Abstract

High temperature stress is the second most important stress, which can strike crop plants at any time and impose severe limitations on crop growth and development. Developing crop plants with improved thermotolerance can mitigate the adverse effects of heat stress. However, a thorough understanding of physiological responses of plants to high temperature and mechanisms involved for thermotolerance is imperative. Brassica is an important oilseed crop and its early sowing implies many important advantages. However, the crop sown early encounters high temperature stress, which causes a great yield lost. Many putative signaling molecules like SA, ABA, H₂O₂ and CaCl₂ and heat acclimation have been found to be involved in inducing thermotolerance as well as in initiating the underlying signal transduction pathway for upregulating various genes involved in thermotolerace. In the present investigation, we observed the effects of heat shock, heat acclimation and SA in four genotypes of Brassica; TL15, PBT37, RL1359 and PBR210. Heat acclimation for 3 h at sublethal temperature and SA pretreatments at 10 and 20 µM for 2 h prior to heat shock were found to be effective in imparting thermoprotection at seedling stage, which is the crucial stage of plant establishment. These pretreatments helped seedlings to recover from heat stress by increasing seedling length, reduced electrolyte leakage and conferring membrane protection. Increased level of total soluble sugars, fresh/dry weight, and also increase in enzymatic activities of invertase, CAT, POX conferred thermotolerance. Further, enhanced expression of some new proteins including heat shock proteins (HSPs) was observed by both of the pretreatments through SDS-PAGE. We assume that heat acclimation and SA pretreatments induced thermotolerance and definitely play a role in initiating various mechanisms involved in overcoming high temperature limitations.

Key words: Brassica, heat acclimation, heat shock proteins, high temperature stress, salicylic acid, thermotolerance.

Abbreviation

Abbreviations: ABA, abscisic acid; CAT, catalase; HSPs, heat shock proteins; POX, peroxidase; ROS, reactive oxygen species; SA, salicylic acid.