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

Cheng Huang,Muhammad Jawad Hassan,Yulong Tian,Zhou Li,Bingbing Zhang,Yongqun Zhu

doi:10.3390/molecules26175337

Cheng Huang, Muhammad Jawad Hassan + Show 4 more

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https://doi.org/10.3390/molecules26175337

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Abstract

Chitosan (CTS) is a deacetylated derivative of chitin that is involved in adaptive response to abiotic stresses. However, the regulatory role of CTS in heat tolerance is still not fully understood in plants, especially in grass species. The aim of this study was to investigate whether the CTS could reduce heat-induced senescence and damage to creeping bentgrass associated with alterations in antioxidant defense, chlorophyll (Chl) metabolism, and the heat shock pathway. Plants were pretreated exogenously with or without CTS (0.1 g L−1) before being exposed to normal (23/18 °C) or high-temperature (38/33 °C) conditions for 15 days. Heat stress induced detrimental effects, including declines in leaf relative water content and photochemical efficiency, but significantly increased reactive oxygen species (ROS) accumulation, membrane lipid peroxidation, and Chl loss in leaves. The exogenous application of CTS significantly alleviated heat-induced damage in creeping bentgrass leaves by ameliorating water balance, ROS scavenging, the maintenance of Chl metabolism, and photosynthesis. Compared to untreated plants under heat stress, CTS-treated creeping bentgrass exhibited a significantly higher transcription level of genes involved in Chl biosynthesis (AsPBGD and AsCHLH), as well as a lower expression level of Chl degradation-related gene (AsPPH) and senescence-associated genes (AsSAG12, AsSAG39, Asl20, and Ash36), thus reducing leaf senescence and enhancing photosynthetic performance under heat stress. In addition, the foliar application of CTS significantly improved antioxidant enzyme activities (SOD, CAT, POD, and APX), thereby effectively reducing heat-induced oxidative damage. Furthermore, heat tolerance regulated by the CTS in creeping bentgrass was also associated with the heat shock pathway, since AsHSFA-6a and AsHSP82 were significantly up-regulated by the CTS during heat stress. The potential mechanisms of CTS-regulated thermotolerance associated with other metabolic pathways still need to be further studied in grass species.

Highlights

Exogenous CTS had no significant impacts on relative water content (RWC) and osmotic potential (OP) in leaves under normal conditions (Figure 1A,B)
Photochemical efficiency and significant increases in reactive oxygen species (ROS) accumulation, membrane lipid peroxidation, and Chl degradation were detected in the leaves of creeping bentgrass
The exogenous application of an optimal dose of CTS significantly alleviated heat-induced stress damage to creeping bentgrass associated with an improvement in water balance, ROS scavenging, and the maintenance of Chl metabolism and photosynthesis

Summary

Introduction

Heat stress adversely affects turfgrass growth and management, leading to a significant decrease in turf quality during summer as well as an increase in lawn maintenance costs [3,4]. The exogenous application of chemical compounds can effectively improve the tolerance of plants to various abiotic stresses such as drought, salinity, and high temperatures. The exogenous application of spermidine and sucrose could significantly improve tolerance to heat stress in rice (Oryza sativa), tomato (Lycopersicon esculentum), and potato (Solanum tuberosum) by enhancing photosynthesis and antioxidant capacity [5,6,7]. Heat tolerance could be improved significantly by exogenous methyl jasmonate in perennial ryegrass associated with the altered osmotic adjustment, antioxidant defense, and transcript levels of jasmonate-responsive genes [11]

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