Abstract
Temperatures above the threshold levels limit many physiological and biochemical processes required for plant survival. Therefore, the aim of the present experiment was to determine the individual and combined effects of sodium nitroprusside (SNP) and calcium (Ca) on the physiological attributes of tomato (Solanum lycopersicum) plants under heat stress (HS) and non-HS conditions. Heat stress significantly increased the chlorophyll (Chl) degradation, malondialdehyde (MDA), hydrogen peroxide (H2O2), proline (Pro) and glycinebetaine (GB) content, and decreased the photosynthetic pigment (Chl a and Chl b) and total soluble carbohydrate (TSC) content and the activities of Rubisco, carbonic anhydrase (CA), and nitrate reductase (NR). However, compared to the individual treatments, the combined application of SNP and Ca was more effective in subsiding the damaging effects of HS by reducing the accumulation of MDA and reactive oxygen species and by stimulating the biosynthesis of compatible solutes (Pro and GB), TSC, and photosynthetic pigments (Chl a and b), and also by enhancing the activities of Rubisco, CA, NR, superoxide dismutase, catalase, peroxidase, glutathione reductase, and ascorbate peroxidase.