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Abstract <p>Heat stress is a major abiotic factor that limits rice productivity by disrupting plant growth, physiological processes, and molecular regulation. This study evaluated the physiological, biochemical, and molecular responses of <i>Oryza sativa</i> L. ssp. japonica seedlings exposed to high-temperature conditions (42/35°C) for 1, 3, 6, 24, 48, and 72 h. Heat stress significantly reduced shoot fresh weight, shoot dry weight, and the SFW/SDW ratio, indicating reduced shoot biomass accumulation. In contrast, root length, root fresh weight, and the RFW/RDW ratio increased, suggesting an adaptive response to maintain water uptake under stress conditions. Chlorophyll content declined under elevated temperature and was associated with increased accumulation of reactive oxygen species and membrane damage. Antioxidant enzyme activities, including superoxide dismutase, catalase, and peroxidase, were significantly enhanced, indicating activation of the antioxidant defense system to mitigate oxidative stress. Bioinformatic analyses of stress-responsive genes (<i>SAG</i>, <i>SGR2</i>, <i>HSP70</i>, and <i>DHN2</i>) using MEME, GSDS and STRING databases revealed conserved motifs, functional domains, and interaction networks associated with thermotolerance. Quantitative real-time PCR analysis showed early induction of <i>SAG</i>, <i>SGR2</i>, and <i>HSP70</i>, while <i>DHN2</i> exhibited time-dependent expression patterns. Correlation analysis indicated coordinated regulation among these genes, particularly between <i>SAG</i> and <i>DHN2</i>, suggesting a functional link between senescence regulation and dehydration tolerance. Overall, the study demonstrates that japonica rice activates integrated physiological, antioxidant, and gene regulatory mechanisms to enhance thermotolerance under heat stress.</p>

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Heat Shock Stress-Induced Physiological and Molecular Changes in Japonica Rice Seedlings

  • 期刊论文

  • 发表日期：

    2026年6月29日

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  • I. Hussain,
  • E. Hanzawa

摘要

Abstract

Heat stress is a major abiotic factor that limits rice productivity by disrupting plant growth, physiological processes, and molecular regulation. This study evaluated the physiological, biochemical, and molecular responses of Oryza sativa L. ssp. japonica seedlings exposed to high-temperature conditions (42/35°C) for 1, 3, 6, 24, 48, and 72 h. Heat stress significantly reduced shoot fresh weight, shoot dry weight, and the SFW/SDW ratio, indicating reduced shoot biomass accumulation. In contrast, root length, root fresh weight, and the RFW/RDW ratio increased, suggesting an adaptive response to maintain water uptake under stress conditions. Chlorophyll content declined under elevated temperature and was associated with increased accumulation of reactive oxygen species and membrane damage. Antioxidant enzyme activities, including superoxide dismutase, catalase, and peroxidase, were significantly enhanced, indicating activation of the antioxidant defense system to mitigate oxidative stress. Bioinformatic analyses of stress-responsive genes (SAG, SGR2, HSP70, and DHN2) using MEME, GSDS and STRING databases revealed conserved motifs, functional domains, and interaction networks associated with thermotolerance. Quantitative real-time PCR analysis showed early induction of SAG, SGR2, and HSP70, while DHN2 exhibited time-dependent expression patterns. Correlation analysis indicated coordinated regulation among these genes, particularly between SAG and DHN2, suggesting a functional link between senescence regulation and dehydration tolerance. Overall, the study demonstrates that japonica rice activates integrated physiological, antioxidant, and gene regulatory mechanisms to enhance thermotolerance under heat stress.