Metabolic regulation of polyamines and γ‐aminobutyric acid in relation to spermidine‐induced heat tolerance in white clover

Abstract

• Heat stress decreases crop growth and yield worldwide. Spermidine (Spd) is a small aliphatic amine and acts as a ubiquitous regulator for plant growth, development and stress tolerance. • Objectives of this study were to determine effects of exogenous Spd on changes in endogenous polyamine (PA) and c-aminobutyric acid (GABA) metabolism, oxidative damage, senescence and heat shock protein (HSP) expression in white clover subjected to heat stress. Physiological and molecular methods, including colorimetric assay, high performance liquid chromatography and qRT-PCR, were applied. • Results showed that exogenous Spd significantly alleviated heat-induced stress damage. Application of Spd not only increased endogenous putrescine, Spd, spermine and total PA accumulation, but also accelerated PA oxidation and improved glutamic acid decarboxylase activity, leading to GABA accumulation in leaves under heat stress. The Spd-pretreated white clover maintained a significantly higher chlorophyll (Chl) content than untreated plants under heat stress, which could be related to the roles of Spd in up-regulating genes encoding Chl synthesis (PBGD and Mg-CHT) and maintaining reduced Chl degradation (PaO and CHLASE) during heat stress. In addition, Spd upregulated HSP70, HSP70B and HSP70-5 expression, which might function in stabilizing denatured proteins and helping proteins to folding correctly in white clover under high temperature stress. • In summary, exogenous Spd treatment improves the heat tolerance of white clover by altering endogenous PA and GABA content and metabolism, enhancing the antioxidant system and HSP expression and slowing leaf senescence related to an increase in Chl biosynthesis and a decrease in Chl degradation during heat stress.

γ-Aminobutyric Acid Enhances Heat Tolerance Associated with the Change of Proteomic Profiling in Creeping Bentgrass

“…An previous study in creeping bentgrass has shown that the GABA exhibited positive function in alleviating heat-induced chlorophyll loss and photoinhibition [ 13 ]. The recent study also found that enhanced GABA accumulation and metabolism helped to maintain chlorophyll synthesis and decrease chlorophyll degradation in white clover, thereby mitigating the decline in photosynthesis during heat stress [ 12 ]. In current study, the creeping bentgrass with GABA priming maintained better photochemical efficiency (Fv/Fm), photosynthetic performance (PIABS), cell membrane stability, and OA than untreated plants in response to a prolonged period of heat stress, indicating that the beneficial function of GABA on alleviating heat damage could be associated with better photoprotective response and water regulation.…”

“…Antioxidant capacity and water balance regulated by exogenous GABA helped rice ( Oryza sativa ) seedlings to acclimate heat stress [ 11 ]. Enhanced GABA accumulation and metabolism contributed to the alleviation of heat-induced leaf senescence associated with significant increase in chlorophyll synthesis in white clover ( Trifolium repens ) [ 12 ]. Previous studies also found that foliar application of GABA significantly improved the thermotolerance of creeping bentgrass ( Agrostis stolonifera ) in relation to organic metabolites accumulation and upregulation of genes encoding antioxidant enzymes, stress-defensive proteins, and transcription factors [ 13 , 14 ].…”

Spermidine Induces Expression of Stress Associated Proteins (SAPs) Genes and Protects Rice Seed from Heat Stress-Induced Damage during Grain-Filling

“…Polyamines (PA), including putrescine (Put), spermidine (Spd), and spermine (Spm), are a class of significant physiologically active substances in plants, involved in plant growth and development and response to various abiotic stresses, among which Spd is closely related to seed development and plant heat tolerance [7][8][9][10][11]. Soaking seeds in Spd significantly enhanced seed vigor, while exogenous cyclohexylamine (CHA), a Spd synthesis inhibitor, significantly inhibited seed germination and reduced seed vigor [12].…”

Chitosan (CTS) Alleviates Heat-Induced Leaf Senescence in Creeping Bentgrass by Regulating Chlorophyll Metabolism, Antioxidant Defense, and the Heat Shock Pathway

“…The Fv/Fm reflects the main photochemical efficiency of PSII and PIABS synthetically indicates the maximum photochemical efficiency of PSII, with the total number of activated reactive centers functioning as a sensitive photosynthetic indicator of photosynthetic performance, as well as for the health status of photosynthetic organs in plants under abiotic stress [ 28 , 29 ]. Some studies have shown that heat stress leads to a significant decrease in the Fv/Fm and PIABS of wheat, white clover, and creeping bentgrass [ 3 , 30 , 31 ]. Our results showed that Fv/Fm and PIABS decreased significantly under heat stress in the leaves of creeping bentgrass, and that exogenous CTS could mitigate the adverse effect of heat stress on the Fv/Fm and PIABS of creeping bentgrass.…”

“…This could be related to the fact that CTS has been proven to significantly increase AsPBGD expression, as well as effectively alleviate heat-induced declines in AsCHLH expression while increasing the AsPPH transcript levels. Our previous studies found that mannose-regulated leaf senescence was not correlated with PBGD expression in white clover under water stress [ 39 ], but spermidine significantly up-regulated the PBGD expression, contributing to less Chl degradation occurring in the leaves of white clover during heat stress [ 31 ]. These findings indicate that different exogenous additives cause different effects on Chl metabolism.…”