Exogenous Application of GABA Improves PEG-Induced Drought Tolerance Positively Associated with GABA-Shunt, Polyamines, and Proline Metabolism in White Clover.

Bin Yong,Yan Peng,Yan Zhang,Huan Xie,Xin-Quan Zhang,Lin-Kai Huang,Yan-Hong Yan,Xiao Ma,Gang Nie,Ya-Ping Li,Zhou Li

doi:10.3389/fphys.2017.01107

Abstract

In order to investigate the physiological effects of exogenous γ-aminobutyric acid (GABA) on drought tolerance in white clover (Trifolium repens), GABA shunt, polyamines (PAs), and proline (Pro) metabolism were examined after plants pretreated with or without GABA (8 mM) and then exposed to water or 15% PEG-induced drought stress in growth chamber. In this study, exogenous application of GABA effectively alleviated drought-induced damage in leaves, as reflected by significantly higher relative water content, lower electrolyte leakage, lipid peroxidation, and leaf wilt. Exogenous GABA further promoted drought-induced increases in GABA transaminase and alpha ketone glutarate dehydrogenase activities, but inhibited glutamate decarboxylase activity under both control and drought conditions, resulting in an increase in endogenous glutamate (Glu) and GABA content. Besides, exogenous GABA could well accelerated PAs synthesis and suppressed PAs catabolism, which lead to the extremely enhanced different types of PAs content (free Put and Spd, insoluble bound Spd and Spm, soluble conjugated Spd and Spm, and total Put, Spd and Spm) under drought stress. In addition, exogenous GABA application further activated drought-induced Δ1-pyrroline-5-carboxylate synthetase and proline dehydrogenase activities, but suppressed drought-facilitated ornithine -δ-amino transferase activities, leading to a higher Pro accumulation and metabolism in GABA-pretreated plants in the middle and last period of drought. The results suggested that increased endogenous GABA by exogenous GABA treatment could improve drought tolerance of white clover associated with a positive regulation in the GABA-shunt, PAs and Pro metabolism.

Highlights

Drought stress is one of the most severe limiting factors that negatively affects plant growth and development in perennial forage species around the world (Annicchiarico and Piano, 2004)
The biosynthesis of endogenous GABA is mainly involved in two pathways: one is the decarboxylation of Glu from the catalytic action of glutamate decarboxylase (GAD) in the cytosol and the other was from the degradation of PAs through diamine oxidase (CuAO) and polyamine oxidase (PAO) (Bhatnagar et al, 2001)
PEG-induced drought stress caused a rapid accumulation of endogenous GABA contents, GABA+PEG treatment showed significantly 33.33 and 23.08% higher GABA contents compared with PEG treatment at 10 and 17 days of drought, respectively

Summary

Introduction

Drought stress is one of the most severe limiting factors that negatively affects plant growth and development in perennial forage species around the world (Annicchiarico and Piano, 2004). Exogenous GABA Improves Drought Tolerance of physiological, biochemical, and metabolic responses to drought stress including the synthesis or degradation of phytohormone, plant growth regulators (PGRs), osmolytes, and antioxidants defense associated with drought tolerance. The exogenous application of PGRs is an effective strategy to alleviate drought damage in plant, such as glutamic (Glu), proline (Pro), polyamines (Pas; Yamaguchi et al, 2007; Li et al, 2016b) and γ-aminobutyric acid (GABA; Hu et al, 2015). The biosynthesis of endogenous GABA is mainly involved in two pathways: one is the decarboxylation of Glu from the catalytic action of glutamate decarboxylase (GAD) in the cytosol and the other was from the degradation of PAs through diamine oxidase (CuAO) and polyamine oxidase (PAO) (Bhatnagar et al, 2001)

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Discussion

Conclusion