Abstract
As an important plant growth regulator, the role of γ-aminobutyric acid (GABA) in regulating seeds germination was less well elucidated under water stress. The present study was conducted to investigate the impact of GABA pretreatment on seeds germination of white clover (Trifolium repens) under water deficient condition. Results demonstrated that seeds pretreated with 2μmol/l GABA significantly alleviated decreases in endogenous GABA content, germination percentage, germination potential, germination index, root length, and fresh weight along with marked reduction in mean germination time after 7days of germination under drought stress. In addition, seeds priming with GABA significantly increased the accumulation of soluble sugars, non-enzymatic antioxidants [reduced ascorbate, dehydroascorbic acid, oxidized glutathione (GSSG), and reduced glutathione (GSH)], and enzymes [superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathioe reductase, and monodehydroasorbate reductase (MDHR)] activities involved in antioxidant metabolism, which could be associated with significant reduction in osmotic potential and the accumulation of superoxide anion, hydrogen peroxide, electrical leakage, and malondialdehyde in seeds under drought stress. The GABA-pretreated seeds exhibited significantly higher abundance of dehydrin (DHN, 56 KDa) and expression levels of DHNs encoding genes (SK2, Y2K, Y2SK, and Dehydrin b) and transcription factors (DREB2, DREB3, DREB4, and DREB5) than the untreated seeds during germination under water-limited condition. These results indicated that the GABA regulated improvement in seeds germination associated with enhancement in osmotic adjustment, antioxidant metabolism, and DREB-related DHNs expression. Current study will provide a better insight about the GABA-regulated defense mechanism during seeds germination under water-limited condition.
Highlights
More than one third of the earth’s land is distributed in arid and semi-arid areas worldwide
Water stress significantly decreased germination percentage (GP), GV, germination index (GI), and seed vigor index (SVI), while the mean germination time (MGT) significantly increased under water-limited condition (Figure 1)
The GABA priming did not show significantly effect on seedlings dry weight (DW) under normal and water stress conditions (Figure 2D), but significantly improved seedlings fresh weight (FW) under water stress (Figure 2E). These results showed that exogenous application of GABA could significantly improve endogenous GABA content and germination characteristics of white clover seeds under water stress
Summary
More than one third of the earth’s land is distributed in arid and semi-arid areas worldwide. The production and cleansing of reactive oxygen species (ROS) are in a dynamic balance Water stresses such as drought promote the production of ROS leading toward cell membrane lipid peroxidation, inhibiting seeds germination and seedling growth (Lyons and Raison, 1970; Na et al, 2012). To resist this threat, plants are inclined to enhance activities of various antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and catalase (CAT) and promote non-enzymatic antioxidants metabolism, such as reduced glutathione (GSH), oxidized glutathione (GSSG), ascorbic acid (ASA), and dehydroascorbic acid (DHA). The maintenance of better antioxidative capacity is essential for seeds germination when seeds are subjected to an unfavorable environmental condition
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