The effect of calcium chloride on growth, photosynthesis, and antioxidant responses of Zoysia japonica under drought conditions

Role of calcium acetate in promoting Vibrio campbellii bioluminescence and alleviating salinity stress in Episcia cupreata

This study examines the role of calcium in regulating the bioluminescence of Vibrio campbellii PSU5986 and its potential to alleviate salt stress in plants, which has implications for developing light-emitting plants (LEPs). The effects of organic calcium acetate (C₄H₆CaO₄) were compared to inorganic calcium chloride (CaCl₂) and skim milk regarding their impact on bacterial bioluminescence and plant physiology. While skim milk induced the highest initial luminescence, both C₄H₆CaO₄ and CaCl₂ prolonged light emission for over 16 h. Notably, C₄H₆CaO₄ prevented leaf shrinkage, a condition observed with inorganic salts after 24 h. Periodic supplementation of C₄H₆CaO₄ (every 6 h) improved bacterial immobilization and colonization, extending luminescence over 4 cycles (24 h). Bacterial enumeration revealed colonization densities of approximately 6.82 × 106 CFU cm⁻2 within leaf tissues and 5.22 × 1011 CFU cm⁻2 on the leaf surface. Quantitative PCR analysis indicated that luxG exhibited significantly higher copy numbers than luxA and luxC, highlighting its critical role in bioluminescence through flavin reductase activity. Additionally, C₄H₆CaO₄ reduced salt-induced oxidative stress by increasing chlorophyll levels while decreasing carotenoid (40.00%), anthocyanin (36.94%), proline (14.13%), and malondialdehyde (21.84%) accumulation compared to NaCl-treated plants. These findings emphasize the potential of C₄H₆CaO₄ to sustain bacterial luminescence and enhance plant resilience, contributing to the advancement of LEP technology as a sustainable bioenergy alternative.

Improvement of salt tolerance in Vicia faba (L.) seedlings: a comprehensive investigation of the effects of exogenous calcium chloride

BACKGROUND

This study investigated the effects of the different concentrations of CaCl2 (10 and 15 mol m-3) on the growth, physiology, and cytological characteristics of salt-stressed Vicia faba (L.) seedlings grown under greenhouse conditions.

RESULTS

Salinity stress (150 mol m-3 NaCl) had detrimental effects on all measured growth parameters, increased the micronucleus count number (MCN) by 26.6 micronuclei/1000 cells, decreased the mitotic index (MI) by 66.6%, and caused various chromosomal aberrations, nuclear alterations, and chromatin bridges in salt-stressed seedlings compared to the untreated plant. Nevertheless, the seed priming with CaCl2 (10 and 15 mol m-3) significantly alleviated the toxic effects induced by salinity stress, improved growth parameters, total chlorophyll (TChl), proline, and total soluble sugar (TSS) contents in salt-stressed faba bean seedling compared with seedlings germinated from non-primed seeds. The antioxidative system of salt-stressed faba bean was highly stimulated by increasing the activity of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) enzymes as well as phenolics and flavonoids were increased in all salt-stressed seedlings germinated from seeds primed with CaCl2 (10 and 15 mol m-3) indicating an improved tolerance of faba bean plant to salinity stress. Notably, the pretreatment with CaCl2 (10 mol m-3) reduced the micronuclei number per 1000 cells by 91.3% and decreased the abnormality index by 58.9% more effectively than CaCl2 (15 mol m-3). SDS-PAGE profiling revealed the presence of 16 proteins with different molecular weights, including two peptides, induced by CaCl2 (10 mol m-3) in response to salinity stress.

CONCLUSIONS

This study showed that 10 mol m-3 CaCl2 significantly improved salt tolerance in treated faba bean plants mitigating the antagonistic effects of salt stress on several physiological and cytological parameters.

Optimizing growth, yield, and water use efficiency of Allium hirtifolium with salicylic acid under water stress condiions

Water stress significantly limits the growth and productivity of crops, particularly medicinal plants in arid and semi-arid regions. This study explores the use of salicylic acid (SA) as a means to enhance shallot (Allium hirtifolium) resistance to water stress, as well as improve growth, yield, and water use efficiency (WUE) under various irrigation levels. Conducted over three consecutive growing seasons in a field (2016-2019), The study was conducted as split plot based on randomized complete block design with four replications. Irrigation as the main factors included 100 % (full irrigation), 75 % and 50 % of plant water requirement and no irrigation (dryland) and SA foliar application as sub-factors including 0, 0.5, 0.75 and 1 mM in this study. After ensuring uniformity of variance of experimental errors for three years, composite analysis of data was performed for three years. The results of combined analysis of three-years data showed that water stress reduced several growth parameters, including plant height, leaf dimensions, bulb size, onion and grain weight, and yield. However, SA application notably mitigated these adverse effects. Specifically, applying 1 mM SA in dryland conditions, increased the pod diameter and 1000-seed weight by 10.17 % and 19.97 %, respectively. Also, in the condition of 50 % plant water requirement, 1 mM SA enhanced onion dry weight, daughter onion weight and plant height by 12.41 %, 21.68 % and 19.18 % respectively. Furthermore, shallot yield increased by 15.12 % in dryland and by 29.4 % under 50 % of the plant's water requirement with 1 mM SA. The WUE in the treatment of 50 % of the water requirement of the plant and the use of 1 mM SA increased by 19.1 % compared to the non-use. These findings suggest that applying 1 mM SA can be a viable strategy for improving the growth, yield, and water use efficiency of shallot plants under water-stressed environments.

Foliar applied calcium chloride alleviated drought stress in pearl millet (Pennisetum glaucum L.) by improving growth and yield contributing traits and antioxidant activity

Drought-induced stress presents a substantial threat as it disrupts the normal growth of cereal crops and leads to decreased yields. The persistent occurrence of drought conditions significantly impacts the growth and development of pearl millet. This study aimed to explore how calcium chloride (CaCl2) regulates the growth of pearl millet when it faces a lack of water. Over two years, field experiments were conducted at the College of Agriculture, Bahauddin Zakariya University, Bahadur Sub-Campus Layyah. During the study, we exposed pearl millet to various foliar applications of CaCl2 (0 mg/L, 25 mg/L, 50 mg/L, and 75 mg/L) while subjecting it to two different irrigation conditions: full irrigation and drought stress during the booting stage. Results revealed that a significant reduction in the growth (plant height; PH, stem diameter; SD, fresh leaf weight; FLW, stem fresh weight; SFW, stem dry weight; SDW, root fresh weight; RFW, root dry weight; RDW, and plant dry weight; PDW), yield (panicle length; PL, grain per panicle; GPP, grain weight; GW, thousand grain weight; TGW, grain yield; GY, biological yield; BY, and harvest index; HI), and physiological attributes (membrane stability index; MSI, and soil plant analysis development; SPAD) were found under water drought stress condition, while increment in antioxidant level was observed due to low moisture contents in soil. In both years, foliar applied CaCl2 enhanced all the physiological, growth and yield traits as well as some of the antioxidants like superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX). Study concluded that a concentration of 50 mg/L of CaCl2 is optimal for enhancing all examined attributes of pearl millet under both drought and full irrigation conditions. The results strongly advocate for the use of CaCl2 as the most effective treatment for the cultivation of pearl millet in arid and semi-arid regions.

Influence of nitrogen speciation on Cd-induced toxicity in Landoltia punctata

Nitrogen (N) plays an important role in plant growth and developmental metabolic processes, research on nitrogen speciation regulating Cd accumulation in duckweed is still limited. In this study, the effects of three nitrogen sources (NH4Cl, Ca(NO3)2 and NH4NO3) on the growth, Cd accumulation, and photosynthetic parameters of Landoltia punctata (L. punctata) were analyzed. The results showed that Cd enrichment in L. punctata was significantly reduced (p < 0.05) with different nitrogen treatments compared to the control (CK). Ammonium nitrogen (NH4-N) is more conducive to the accumulation of Cd in L. punctata than nitrate nitrogen (NO3-N). The sum of the cell wall components and soluble components of Cd in the NH4-N treatment group was greater than that in the NO3-N treatment group. The proportion of FNaCl extracts in the NH4-N treatment group was greater than in the NO3-N treatment group. NO3-N led to a greater reduction in photosynthetic pigment content than NH4-N. Overall, applying different forms of nitrogen can alleviate Cd toxicity in L. punctata, and the detoxification effect of the NH4-N treatment is stronger than that of NO3-N treatment. This study will provide theoretical and practical support for the application of duckweed in Cd phytoremediation even in eutrophic aquatic environments.

