Exogenous Application Of Calcium Research Articles

Transcriptome and Flavonoid Compounds Metabolome Analyses Reveal the Mechanisms of Heat Stress in Rhododendron with Exogenously Applied Calcium

Rhododendron plants have ornamental, commercial, and medicinal value to people. Flavonoids are one of the components used in traditional remedies, and Rhododendron plants are found to be rich in flavonoids. Flavonoids can reduce the risk of human disease and participate in the regulation of antioxidant defense systems in response to heat stress. Rhododendron prefers cold climates, so the relatively high temperatures of cities affect the extraction of medicinal ingredients and limit the cultivation environment. Recent studies found that the exogenous application of calcium acts to alleviate heat stress in Rhododendron plants. This study explores the mechanism by which exogenous calcium alleviates heat stress and the role of flavonoids in regulating the antioxidative system in Rhododendron × pulchrum Sweet using combined transcriptomic and metabolomic methods. The activities of peroxidase, catalase and superoxide enzymes were found to increase in response to heat stress and external CaCl2 in the leaves of R. × pulchrum. In total, 433 metabolic components and 370 DEGs were identified as being differentially expressed in response to heat stress and external calcium chloride (CaCl2) in the leaves of R. × pulchrum. These results illustrate that heat stress induces oxidative stress and that external CaCl2 can enhance the heat tolerance of Rhododendron. Flavonoid compounds are responsible for the antioxidant scavenging of reactive oxygen species in R. × pulchrum leaves exposed to heat stress and external calcium.

Exogenous application of calcium ameliorates salinity stress of mungbean

An experiment was conducted to investigate the impact of exogenous Ca in alleviating salinity stress of mungbean. Two mungbean genotypes, BD 6895 and BD 6905, were used with four different Ca levels (5, 10, 15 and 20 mM) under 10 dSm-1 salinity conditions in a hydroponic culture. The application of exogenous Ca positively influenced on overall plant growth and development. Although both genotypes exhibited similar plant heights, they gave the peak (56.65 and 48.6 cm for BD 6895 and BD 6905, respectively) at 10 mM Ca. Higher levels of exogenous Ca were associated with increased chlorophyll content. Maximum Chlorophyll (1.6 mg g-1) was observed at 15 mM Ca treatment. Furthermore, exogenous Ca application reduced Malondialdehyde levels (at 15 mM Ca: 1.14 and 1.69 μmole/g for BD 6895 and BD 6905, respectively). Both the genotypes exhibited a proline content pattern, demonstrating proline content upsurge with increased Ca application. Microscopic analysis revealed larger vascular areas with exogenous Ca (BD 6895: 402 µm, BD 6905: 398.3 µm) compared to smaller areas under salinity stress (BD 6895: 258.7 µm, BD 6905: 248.4 µm). Salinity stress induced changes in upper epidermis thickness, leaf tissue compactness, chloroplast breakdown and chlorosis in mungbean plants. However, exogenous Ca application counteracted these detrimental effects, enabling mungbean plants to thrive in saline conditions. In conclusion, the study highlights the positive influence of exogenous Ca (10-15 mM) in promoting mungbean growth and managing salt stress. Ann. Bangladesh Agric. (2023) 27 (2): 91-104

Expression of TaNCL2-A ameliorates cadmium toxicity by increasing calcium and enzymatic antioxidants activities in arabidopsis

