Calcium regulates antioxidative isozyme activity for enhancing rice adaption to acid rain stress

Heat Stress Alleviation by Exogenous Calcium in the Orchid Dendrobium nobile Lindl: A Biochemical and Transcriptomic Analysis

The growth of Dendrobium nobile is sensitive to heat stress. To find an effective method for enhancing heat tolerance, this study investigated the relieving effect of exogenous calcium at different concentrations (0 mmol/L, 5 mmol/L, 10 mmol/L, 15 mmol/L, 20 mmol/L CaCl2) on heat stress in D. nobile. Principal component analysis was used to screen the optimal exogenous calcium concentration, and transcriptome analysis was used to reveal its possible heat tolerance mechanism. The results showed that compared with the T0, a 10 mmol/L calcium treatment: increased the average leaf length, leaf width, plant height, and fresh matter accumulation of D. nobile by 76%, 103.39%, 12.97%, and 12.24%, respectively (p < 0.05); significantly increased chlorophyll a (Chla), chlorophyll b (Chlb), carotenoids(Car), ascorbic acid (ASA), glutathione (GSH), and flavonoids by 15.72%, 8.54%, 11.88%, 52.17%, 31.54%, and 36.12%, respectively; and effectively enhanced the enzyme activity of the antioxidant system, increasing superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) by 1.38, 1.61, and 2.16 times, respectively (p < 0.05); At the same time, the treatment can effectively reduce the yellow leaf rate and defoliation rate of D. nobile under heat stress. The principal component analysis method and membership function were used to calculate the D value to rank the relief effects of each calcium treatment group, and the results also showed that 10 mmol/L CaCl2 had the best relief effect. Transcriptomics testing identified 7013 differentially expressed genes, of which 2719 were upregulated, and 294 were downregulated. Among them, genes such as HSPA1s, HSP90A, HSPBP1, ATG8, COMT, REF1, E1.11.1.7, along with transcription factors such as MYB, bHLH, WRKY, and NAC, formed the network of tolerance to heat stress in D. nobile. This study provides new insights for improving the cultivation techniques of D. nobile.

Calcium signaling-mediated transcriptional reprogramming during abiotic stress response in plants

Calcium (Ca2+) is a second messenger in plants growth and development, as well as in stress responses. The transient elevation in cytosolic Ca2+ concentration have been reported to be involved in plants response to abiotic and biotic stresses. In plants, Ca2+-induced transcriptional changes trigger molecular mechanisms by which plants adapt and respond to environment stresses. The mechanism for transcription regulation by Ca2+ could be either rapid in which Ca2+ signals directly cause the related response through the gene transcript and protein activities, or involved amplification of Ca2+ signals by up-regulation the expression of Ca2+ responsive genes, and then increase the transmission of Ca2+ signals. Ca2+ regulates the expression of genes by directly binding to the transcription factors (TFs), or indirectly through its sensors like calmodulin, calcium-dependent protein kinases (CDPK) and calcineurin B-like protein (CBL). In recent years, significant progress has been made in understanding the role of Ca2+-mediated transcriptional regulation in different processes in plants. In this review, we have provided a comprehensive overview of Ca2+-mediated transcriptional regulation in plants in response to abiotic stresses including nutrition deficiency, temperature stresses (like heat and cold), dehydration stress, osmotic stress, hypoxic, salt stress, acid rain, and heavy metal stress.

Effect of calcium levels on structure and function of mitochondria in yeast under high glucose fermentation

In this study, the effects of calcium levels on structure and function of mitochondria under high glucose environment were studied. In the high glucose environment, yeast growth capacity was inhibited, and intracellular reactive oxygen species (ROS) content was increased from 6 h to 12 h, while ROS content was reduced in group with 1 × 10-1 and 1 g/L CaCl2 level from 24 h to 36 h. Exogenous calcium addition had a significant effect on the elevation of intracellular Ca2+ and cytochrome C content in yeast from 6 h to 12 h; mitochondrial membrane potential decreased with the increase of CaCl2 level under high glucose levels. Mitochondrial swelling of yeast was influenced by high glucose levels and showed a regulatory dynamic change by Ca2+ levels. Isocitrate dehydrogenase activity increased in 1 × 10-3 g/L CaCl2 level from 6 h to 12 h, α-ketoglutarate dehydrogenase activity increased with an increase in CaCl2 level from 6 h to 24 h. Calcium affected the structure and function of mitochondria by regulating the intracellular signal, enzymes in tricarboxylic acid cycle, and cytochrome system of yeast under high glucose stress.