Adaptation of the Invasive Plant Sphagneticola trilobata (L.) Pruski to Drought Stress

Invasive species and their hybrids with native species threaten biodiversity. However, there are few reports on the drought stress adaptability of invasive species Sphagneticola trilobata (L.) Pruski and its hybrid with native species S. calendulacea. In this study, relative water content (RWC), abscisic acid (ABA), reactive oxygen species, antioxidant capacity, and photosynthetic capacity were measured in the hybrid and its parents under drought stress (13% PEG-6000). Under drought stress, the ABA content and RWC in S. trilobata were the highest. RWC decreased by 28% in S. trilobata, 41% in S. calendulacea, and 33% in the hybrid. Activities of the antioxidant enzymes in S. trilobata were the highest, and the accumulation of malondialdehyde (MDA) was the lowest (4.3 μg g-1), while it was the highest in S. calendulacea (6.9 μg g-1). The maximum photochemical efficiency (Fv/Fm) of S. calendulacea was the lowest (0.71), and it was the highest in S. trilobata (7.5) at 8 h under drought stress. The results suggest that the drought resistance of the hybrid was weaker than that of S. trilobata but stronger than that of S. calendulacea. Therefore, the survival of S. calendulacea may be threatened by both the invasive species S. trilobata and the hybrid.

Effect of GA3 and calcium on growth, biochemical, and fatty acid composition of linseed under chloride-dominated salinity

The accumulation of salts in soil is an environmental threat affecting plant growth and crop yield. Linseed or flax is an ancient crop that has multifarious utilities in terms of industrial oil, textile fiber, and products. Salt susceptibility adversely affects linseed production, particularly to meet the growing demand for nutritional and nutraceutical products. In the present study, the ameliorative potential of gibberellic acid (GA3) and calcium (Ca2+) in mitigating the adverse effects of chloride-dominated salinity stress on the growth and physiological and biochemical processes in linseed was determined. Severe salinity treatment (10 dSm-1) resulted in stunted growth of tested linseed genotypes causing a significant reduction in biomass while proline content, phenol, H2O2, lipid peroxidation, and DPPH activity were increased in comparison to control. The exogenous application of 10-6 M GA3 and/or 10 mg CaCl2 kg-1 was found to mitigate the adverse effects of salinity stress. The mitigation was accomplished through the improvement of growth indicators, increased osmoprotectants such as proline and phenol content, stimulating DPPH activity, and reduction of H2O2 content and lipid peroxidation. The comparative evaluation of different saline treatments imposed individually and in combination with GA3 and Ca2+ revealed that combined GA3 and Ca2+ application exhibited synergistic effects and was most effective in mitigating the negative impacts of salt stress. The present study unravels the ameliorative role of GA3 and Ca2+ (individual or combined) in the physiologic-biochemical adaptive response of linseed plants grown under chloride-dominated salinity and thus aids in a better understanding of the underlying tolerance mechanisms of plants to withstand stress in saline environments.

Foliar Application of Chelated Sugar Alcohol Calcium Improves Photosynthesis and Tuber Quality under Drought Stress in Potatoes (Solanum tuberosum L.)

Drought stress is a major threat to sustainable crop production worldwide. Despite the positive role of calcium (Ca2+) in improving plant drought tolerance in different crops, little attention has been paid to its role in mitigating drought stress in potatoes. In the present study, we studied the effect of foliar chelated sugar alcohol calcium treatments on two potato cultivars with different drought responses applied 15 and 30 days after limiting soil moisture. The results showed that the foliar application of calcium treatments alleviated the SPAD chlorophyll loss of the drought-sensitive cultivar 'Atlantic' (Atl) and reduced the inhibition of photosynthetic parameters, leaf anatomy deformation, and MDA and H2O2 content of both cultivars under drought stress. The Ca2+ treatments changed the expression of several Calcium-Dependent Protein Kinase (StCDPK) genes involved in calcium sensing and signaling and significantly increased antioxidant enzyme activities, average tuber weight per plant, and tuber quality of both cultivars. We conclude that calcium spray treatments improved the drought tolerance of both potato cultivars and were especially effective for the drought-sensitive cultivar. The present work suggests that the foliar application of calcium is a promising strategy to improve commercial potato yields and the economic efficiency of potato production under drought stress conditions.

Positive effects of Cordyceps cateniannulata colonization in tobacco: Growth promotion and resistance to abiotic stress

Background

Entomopathogenic fungi can live in insects to cause disease and death and are the largest group of entomopathogenic microorganisms. Therefore, these fungi are best known for their microbial control potential. Importantly, they also have other beneficial effects, including promoting plant growth and development by colonizing plant. Here, the study sought to identify specific strains of the entomopathogenic fungus, Cordyceps cateniannulata that would form endophytic associations with tobacco, thus benefiting plant growth and resistance to abiotic stresses, thereby highlighting the application of entomopathogenic fungi in tobacco.

Methods

The C. cateniannulata-tobacco symbiont was constructed by root irrigation. The effects of C. cateniannulata on tobacco growth were evaluated by measuring the maximum leaf length, maximum leaf width, number of leaves, plant height, stem thickness, stem circumference, dry and fresh shoot weight 7, 14, 21, and 28 days after colonization. The peroxidase, catalase, superoxide dismutase, and malondialdehyde were measured to observe the impact of C. cateniannulata on tobacco defense enzyme activity. Finally, high-throughput sequencing was used to access microbial communities in the rhizosphere, with data subsequently linked to growth indicators.

Results

After tobacco was inoculated with C. cateniannulata X8, which significantly promoted growth and related enzyme activity, malondialdehyde was decreased. The most significant impact was on peroxidase, with its activity being upregulated by 98.20, 154.42, 180.65, and 170.38% in the four time periods, respectively. The high throughput sequencing results indicated that C. cateniannulata had changed the rhizosphere microbial relative abundances, such as increasing Acidobacteria and Ascomycetes, and decreasing Actinomycetes and Basidiomycetes. The redundancy analysis showed that C. cateniannulata significantly boosted tobacco growth by reducing the abundance of specific dominant genera such as Stachybotrys, Cephalotrichum, Streptomyces, Isoptericola, and Microbacterium.

Conclusion

Specific strains of C. cateniannulata can be introduced into host plants as endophytes, resulting in promotion of host plant growth and increased resistance to abiotic stress and microbial pathogens. The study provides a foundation for future studies of C. cateniannulata as an ecological agent.

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.

Instigating prevalent abiotic stress resilience in crop by exogenous application of phytohormones and nutrient

In recent times, the demand for food and feed for the ever-increasing population has achieved unparalleled importance, which cannot afford crop yield loss. Now-a-days, the unpleasant situation of abiotic stress triggers crop improvement by affecting the different metabolic pathways of yield and quality advances worldwide. Abiotic stress like drought, salinity, cold, heat, flood, etc. in plants diverts the energy required for growth to prevent the plant from shock and maintain regular homeostasis. Hence, the plant yield is drastically reduced as the energy is utilized for overcoming the stress in plants. The application of phytohormones like the classical auxins, cytokinins, ethylene, and gibberellins, as well as more recent members including brassinosteroids, jasmonic acids, etc., along with both macro and micronutrients, have enhanced significant attention in creating key benefits such as reduction of ionic toxicity, improving oxidative stress, maintaining water-related balance, and gaseous exchange modification during abiotic stress conditions. Majority of phytohormones maintain homeostasis inside the cell by detoxifying the ROS and enhancing the antioxidant enzyme activities which can enhance tolerance in plants. At the molecular level, phytohormones activate stress signaling pathways or genes regulated by abscisic acid (ABA), salicylic acid (SA), Jasmonic acid (JA), and ethylene. The various stresses primarily cause nutrient deficiency and reduce the nutrient uptake of plants. The application of plant nutrients like N, K, Ca, and Mg are also involved in ROS scavenging activities through elevating antioxidants properties and finally decreasing cell membrane leakage and increasing the photosynthetic ability by resynthesizing the chlorophyll pigment. This present review highlighted the alteration of metabolic activities caused by abiotic stress in various crops, the changes of vital functions through the application of exogenous phytohormones and nutrition, as well as their interaction.