Cadmium (Cd) is a heavy metal that occurs naturally in the environment and is toxic to both animals and plants. The impact of Cd toxicity is shown to be reduced by the exogenous application of calcium (Ca) in crop plants. The sodium/calcium exchanger-like (NCL) protein is involved in Ca enrichment in the cytoplasm by transporting it from the vacuole in the exchange of cytosolic sodium (Na). However, it has not been utilized to ameliorate the Cd toxicity, to date. An elevated expression of TaNCL2-A gene in the root and shoot tissues of bread wheat seedlings, and a higher growth rate of recombinant yeast cells, suggested its role in Cd stress response. The TaNCL2-A expressing transgenic Arabidopsis lines exhibited significant Cd tolerance with increased Ca (∼10-fold) accumulation. The proline content and antioxidant enzymes activities were increased while oxidative stress-related molecules such as H2O2 and MDA were reduced in the transgenic lines. In addition, the growth and yield parameters of transgenic lines such as seed germination rate, root length, leaf biomass, leaf area index, rosette diameter, leaf length and width, and silique count, along with various physiological indicators like chlorophyll, carotenoid, and relative water contents were also improved in comparison to the control plants. Further, the transgenic lines exhibited significant salinity and osmotic stress tolerance, as well. Taken together, these results suggested that the TaNCL2-A could mitigate Cd toxicity along with salinity and osmotic stress. This gene may also be utilized for phytoremediation and Cd sequestration in future studies.

Exogenous Application of Calcium Ameliorates Salinity Stress Tolerance of Tomato (Solanum lycopersicum L.) and Enhances Fruit Quality.

Tomato is affected by various biotic and abiotic stresses, especially salinity, which drastically hinders the growth and yield of tomato. Calcium (Ca) is a vital macronutrient which plays physiological and biochemical roles in plants. Hence, we studied the protective roles of Ca against salinity stress in tomato. There were eight treatments comprising control (nutrient solution), 5 mM Ca, 10 mM Ca, 15 mM Ca, 12 dS m-1 NaCl, 12 dS m-1 NaCl + 5 mM Ca, 12 dS m-1 NaCl + 10 mM Ca and 12 dS m-1 NaCl + 15 mM Ca, and two tomato varieties: BARI tomato-2 and Binatomato-5. Salinity significantly decreased the plant-growth and yield attributes, relative water content (RWC), photosynthetic pigments (SPAD value) and the uptake of K, Ca and Mg in leaves and roots. Salinity-induced oxidative stress was present in the form of increased Na+ ion concentration, hydrogen peroxide (H2O2) content and lipid peroxidation (MDA). Ca application reduced oxidative stress through the boosting of antioxidant enzymatic activity. Exogenous Ca application enhanced proline and glycine betaine content and reduced Na+ uptake, which resulted in the inhibition of ionic toxicity and osmotic stress, respectively. Hence, Ca application significantly increased the growth and yield attributes, RWC, SPAD value, and uptake of K, Ca and Mg. Calcium application also had a significant effect on the fruit quality of tomato and the highest total soluble solid, total sugar, reducing sugar, β-carotene, vitamin C and juice pH were found for the combined application of NaCl and Ca. Therefore, application of Ca reversed the salt-induced changes through increasing osmoprotectants, activation of antioxidants enzymes, and by optimizing mineral nutrient status.

English

This study focused on the improving effect of external application of calcium and potassium on growth, ions and organic solutes accumulation in tossa jute plants grown under salt stress. Young plants were subjected in pots to ten treatments including the control without NaCl, 120 mM NaCl and a combination of 120 mM NaCl and an addition of 40 or 60 mM CaSO4, CaCl2, K2SO4 or KNO3. Plant growth, sodium, potassium, proline and soluble sugars contents were determined after two weeks. Results revealed that only the external application of CaSO4 and K2SO4 at 40 mM significantly improved the growth reduction induced by NaCl followed by CaCl2; whereas at 60 mM, only CaSO4 induced similar changes in plant growth. Only, the exogenous application of calcium at 40 mM induced a significant decrease (p<0.05) in the Na+ content and a significant increase (p<0.001) of the K+/Na+ ratio of leaves in comparison with salt stressed plants, while the two forms of calcium and K2SO4 induced a significant increase (p=0.05) in the K+ content. CaSO4 had the best improving effects on plants growth under salt stress, followed by K2SO4 and CaCl2 at 40 mM. This improving effect is due to a better exclusion of Na+ from the leaves, the maintenance of a high ionic selectivity ratio K/Na and/or a better accumulation of K+.   Key words: Corchorus olitorius, sodium, potassium, calcium sulphate, calcium chloride, potassium sulphate, potassium nitrate, proline, soluble sugars.&nbsp

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.

