Effects of γ-Aminobutyric Acid, Glutamic Acid, and Calcium Chloride on Rice (Oryza sativa L.) Under Cold Stress During the Early Vegetative Stage

Rice (Oryza sativa L.) is one of the most important cereals grown worldwide, mostly in warm regions. However, cold temperature is a major environmental factor that limits rice cultivation in temperate climates. γ-Aminobutyric acid (GABA), glutamic acid (Glu), and calcium chloride (CaCl2) play significant roles in key regulatory pathways throughout plant development. Here, we investigated the effects of Glu, CaCl2, and GABA in the culture medium on the cold tolerance of rice at the seedling stage. The medium components for cold tolerance of rice were optimized using response surface methodology (RSM). Plants treated with cold stress alone (without Glu, CaCl2, or GABA applications) displayed decreased weight, lower relative water content (RWC), maximum photochemical efficiency of PSII (Fv/Fm) and PSII efficiency, and higher relative electrolyte leakage (REL). However, after application of Glu, CaCl2, and GABA, the opposite results were documented, which could be due to an alleviation of cold-induced effects by restoration of membrane integrity. However, the levels of REL were considerably decreased due to Glu, CaCl2, and GABA treatment. RWC, Fv/Fm, PSII efficiency, and the average of subordinate functional values (ASFV) increased with the addition of Glu, CaCl2 and GABA. A central composite design indicated that the optimal concentrations of culture components for the cold tolerance of rice were 2.21 mg/mL, 2.94 mM and 2.68 mM of Glu, CaCl2, and GABA, respectively, and the maximal ASFV (0.987) was obtained under optimal conditions. Analysis of variance for the regression model suggested that the model can predict exactly the cold tolerance of rice seedlings, and the optimal culture components can be used to enhance the cold tolerance of rice seedlings.