Genome-wide transcriptome analysis of the orphan crop tef (Eragrostis tef (Zucc.) Trotter) under long-term low calcium stress

Calcium (Ca²⁺) is one of the essential mineral nutrients for plant growth and development. However, the effects of long-term Ca²⁺ deficiency in orphan crops such as Tef [(Eragrostis tef) (Zucc.) Trotter], which accumulate high levels of Ca in the grains, remained unknown. Tef is a staple crop for nearly 70 million people in East Africa, particularly in Ethiopia and Eritrea. It is one of the most nutrient-dense grains, and is also more resistant to marginal soils and climatic conditions than main cereals like corn, wheat, and rice. In this study, tef plants were grown in a hydroponic solution containing optimum (1 mM) or low (0.01 mM) Ca²⁺, and plant growth parameters and whole-genome transcriptome were analyzed. Ca⁺²-deficient plants exhibited leaf necrosis, leaf curling, and growth stunting symptoms. Ca²⁺ deficiency significantly decreased root and shoot Ca, potassium (K), and copper content in both root and shoots. At the same time, it greatly increased root iron (Fe) content, suggesting the role of Ca²⁺ in the uptake and/or translocation of these minerals. Transcriptomic analysis using RNA-seq revealed that members of Ca²⁺ channels, including the cyclic nucleotide-gated channels and glutamate receptor-like channels, Ca²⁺-transporters, Ca²⁺-binding proteins and Ca²⁺-dependent protein kinases were differentially regulated by Ca⁺² treatment. Moreover, several Fe/metal transporters, including members of vacuolar Fe transporters, yellow stripe-like, natural resistance-associated macrophage protein, and oligo-peptide transporters, were differentially regulated between shoot and root in response to Ca²⁺ treatment. Taken together, our findings suggest that Ca²⁺ deficiency affects plant growth and mineral accumulation by regulating the transcriptomes of several transporters and signaling genes.

Roles of Calcium Signaling in Gene Expression and Photosynthetic Acclimatization of Solanum lycopersicum Micro-Tom (MT) after Mechanical Damage

A momentary increase in cytoplasmic Ca²⁺ generates an oscillation responsible for the activation of proteins, such as calmodulin and kinases, which interact with reactive oxygen species (ROS) for the transmission of a stress signal. This study investigated the influence of variations in calcium concentrations on plant defense signaling and photosynthetic acclimatization after mechanical damage. Solanum lycopersicum Micro-Tom was grown with 0, 2 and 4 mM Ca²⁺, with and without mechanical damage. The expression of stress genes was evaluated, along with levels of antioxidant enzymes, hydrogen peroxide, lipid peroxidation, histochemistry, photosynthesis and dry mass of organs. The ROS production generated by mechanical damage was further enhanced by calcium-free conditions due to the inactivation of the oxygen evolution complex, contributing to an increase in reactive species. The results indicated that ROS affected mechanical damage signaling because calcium-free plants exhibited high levels of H₂O₂ and enhanced expression of kinase and RBOH1 genes, necessary conditions for an efficient response to stress. We conclude that the plants without calcium supply recognized mechanical damage but did not survive. The highest expression of the RBOH1 gene and the accumulation of H₂O₂ in these plants signaled cell death. Plants grown in the presence of calcium showed higher expression of SlCaM2 and control of H₂O₂ concentration, thus overcoming the stress caused by mechanical damage, with photosynthetic acclimatization and without damage to dry mass production.

Phylogenomics and gene selection in Aspergillus welwitschiae: Possible implications in the pathogenicity in Agave sisalana

Aspergillus welwitschiae causes bole rot disease in sisal (Agave sisalana and related species) which affects the production of natural fibers in Brazil, the main worldwide producer of sisal fibers. This fungus is a saprotroph with a broad host range. Previous research established A. welwitschiae as the only causative agent of bole rot in the field, but little is known about the evolution of this species and its strains. In this work, we performed a comparative genomics analysis of 40 Aspergillus strains. We show the conflicting molecular identity of this species, with one sisal-infecting strain sharing its last common ancestor with Aspergillus niger, having diverged only 833 thousand years ago. Furthermore, our analysis of positive selection reveals sites under selection in genes coding for siderophore transporters, Sodium‑calcium exchangers, and Phosphatidylethanolamine-binding proteins (PEBPs). Herein, we discuss the possible impacts of these gene functions on the pathogenicity in sisal.

Optimal exogenous calcium alleviates the damage of Snow-melting agent to Salix matsudana seedlings

As the main component of snowmelt agents, NaCl is widely used in northern winters and significantly impacts the expected growth of garden plants in north China. Salix matsudana is also faced with salt stress caused by snowmelt, which seriously affects its development as the main tree species in the northern landscape. However, how exogenous calcium alleviates salt stress in Salix matsudana is not yet clear. In this study, the indicators of growth indices, photosynthetic characteristics and stress resistance were measured by hydroponic assays in combination with three NaCl conditions (0, 50 and 200 mmol·L^-1) and five calcium concentrations (0, 2.5, 5, 10 and 20 mmol·L^-1). The study's results indicated that the application of exogenous calcium remarkably promoted the growth of Salix matsudana seedlings under NaCl stress. When the exogenous calcium concentration was 10 mmol·L^-1, the plant height and basal diameter of Salix matsudana seedlings increased significantly, and the biomass of all parts reached the maximum (P< 0.05). Exogenous calcium can substantially improve the photosynthesis of Salix matsudana seedlings under salt stress. The photosynthetic parameters, photosynthetic pigment content and photosynthetic product synthesis of Salix matsudana seedlings were significantly increased at an exogenous calcium concentration of 10 mmol·L^-1, and the photosynthetic level of Salix matsudana seedlings reached the highest value. The chlorophyll fluorescence parameters (F _v /F _m, F _v /F ₀) of Salix matsudana seedlings were significantly decreased under different concentrations of NaCl stress. The maximum photochemical efficiency (F _v /F _m) and potential photochemical efficiency (F _v /F ₀) of Salix matsudana seedlings peaked when the exogenous calcium concentration was 10 mmol·L^-1, which was significantly higher than that of the other treatments (P< 0.05). The water use efficiency of Salix matsudana was affected considerably by NaCl stress. The WUE and iWUE peak values of Salix matsudana were significantly higher than those of other calcium concentrations at 10 mmol·L^-1 (P< 0.05). Exogenous calcium can increase the activities of CAT, SOD and POD enzymes in Salix matsudana seedlings under different NaCl concentrations. Under NaCl stress, adding exogenous calcium promoted the survival rate and growth of Salix matsudana seedlings. In conclusion, the optimum exogenous calcium concentration for Salix matsudana seedlings was 10 mmol·L^-1. High or low concentrations of exogenous calcium did not achieve the best results in alleviating salt stress in Salix matsudana.

Calcium affects uranium responses in Arabidopsis thaliana: From distribution to toxicity

Uranium, a heavy metal and primordial radionuclide, is present in surface waters and soils both naturally and due to industrial activities. Uranium is known to be toxic to plants and its uptake and toxicity can be influenced by multiple factors such as pH and the presence of different ions. However, the precise role of the different ions in uranium uptake is not yet known. Here we investigated whether calcium influences uranium uptake and toxicity in the terrestrial plant Arabidopsis thaliana. To this end, A. thaliana plants were exposed to different calcium and uranium concentrations and furthermore, calcium channels were blocked using the calcium channel blocker lanthanum chloride (LaCl₃). Fresh weight, relative growth rate, concentration of nutrients and uranium and gene expression of oxidative stress-related genes and calcium transporters were determined in roots and shoots. Calcium affected plant growth and oxidative stress in both control (no uranium) and uranium-exposed plants. In shoots, this was influenced by the total calcium concentration, but not by the different tested uranium concentrations. Uranium in turn did influence calcium uptake and distribution. Uranium-exposed plants grown in a medium with a higher calcium concentration showed an increase in gene expression of NADPH oxidases RBOHC and RBOHE and calcium transporter CAX7 after uranium exposure. In roots, these calcium-dependent responses in gene expression were not observed. This indicates that calcium indeed affects uranium toxicity, but only in shoots. In addition, a clear influence of uranium and LaCl₃ (separately and combined) on the expression of calcium transporters was observed.

Plant Nutrition: An Effective Way to Alleviate Abiotic Stress in Agricultural Crops

By the year 2050, the world's population is predicted to have grown to around 9-10 billion people. The food demand in many countries continues to increase with population growth. Various abiotic stresses such as temperature, soil salinity and moisture all have an impact on plant growth and development at all levels of plant growth, including the overall plant, tissue cell, and even sub-cellular level. These abiotic stresses directly harm plants by causing protein denaturation and aggregation as well as increased fluidity of membrane lipids. In addition to direct effects, indirect damage also includes protein synthesis inhibition, protein breakdown, and membranous loss in chloroplasts and mitochondria. Abiotic stress during the reproductive stage results in flower drop, pollen sterility, pollen tube deformation, ovule abortion, and reduced yield. Plant nutrition is one of the most effective ways of reducing abiotic stress in agricultural crops. In this paper, we have discussed the effectiveness of different nutrients for alleviating abiotic stress. The roles of primary nutrients (nitrogen, phosphorous and potassium), secondary nutrients (calcium, magnesium and sulphur), micronutrients (zinc, boron, iron and copper), and beneficial nutrients (cobalt, selenium and silicon) in alleviating abiotic stress in crop plants are discussed.

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.