Ions and Organic Solutes as Implicated in the Ameliorative Effect of Exogenous Application of Calcium on Salt Stressed Tomato (Lycopersicon esculentum Mill.) Plants

Aims: This study evaluated the role of sodium, potassium, proline and soluble sugars accumulation in the ameliorative effect of an exogenous application of calcium on the detrimental effect of salinity on tomato plants.&#x0D; Study Design: The experiment was implemented as a Completely Randomized Design (RCD) with four treatments and three replications.&#x0D; Place and Duration of Study: The experiment was realized in a green house of the Faculty of Agronomical Sciences, University of Abomey-Calavi, Benin Republic from June to July 2020. Methodology: Three weeks old plants of the tomato cultivar “Padma” was submitted in pots to four treatments comprising the control (without NaCl); salt stress (120 mM NaCl) and a combination of 120 mM NaCl and exogenous application of 40 mM CaSO4 or Ca (NO3)2 by irrigation every two days. Plants growth, sodium (Na) and potassium (K) as well as proline and soluble sugars contents of leaves and roots were determined after two weeks.&#x0D; Results: Salt effect reduced significantly plant growth at P =.05, root K content at P =.05 and leaf K/Na ratio at P =.01 whereas it increased significantly leaf Na at P =.05 and root soluble sugars content at P =.05. The application of exogenous calcium (Ca) induced a significant amelioration of plant growth at P =.01 more marked with CaSO4 than with Ca (NO3)2. This treatment induced a significant decrease at P =.01 in leaf and root Na content and a significant increase at P =.05 in root K content only for CaSO4, a significant increase at P =.01 in leaf K/Na ratio and a significant increase at P =.01 in leaf and root proline content only for Ca(NO3)2.&#x0D; Conclusion: The ameliorative effect of both forms of calcium was due mainly to sodium (Na) exclusion from leaves and potassium (K) accumulation associated to a maintain of high K/Na ratio mainly in leaves. The importance of proline accumulation as an indicator of this ameliorative effect was associated only to Ca(NO3)2.

Physiological Responses of Handeliodendron bodinieri (Levl.) Rehd. to Exogenous Calcium Supply under Drought Stress

The soils in karst regions, with carbonate rocks as the background material, are characterized by two main factors, drought and high calcium levels. Handeliodendron bodinieri (Levl.) Rehd is an endemic plant species in this area of China. However, few studies have been carried out on the adaptation mechanism of H. bodinieri to drought and high calcium soil. To reveal the physiological responses of H. bodinieri to exogenous calcium under drought stress, 10% PEG-6000 was used to simulate drought stress, and the effects of exogenous calcium at different concentrations on the physiology of H. bodinieri seedlings under drought stress were studied. The results showed that drought stress significantly reduced the relative water content and water potential of H. bodinieri seedlings. Malondialdehyde (MDA) content, O2− and H2O2 production rates significantly increased under drought stress. The addition of exogenous calcium significantly reduced MDA content and O2− and H2O2 production rates. Moreover, peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), ascorbic acid peroxidase (APX) and glutathione peroxidase (GPX) activities increased significantly under drought stress. At the same time, the accumulation of osmotic regulators such as soluble sugar, betaine and free proline also increased significantly. The addition of exogenous calcium further increased the activity of antioxidant enzymes and the accumulation of osmotic regulatory substances. Consequently, the oxidative stress and osmotic stress induced by drought decreased. Finally, exogenous calcium enhanced the photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of H. bodinieri under drought stress and significantly improved water use efficiency (WUE). This study confirmed that the application of exogenous calcium can enhance the water condition, photosynthetic capacity, osmotic regulation and antioxidant capacity of H. bodinieri under drought stress. Of the treatments, the 10 mmol·L−1 CaCl2 treatment is more likely to improve survival of H. bodinieri under drought tolerance. This study provides an important reference for describing the adaptation mechanism and appropriate conservation of H. bodinieri under drought and high calcium conditions.

