops, in an IPM approach.

Exogenous 24-epibrassinolide boosts plant growth under alkaline stress from physiological and transcriptomic perspectives: The case of broomcorn millet (Panicum miliaceum L.)

Land alkalization is an abiotic stress that affects global sustainable agricultural development and the balance of natural ecosystems. In this study, two broomcorn millet cultivars, T289 (alkaline-tolerant) and S223 (alkaline-sensitive), were selected to investigate the response of broomcorn millet to alkaline stress and the role of brassinolide (BR) in alkaline tolerance. Phenotypes, physiologies, and transcriptomes of T289 and S223 plants under only alkaline stress (AS) and alkaline stress with BR (AB) were compared. The results showed that alkaline stress inhibited growth, promoted the accumulation of soluble sugars and malondialdehyde, enhanced electrolyte leakage, and destroyed the integrity of broomcorn millet stomata. In contrast, BR lessened the negative effects of alkaline stress on plants. Transcriptome sequencing analysis showed that relative to control groups (CK, nutrient solution), in AS groups, 21,113 and 12,151 differentially expressed genes (DEGs) were identified in S223 and T289, respectively. Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed various terms and pathways related to metabolism. Compared to S223, alkaline stress strongly activated the brassinosteroid biosynthesis pathway in T289. Conversely, ARF, TF, and TCH4, associated with cell growth and elongation, were inhibited by alkaline stress in S223. Moreover, alkaline stress induced the activation of the mitogen-activated protein kinase (MAPK) pathway, the abscisic acid signaling pathway that initiates stomatal closure, as well as the starch and sucrose metabolism. The EG and BGL genes, which are associated with cellulose degradation, were notably activated. BR enhanced alkaline tolerance, thereby alleviating the transcriptional responses of the two cultivars. Cultivar T289 is better in alkalized regions. Taken together, these results reveal how broomcorn millet responds to alkaline stress and BR mitigates alkaline stress, thus promoting agriculture in alkalized regions.

Calcium and Boron Fertilization Improves Soybean Photosynthetic Efficiency and Grain Yield

Foliar fertilization with calcium (Ca) and boron (B) at flowering can promote flower retention and pod fixation, thereby increasing the number of pods per plant and, in turn, crop productivity. The objective of this work was to investigate the effects of Ca + B fertilization during flowering on the nutritional, metabolic and yield performance of soybean (Glycine max L.) The treatments consisted of the presence and the absence of Ca + B fertilization in two growing seasons. Crop nutritional status, gas exchange parameters, photosynthetic enzyme activity (Rubisco), total soluble sugar content, total leaf protein concentration, agronomic parameters, and grain yield were evaluated. Foliar Ca + B fertilization increased water use efficiency and carboxylation efficiency, and the improvement in photosynthesis led to higher leaf sugar and protein concentrations. The improvement in metabolic activity promoted a greater number of pods and grains plant^-1, culminating in higher yields. These results indicate that foliar fertilization with Ca + B can efficiently improve carbon metabolism, resulting in better yields in soybean.

The significance of calcium-sensing receptor in sustaining photosynthesis and ameliorating stress responses in plants

Calcium ions (Ca²⁺) regulate plant growth and development during exposure to multiple biotic and abiotic stresses as the second signaling messenger in cells. The extracellular calcium-sensing receptor (CAS) is a specific protein spatially located on the thylakoid membrane. It regulates the intracellular Ca²⁺ responses by sensing changes in extracellular Ca²⁺ concentration, thereby affecting a series of downstream signal transduction processes and making plants more resilient to respond to stresses. Here, we summarized the discovery process, structure, and location of CAS in plants and the effects of Ca²⁺ and CAS on stomatal functionality, photosynthesis, and various environmental adaptations. Under changing environmental conditions and global climate, our study enhances the mechanistic understanding of calcium-sensing receptors in sustaining photosynthesis and mediating abiotic stress responses in plants. A better understanding of the fundamental mechanisms of Ca²⁺ and CAS in regulating stress responses in plants may provide novel mitigation strategies for improving crop yield in a world facing more extreme climate-changed linked weather events with multiple stresses during cultivation.

