Rapid induction of small heat shock proteins improves physiological adaptation to high temperature stress in peanut

With the changing climatic scenario and increasing global mean temperature, heat stress became a major limiting factor for today's agriculture. To identify the underlying mechanism associated with heat tolerance in peanut, two experiments (field and growth chamber) were conducted with four genotypes (ICGS 44, GG 7, AK 159 and DRG 1) having differential high temperature stress sensitivity. Field grown plants under three different temperature (D-1, D-2 and D-3) regimes simulated three temperature treatment effects with a variability of 3-4/4-5 degrees C in mean day/night temperature, respectively. In growth chamber, imposition of heat shock (10 degrees C above ambient inside growth chamber) revealed not only rapid induction (within 0.5hr) of HSPs, especially small HSPs (HSP 17, HSP 40) in tolerant genotypes, but also its sustenance for longer duration (2hr), which might help them to have better physiological adaptation strategies under high temperature stress. This was evident from significant advancement in phenophases observed with increase in temperature by 15-18days at physiological maturity, while pollen viability and membrane stability reduced below 50% and 41%, respectively in DRG 1 with increase in mean day/night temperature. Maintenance of higher photosynthesis and transpiration rate and stomatal conductance helped the tolerant genotype ICGS 44 to keep relatively cooler canopy and higher photosynthates, ensuring better physiological condition in this genotype under heat stress. Significant increase (similar to 2.5-fold) in inositol and hexoses (glucose and fructose) content and reduction (>50%) in sucrose content in leaf tissues indicated degradation of storage carbohydrates for improved osmotic adjustment especially in tolerant genotypes under elevated temperature.