Effect of Weather Conditions on α-Amylase of Ripening Wheat (Triticum aestivum L.) Grain

Abstract

The effects of weather conditions on a-amylase activity and its isozymes at maturity were investigat-ed in the three winter wheat (Triticum aestivum L.) varieties of Chihokukomugi (susceptible to pre-harvest sprouting), Kitakei-1354 (tolerant) and Lancer (tolerant) using environment cabinets. The results were: 1) In Chihokukomugi, wheat grains which were exposed to cool and wet conditions (20°C/10°C and from 80 to 100% relative humidity) at the early and middle stages of ripening exhibited relatively high α-amylase activity, due to Amy-2 isozymes, in the absence of germination (RPA: retention of pericarp α-amylase). Under cool and wet conditions in the late stage of ripening, grains germinated at maturity and with high p1 isozymes of Amy-1 were activated (PrMS: pre-maturity sprouting α-amylase). 2) Since Kitakei-1354 showed a dull response to weather conditions during the ripening stage, low α-amylase activity and little germination were observed consistently. 3) In Lancer, Amy-1 was activated in the absence of germination (PMAA: pre-maturity α-amylase) under not only cool and wet conditions but also under hot and dry conditions. 4) Accordingly, three pathways (RPA, PrMS and PMAA) of α-amylase formation at maturity were observed in Hokkaido. Since certain varieties like Lancer often exhibited high α-amylase activity at maturity in spite of high tolerance to pre-harvest sprouting, α-amylase activity at maturity as well as dormancy of wheat grain was an important criteria. Further investigations are needed to clarify the precise environmental factors which induce PMAA formation.