The Dynamics of Cytoplasmic HSP70 and Chloroplast HSP70B Chaperone Levels under Heat Stress Differs in Three Pumpkin Species with Different Stress Resistance

The chaperone system of the cell is the first line of defense in plants under stress. In the present work, the effect of heat stress on the levels of cytoplasmic HSP70 and chloroplast HSP70B chaperones in three Cucurbita species (C. maxima Duchesne, C. pepo L., and C. moschata, Duchesne) differing in their stress resistance was studied. A correlation between the levels of cytoplasmic HSP70 and chloroplast HSP70B chaperones and pumpkin species under heat stress was demonstrated. Under stress, a significant increase in the chaperone levels was observed in the cells of the C. maxima pumpkin, namely, the level of the cytoplasmic HSP70 increased by 3.6 times, and the level of chloroplast HSP70B increased by two times. Heat stress caused a 1.7-fold increase in the level of the cytoplasmic chaperone HSP70 in the cells of the C. pepo pumpkin, while no significant change in the level of the HSP70B protein was observed. However, heat stress led to a decrease in the levels of both HSP70 and HSP70B compared to untreated plants in the C. moschata pumpkin. The dynamics of changes in the levels of cytoplasmic and chloroplast chaperones under heat stress is similar. It should be noted that the constitutive levels of HSP70 and HSP70B under normal conditions are higher in C. moschata and C. pepo compared to C. maxima. The analysis of the obtained data revealed an interesting pattern: high constitutive levels of HSPs result in an insignificant induction of HSPs, and, vice versa, low constitutive levels of these proteins correlate with the high induction rate of these proteins after exposure to heat stress. These findings are important in understanding the mechanisms of plant stress resistance and may be useful for selection and development of highly resistant productive varieties of agriculturally important plants.