Abstract
This study was conducted in order to determine the effect of priming with γ-aminobutyric acid (GABA) at 0.5 mM on rice (Oryza sativa L.) seed germination under osmotic stress (OS) induced by polyethylene glycol (30 g/L PEG 6000); and salinity stress (S, 150 mM NaCl) and their combination (OS+S). Priming with GABA significantly alleviated the detrimental effects of OS, S and OS+S on seed germination and seedling growth. The photosynthetic system and water relation parameters were improved by GABA under stress. Priming treatment significantly increased the GABA content, sugars, protein, starch and glutathione reductase. GABA priming significantly reduced Na+ concentrations, proline, free radical and malonaldehyde and also significantly increased K+ concentration under the stress condition. Additionally, the activities of antioxidant enzymes, phenolic metabolism-related enzymes, detoxification-related enzymes and their transcription levels were improved by GABA priming under stress. In the GABA primed-plants, salinity stress alone resulted in an obvious increase in the expression level of Calcineurin B-like Protein-interacting protein Kinases (CIPKs) genes such as OsCIPK01, OsCIPK03, OsCIPK08 and OsCIPK15, and osmotic stress alone resulted in obvious increase in the expression of OsCIPK02, OsCIPK07 and OsCIPK09; and OS+S resulted in a significant up-regulation of OsCIPK12 and OsCIPK17. The results showed that salinity, osmotic stresses and their combination induced changes in cell ultra-morphology and cell cycle progression resulting in prolonged cell cycle development duration and inhibitory effects on rice seedlings growth. Hence, our findings suggested that the high tolerance to OS+S is closely associated with the capability of GABA priming to control the reactive oxygen species (ROS) level by inducing antioxidant enzymes, secondary metabolism and their transcription level. This knowledge provides new evidence for better understanding molecular mechanisms of GABA-regulating salinity and osmotic-combined stress tolerance during rice seed germination and development.
Highlights
Rice is one of the most important cereal crops that serves as the staple food for almost half of the world’s population
We have investigated the effects of GABA on rice Calcineurin B-like Protein-interacting protein Kinases (CIPKs) genes in responses to the combination of salinity and osmotic stresses to evaluate the potential usefulness of the stress-responsive CIPK genes in genetic improvement of stress tolerance
The present study reported that GABA-activated antioxidant enzymes could play vital roles in scavenging free radicals induced by H2O2 and O2− and reduced lipid peroxidation by up-regulating the genes (APXa, CATa and SOD1) involved in antioxidant enzymes during rice seed germination and seedling growth under salinity and osmotic stress and their combination (Figure 3)
Summary
Rice is one of the most important cereal crops that serves as the staple food for almost half of the world’s population. The mechanism by which rice can tolerate salinity stress is mainly related to the maintenance of ion homeostasis, predominantly low Na+/K+ or high K+/Na+ ratios, through exclusion, compartmentation, and partitioning of Na+ [1]. The tolerance limit of rice to saline conditions may vary among the different growth and developmental stages. In this regards, Zhu et al [5] reported that rice is more tolerance to salinity during the germination and tillering stages, whereas it seems to be more sensitive during early vegetative and reproductive stages
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