Role of calcium in regulating anthocyanin accumulation in ‘Manicure Finger’ grape berries

The objective of this study was to clarify the effects of calcium treatments on the anthocyanin accumulation of ‘Manicure Finger’ grape berries. Calcium treatments increased the calcium contents and enhanced the calmodulin activities in grapevine leaves and berries, upregulated the expression of the sugar transporter genes SUC12 and SUC27 in leaves, promoted the transport of photosynthetic products to berries, and increased the expression of anthocyanin biosynthesis-related genes in the grape berry skin. These results indicate that the application of exogenous calcium enhances anthocyanin accumulation in ‘Manicure Finger’ grape berries in the following two ways: (1) calcium promotes the transport of photosynthetic products to berries, thereby providing the basic material required for anthocyanin biosynthesis; (2) calcium induces anthocyanin biosynthesis by regulating the expression of relevant structural and regulatory genes. Our results will help researchers characterize the mechanism responsible for the calcium-mediated promotion of anthocyanin biosynthesis in grapevine and related plant species.

Sperm Entry into the Egg Cell Induces the Progression of Karyogamy in Rice Zygotes.

Karyogamy is a prerequisite event for plant embryogenesis, in which dynamic changes in nuclear architecture and the establishment of appropriate gene expression patterns must occur. However, the precise role of the male and female gametes in the progression of karyogamy still remains elusive. Here, we show that the sperm cell possesses the unique property to drive steady and swift nuclear fusion. When we fertilized egg cells with sperm cells in vitro, the immediate fusion of the male and female nuclei in the zygote progressed. This rapid nuclear fusion did not occur when two egg cells were artificially fused. However, the nuclear fusion of two egg nuclei could be accelerated by additional sperm entry or the exogenous application of calcium, suggesting that possible increase of cytosolic Ca2+ level via sperm entry into the egg cell efficiently can facilitate karyogamy. In contrast to zygotes, the egg-egg fusion cells failed to proliferate beyond an early developmental stage. Our transcriptional analyses also revealed the rapid activation of zygotic genes in zygotes, whereas there was no expression in fused cells without the male contribution. Thus, the male sperm cell has the ability to cause immediate karyogamy and to establish appropriate gene expression patterns in the zygote.

Exogenous application of calcium to 24-epibrassinosteroid pre-treated tomato seedlings mitigates NaCl toxicity by modifying ascorbate\u2013glutathione 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.

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.

Effects of exogenous calcium on mesophyll cell ultrastructure, gas exchange, and photosystem II in tobacco (Nicotiana tabacum Linn.) under drought stress

The effects of calcium chloride solution (10 mmol L–1) on mesophyll cell ultrastructure, gas exchange, chlorophyll and carotenoid content, and PSII in tobacco leaf were studied by simulating water deficit conditions via treatment with 25% PEG-6000 for 24 h. The results showed that under drought stress, the mesophyll cell structure and morphology were destroyed, photosynthesis and gas-exchange processes changed, photosynthetic pigment content decreased, and the electron transfer efficiency in PSII reduced. However, compared with the control treatment, under drought conditions, the addition of exogenous calcium could stabilize the structure and function of the chloroplasts, mitochondria, and endomembrane system in the mesophyll cells, maintain normal leaf net photosynthetic rate and gas exchange, alleviate the degree of photosynthetic pigment degradation, and increase the electron transfer energy in the leaves in PSII. As a means of ensuring normal photosynthesis under drought stress, we discovered that the application of exogenous calcium was more important for stabilization of the structure of the organelles, regulation of the osmotic balance, and increase of the photosynthetic pigment content, and proved to be less important for regulation of stomatal opening and closing.

