In vivo studies on artificial induction of thermotolerance to detached panicles of wheat (Triticum aestivum L) cultivars under heat stress

The mechanism imparting thermotolerance by gibberellic acid (GA(3)) and abscisic acid (ABA) is still unresolved using either spraying technique or in vitro conditions. Alternative way of studying these effects under near in vivo conditions is through the use of liquid culturing technique. Effects of GA(3) and ABA (100 mu M) on sucrose metabolism (invertase and sucrose synthase) and aminotransferases (GOT and GPT) in relation to starch and protein accumulation were studied in detached panicles of three wheat (Triticum aestivum L.) cultivars PBW 343, C 306 (heat tolerant) and WH 542 (heat susceptible) cultured in a liquid medium. Ears were subjected to heat shock treatment (45 degrees C for 2 h) and then maintained at 25 degrees C for 5 days. Heat shock treatment resulted in a significant decline in starch content but caused a marked build -up of total free sugars and protein content in grains of all cultivars. However, activities of acid and neutral invertases increased only in tolerant cultivars but reduced in susceptible cultivar. Following treatment with GA(3) contents of starch and free sugars increased in grains maintained at 25 degrees C but free sugar content decreased in stressed grains compared to control. ABA application showed inhibitory effect on starch accumulation under normal temperature but was promotory under stress conditions. Concomitantly, soluble protein content also increased in conjunction with an increase in the activities of glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT). Apparently, the wheat grain responds to heat shock mediated disruption of carbon metabolism by a compensatory effect on nitrogen metabolism. GA(3) stimulated grain sink activity both under stress and non stress condition while ABA was promotory only under stress condition.