Volume 15, Issue 4 (12-2025)
2025, 15(4): 35-54 |
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Gholami M, Akbari E, Baninasab B. Effect of Calcium Chloride on γ-Aminobutyric Acid (GABA) Metabolic Pathway in Strawberry Plants Under Heat Stress Conditions. Journal of Crop Production and Processing 2025; 15 (4) :35-54
URL: http://jcpp.iut.ac.ir/article-1-3372-en.html
URL: http://jcpp.iut.ac.ir/article-1-3372-en.html
Department of Horticulture, College of Agriculture, Isfahan University of Technology, 84156 83111 Isfahan, Iran. , mah.gholami@iut.ac.ir
Abstract: (65 Views)
Extended Abstract
Introduction: Over the last century, the increase in the concentration of greenhouse gases due to the burning of fossil fuels is the major reason for the global warming associated with changing climate patterns. One of the serious consequences of heat stress is generation of reactive oxygen species (ROS). The accumulation of osmolytes during heat stress has been reported previously for proline, glycine betaine, and trehalose in different plant species. These osmolytes serve several functions in the cells subjected to stress, including turgor generation, protection of the integrity of membranes and enzymes, photosynthetic apparatus, and acting as antioxidants to maintain the redox balance. When plants experience stress, they often show a decrease in their mineral content. Adding essential mineral nutrients can help reduce the harmful effects of stress on these plants and greatly enhance the absorption of these nutrients during challenging situations. Calcium helps regulate plant responses to various adverse environmental conditions such as high temperature stress. Studies showed that external application of calcium chloride increased proline content, soluble sugar, calcium ion and chlorophyll content and decreased malondialdehyde content and relative electrical conductivity in tea plant leaves compared to plants without calcium treatment in under heat stress. Studies showed that external application of GABA and calcium chloride to rice seedlings under low temperature stress reduced the negative effects of abiotic stresses and promoted plant growth and development. Calcium binds to calmodulin to form a calcium/calmodulin complex, and this complex stimulates the activity of the enzyme glutamate decarboxylase and the accumulation of GABA (10). GABA can act as a protective substance (such as an antioxidant molecule, chelating agent, osmotic regulator) and is involved in energy metabolism in response to stress conditions. The aim of this study was to investigate the effect of exogenous calcium chloride as a GABA synthesis stimulant compound on the induction of high temperature stress tolerance in ʻCamarosaʼ cultivar of strawberry. The results of this experiment indicate the effect of external application of calcium chloride in increasing endogenous GABA and regulating tolerance mechanisms under high temperature stress conditions by increasing the production of osmolytes and the relative expression of heat shock proteins in the ʻCamarosaʼ strawberry.
Materials and Methods: Strawberry plants at the 5-6 fully expanded leaf stage received chemical and temperature treatments. Chemical treatments included calcium chloride at concentrations of 10, 15 and 20 mM as foliar spray for 3 consecutive days and heat stress started on the fourth day. After applying chemical treatments, plants were transferred to a growth chamber with a temperature of 25°C, relative humidity of 70%, 16 hours of light, 8 hours of darkness and 1200 lux of light. Heat stress was applied immediately for 10 h. Temperature treatments included 25 and 40°C. After 10 h of applying the desired temperature stress, the plants were taken out of the growth chamber and some morphological, physiological and biochemical traits were measured. Based on the obtained physiological and biochemical data, a concentration of 15 mM calcium chloride was used to investigate the changes in the expression of SSADH, HSP70 and HSP90 genes. The leaves of the plants were collected after 2 h of applying the temperature stress at 40 °C and immediately frozen in liquid nitrogen and stored at -80 °C until the extraction of total RNA.
Results and Discussion: Application of 15 mM calcium chloride after imposing the temperature stress at 40 °C for 10 h in the ʻCamarosaʼ cultivar caused a significant decrease in the apparent damage index and also an increase in the leaf soluble carbohydrate, proline, internal GABA, and total soluble protein concentrations, and maximum quantum efficiency of photosystem II compared to plants without chemical treatment. Calcium pretreatment increased the proline, soluble carbohydrates, and chlorophyll concentrations, but decreased the malondialdehyde concentration and relative electrical conductivity in C. sinensis leaves under heat stress, which is consistent with the enhanced leaf soluble carbohydrate and proline concentrations and photochemical efficiency of photosystem II in our experiment. During the storage of apple fruits, GABA concentration increased in response to external calcium application, indicating the effect of increasing intracellular calcium concentration in inducing an increase in GABA content. Strawberry plants exposed to 2 h of 40°C temperature stress and external application of 15 mM calcium chloride showed significant increase in the expression of SSADH, HSP70 and HSP90 genes compared to plants without chemical treatment. GABA is catalyzed by the activity of the enzyme GABA transaminase to succinic semialdehyde and by succinic semialdehyde dehydrogenase to succinic acid (37). External application of calcium chloride increases the activity of the GABA pathway by increasing the expression levels of the MdGABA-T1/2 and MdSSADH genes (19). In strawberry plants, the upregulation of HSP 90-alpha 1-like gene increased with a gradual increase in temperature. Applying heat stress to creeping bentgrass significantly increased the relative expression of HSP 90-1 gene, which is consistent with the results of present experiment.
Conclusions: According to the results of this experiment, concomitant application of 40°C temperature stress and 15 mM calcium chloride significantly reduced the apparent damage index, despite increases in leaf soluble carbohydrates, proline, internal GABA, and total soluble protein concentrations and maximum quantum efficiency of photosystem II of strawberry plants of ʻCamarosaʼ cultivar, compared to plants without chemical treatment. Also, exposure to 2 h of 40°C temperature stress and external application of 15 mM calcium chloride significantly increased the expression of SSADH, HSP70 and HSP90 genes compared to plants without chemical treatment. According to the results of this experiment, thus, external application of 15 mM calcium chloride was able to help tolerate high temperature stress conditions in strawberry plants of ʻCamarosaʼ cultivar by inducing the GABA metabolic pathway.