The Growth, physiological and biochemical response of foxtail millet to atrazine herbicide

Foxtail millet (Pennisetum glaucum L.) is a vital crop that is planted as food and fodder crop around the globe. There is only limited information is present for abiotic stresses on the physiological responses to atrazine. A field experiment was conducted to investigate the effects of different atrazine dosages on the growth, fluorescence and physiological parameters i.e., malonaldehyde (MDA) and reactive oxygen species (ROS) (H₂O₂ and O₂) in the leaves to know the extent of atrazine on oxidative damage of foxtail millet. Our experiment consisted of 0, 2.5, 12.5, 22.5 and 32.5 (mg/kg) of labeled atrazine doses on 2 foxtaill millet varieties. High doses of atrazine significantly enhanced ROS and MDA synthesis in the plant leaves. Enzymes activities like ascorbate peroxidase (APX) and peroxidase (POD) activities enhanced, while catalase (CAD) and superoxide dismutase (SOD) activities reduced with increasing atrazine concentrations. Finally atrazine doses at 32.5 mg/kg reduced chlorophyll contents, while chlorophyll (a/b) ratio also enhanced. Biomass, plant height, chlorophyll fluorescence parameters, minimal and maximal fluorescence (Fo, Fm), maximum and actual quantum yield, photochemical quenching coefficient, and electron transport rate are decreased with increasing atrazine doses.

Biosynthesis and characterization of titanium dioxide nanoparticles and its effects along with calcium phosphate on physicochemical attributes of wheat under drought stress

Drought stress is reducing the production of crops globally. This research was designed to evaluate the role of titanium dioxide (TiO₂ NPs) nanoparticles and calcium phosphate on wheat facing drought stress. TiO₂ NPs were prepared by green synthesis and their characterization (by UV-visible spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX)) was also done. The results showed that TiO₂ NPs worked efficiently and improved plant growth under drought. However, the best results were obtained from combined applications of 40 ppm TiO₂ NPs and 40 ppm calcium phosphate on plants. They increased root length (33%), shoot length (53%), fresh weight (48%), and dry weight (44%) of wheat as compared to control. The physiological parameters including chlorophyll content, relative water content, membrane stability index, and osmolyte content (proline and sugar) were also improved. The increase in superoxide dismutase, peroxidase and, catalase activity by the combined application of TiO₂ NPs and calcium phosphate was 83% and 78%, 74% and 52%, 81%, and 67% in Pakistan-13 and Zincol-16 respectively, as compared to untreated drought exposed plants. They also enhanced the nutrients uptake (including potassium, phosphorus, and nitrogen) that ultimately improved plant biomass. They also maintained the level of growth hormones in plants. These hormones regulate cellular processes and are responsible for germination, development, and plant reaction in drought stress. The increase in the yield was also significant, hence it is recommended that the 40 ppm concentration of TiO₂ NPs along with calcium phosphate improves the productivity of wheat under drought stress.

Composite Films of Thermoplastic Starch and CaCl2 Extracted from Eggshells for Extending Food Shelf-Life

Calcium chloride (CaCl2) has been widely used to maintain the quality of fresh-cut fruits and vegetables because it stabilizes and strengthens the membrane system against fungal attacks. It is mainly applied via spray coating and dip coating techniques. This study explored a method of incorporating calcium chloride extracted from eggshells in a packaging material, thermoplastic starch (TPS), via a hot-melt extrusion process. The composites were characterized by FTIR, DSC, SEM-EDX and tensile testing. FTIR confirmed the chemical reactions between CaCl2 and TPS. DSC results showed a significant decrease in the heat of fusion by adding 20 wt% of CaCl2 content in TPS, indicating a drop in the degree of crystallinity. The Young’s modulus of TPS was not significantly affected by the incorporation of 10 wt% CaCl2 (P = 0.968), but reduced notably with the addition of 20 wt% CaCl2 (P = 0.05), indicating the plasticizer effect of the CaCl2. Physiochemical analysis of fresh-cut apple slices was assessed. Samples placed on the surface of the TPS/CaCl2 composites displayed less pH reduction, reduced antioxidant activity, more weight loss and increased reducing sugar compared to the samples placed on the surface of virgin TPS films. CaCl2 released from the TPS/CaCl2 films was measured and their antimicrobial activity was confirmed by bacterial inhibitory growth assessment. Fungal growth was observed on apple slices placed on virgin TPS film by day 21 while apple slices placed on TPS/CaCl2 20 wt% composites did not support any fungal growth for 28 days. In summary, TPS and eggshell-extracted CaCl2 showed the ability to maintain the quality of fresh-cut apples, and TPS/CaCl2 10 wt% composite could be a good option as a packaging material for fresh-cut fruits due to active antimicrobial activity and maintained Young’s modulus.

Thermal Preparation and Application of a Novel Silicon Fertilizer Using Talc and Calcium Carbonate as Starting Materials

The deficiency of available silicon (Si) incurred by year-round agricultural and horticultural practices highlights the significance of Si fertilization for soil replenishment. This study focuses on a novel and economical route for the synthesis of Si fertilizer via the calcination method using talc and calcium carbonate (CaCO3) as starting materials. The molar ratio of talc to CaCO3 of 1:2.0, calcination temperature of 1150 °C and calcination time of 120 min were identified as the optimal conditions to maximize the available Si content of the prepared Si fertilizer. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) characterizations elucidate the principles of the calcination temperature-dependent microstructure evolution of Si fertilizers, and the akermanite Ca2Mg(Si2O7) and merwinite Ca3Mg(SiO4)2 were identified as the primary silicates products. The results of release and solubility experiments suggest the content of available metallic element and slow-release property of the Si fertilizer obtained at the optimum preparation condition (Si-OPC). The surface morphology and properties of Si-OPC were illuminated by the results of scanning electron microscope (SEM), surface area and nitrogen adsorption analysis. The acceleration action of CaCO3 in the decomposition process of talc was demonstrated by the thermogravimetry-differential scanning calorimetry (TG-DSC) test. The pot experiment corroborates that 5 g kg-1 soil Si-OPC application sufficed to facilitate the pakchoi growth by providing nutrient elements. This evidence indicates the prepared Si fertilizer as a promising candidate for Si-deficient soil replenishment.

Role of Jasmonates, Calcium, and Glutathione in Plants to Combat Abiotic Stresses Through Precise Signaling Cascade

Plant growth regulators have an important role in various developmental processes during the life cycle of plants. They are involved in abiotic stress responses and tolerance. They have very well-developed capabilities to sense the changes in their external milieu and initiate an appropriate signaling cascade that leads to the activation of plant defense mechanisms. The plant defense system activation causes build-up of plant defense hormones like jasmonic acid (JA) and antioxidant systems like glutathione (GSH). Moreover, calcium (Ca2+) transients are also seen during abiotic stress conditions depicting the role of Ca2+ in alleviating abiotic stress as well. Therefore, these growth regulators tend to control plant growth under varying abiotic stresses by regulating its oxidative defense and detoxification system. This review highlights the role of Jasmonates, Calcium, and glutathione in abiotic stress tolerance and activation of possible novel interlinked signaling cascade between them. Further, phyto-hormone crosstalk with jasmonates, calcium and glutathione under abiotic stress conditions followed by brief insights on omics approaches is also elucidated.

Synergism between calcium nitrate applications and fungal endophytes to increase sugar concentration in Festuca sinensis under cold stress

Epichloë endophytes have been shown to increase tolerance to biotic and abiotic stresses in many cool-season grasses. We investigated the impact of endophyte infection of Festuca sinensis, on root metabolic activity, photosynthetic pigments, leaf relative water content (RWC) and soluble carbohydrates in a field experiment carried out during chilling and irrigation with Ca(NO₃)₂. A highly significant (P < 0.001) correlation for Epichloë endophytes was observed for root metabolic activity. Ca(NO₃)₂ affected very significantly root metabolic activity and total chlorophyll (P < 0.001). Low temperature led to highly significant (P < 0.001) reductions in root metabolic activity, RWC, total chlorophyll, chlorophyll a/b ratio, and carotenoid contents. In addition, the fructose concentrations of shoots were greater on the 14th day than on the 28th day and before treatment, whilst the glucose concentration of roots was much higher on the 28th day than before and after 14 days treatment. Moreover, our results indicated that the addition of calcium nitrate contributed to higher levels of total chlorophylls, soluble sugars, sucrose, fructose or glucose in the shoots and roots in both E+ and E- plants during long periods of chilling. These results suggest that Epichloë endophyte infection and/or exogenous calcium nitrate can confer better tolerance to cold stress.

