Application of exogenous glutathione confers salinity stress tolerance in tomato seedlings by modulating ions homeostasis and polyamine metabolism

The objective of this study was to investigate the effects of exogenous glutathione (GSH) on the ion balance and micro-distribution, polyamine metabolism (PA) levels, activity of key enzymes, expression of PA synthesis and metabolism genes in tomato (Solanum lyeopersicurn L. cv. Zhongshu No. 4) seedlings under salt (NaCl) stress (100 mM). we found that NaCl stress caused damage to tomato, including seedling growth inhibition, imbalanced intracellular ion homeostasis caused by the accumulation of Na+ and Cl- in roots and leaves, and reduced transport capacity of K+, Ca2+, and Mg2+ from roots to leaves. Salt stress also led to a significant increase in polyamine levels in leaves. BSO (L-Buthionine-sulfoximine, an inhibitor of key GSH synthesis enzyme gamma-glutamylcysteine synthetase) application under salt stress exacerbated growth inhibition and ion imbalance in tomato seedlings and induced further accumulation of polyamine. However, the application of exogenous GSH reduced the Na+ and Cl- content of roots and leaves of plants under salt stress and NB (NaCI + BSO) treatments, regulated ion homeostasis and microdomain distribution, inhibited the selective transport of Na+ and promoted the selective transport of K+ and Ca2+ from root to leaf, thus alleviating the ion imbalance and poisoning caused by salt stress. In addition, exogenous GSH also down-regulated the activities and transcriptional levels of the PA synthesis- and degradation-related key enzymes ADC (arginine decarboxylase), SAMDC (S-adenosylmethionine decarboxylase), and DAD (diamine oxidase) under salt stress and NB treatments, and up-regulated the activities and the transcriptional levels of PAO (PA oxidase) and ODC (ornithine decarboxylase), thereby reducing the level of PAs and promoting the transformation of polyamines between different morphologies. These findings suggest that exogenous GSH applied to salt-stressed tomato confers salinity tolerance in tomato seedlings by modulating ion absorption, microdomain distribution, and the ion selective transport ratio and by regulating polyamine synthesis and metabolism to maintain cellular ions and polyamine homeostasis. This is the first study to provide evidence of the interaction between GSH and PAs in plant adaptive responses to salinity.