Effect of temperature on the synthesis and secretion of alpha-amylase in barley aleurone layers

Abstract

The effect of temperature on alpha-amylase synthesis and secretion from barley (c.v. Himalaya) half-seeds and aleurone layers is reported. Barley half-seeds incubated at 15 C in gibberellic acid (GA) concentrations of 0.5 and 5 micromolar for 16 hours do not release alpha-amylase. Similarly, isolated aleurone layers of barley do not release alpha-amylase when incubated for 2 or 4 hours at temperatures of 15 C or below following 12 hours incubation at 25 C at GA concentrations from 50 nanomolar to 50 micromolar. There is an interaction between temperature and GA concentration for the process of alpha-amylase release from aleurone layers; thus, with increasing GA concentration, there is an increase in the Q(10) of this process. A thermal gradient bar was used to resolve the temperature at which the rate of alpha-amylase release changes; thermal discontinuity was observed between 19 and 21 C. The time course of the response of aleurone tissue to temperature was determined using a continuous monitoring apparatus. Results show that the effect of low temperature is detectable within minutes, whereas recovery from exposure to low temperature is also rapid. Although temperature has a marked effect on the amount of alpha-amylase released from isolated aleurone layers, it does not significantly affect the accumulation of alpha-amylase within the tissue. At all GA concentrations above 0.5 nanomolar, the level of extractable alpha-amylase is unaffected by temperatures between 10 and 28 C. It is concluded that the effect of temperature on alpha-amylase production from barley aleurone layers is primarily on the process of enzyme secretion.