Exogenous Ca2+ priming can improve peanut photosynthetic carbon fixation and pod yield under early sowing scenarios in the field

Harnessing cold-resilient and calcium-enriched peanut production technology are crucial for high-yielding peanut cultivation in high-latitude areas. However, there is limited field data about how exogenous calcium (Ca²⁺) application would improve peanut growth resilience during exposure to chilling stress at early sowing (ES). To help address this problem, a two-year field study was conducted to assess the effects of exogenous foliar Ca²⁺ application on photosynthetic carbon fixation and pod yield in peanuts under different sowing scenarios. We measured plant growth indexes, leaf photosynthetic gas exchange, photosystems activities, and yield in peanuts. It was indicated that ES chilling stress at the peanut seedling stage led to the reduction of Pn, g_s, Tr, Ls, WUE, respectively, and the excessive accumulation of non-structural carbohydrates in leaves, which eventually induced a chilling-dependent feedback inhibition of photosynthesis due mainly to weaken growth/sink demand. While exogenous Ca²⁺ foliar application improved the export of nonstructural carbohydrates, and photosynthetic capacity, meanwhile activated cyclic electron flow, thereby enhancing growth and biomass accumulation in peanut seedlings undergoing ES chilling stress. Furthermore, ES combined with exogenous Ca²⁺ application can significantly enhance plant chilling resistance and peanut yield ultimately in the field. In summary, the above results demonstrated that exogenous foliar Ca²⁺ application restored the ES-linked feedback inhibition of photosynthesis, enhancing the growth/sink demand and the yield of peanuts.

Mycorrhizal symbiosis reprograms ion fluxes and fatty acid metabolism in wild jujube during salt stress

Chinese jujube (Ziziphus jujuba) is an important fruit tree in China, and soil salinity is the main constraint affecting jujube production. It is unclear how arbuscular mycorrhizal (AM) symbiosis supports jujube adaptation to salt stress. Herein, we performed comparative physiological, ion flux, fatty acid (FA) metabolomic, and transcriptomic analyses to examine the mechanism of AM jujube responding to salt stress. AM seedlings showed better performance during salt stress. AM symbiosis altered phytohormonal levels: indole-3-acetic acid and abscisic acid contents were significantly increased in AM roots and reduced by salt stress. Mycorrhizal colonization enhanced root H+ efflux and K+ influx, while inducing expression of plasma membrane-type ATPase 7 (ZjAHA7) and high-affinity K+ transporter 2 (ZjHAK2) in roots. High K+/Na+ homeostasis was maintained throughout salt exposure. FA content was elevated in AM leaves as well as roots, especially for palmitic acid, oleic acid, trans oleic acid, and linoleic acid, and similar effects were also observed in AM poplar (Populus. alba × Populus. glandulosa cv. 84K) and Medicago truncatula, indicating AM symbiosis elevating FA levels could be a conserved physiological effect. Gene co-expression network analyses uncovered a core gene set including 267 genes in roots associated with AM symbiosis and conserved transcriptional responses, for example, FA metabolism, phytohormone signal transduction, SNARE interaction in vesicular transport, and biotin metabolism. In contrast to widely up-regulated genes related to FA metabolism in AM roots, limited genes were affected in leaves. We propose a model of AM symbiosis-linked reprogramming of FA metabolism and provide a comprehensive insight into AM symbiosis with a woody species adaptation to salt stress.