CAX3 (cation/proton exchanger) mediates a Cd tolerance by decreasing ROS through Ca elevation in Arabidopsis

KEY MESSAGE

Over-expression of CAX3 encoding a cation/proton exchanger enhances Cd tolerance by decreasing ROS (Reactive Oxygen Species) through activating anti-oxidative enzymes via elevation of Ca level in Arabidopsis CAXs (cation/proton exchangers) are involved in the sequestration of cations such as Mn, Li, and Cd, as well as Ca, from cytosol into the vacuole using proton gradients. In addition, it has been reported that CAX1, 2 and 4 are involved in Cd tolerance. Interestingly, it has been reported that CAX3 expressions were enhanced by Cd in Cd-tolerant transgenic plants expressing Hb1 (hemoglobin 1) or UBC1 (Ub-conjugating enzyme 1). Therefore, to investigate whether CAX3 plays a role in increasing Cd tolerance, CAX3 of Arabidopsis and tobacco were over-expressed in Arabidopsis thaliana. Compared to control plants, both transgenic plants displayed an increase in Cd tolerance, no change in Cd accumulation, and enhanced Ca levels. In support of these, AtCAX3-Arabidopsis showed no change in expressions of Cd transporters, but reduced expressions of Ca exporters and lower rate of Ca efflux. By contrast, atcax3 knockout Arabidopsis exhibited a reduced Cd tolerance, while the Cd level was not altered. The expression of Δ90-AtCAX3 (deletion of autoinhibitory domain) increased Cd and Ca tolerance in yeast, while AtCAX3 expression did not. Interestingly, less accumulation of ROS (H2O2 and O2-) was observed in CAX3-expressing transgenic plants and was accompanied with higher antioxidant enzyme activities (SOD, CAT, GR). Taken together, CAX3 over-expression may enhance Cd tolerance by decreasing Cd-induced ROS production by activating antioxidant enzymes and by intervening the positive feedback circuit between ROS generation and Cd-induced spikes of cytoplasmic Ca.

Transcriptional and Physiological Analyses to Assess the Effects of a Novel Biostimulant in Tomato

This work aimed to study the effects in tomato (Solanum lycopersicum L.) of foliar applications of a novel calcium-based biostimulant (SOB01) using an omics approach involving transcriptomics and physiological profiling. A calcium-chloride fertilizer (SOB02) was used as a product reference standard. Plants were grown under well-watered (WW) and water stress (WS) conditions in a growth chamber. We firstly compared the transcriptome profile of treated and untreated tomato plants using the software RStudio. Totally, 968 and 1,657 differentially expressed genes (DEGs) (adj-p-value < 0.1 and |log2(fold change)| ≥ 1) were identified after SOB01 and SOB02 leaf treatments, respectively. Expression patterns of 9 DEGs involved in nutrient metabolism and osmotic stress tolerance were validated by real-time quantitative reverse transcription PCR (RT-qPCR) analysis. Principal component analysis (PCA) on RT-qPCR results highlighted that the gene expression profiles after SOB01 treatment in different water regimes were clustering together, suggesting that the expression pattern of the analyzed genes in well water and water stress plants was similar in the presence of SOB01 treatment. Physiological analyses demonstrated that the biostimulant application increased the photosynthetic rate and the chlorophyll content under water deficiency compared to the standard fertilizer and led to a higher yield in terms of fruit dry matter and a reduction in the number of cracked fruits. In conclusion, transcriptome and physiological profiling provided comprehensive information on the biostimulant effects highlighting that SOB01 applications improved the ability of the tomato plants to mitigate the negative effects of water stress.

Comparison of the Ability to Control Water Loss in the Detached Leaves of Wedelia trilobata, Wedelia chinensis, and Their Hybrid

In the process of biological invasion, hybridization between invasive species and native species is very common, which may lead to the formation of hybrids with a stronger adaptability. The hybrid of Wedelia trilobata (an alien invasive species) and Wedelia chinensis (an indigenous congener) has been found in South China. In our previous study, we found that the hybrid showed heterosis under cadmium stress. However, the results of this experiment demonstrated that the leaves of the hybrid had no heterosis in controlling water loss. The results showed that the water loss rate of W. trilobata was the slowest, that of W. chinensis was the fastest, and that of the hybrid was in the middle. Compared with W. chinensis and the hybrid, W. trilobata accumulated more abscisic acid (ABA) in leaves to control water loss. After the leaves were detached, W. chinensis leaves suffered the most serious damage, the lowest maximum photochemical efficiency, the most serious membrane lipid peroxidation, and the largest accumulation of malondialdehyde and reactive oxygen species. Compared with W. chinensis and its hybrid, the leaves of W. trilobata could accumulate more antioxidant enzymes and antioxidants, and the total antioxidant capacity was the strongest. The results demonstrate that the ability of the hybrid to reduce water loss was lower than that of W. trilobata, but higher than that of W. chinensis. They showed that the drought resistance of the hybrid may be higher than that of W. chinensis, and it might threaten the survival of W. chinensis.

CaCl2 pretreatment improves gamma toxicity tolerance in microalga Chlorella vulgaris

The Chlorella vulgaris has been generally recognized as a promising microalgal model to study stress-related responses due to its ability to withstand against ionizing and non-ionizing radiation. The objective of the present study was to investigate the effect of CaCl₂ pre-treatment at different concentrations on the responses of microalga C. vulgaris under gamma radiation toxicity. Changes in growth, physiological parameters and biochemical compositions of the algae pretreated with 0.17 (normal), 5, and 10 mM CaCl₂ were analyzed under 300 Gy gamma irradiation and compared to those of gamma-free control. The results showed that parameters including specific growth rate, cell size, chlorophyll and protein contents, ascorbate peroxidase (APX), and superoxide dismutase (SOD) activity, Ferric Reducing Antioxidant Power (FRAP), and the ratios of nucleic acid to protein negatively affected by gamma irradiation. All these parameters, except for the ratios of nucleic acid to protein significantly increased in the algae when pretreated with a CaCl₂ content higher than normal concentration. The analysis also showed that parameters including catalase activity, proline, and carotenoid content, the level of lipid peroxidation, and electrolyte leakage (EL) significantly increased under gamma irradiation but not affected significantly under different CaCl₂ pre-treatments. Additionally, specific growth rate, chlorophyll a and protein content, APX and SOD activity, FRAP, lipid peroxidation, electrolyte leakage, and the ratios of nucleic acid to protein were the only parameters that significantly affected by the interaction of gamma toxicity and CaCl₂ pretreatment. Overall, the results suggested that regardless of the CaCl₂ effect, the algal cells responded to gamma radiation more efficiently by increasing proline, carotenoids content, and CAT activity. More important, it was concluded that calcium had an essential role in modifying the detrimental effect of gamma toxicity on the algae mainly by increasing the activity of ascorbate peroxidase and superoxide dismutase and maintaining the reducing antioxidant power (FRAP) of the cells at a high level.

Foliar Application of Calcium and Growth Regulators Modulate Sweet Cherry (Prunus avium L.) Tree Performance

Cracking of sweet cherry (Prunus avium L.) fruits is caused by rain events close to harvest. This problem has occurred in most cherry growing regions with significant economic losses. Several orchard management practices have been applied to reduce the severity of this disorder, like the foliar application of minerals or growth regulators. In the present study, we hypothesized that preharvest spray treatments improve the physiological performance of sweet cherry trees and could also mitigate environmental stressful conditions. Effects of repeated foliar spraying of calcium (Ca), gibberellic acid (GA₃), abscisic acid (ABA), salicylic acid (SA), glycine betaine (GB), and the biostimulant Ascophyllum nodosum (AN) on the physiological and biochemical performance of ‘Skeena’ sweet cherry trees during two consecutive years (without Ca in 2015 and in 2016 with addition of Ca) were studied. Results showed that in general spray treatments improved the physiological performance and water status of the trees. AN and ABA sprays were demonstrated to be the best compounds for increasing yield and reducing cherry cracking as well as improving photosynthetic performance and leaf metabolites content. In conclusion, AN and ABA might be promising tools in the fruit production system.

Expression, Subcellular Localization, and Interactions of CPK Family Genes in Maize

Calcium-dependent protein kinase (CPKs) is a key player in the calcium signaling pathway to decode calcium signals into various physiological responses. cDNA sequences of 9 ZmCPK genes were successfully cloned from all four phylogenetic groups in maize. qRT-PCR analysis showed the expression variation of these selected genes under abscisic acid (ABA) and calcium chloride (CaCl2) treatment. Due to the presence of N-myristoylation/palmitoylation sites, the selected ZmCPK members were localized in a plasma membrane. To clarify whether ZmCPK, a key player in calcium signaling, interacts with key players of ABA, protein phosphatase 2Cs (PP2Cs) and the SNF1-related protein kinase 2s (SnRK2s) and mitogen-activated protein kinase (MAPK) signaling pathways in maize, we examined the interaction between 9 CPKs, 8 PP2Cs, 5 SnRKs, and 20 members of the MPK family in maize by using yeast two-hybrid assay. Our results showed that three ZmCPKs interact with three different members of ZmSnRKs while four ZmCPK members had a positive interaction with 13 members of ZmMPKs in different combinations. These four ZmCPK proteins are from three different groups in maize. These findings of physical interactions between ZmCPKs, ZmSnRKs, and ZmMPKs suggested that these signaling pathways do not only have indirect influence but also have direct crosstalk that may involve the defense mechanism in maize. The present study may improve the understanding of signal transduction in plants.

