Heat shock combined with salinity impairs photosynthesis but stimulates antioxidant defense in rice plants

• Published in: Environmental and experimental botany 2024-09, Vol.225, p.105851, Article 105851
• Main Authors: Mendes, Kellyane R., Bonifacio, Aurenivia, Martins, Marcio O., Sousa, Rachel H.V., Monteiro, Matheus V., Silveira, Joaquim A.G.
• Format: Article
• Language: English
• Subjects: Combined stress; Heat; Oryza sativa; Oxidative metabolism; Photosynthesis; Salinity
• ISSN: 0098-8472; 1873-7307
• DOI: 10.1016/j.envexpbot.2024.105851

The interactive mechanisms that occur between heat shock and salt stress and their reflexes on photosynthesis and redox metabolism in plants are little understood yet. We tested the hypothesis that heat shock negatively interacts with salt stress, affecting most intensely K+/Na+ homeostasis, stomatal closure, and CO2 assimilation, in comparison to PSII activity and oxidative stress in rice leaves. 31-day old rice plants were previously exposed to 0 and 100 mM NaCl for eight days at 27 °C and afterwards two groups were transferred to high temperature (42 °C, heat shock) for 10 hours (heat and heat + salt) whereas two other groups remained at 27 °C (control and single salt treatments). Heat-salinity interaction greatly stimulated Na+ accumulation in leaves causing intense decrease in K+/Na+ ratios, inducing significant osmotic and ionic alterations. Stomata were closed intensely causing drastic impairment in CO2 assimilation and decrease in water use efficiency. In contrast, the PSII activity was much lesser affected, corroborated by a low increase in the fraction of closed reaction centers of PSII and slight decrease in electron transport rates. Despite that unbalance in photosynthesis, combined stress partially favored oxidative protection as indicated by a reduction in the levels of H2O2 and lipid peroxidation associated with reduction in the contents of reduced forms of ascorbate and glutathione. These favorable antioxidant responses were accompanied by increases in the activities of ascorbate peroxidases, superoxide dismutases, glutathione peroxidases, and phenol peroxidases whereas catalases and glycolate oxidases decreased. These antioxidant responses were not enough to mitigate overall physiological damages caused by combined stress, as indicated by drastic increase in membrane damage and decrease in relative water content in leaves. Heat shock drastically aggravates the negative effects caused by salt stress on the photosynthetic efficiency, especially CO2 assimilation, despite the heat – salinity interaction has partially favored the antioxidant defense. •Isolate heat shock and salt stress induce distinct effects on photosynthesis and antioxidant defense.•Heat-salinity combined stress drastically affects K+/Na+ homeostasis.•Heat-salinity interaction favors antioxidant defense compared with single salt stress.•Combined stress differentially affects CO2 assimilation and photochemical phases.