NaCl Pretreatment Enhances the Low Temperature Tolerance of Tomato Through Photosynthetic Acclimation

Plants often need to withstand multiple types of environmental stresses (e.g., salt and low temperature stress) because of their sessile nature. Although the physiological responses of plants to single stressor have been well-characterized, few studies have evaluated the extent to which pretreatment with non-lethal stressors can maintain the photosynthetic performance of plants in adverse environments (i.e., acclimation-induced cross-tolerance). Here, we studied the effects of sodium chloride (NaCl) pretreatment on the photosynthetic performance of tomato plants exposed to low temperature stress by measuring photosynthetic and chlorophyll fluorescence parameters, stomatal aperture, chloroplast quality, and the expression of stress signaling pathway-related genes. NaCl pretreatment significantly reduced the carbon dioxide assimilation rate, transpiration rate, and stomatal aperture of tomato leaves, but these physiological acclimations could mitigate the adverse effects of subsequent low temperatures compared with non-pretreated tomato plants. The content of photosynthetic pigments decreased and the ultra-microstructure of chloroplasts was damaged under low temperature stress, and the magnitude of these adverse effects was alleviated by NaCl pretreatment. The quantum yield of photosystem I (PSI) and photosystem II (PSII), the quantum yield of regulatory energy dissipation, and non-photochemical energy dissipation owing to donor-side limitation decreased following NaCl treatment; however, the opposite patterns were observed when NaCl-pretreated plants were exposed to low temperature stress. Similar results were obtained for the electron transfer rate of PSI, the electron transfer rate of PSII, and the estimated cyclic electron flow value (CEF). The production of reactive oxygen species induced by low temperature stress was also significantly alleviated by NaCl pretreatment. The expression of ion channel and tubulin-related genes affecting stomatal aperture, chlorophyll synthesis genes, antioxidant enzyme-related genes, and abscisic acid (ABA) and low temperature signaling-related genes was up-regulated in NaCl-pretreated plants under low temperature stress. Our findings indicated that CEF-mediated photoprotection, stomatal movement, the maintenance of chloroplast quality, and ABA and low temperature signaling pathways all play key roles in maintaining the photosynthetic capacity of NaCl-treated tomato plants under low temperature stress.

MicroRNA Mediated Plant Responses to Nutrient Stress

To complete their life cycles, plants require several minerals that are found in soil. Plant growth and development can be affected by nutrient shortages or high nutrient availability. Several adaptations and evolutionary changes have enabled plants to cope with inappropriate growth conditions and low or high nutrient levels. MicroRNAs (miRNAs) have been recognized for transcript cleavage and translational reduction, and can be used for post-transcriptional regulation. Aside from regulating plant growth and development, miRNAs play a crucial role in regulating plant’s adaptations to adverse environmental conditions. Additionally, miRNAs are involved in plants’ sensory functions, nutrient uptake, long-distance root transport, and physiological functions related to nutrients. It may be possible to develop crops that can be cultivated in soils that are either deficient in nutrients or have extreme nutrient supplies by understanding how plant miRNAs are associated with nutrient stress. In this review, an overview is presented regarding recent advances in the understanding of plants’ responses to nitrogen, phosphorus, potassium, sulfur, copper, iron, boron, magnesium, manganese, zinc, and calcium deficiencies via miRNA regulation. We conclude with future research directions emphasizing the modification of crops for improving future food security.