Modulation of ion uptake in tomato (Lycopersicon esculentum L.) plants with exogenous application of calcium under salt stress condition

Modulation of ion uptake in tomato (Lycopersicon esculentum L.) plants with exogenous application of calcium under salt stress condition

Calcium application mitigates salt stress in Date Palm (Phoenix dactylifera L.( offshoots cultivars of Berhi and Sayer

The effectiveness of exogenous application of calcium in ameliorating the adverse effects of salt stress (15.9 dS m-1) on date palm offshoots (Phoenix dactylifera L. cultivars of Berhi and Sayer) was investigated. Ca-fertilisers Polixal and Rexene were applied either as soil amendments or foliar spray. The results showed that Polixal at 30 ml offshoot-1 significantly increased plant height, leaf area, total chlorophyll content, RWC, proline concentration, peroxidase activity, IAA content, K+ and K+/Na+ ratio in leaves of Berhi cultivar, whereas catalase activity, ABA and Cl- content were decreased. Also Berhi cultivar responded to soil amendments more than to foliar spray. However, Ca-fertilisers mitigated salt stress in the two cultivars and Berhi cultivar was more salt stress tolerant than Sayer cultivar by maintaining the high ratio of K+/Na+ and regulating levels of IAA to ABA, in silty clay loam soil. These results suggest that calcium application can improve the defense system under salt stress conditions.

Exogenous calcium alleviates cadmium-induced oxidative stress in rice (Oryza sativa L.) seedlings by regulating the antioxidant defense and glyoxalase systems

The present study was undertaken to investigate the regulatory role of exogenous application of calcium (Ca) in enhancing the antioxidant defense and glyoxalase systems in mitigating cadmium (Cd) stress in rice. Hydroponically grown 14-day-old rice (Oryza sativa L. cv. BRRI dhan29) seedlings were exposed to 0.25 and 0.5 mM CdCl2 alone and in combination with 2.5 mM CaCl2 for 3 days. Exposure to Cd caused chlorosis, leaf rolling symptoms, and growth inhibition. A higher concentration of Cd in the growth medium resulted in higher Cd accumulation, which induced oxidative stress through overproduction of reactive oxygen species (ROS) by disrupting the antioxidant defense system. Cadmium treatment increased the methylglyoxal (MG) level. Calcium supplementation in the Cd-treated growth medium reduced Cd uptake. Application of Ca also significantly increased the (ascorbate) AsA content, increased the activities of superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR) in the antioxidant system, and increased the glyoxalase I (Gly I) and glyoxalase II (Gly II) activities in the glyoxalase system in rice seedlings exposed to both levels of Cd. Exogenous Ca application regulated the antioxidant defense and glyoxalase systems, which reversed overproduced ROS and detoxified MG, which in turn reduced Cd toxicity.

Effects of Calcium on Photosynthesis, Antioxidant System, and Chloroplast Ultrastructure in Tomato Leaves Under Low Night Temperature Stress

The effect of exogenous CaCl2 on photosynthesis, antioxidant system, and chloroplast ultrastructure of tomato leaves under low night temperature (LNT) was investigated. Tomato seedlings were pretreated with 27 mM CaCl2, 5 mM EGTA, respectively, for 4 days and then exposed to LNT treatment at 6 °C for 7 days. Plants treated with CaCl2 showed higher photosynthesis, increased stomatal aperture and chloroplast area, and decreased number of starch grains under LNT stress than those treated with distilled water. LNT increased the contents of superoxide radicals, hydrogen peroxide, and malondialdehyde, whereas calcium application reduced the contents of these compounds. The increase in antioxidant activities caused by LNT stress was also enhanced by the application of exogenous calcium. The opposite effects were observed with ethylene glycol-bis-(2-aminoethyl) tetraacetic acid pretreatment. CaCl2 application improved photosynthesis in LNT-stressed plants. Such improvement was associated with increased stomatal conductance, improved antioxidant activities, and adjusted chloroplast structure. These results suggest that CaCl2 application improved photosynthesis in LNT-stressed plants. It provided fundamental information for further molecular mechanism research.

Exogenous application of calcium and silica alleviates cadmium toxicity by suppressing oxidative damage in rice seedlings.

