Abstract
Mechanisms of plant root tolerance to high temperatures through antioxidant defense are not well understood. The objective of this study was to investigate whether superior root thermotolerance of heat-tolerant Agrostis scabra relative to its congeneric heat-sensitive Agrostis stolonifera was associated with differential accumulation of reactive oxygen species and antioxidant scavenging systems. A. scabra ‘NTAS’ and A. stolonifera ‘Penncross’ plants were exposed to heat stress (35/30°C, day/night) in growth chambers for 24 d. Superoxide (O2 -) content increased in both A. stolonifera and A. scabra roots under heat stress but to a far lesser extent in A. scabra than in A. stolonifera. Hydrogen peroxide (H2O2) content increased significantly in A. stolonifera roots but not in A. scabra roots responding to heat stress. The content of antioxidant compounds (ascorbate and glutathione) did not differ between A. stolonifera and A. scabra under heat stress. Enzymatic activity of superoxide dismutase was less suppressed in A. scabra than that in A. stolonifera under heat stress, while peroxidase and catalase were more induced in A. scabra than in A. stolonifera. Similarly, their encoded transcript levels were either less suppressed, or more induced in A. scabra roots than those in A. stolonifera during heat stress. Roots of A. scabra exhibited greater alternative respiration rate and lower cytochrome respiration rate under heat stress, which was associated with suppression of O2 - and H2O2 production as shown by respiration inhibitors. Superior root thermotolerance of A. scabra was related to decreases in H2O2 and O2 - accumulation facilitated by active enzymatic antioxidant defense systems and the maintenance of alternative respiration, alleviating cellular damages by heat-induced oxidative stress.
Highlights
Heat stress is a major abiotic factor which limits plant growth and productivity, in cool-season (C3) species
electrolyte leakage (EL) did not differ between A. stolonifera and A. scabra under non-stress conditions whereas it remained significantly lower (11% decrease) in A. scabra compared to A. stolonifera following heat stress treatment
MDA content did not differ between A. stolonifera and A. scabra under non-stress conditions whereas it remained significantly lower (12% decrease) in A. scabra compared to A. stolonifera following heat stress treatment
Summary
Heat stress is a major abiotic factor which limits plant growth and productivity, in cool-season (C3) species. Plants undergo various physiological and cellular changes as heat stress progresses including oxidative damage caused by production of reactive oxygen species. Many of them are important signaling molecules in the regulation of plant growth, overproduction and accumulation of ROS in various plant organs decreases cellular membrane stability leading to oxidative damages of nucleic acid, lipids, and proteins [6,7,8,9].methods which reduce oxidative damages by limiting production or accumulation of ROS are critical for improving plant tolerance or adaptation to heat stress. Non-enzymatic compounds include glutathione (GSH) and ascorbate (ASA) which possess intrinsic antioxidant properties and serve as electron donors to reduce ROS accumulation[10].There are two distinct antioxidant enzymatic pathways in plants, the first of which utilizes superoxide dismutase (SOD), catalase (CAT), and/or peroxidase (POD) located subcellularly in mitochondria, chloroplasts, and peroxisomes [11,12,13]. Most of previous work reported leaf antioxidant mechanisms in relation to stress defense, but limited information is available on how roots may survive high temperature through antioxidant defense
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