Calcium Regulates Growth and Nutrient Absorption in Poplar Seedlings

As a crucial element for plants, calcium (Ca) is involved in photosynthesis and nutrient absorption, and affects the growth of plants. Poplar is an important economic forest and shelter forest species in China. However, the optimum calcium concentration for its growth is still unclear. Herein, we investigated the growth, biomass, photosynthetic pigments, photosynthetic parameters and products, chlorophyll fluorescence parameters, water use efficiency (iWUE), and antioxidant enzyme activity of "Liao Hu NO.1" poplar (P. simonii × P. euphratica) seedlings at 0, 2.5, 5, 10, and 20 mmol·L^-1 concentrations of Ca²⁺, and further studied the absorption, distribution, and utilization of nutrient elements (C, N, P, K, and Ca) in plants. We found that with increasing calcium gradient, plant height and diameter; root, stem, leaf, and total biomasses; net photosynthetic rate (Pn); stomatal conductance (Gs); intercellular carbon dioxide (Ci) level; transpiration rate (Tr); Fv/Fm ratio; Fv/F0 ratio; chlorophyll-a; chlorophyll-b; soluble sugar and starch content; superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) levels; and long-term water use efficiency (iWUE) of poplar seedlings first increased and then decreased. These parameters attained maximum values when the calcium concentration was 5 mmol·L^-1, which was significantly different from the other treatments (P < 0.05). Moreover, a suitable Ca²⁺ level promoted the absorption of C, N, P, K, and Ca by various organs of poplar seedlings. The absorption of C, N, P, and K increased first and then decreased with the increased calcium concentration, but the optimum calcium concentrations for the absorption of different elements by different organs were different, and the calcium concentration in leaves, stems, and roots increased gradually. Furthermore, the increase in exogenous calcium content led to a decreasing trend in the C/N ratio in different organs of poplar seedlings. C/P and N/P ratios showed different results in different parts, and only the N/P ratio in leaves showed a significant positive correlation with Ca²⁺ concentration. In conclusion, the results of this study indicate that 5 mmol·L^-1 concentration of Ca²⁺ is the optimal level, as it increased growth by enhancing photosynthesis, stress resistance, and nutrient absorption.

Phytoremediation of aniline by Salix babylonica cuttings: Removal, accumulation, and photosynthetic response

Aniline, a synthetic compound widely used in industrial and pesticide production, is a potential environmental pollutant. The removal of aniline is extremely important to minimize threats to human health and the surrounding environment. The objectives of this study were to investigate the removal efficiency and physiological response of Salix. babylonica cuttings to aniline pollution. Photosynthesis, chlorophyll fluorescence, spectral reflectance and the concentration of aniline in leaves, stems and roots were analysed. The experiment showed that S. babylonica has a strong removal effect on aniline wastewater. Cuttings from S. babylonica stems and roots played an important role in accumulating aniline. However, this increase in aniline concentration was dose dependent and was not always linear. With increasing aniline concentration in S. babylonica was increasingly stressed, with negative impacts on photosynthesis, chlorophyll fluorescence and spectral reflectance index in S. babylonica leaves. These results indicate that non-stomatal limitations are the main reason for the reduction in Pn in S. babylonica leaves due to chlorophyll structure destruction under aniline stress. In addition, aniline concentrations result in an unbalanced distribution of excitation energy between the two light systems, thereby hindering photosynthetic electron transfer and restricting the efficient operation of photosynthesis. Salix babylonica can endure moderate concentrations of aniline and has potential for the phyto-management of aniline-polluted wastewater, although further studies are needed using polluted wastewater.

The Significance of Chloroplast NAD(P)H Dehydrogenase Complex and Its Dependent Cyclic Electron Transport in Photosynthesis

Chloroplast NAD(P)H dehydrogenase (NDH) complex, a multiple-subunit complex in the thylakoid membranes mediating cyclic electron transport, is one of the most important alternative electron transport pathways. It was identified to be essential for plant growth and development during stress periods in recent years. The NDH-mediated cyclic electron transport can restore the over-reduction in stroma, maintaining the balance of the redox system in the electron transfer chain and providing the extra ATP needed for the other biochemical reactions. In this review, we discuss the research history and the subunit composition of NDH. Specifically, the formation and significance of NDH-mediated cyclic electron transport are discussed from the perspective of plant evolution and physiological functionality of NDH facilitating plants' adaptation to environmental stress. A better understanding of the NDH-mediated cyclic electron transport during photosynthesis may offer new approaches to improving crop yield.

