Functional Characterization of Tomato and Mutants in Response to Heat Stress.

Heat stress (HS) is a prevalent negative factor affecting plant growth and development, as it is predominant worldwide and threatens agriculture on a large scale. PHYTOCHROMES (PHYs) are photoreceptors that control plant growth and development, and the stress signaling response partially interferes with their activity. PHYA, B1, and B2 are the most well-known PHY types in tomatoes. Our study aimed to identify the role of tomato 'Money Maker' and mutants in stable and fluctuating high temperatures at different growth stages. In the seed germination and vegetative growth stages, the mutants were HS tolerant, while during the flowering stage the mutants revealed two opposing roles depending on the HS exposure period. The response of the mutants to HS during the fruiting stage showed similarity to WT. The most obvious stage that demonstrated mutants' tolerance was the vegetative growth stage, in which a high degree of membrane stability and enhanced water preservation were achieved by the regulation of stomatal closure. In addition, both mutants upregulated the expression of heat-responsive genes related to heat tolerance. In addition to lower malondialdehyde accumulation, the mutant enhanced proline levels. These results clarified the response of tomato and mutants to HS.