Morphological and physiological changes in response to heat stress (HS) in tomato are different between accessions, at different growth stages and with various HS exposure periods. H2O2 signaling plays an important role in the regulation of many biological processes and stress conditions. A recent study found that H2O2 acts as a signal during HS memory in a specific man-ner in heat-sensitive and heat-tolerant tomatoes [1]. The triggering of a plant’s defense state can lead to acquired resistance to biotic stress or to acclimatization for abiotic stress [2].  Purpose. The purpose of the research is to highlight the particularities of the response and adaptation reactions of plants of different genotypes in the case of HS action at different growth stages, singular or repeated stress, and depending on the origin of the seed material of the plants.