Alleviation of cadmium-induced genotoxicity and cytotoxicity by calcium chloride in faba bean (Vicia faba L. var. minor) roots

Alleviation of cadmium-induced root genotoxicity and cytotoxicity by calcium chloride (CaCl₂) in faba bean (Vicia faba L. var. minor) seedlings were studied. Faba bean seeds were treated with H₂O or 2% CaCl₂ for 6 h before germination. Seeds were then exposed to 0 and 50 µM CdCl₂ concentrations for 7 days. Genotoxic damaging effects of Cd was examined through the determination of the mitotic index (MI), chromosomal aberrations (CA) and micronucleus (MN) in the meristem cells of faba bean roots. Similarly, effects of Cd stress on metal accumulation, total membrane lipid contents, total fatty acid composition (TFA), lipid peroxidation as indicated by malondialdehyde production, soluble protein and non-protein thiols (NP-SH) contents, hydrogen peroxide production and the activities of superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (GPX) were evaluated after 7 days of Cd stress in the seedling roots. Cd stress resulted in the reduction of MI, in addition to MN formation and CA induction in the roots of non-primed seeds (treated with H₂O). Moreover, Cd induced lipid peroxidation, H₂O₂ overproduction and loss of membrane lipid amount and soluble protein content, and changes in the TFA composition in roots of faba bean seedlings. SOD activity declined, but CAT and GPX activities increased. However, seed pre-treatment with CaCl₂ attenuated the genotoxic and cytotoxic effects of Cd on Vicia faba roots. The results showed that CaCl₂ induced reduction of Cd accumulation, improved cell membrane stability and increased the antioxidant defence systems, thus reducing and alleviating Cd genotoxicity and oxidative damage.

Different effects of calcium and penconazole on primary and secondary metabolites of Brassica napus under drought

The effects of penconazole (PEN) and calcium (Ca²⁺) on physiological and biochemical parameters were investigated in two canola cultivars (RGS003 and Sarigol) under water stress. Drought increased protein content in RGS003, but PEN, Ca²⁺ and PEN-Ca²⁺ treatment induced protein content in Sarigol. PEN, Ca²⁺ and PEN-Ca²⁺ treatment enhanced soluble sugar content in RGS003. In contrast to Sarigol, drought and PEN treatment induced total phenol content in RGS003. Flavonoid content increased by drought, but Ca²⁺ and PEN-Ca²⁺ treatment decreased it in both cultivars. Ca²⁺ and PEN-Ca²⁺ treatment enhanced tocopherol content in both cultivars under drought stress. Drought stress increased Phenylalanine ammonia-lyase (PAL) activity in Sarigol. PEN-Ca²⁺ treatment increased relative expression of PAL and its activity in RGS003. Fatty acid composition was modified by drought, PEN and Ca²⁺. Saturated fatty acid (stearic acid) content declined but unsaturated fatty acid (oleic acid) content enhanced in both cultivars under drought. The application of PEN and Ca²⁺ decreased unsaturated fatty acids (linoleic and linolenic acid) in RGS003 under drought. According to our results, PEN and Ca²⁺ changed physiological and biochemical parameters and therefore these compounds are suggested for reduction of the negative effects of drought stress in canola.

Effect of exogenous calcium on growth, nutrients uptake and plasma membrane H+-ATPase and Ca2+-ATPase activities in soybean (Glycine max) seedlings under simulated acid rain stress

Calcium (Ca) is one of essential elements for plant growth and development, and also plays a role in regulating plant cell physiology and cellular response to the environment. Here, we studied whether calcium played a role in enhancing tolerance of plants to acid rain stress by hydroponics and simulating acid rain stress. Our results show that acid rain (pH 4.5/pH 3.0) caused decreases in dry weight biomass, chlorophyll content and uptake of nutrients elements (NO3-, P, K, Mg, Zn and Mo) and an increase in membrane permeability of root. However, all parameters in soybean treated with exogenous calcium (5 mM) and acid rain at pH 4.5 were closed to the control levels. In addition, exogenous calcium (5 mM) alleviated the inhibition induced by pH 3.0 acid rain on the activity of plasma membranes H+-ATPase and the expression of GmPHA1 at transcriptional level, being benefiting to maintaining uptake of nutrients (NO3-, P, K, Mg, and Zn), and then lower the decrease in dry weight biomass and chlorophyll content. After a 5-day recovery (without acid rain stress), all parameters in soybean treated with acid rain at pH 3.0 and exogenous calcium were still worse than those of the control, but obviously better than those treated with acid rain at pH 3.0. Higher activity of plasma membrane H+-ATPase in soybean treated with acid rain at pH 3.0 and exogenous calcium was good to uptake of nutrients and promoted the recovery of soybean growth, compared with soybean treated with acid rain at pH 3.0. In conclusion, exogenous calcium could alleviate the inhibition caused by acid rain on soybean growth by increasing the activity of plasma membrane H+-ATPase for providing driving force to nutrient absorption, and its regulating effect was limited by intensity of acid rain. Furthermore, the application of exogenous calcium can be one of ways to alleviate the damage caused by acid rain to plants.

Chloroplasts at the Crossroad of Photosynthesis, Pathogen Infection and Plant Defense

Photosynthesis, pathogen infection, and plant defense are three important biological processes that have been investigated separately for decades. Photosynthesis generates ATP, NADPH, and carbohydrates. These resources are utilized for the synthesis of many important compounds, such as primary metabolites, defense-related hormones abscisic acid, ethylene, jasmonic acid, and salicylic acid, and antimicrobial compounds. In plants and algae, photosynthesis and key steps in the synthesis of defense-related hormones occur in chloroplasts. In addition, chloroplasts are major generators of reactive oxygen species and nitric oxide, and a site for calcium signaling. These signaling molecules are essential to plant defense as well. All plants grown naturally are attacked by pathogens. Bacterial pathogens enter host tissues through natural openings or wounds. Upon invasion, bacterial pathogens utilize a combination of different virulence factors to suppress host defense and promote pathogenicity. On the other hand, plants have developed elaborate defense mechanisms to protect themselves from pathogen infections. This review summarizes recent discoveries on defensive roles of signaling molecules made by plants (primarily in their chloroplasts), counteracting roles of chloroplast-targeted effectors and phytotoxins elicited by bacterial pathogens, and how all these molecules crosstalk and regulate photosynthesis, pathogen infection, and plant defense, using chloroplasts as a major battlefield.

Ecophysiological Responses of Calcicole Cyclobalanopsis glauca (Thunb.) Oerst. to Drought Stress and Calcium Supply

Water deficit and high calcium (Ca2+) content and are two typical soil characteristics in the Karst region. However, the problem of whether high Ca2+ in Karst calcareous soil could increase drought tolerance in calcicole plants has not been solved. We investigated the ecophysiological responses of Cyclobalanopsis glauca (Thunb.) Oerst. cuttings to short-term drought stress and Ca2+ application. Drought stress (10% PEG-6000) markedly reduced relative water content (RWC) and water potential (WP), and enhanced the levels of reactive oxygen species (ROS) production (H2O2 and O2•−) and malondialdehyde (MDA) content in C. glauca leaves. Under drought treatment, exogenous Ca2+ application (20 mM CaCl2) markedly increased the RWC and WP, and reduced the H2O2, O2•−, and MDA content. Furthermore, water deficit induced a significant increase in the activities of antioxidant enzymes such as peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and glutathione peroxidase (GPX), and increased the accumulation of osmoregulation substances. External Ca2+ alleviated drought-induced oxidative stress and osmotic stress with further increased activities of antioxidant enzymes, and enhanced the accumulation of osmoregulation substances. In addition, exogenous Ca2+ treatment alleviated the reduction of the photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and chlorophyll content (SPAD), and further increased water use efficiency (WUE) under drought stress. This study confirms that exogenouos Ca2+ application induces improvements in the water status, osmotic adjustment, antioxidant defense, and photosynthesis efficiency of C. glauca under drought stress.

