CORRIGENDUM

Abstract

The lag phase between application of gibberellic acid to barley aleurone layers and the beginning of amylase synthesis is at a minimum at 30 °C. This temperature is also the optimum for enzyme synthesis. Incubation temperature has little effect on the background activity found in the absence of gibberellic acid, or on the concentration of enzyme retained in the tissue in the presence of hormone. When aleurone layers spend only 2 h of the lag period at 30 °C, and the remainder of the incubation at 25 or 15 °C, the lag period is considerably reduced. Short-term incubation at 30 °C is most effective in reducing the lag period at 25 °C when given for the first 2 h after gibberellic-acid addition. Under these conditions ('tempera ture stepdown incubation') the lag period is reduced to that with the whole incubation at 30 °C. The temperature stepdown incubation has a sharp pH optimum of 5-00-5-05 and its effectiveness is increased by the presence of iron in the medium. There are thus two rate limiting reactions during the lag period, the first highly temperature sensitive, the second relatively temperature insensitive.