The present study was undertaken to examine the possible roles of calcium (Ca(2+)) and silica (Si) in protection against oxidative damage due to Cd(2+) toxicity in rice (Oryza sativa L.) seedlings grown in hydroponics. Rice seedlings raised for 12days in hydroponics containing Cd(NO3)2 (75μM) showed reduced growth; increase in the level of reactive oxygen species (ROS) (O2 (·-) and H2O2), thiobarbituric acid reactive substances (TBARSs) and protein carbonylation; and increase in the activity of antioxidant enzymes-superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (GPX) compared to untreated controls. Exogenously added Ca(2+) (2mM) and Si (200μM) significantly alleviated negative effect of Cd(2+) by restoration of growth of the seedlings, suppression of Cd(2+) uptake and restoration of root plasma membrane integrity. The levels of O2 (·-), H2O2, lipid peroxidation and protein carbonyls were much lower when Ca(2+) and Si were added in the growth medium along with Cd(2+) as compared to Cd-alone-treated seedlings. Ca(2+) and Si lowered Cd-induced increase in SOD, GPX and APX activities while they elevated Cd-induced decline in CAT activity. Using histochemical staining of O2 (·-) and H2O2 in leaf tissues, it was further confirmed that added Ca(2+) and Si suppressed Cd-induced accumulation of O2 (·-) and H2O2 in the leaves. The results suggest that exogenous application of Ca(2+) and Si appears to be advantageous for rice plants in alleviating Cd(2+) toxicity effects by reducing Cd(2+) uptake, decreasing ROS production and suppressing oxidative damage. The observations indicate that Ca(2+) and Si treatments can help in reducing Cd(2+) toxicity in rice plants.

Determination of calcium responsiveness towards exogenous application in two genotypes of Eleusine coracana L. differing in their grain calcium content

In order to investigate the influence of exogenous application of calcium (Ca) on its accumulation in finger millet, two genotypes (GPHCPB-1 and GPHCPB-45), which posses low and high grain Ca contents, respectively, were subjected to regular fertigation of varying levels of Ca in Hoagland’s nutrient medium. The responsiveness of both the genotypes towards increasing exogenous application of Ca (0.1, 5.0, 10 and 20) was determined in terms of changes in tissue Ca levels, agro-morpho-physio-biochemical parameters. Sharp increase of Ca content in root, stem and spike was observed up to excess level of Ca (10 mM) in GPHCPB-1 while in case of GPHCPB-45 an increase in Ca content was observed only up to sufficient level of Ca (5 mM) and above that its accumulation remained constant or declined in both the genotypes. In case of leaf the level of Ca increased linearly at all concentrations of supplied Ca in both the genotypes. Both the genotypes behave differentially as GPHCPB-45 genotype accumulated more Ca and was also superior in root length, root dry matter accumulation, plant height and relative water content at Ca deficient condition (0.1 mM) as compared to GPHCPB-1 genotype. The continuous rise in stem diameter, biomass, seed yield, chlorophyll content, SPAD value, seed oxalic acid and phytic acid content were recorded in both the genotypes up to excess or toxic levels of supplied Ca. On the basis of present study it was concluded that Ca accumulation in plant is determined by both genetic (genotype dependent) as well as environmental factors (availability of Ca in rhizosphere).

Exogenous Calcium Improves Viability of Biocontrol Yeasts Under Heat Stress by Reducing ROS Accumulation and Oxidative Damage of Cellular Protein

In this article, we investigated the effect of exogenous calcium on improving viability of Debaryomyces hansenii and Pichia membranaefaciens under heat stress, and evaluated the role of calcium in reducing oxidant damage of proteins in the yeast cells. The results indicated that high concentration of exogenous calcium in culture medium was beneficial for enhancing the tolerance of the biocontrol yeasts to heat stress. The possible mechanism of calcium improving the viability of yeasts was attributed to enhancement of antioxidant enzyme activities, decrease in ROS accumulation and reduction of oxidative damage of intracellular protein in yeast cells under heat stress. D. hansenii is more sensitive to calcium as compared to P. membranaefaciens. Our results suggest that application of exogenous calcium combined with biocontrol yeasts is a practical approach for the control of postharvest disease in fruit.