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.

Improving yield and quality of rice under acid rain stress by regulating nitrogen assimilation with exogenous Ca2

Acid rain threatens crop yield and nutritional quality, and Ca²⁺ can regulate plant responses to abiotic stresses. To improve the yield and nutritional quality of crops under acid rain stress, we applied exogenous Ca²⁺ to regulate nitrogen assimilation in rice seedlings under simulated acid rain stress (pH 4.5 or 3.0), taking yield and nutritional quality of rice as evaluation criteria. We found that Ca²⁺ (5 mM) maintained the total nitrogen content of rice at the seedling and booting stages to alleviate the inhibitory effect of simulated acid rain on rice yield. Meanwhile, Ca²⁺ improved the activity of glutamate synthase to eliminate the disruption of glutamine synthetase/glutamate synthase balance under simulated acid rain. It decreased the efficiency of nitrogen assimilation, thereby reducing the inhibition of essential amino acid content in rice. The mitigation effect on simulated acid rain at pH 4.5 was better than that of simulated acid rain at pH 3.0. Overall, Ca²⁺ may reduce the negative effect of acid rain on the yield and nutritional quality of crops.

Crosstalk between Ca2+ and Other Regulators Assists Plants in Responding to Abiotic Stress

Plants have evolved many strategies for adaptation to extreme environments. Ca²⁺, acting as an important secondary messenger in plant cells, is a signaling molecule involved in plants' response and adaptation to external stress. In plant cells, almost all kinds of abiotic stresses are able to raise cytosolic Ca²⁺ levels, and the spatiotemporal distribution of this molecule in distant cells suggests that Ca²⁺ may be a universal signal regulating different kinds of abiotic stress. Ca²⁺ is used to sense and transduce various stress signals through its downstream calcium-binding proteins, thereby inducing a series of biochemical reactions to adapt to or resist various stresses. This review summarizes the roles and molecular mechanisms of cytosolic Ca²⁺ in response to abiotic stresses such as drought, high salinity, ultraviolet light, heavy metals, waterlogging, extreme temperature and wounding. Furthermore, we focused on the crosstalk between Ca²⁺ and other signaling molecules in plants suffering from extreme environmental stress.

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.

A rice transcription factor, OsMADS57, positively regulates high salinity tolerance in transgenic Arabidopsis thaliana and Oryza sativa plants

MADS-box transcription factors (TFs) play indispensable roles in various aspects of plant growth, development as well as in response to environmental stresses. Several MADS-box genes have been reported to be involved in the salt tolerance in different plant species. However, the role of the transcription factor OsMADS57 under salinity stress is still unknown. Here, the results of this study showed that OsMADS57 was mainly expressed in roots and leaves of rice plants (Oryza sativa). Gene expression pattern analysis revealed that OsMADS57 was induced by NaCl. Overexpression of OsMADS57 in both Arabidopsis thaliana (A. thaliana) and rice could improve their salt tolerance, which was demonstrated by higher germination rates, longer root length and better growth status of overexpression plants than wild type (WT) under salinity conditions. In contrast, RNA interference (RNAi) lines of rice showed more sensitivity towards salinity. Moreover, less reactive oxygen species (ROS) accumulated in OsMADS57 overexpressing lines when exposed to salt stress, as measured by 3, 3'-diaminobenzidine (DAB) or nitroblue tetrazolium (NBT) staining. Further experiments exhibited that overexpression of OsMADS57 in rice significantly increased the tolerance ability of plants to oxidative damage under salt stress, mainly by increasing the activities of antioxidative enzymes such as superoxide dismutase (SOD) and peroxidase (POD), reducing malonaldehyde (MDA) content and improving the expression of stress-related genes. Taken together, these results demonstrated that OsMADS57 plays a positive role in enhancing salt tolerance by activating the antioxidant system.