Melatonin Enhances Drought Tolerance by Regulating Leaf Stomatal Behavior, Carbon and Nitrogen Metabolism, and Related Gene Expression in Maize Plants

It is commonly known that exogenously applied melatonin can alleviate the impact of drought stress, but the mechanism used by melatonin to regulate stomatal behavior and carbon (C) and nitrogen (N) metabolism to increase drought resistance remains elusive. Herein, our aim was to investigate the influence of exogenous melatonin on the regulation of C and N metabolism in maize plants under water deficit. In this study, we analyzed stomatal behavior, the key components of C and N metabolism, and the gene expression and activity of enzymes involved in the C and N metabolism in maize plants. The results showed that the application of melatonin (100 μM) significantly increased maize growth and sustained the opening of stomata, and secondarily increased the photosynthetic capacity in maize. Under drought stress, foliar application of melatonin induced the gene transcription and activities of sucrose phosphate synthetase, ADP-glucose pyrophosphorylase, phosphoenolpyruvate carboxylase, and citrate synthase, resulting in the enhancement of sucrose and starch synthesis and the tricarboxylic acid (TCA) cycle. This enhancement in sugar biosynthesis and the TCA cycle might lead to stronger N assimilation. As anticipated, NO₃ ^- reduction and NH₄ ⁺ assimilation were also strengthened after melatonin treatment under drought stress. An increase was observed in some key enzymatic activities and transcription involved in nitrogen metabolism, such as that of nitrate reductase, nitrite reductase, glutamate synthase, and glutamine synthetase, in melatonin-treated, drought-stressed maize. Moreover, melatonin attenuated the drought-induced damage by reducing protein degradation and increasing the level of proline. Conclusively, our results indicate that exogenous melatonin enhances drought tolerance in maize via promoting stomatal opening and regulating C and N metabolism and related gene expression.

The Physiological Functionality of PGR5/PGRL1-Dependent Cyclic Electron Transport in Sustaining Photosynthesis

The cyclic electron transport (CET), after the linear electron transport (LET), is another important electron transport pathway during the light reactions of photosynthesis. The proton gradient regulation 5 (PGR5)/PRG5-like photosynthetic phenotype 1 (PGRL1) and the NADH dehydrogenase-like complex pathways are linked to the CET. Recently, the regulation of CET around photosystem I (PSI) has been recognized as crucial for photosynthesis and plant growth. Here, we summarized the main biochemical processes of the PGR5/PGRL1-dependent CET pathway and its physiological significance in protecting the photosystem II and PSI, ATP/NADPH ratio maintenance, and regulating the transitions between LET and CET in order to optimize photosynthesis when encountering unfavorable conditions. A better understanding of the PGR5/PGRL1-mediated CET during photosynthesis might provide novel strategies for improving crop yield in a world facing more extreme weather events with multiple stresses affecting the plants.

Exogenous Calcium Alleviates Nocturnal Chilling-Induced Feedback Inhibition of Photosynthesis by Improving Sink Demand in Peanut (Arachis hypogaea)

Arachis hypogaea (peanut) is a globally important oilseed crop with high nutritional value. However, upon exposure to overnight chilling stress, it shows poor growth and seedling necrosis in many cultivation areas worldwide. Calcium (Ca²⁺) enhances chilling resistance in various plant species. We undertook a pot experiment to investigate the effects of exogenous Ca²⁺ and a calmodulin (CaM) inhibitor on growth and photosynthetic characteristics of peanut exposed to low night temperature (LNT) stress following warm sunny days. The LNT stress reduced growth, leaf extension, biomass accumulation, gas exchange rates, and photosynthetic electron transport rates. Following LNT stress, we observed larger starch grains and a concomitant increase in nonstructural carbohydrates and hydrogen peroxide (H₂O₂) concentrations. The LNT stress further induced photoinhibition and caused structural damage to the chloroplast grana. Exogenous Ca²⁺ enhanced plant growth following LNT stress, possibly by allowing continued export of carbohydrates from leaves. Foliar Ca²⁺ likely alleviated the nocturnal chilling-dependent feedback limitation on photosynthesis in the daytime by increasing sink demand. The foliar Ca²⁺ pretreatment protected the photosystems from photoinhibition by facilitating cyclic electron flow (CEF) and decreasing the proton gradient (ΔpH) across thylakoid membranes during LNT stress. Foliar application of a CaM inhibitor increased the negative impact of LNT stress on photosynthetic processes, confirming that Ca²⁺-CaM played an important role in alleviating photosynthetic inhibition due to the overnight chilling-dependent feedback.