Introduction: Over the last century, the increase in the concentration of greenhouse gases due to the burning of fossil fuels is the major reason for the global warming associated with changing climate patterns. One of the serious consequences of heat stress is generation of reactive oxygen species (ROS). The accumulation of osmolytes during heat stress has been reported previously for proline, glycine betaine, and trehalose in different plant species. These osmolytes serve several functions in the cells subjected to stress, including turgor generation, protection of the integrity of membranes and enzymes, photosynthetic apparatus, and acting as antioxidants to maintain the redox balance. When plants experience stress, they often show a decrease in their mineral content. Adding essential mineral nutrients can help reduce the harmful effects of stress on these plants and greatly enhance the absorption of these nutrients during challenging situations. Calcium helps regulate plant responses to various adverse environmental conditions such as high temperature stress. Studies showed that external application of calcium chloride increased proline content, soluble sugar, calcium ion and chlorophyll content and decreased malondialdehyde content and relative electrical conductivity in tea plant leaves compared to plants without calcium treatment in under heat stress. Studies showed that external application of GABA and calcium chloride to rice seedlings under low temperature stress reduced the negative effects of abiotic stresses and promoted plant growth and development. Calcium binds to calmodulin to form a calcium/calmodulin complex, and this complex stimulates the activity of the enzyme glutamate decarboxylase and the accumulation of GABA (10). GABA can act as a protective substance (such as an antioxidant molecule, chelating agent, osmotic regulator) and is involved in energy metabolism in response to stress conditions. The aim of this study was to investigate the effect of exogenous calcium chloride as a GABA synthesis stimulant compound on the induction of high temperature stress tolerance in ʻCamarosaʼ cultivar of strawberry. The results of this experiment indicate the effect of external application of calcium chloride in increasing endogenous GABA and regulating tolerance mechanisms under high temperature stress conditions by increasing the production of osmolytes and the relative expression of heat shock proteins in the ʻCamarosaʼ strawberry.
Materials and Methods: Strawberry plants at the 5-6 fully expanded leaf stage received chemical and temperature treatments. Chemical treatments included calcium chloride at concentrations of 10, 15 and 20 mM as foliar spray for 3 consecutive days and heat stress started on the fourth day. After applying chemical treatments, plants were transferred to a growth chamber with a temperature of 25°C, relative humidity of 70%, 16 hours of light, 8 hours of darkness and 1200 lux of light. Heat stress was applied immediately for 10 h. Temperature treatments included 25 and 40°C. After 10 h of applying the desired temperature stress, the plants were taken out of the growth chamber and some morphological, physiological and biochemical traits were measured. Based on the obtained physiological and biochemical data, a concentration of 15 mM calcium chloride was used to investigate the changes in the expression of SSADH, HSP70 and HSP90 genes. The leaves of the plants were collected after 2 h of applying the temperature stress at 40 °C and immediately frozen in liquid nitrogen and stored at -80 °C until the extraction of total RNA.
Results and Discussion: Application of 15 mM calcium chloride after imposing the temperature stress at 40 °C for 10 h in the ʻCamarosaʼ cultivar caused a significant decrease in the apparent damage index and also an increase in the leaf soluble carbohydrate, proline, internal GABA, and total soluble protein concentrations, and maximum quantum efficiency of photosystem II compared to plants without chemical treatment. Calcium pretreatment increased the proline, soluble carbohydrates, and chlorophyll concentrations, but decreased the malondialdehyde concentration and relative electrical conductivity in C. sinensis leaves under heat stress, which is consistent with the enhanced leaf soluble carbohydrate and proline concentrations and photochemical efficiency of photosystem II in our experiment. During the storage of apple fruits, GABA concentration increased in response to external calcium application, indicating the effect of increasing intracellular calcium concentration in inducing an increase in GABA content. Strawberry plants exposed to 2 h of 40°C temperature stress and external application of 15 mM calcium chloride showed significant increase in the expression of SSADH, HSP70 and HSP90 genes compared to plants without chemical treatment. GABA is catalyzed by the activity of the enzyme GABA transaminase to succinic semialdehyde and by succinic semialdehyde dehydrogenase to succinic acid (37). External application of calcium chloride increases the activity of the GABA pathway by increasing the expression levels of the MdGABA-T1/2 and MdSSADH genes (19). In strawberry plants, the upregulation of HSP 90-alpha 1-like gene increased with a gradual increase in temperature. Applying heat stress to creeping bentgrass significantly increased the relative expression of HSP 90-1 gene, which is consistent with the results of present experiment.
Conclusions: According to the results of this experiment, concomitant application of 40°C temperature stress and 15 mM calcium chloride significantly reduced the apparent damage index, despite increases in leaf soluble carbohydrates, proline, internal GABA, and total soluble protein concentrations and maximum quantum efficiency of photosystem II of strawberry plants of ʻCamarosaʼ cultivar, compared to plants without chemical treatment. Also, exposure to 2 h of 40°C temperature stress and external application of 15 mM calcium chloride significantly increased the expression of SSADH, HSP70 and HSP90 genes compared to plants without chemical treatment. According to the results of this experiment, thus, external application of 15 mM calcium chloride was able to help tolerate high temperature stress conditions in strawberry plants of ʻCamarosaʼ cultivar by inducing the GABA metabolic pathway.
Keywords: Abiotic stress, GABA shunt pathway, Heat shock protein, Succinic semialdehyde dehydrogenase
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