Abstract
Salt stress is one of the most serious abiotic stresses limiting plant growth and development. Calcium as an essential nutrient element and important signaling molecule plays an important role in ameliorating the adverse effect of salinity on plants. This study aimed to investigate the impact of exogenous calcium on improving salt tolerance in Tartary buckwheat cultivars, cv. Xinong9920 (salt-tolerant) and cv. Xinong9909 (salt-sensitive). Four-week-old Tartary buckwheat seedlings under 100 mM NaCl stress were treated with and without exogenous calcium chloride (CaCl<sub>2</sub>), Ca<sup>2+</sup> chelator ethylene glycol tetraacetic acid (EGTA) and Ca<sup>2+</sup>-channel blocker lanthanum chloride (LaCl<sub>3</sub>) for 10 days. Then, some important physiological and biochemical indexes were determined. The results showed that salt stress significantly reduced seedling growth, decreased photosynthetic pigments, inhibited antioxidants and antioxidant enzyme activities. However, it increased the reactive oxygen species (ROS) levels in the two Tartary buckwheat cultivars. Exogenous 10 mM CaCl<sub>2</sub> application on salt-stressed Tartary buckwheat seedlings obviously mitigated the negative effects of NaCl stress and partially restored seedlings growth. Ca<sup>2+</sup>-treated salt-stressed seedlings diplayed a suppressed accumulation of ROS, increased the contents of total chlorophyll, soluble protein, proline and antioxidants, and elevated the activities of antioxidant enzymes compared with salt stress alone. On the contrary, the addition of 0.5 mM LaCl<sub>3</sub> and 5 mM EGTA on salt-stressed Tartary buckwheat seedlings exhibited the opposite effects to those with CaCl<sub>2</sub> treatment. These results indicate that exogenous Ca<sup>2+</sup> can enhance salt stress tolerance and Ca<sup>2+</sup> supplementation may be an effective practice to cultivate Tartary buckwheat in saline soils.
Highlights
Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.) originated in southwestern China, and has currently been cultivated all over the world due to its good economic benefits and nutrient values
We aimed to investigate the effect of exogenous Ca2+, Ca2+ chelator ethylene glycol tetraacetic acid (EGTA) and Ca2+ channel blocker LaCl3 on some physiological and biochemical parameters and revealed the function and mechanism of calcium signaling in two Tartary buckwheat cultivars exposed to salt stress
3.2 Exogenous Ca2+ Alleviated the Degradation of Chlorophyll Content in Tartary Buckwheat under Salt Stress Salinity impaired the photosynthetic pigments of Tartary buckwheat seedlings
Summary
Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.) originated in southwestern China, and has currently been cultivated all over the world due to its good economic benefits and nutrient values. Abiotic stresses, including drought, salt, low or high temperature, and flood, are the main cause of crop productivity decline, which seriously affect the growth and development of crops [5,6]. Osmotic stress and ionic imbalance will further cause secondary damage to cells, such as excessive production of reactive oxygen species (ROS), including hydrogen peroxide (H2O2), superoxide (O2−.) and hydroxyl radicals (⋅OH), which can cause oxidative damage to plants, such as membrane damage, enzymatic inhibition, cell death, and inhibition of plant growth and development [14–16]. After a long period of adaptation, plants have developed a series of complex defense systems to neutralize and scavenge the generated ROS Such systems include non-enzymatic antioxidants and enzymatic antioxidants such as ascorbic acid (AsA), glutathione (GSH), ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), and glutathione peroxidase (GPX), which prevent cellular damage from ROS [17–19]
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