Star of biochemical traits of heat-tolerant and heat-sensitive Phaseolus genotypes in coping with heat stress

Abstract Heat stress due to climate change irreparably affects all physiological and biochemical processes of plants, such as photosynthesis, respiration, and hormonal metabolism, decreasing growth and development and reducing yield and quality traits. It is, therefore, imperative to be acquainted with stress-related physiological responses of plants to cope with heat stress, which is predicted to continue to increase due to climate change. The goals of this study were to compare abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA) contents and chlorophyll content (SPAD) and maximum quantum efficiency of PSII ( F v /F m ) values in Phaseolus species under heat-stress and non-stress conditions. Eight heat-tolerant and two heat-sensitive bean genotypes, including common bean ( P. vulgaris L.), tepary bean ( P. acutifolius A. Gray), runner bean ( P. coccineus L.), and lima bean ( P. lunatus L.), were grown in the greenhouse. ABA, JA, and SA significantly varied among Phaseolus species and between heat-tolerant and heat-sensitive bean genotypes. ABA, JA, and SA contents were higher under heat-stress conditions than under non-stress conditions, suggesting that these stress-related hormones played a crucial role in survival strategy. In contrast, chlorophyll content and maximum quantum efficiency of PSII values were higher under non-stress conditions. Under non-stress conditions, the heat-tolerant genotypes commonly had lower JA and SA contents than the heat-sensitive genotypes, indicating that the heat-tolerant genotypes had a superior stress threshold. The lower JA and SA contents might be evaluated as selection criteria to discriminate heat-tolerant and heat-sensitive genotypes without exposure to heat stress. Additionally, path analysis was conducted to determine the direct and indirect effects of biochemical and physiological traits on chlorophyll content. The analysis revealed that the fold change in SA had the most significant positive direct effect on chlorophyll content, while the fold change in total phytohormones exhibited a strong negative direct effect. Indirect effects highlighted the complex interactions among phytohormones, particularly the antagonistic influence of ABA over SA. Besides, heat-tolerant genotypes had acquired unique adaptive characteristics to cope with heat stress, probably during the evolutionary process before domestication.