Homobrassinolide-Induced Thermotolerance in Brassica Species

Abstract

The Brassica crop encounters high temperatures during harvest leading to fruit shattering. Early sowing of the crop may help in overcoming this problem. However, the early sown crop may be exposed to high temperature during seedling stage, and high soil temperature may cause profound modification of growth and metabolic processes in young seedlings. Growth regulators have widely been used for acquisition of thermotolerance in a variety of crops, so efficacy of homobrassinolide (HBR) in inducing thermotolerance was tested in different cultivars of Brassica, namely RL-1359 (Brassica juncea), PBR-210 (Brassica juncea), and PC-5 (Brassica carinata). Application of homobrassinolide HBR at 0.1 and 0.2 μg ml−1 as pretreatment to four-day-old Brassica seedlings before exposing them to lethal temperatures increased the values of the following characteristics: seedling length, vigor index of seedlings, total soluble sugar content, and enzymatic activities, and caused remarkable reduction in relative injury of membranes measured by electrolyte leakage. Separation of proteins through SDS-PAGE revealed the accumulation of some new proteins in HBR-treated seedlings. Activities of enzymes peroxidase and invertase increased remarkably, whereas catalase showed a reduction in activity. The scavenging of reactive oxygen species like H2O2 and superoxide ions by antioxidant enzymes plays a key role in imparting thermotolerance. Thus high peroxidase activity, high invertase activity, and low electrolyte leakage of membranes could be directly linked with enhanced tolerance to heat-induced oxidative damage and could be involved in the processes leading to acclimation during heat stress. These features could be exploited to improve thermotolerance of crop plants by suitable breeding strategies.