Exogenous application of calcium to 24-epibrassinosteroid pre-treated tomato seedlings mitigates NaCl toxicity by modifying ascorbate-glutathione cycle and secondary metabolites

The present study tested the efficacy of 24-epibrassinolide (EBL) and calcium (Ca) for mediating salinity tolerance in tomato. Salinity stress affected the morphological parameters of tomato as well as leaf relative water content (LRWC), photosynthetic and accessory pigments, leaf gas exchange parameters, chlorophyll fluorescence and the uptake of essential macronutrients. The salt (NaCl) treatment induced oxidative stress in the form of increased Na+ ion concentration by 146%, electrolyte leakage (EL) by 61.11%, lipid peroxidation (MDA) 167% and hydrogen peroxide (H2O2) content by 175%. Salt stress also enhanced antioxidant enzyme activities including those in the ascorbate-glutathione cycle. Plants treated with EBL or Ca after salt exposure mitigated the ill effects of salt stress, including oxidative stress, by reducing the uptake of Na+ ions by 52%. The combined dose of EBL + Ca reversed the salt-induced changes through an elevated pool of enzymes in the ascorbate-glutathione cycle, other antioxidants (superoxide dismutase, catalase), and osmoprotectants (proline, glycine betaine). Exogenously applied EBL and Ca help to optimize mineral nutrient status and enable tomato plants to tolerate salt toxicity. The ability of tomato plants to tolerate salt stress when supplemented with EBL and Ca was attributed to modifications to enzymatic and non-enzymatic antioxidants, osmolytes and metabolites.

Genome-Wide Analyses of Calcium Sensors Reveal Their Involvement in Drought Stress Response and Storage Roots Deterioration after Harvest in Cassava

Calcium (Ca²⁺) plays a crucial role in plant development and responses to environmental stimuli. Currently, calmodulins (CaMs), calmodulin-like proteins (CMLs), and calcineurin B-like proteins (CBLs), such as Ca²⁺ sensors, are not well understood in cassava (Manihotesculenta Crantz), an important tropical crop. In the present study, 8 CaMs, 48 CMLs, and 9 CBLs were genome-wide identified in cassava, which were divided into two, four, and four groups, respectively, based on evolutionary relationship, protein motif, and gene structure analyses. Transcriptomic analysis revealed the expression diversity of cassava CaMs-CMLs-CBLs in distinct tissues and in response to drought stress in different genotypes. Generally, cassava CaMs-CMLs-CBLs showed different expression profiles between cultivated varieties (Arg7 and SC124) and wild ancestor (W14) after drought treatment. In addition, numerous CaMs-CMLs-CBLs were significantly upregulated at 6 h, 12 h, and 48 h after harvest, suggesting their possible role during storage roots (SR) deterioration. Further interaction network and co-expression analyses suggested that a CBL-mediated interaction network was widely involved in SR deterioration. Taken together, this study provides new insights into CaMs-CMLs-CBLs-mediated drought adaption and SR deterioration at the transcription level in cassava, and identifies some candidates for the genetic improvement of cassava.

Physiological and molecular responses of pearl millet seedling to atrazine stress

Pearl millet has been recommended beneficial for several therapeutic purposes. However, little is known of the physiological responses to abiotic stressors, especially of atrazine. In order to elucidate the physiological and molecular responses of pearl millet to atrazine stress, we studied the response of various biomarkers under increasing herbicide concentrations (0, 5, 10, and 50 mg/kg). We also quantified the levels of malondialdehyde (MDA) and reactive oxygen species (ROS) (H₂O₂ and O₂•^-) produced in the leaves to evaluate the extent of oxidative damage. Increasing atrazine concentrations significantly increased ROS and MDA production in the plant leaves. Ascorbate peroxidase (APX) and peroxidase (POD) activities increased, while catalase (CAT) and superoxide dismutase activities reduced with increasing atrazine concentrations. Generally, atrazine applied at 50 mg/kg suppressed chlorophyll contents, whereas, chlorophyll (a/b) ratio was increased. Atrazine applied at 50 mg/kg significantly suppressed antioxidant gene expressions to the lowest. The APX gene showed overall low response to the atrazine treatments. The chloroplastic psbA gene showed highest expression with 10 mg/kg atrazine, whereas atrazine at 50 mg/kg significantly suppressed the gene expression to its lowest. Pearl millet was able to suppress oxidative stress under low atrazine levels, but high atrazine concentration could induce more oxidative damage.

Improved short-term drought response of transgenic rice over-expressing maize C4 phosphoenolpyruvate carboxylase via calcium signal cascade

To understand the link between long-term drought tolerance and short-term drought responses in plants, transgenic rice (Oryza sativa L.) plants over-expressing the maize C_4-pepc gene encoding phosphoenolpyruvate carboxylase (PC) and wild-type (WT) rice plants were subjected to PEG 6000 treatments to simulate drought stress. Compared with WT, PC had the higher survival rate and net photosynthetic rate after 16days of drought treatment, and had higher relative water content in leaves after 2h of drought treatment as well, conferring drought tolerance. WT accumulated higher amounts of malondialdehyde, superoxide radicals, and H₂O₂ than PC under the 2-h PEG 6000 treatment, indicating greater damages in WT. Results from pretreatments with a Ca²⁺ chelator and/or antagonist showed that the regulation of the early drought response in PC was Ca²⁺-dependent. The NO and H₂O₂ levels in PC lines were also up-regulated via Ca²⁺ signals, indicating that Ca²⁺ in PC lines also reacted upstream of NO and H₂O₂. 2-h drought treatment increased the transcripts of CPK9 and CPK4 in PC via positive up-regulation of Ca²⁺. The transcripts of NAC6 [NACs (NAM, ATAF1, ATAF2, and CUC2)] and bZIP60 (basic leucine zipper, bZIP) were up-regulated, but those of DREB2B (dehydration-responsive element-binding protein, DREB) were down-regulated, both via Ca²⁺ signals in PC. PEPC activity, expressions of C₄-pepc, and the antioxidant enzyme activities in PC lines were up-regulated via Ca²⁺. These results indicated that Ca²⁺ signals in PC lines can up-regulate the NAC6 and bZIP60 and the downstream targets for early drought responses, conferring drought tolerance for the long term.

Calcium and Calmodulin Are Involved in Nitric Oxide-Induced Adventitious Rooting of Cucumber under Simulated Osmotic Stress

Osmotic stress is a major form of abiotic stress that adversely affects growth and development of plants and subsequently reduces yield and quality of crops. In this study, the effect of nitric oxide (NO) and calcium (Ca2+) on the process of adventitious rooting in cucumber (Cucumis sativus L.) under simulated osmotic stress was investigated. The results revealed that the effect of exogenous NO and Ca2+ in promoting the development of adventitious roots in cucumber seedlings under simulated osmotic stress was dose-dependent, with a maximal biological response at 10 μM NO donor nitroprusside (SNP) or 200 μM Ca2+. The application of Ca2+ chelators or channel inhibitors and calmodulin (CaM) antagonists significantly reversed NO-induced adventitious rooting, implying that endogenous Ca2+/CaM might be involved in NO-induced adventitious rooting under osmotic stress. Moreover, intracellular Ca amount was also increased by NO in cucumber hypocotyls during the development of adventitious roots under osmotic stress. This increase of endogenous Ca2+ was inhibited by NO specific scavenger 2-(4-carboxyphenyl) -4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO), nitrate reductase inhibitors tungstate (Na2WO4) and sodium azide (NaN3). This gives an indication that Ca2+ might be a downstream signaling molecule in the adventitious root development by NO under osmotic condition. The results also show that NO or Ca2+ play a positive role in improving plant water status and photosynthetic system by increasing chlorophyll content and photochemical activity in leaves. Furthermore, NO and Ca2+ treatment might alleviate the negative effects of osmotic stress by decreasing membrane damage and reactive oxygen species (ROS) production by enhancing the activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX). Therefore, Ca2+/CaM may act as a downstream signaling molecule in NO-induced development of adventitious root under simulated osmotic stress through improving the photosynthetic performance of leaves and activating antioxidative system in plants.

Proteomic Analysis of Calcium Effects on Soybean Root Tip under Flooding and Drought Stresses

Flooding and drought are disadvantageous environmental conditions that induce cytosolic calcium in soybean. To explore the effects of flooding- and drought-induced increases in calcium, a gel-free/label-free proteomic analysis was performed. Cytosolic calcium was decreased by blocking calcium channels in the endoplasmic reticulum (ER) and plasma membrane under both stresses. Calnexin, protein disulfide isomerase, heat shock proteins and thioredoxin were predominantly affected as the ER proteins in response to calcium, and ER-associated degradation-related proteins of HCP-like superfamily protein were up-regulated under stress exposure and then down-regulated. Glycolysis, fermentation, the tricarboxylic acid cycle and amino acid metabolism were mainly induced as the types of cellular metabolism in response to calcium under both stresses. Pyruvate decarboxylase was increased and decreased under flooding and drought, respectively, and was further decreased by the reduction of cytosolic calcium; however, it was recovered by exogenous calcium under both stresses. Furthermore, pyruvate decarboxylase activity was increased under flooding, but decreased under drought. These results suggest that calcium is involved in protein folding in the ER, and ER-associated degradation might alleviate ER stress during the early stage of both stresses. Furthermore, calcium appears to modify energy metabolism, and pyruvate decarboxylase may be a key enzyme in this process under flooding and drought.

Role of calcium in AMF-mediated alleviation of the adverse impacts of cadmium stress in Bassia indica [Wight] A.J. Scott

The aim of this study was to evaluate cadmium stress induced changes in the growth, lipid peroxidation and antioxidant activity of Bassia indica associated with arbuscular mycorrhizal fungi (AMF) and their amelioration by calcium application. Cadmium stress can cause alterations in the physiological and biochemical processes in plants. A calcium application combined with an AMF treatment resulted in the reduction of lipid peroxidation and the production of hydrogen peroxide, thereby mediating the mitigation of cadmium induced oxidative stress. The activity of antioxidant enzymes increased with cadmium application, whereas AMF inoculation combined with a calcium application further enhanced their activity. An increase in the content of non-enzymatic antioxidants such as ascorbate, reduced glutathione (GSH), oxidized glutathione (GSSG) and S-nitrosoglutathione (GSNO) in AMF-inoculated and calcium-treated plants further suggests their role in strengthening the antioxidant defense system that results in maintained growth. The application of calcium combined with the AMF treatment caused a significant reduction in lipid peroxidation and in the production of hydrogen peroxide, thereby mediating the mitigation of the cadmium induced oxidative stress. Increased proline accumulation was clearly evident in stressed plants, and the calcium application as well as the AMF inoculation further induced proline synthesis, thereby providing efficient protection against cadmium stress by increasing the maintenance of the systemic resistance criteria.

Exogenous calcium induces tolerance to atrazine stress in Pennisetum seedlings and promotes photosynthetic activity, antioxidant enzymes and psbA gene transcripts

Calcium (Ca) has been reported to lessen oxidative damages in plants by upregulating the activities of antioxidant enzymes. However, atrazine mediated reactive oxygen species (ROS) reduction by Ca is limited. This study therefore investigated the effect of exogenously applied Ca on ROS, antioxidants activity and gene transcripts, the D1 protein (psbA gene), and chlorophyll contents in Pennisetum seedlings pre-treated with atrazine. Atrazine toxicity increased ROS production and enzyme activities (ascorbate peroxidase APX, peroxidase POD, Superoxide dismutase SOD, glutathione-S-transferase GST); but decreased antioxidants (APX, POD, and Cu/Zn SOD) and psbA gene transcripts. Atrazine also decreased the chlorophyll contents, but increased chlorophyll (a/b) ratio. Contrarily, Ca application to atrazine pre-treated seedlings lowered the harmful effects of atrazine by reducing ROS levels, but enhancing the accumulation of total chlorophyll contents. Ca-protected seedlings in the presence of atrazine manifested reduced APX and POD activity, whereas SOD and GST activity was further increased with Ca application. Antioxidant gene transcripts that were down-regulated by atrazine toxicity were up-regulated with the application of Ca. Calcium application also resulted in up-regulation of the D1 protein. In conclusion, ability of calcium to reverse atrazine-induced oxidative damage and calcium regulatory role on GST in Pennisetum was presented.

Role of calcium in the mitigation of heat stress in the cyanobacterium Anabaena PCC 7120

The effects of exogenously added CaCl₂ (0.25mM) on photopigments, photosynthetic O₂-evolution, antioxidative enzyme activity, membrane damage, expression of two heat shock genes (groEL and groES) and apoptotic features in Anabaena 7120 under heat stress (45°C) for up to 24h were investigated. Heat stress lowered the level of photopigments; however, Ca²⁺--supplemented cultures showed a low level reduction in Chl a but induced accumulation of carotenoids and phycocyanin under heat stress. Photosynthetic O₂-evolving capacity was maintained at a higher level in cells from Ca²⁺-supplemented medium. Among the antioxidative enzymes, superoxide dismutase activity was unaffected by the presence or absence of Ca²⁺ in contrast to increases in catalase, ascorbate peroxidase and glutathione reductase activities in cells grown in Ca²⁺-supplemented medium. Lower levels of lipid peroxidation were recorded in Anabaena cells grown in Ca²⁺-supplemented medium in comparison to cells from Ca²⁺--deprived medium. Target cells grown in Ca²⁺-deprived medium developed apoptotic features in the early stages of heat shock, while Ca²⁺ application seemed to interfere with apoptosis because only a few cells showed such features after 24 h of heat exposure, indicating a role for Ca²⁺ in maintaining cell viability under heat stress. There was also continuous up regulation of two important heat shock genes (groEL and groES) in Ca²⁺-supplemented cultures, exposed to heat shock, again indicating a role for Ca²⁺ in stress management.

Comparative Proteomic Analysis Reveals the Effects of Exogenous Calcium against Acid Rain Stress in Liquidambar formosana Hance Leaves

Acid rain (AR) impacts forest health by leaching calcium (Ca) away from soils and plants. Ca is an essential element and participates in various plant physiological responses. In the present study, the protective role of exogenous Ca in alleviating AR stress in Liquidambar formosana Hance at the physiological and proteomic levels was examined. Our results showed that low Ca condition resulted in the chlorophyll content and photosynthesis decreasing significantly in L. formosana leaves; however, these effects could be reversed by high Ca supplementation. Further proteomic analyses successfully identified 81 differentially expressed proteins in AR-treated L. formosana under different Ca levels. In particular, some of the proteins are involved in primary metabolism, photosynthesis, energy production, antioxidant defense, transcription, and translation. Moreover, quantitative real time polymerase chain reaction (qRT-PCR) results indicated that low Ca significantly increased the expression level of the investigated Ca-related genes, which can be reversed by high Ca supplementation under AR stress. Further, Western blotting analysis revealed that exogenous Ca supply reduced AR damage by elevating the expression of proteins involved in the Calvin cycle, reactive oxygen species (ROS) scavenging system. These findings allowed us to better understand how woody plants respond to AR stress at various Ca levels and the protective role of exogenous Ca against AR stress in forest tree species.

Mathematical modelling of diurnal regulation of carbohydrate allocation by osmo-related processes in plants

Plants synthesize sucrose in source tissues (mainly mature leafs) and supply it for growth of sink tissues (young leafs). Sucrose is derived from photosynthesis during daytime and from starch at night. Because the diurnal regulation of sucrose fluxes is not completely understood, we built a mathematical model designed to reproduce all key experimental observations. For this, assumptions were made about the molecular mechanisms underlying the regulations, which are all motivated by experimental facts. The key regulators in our model are two kinases (SnRK1 and osmo-sensitive kinase OsmK) under the control of the circadian clock. SnRK1 is activated in the night to prepare for regularly occurring carbon-limiting conditions, whereas OsmK is activated during the day to prepare for water deficit, which often occurs in the afternoon. Decrease of SnRK1 and increase of OsmK result in partitioning of carbon towards sucrose to supply growing sink tissues. Concomitantly, increasing levels of the growth regulator trehalose-6-phosphate stimulates the development of new sink tissues and thus sink demand, which further activates sucrose supply in a positive feedback loop. We propose that OsmK acts as a timer to measure the length of the photoperiod and suggest experiments how this hypothesis can be validated.

De novo assembly of the Japanese lawngrass (Zoysia japonica Steud.) root transcriptome and identification of candidate unigenes related to early responses under salt stress

Japanese lawngrass (Zoysia japonica Steud.) is an important warm-season turfgrass that is able to survive in a range of soils, from infertile sands to clays, and to grow well under saline conditions. However, little is known about the molecular mechanisms involved in its resistance to salt stress. Here, we used high-throughput RNA sequencing (RNA-seq) to investigate the changes in gene expression of Zoysia grass at high NaCl concentrations. We first constructed two sequencing libraries, including control and NaCl-treated samples, and sequenced them using the Illumina HiSeq™ 2000 platform. Approximately 157.20 million paired-end reads with a total length of 68.68 Mb were obtained. Subsequently, 100,800 unigenes with an N50 length of 1104 bp were assembled using Trinity, among which 70,127 unigenes were functionally annotated (E ≤ 10(-5)) in the non-redundant protein (NR) database. Furthermore, three public databases, the Kyoto Encyclopedia of Genes and Genomes (KEGG), Swiss-prot, and Clusters of Orthologous Groups (COGs), were used for gene function analysis and enrichment. The annotated genes included 46 Gene Ontology (GO) terms, 120 KEGG pathways, and 25 COGs. Compared with the control, 6035 genes were significantly different (false discovery rate ≤0.01, |log2Ratio|≥1) in the NaCl-treated samples. These genes were enriched in 10 KEGG pathways and 58 GO terms, and subjected to 25 COG categories. Using high-throughput next-generation sequencing, we built a database as a global transcript resource for Z. japonica Steud. roots. The results of this study will advance our understanding of the early salt response in Japanese lawngrass roots.