Characteristics of α-amylase induced in distal half-grains of wheat

α-Amylase activity was measured in distal half-grains of four wheat lines, RL4137, OS21-5, Shirogane-komugi (Shirogane) and Hokkai250, after 72 h soaking at 20°C. The half-grains of RL4137 and Hokkai250 at the maturity stage (about 15% water content) showed a significantly (P < 0.01) higher α-amylase activity after 72 h soaking (3.95 mU/mg, and 2.14 mU/mg, respectively) than those of OS21-5 and Shirogane (1.05 mU/mg and 0.91 mU/mg). During grain development, 30 to 50 days postanthesis (DPA), soaking also induced the production of α-amylase in the half-grains of RL4137 after 72 h. The α-amylases induced consisted of heat-labile α-AMY2 (low pI) type of enzymes. They were similar to α-AMY2 which was reported to be induced in the developing pericarp in the absence of stimulus from gibber-ellic acid (GA), but different from heat-resistant α-AMY2 expressed in the aleurone tissue after stimulation by GA. It is suggested that the RL4137 aleurone tissue has a potential for the synthesis of heat-labile α-AMY2, although the level of induced α-amylase activity was very low compared with that of the enzyme synthesized in the embryo and endosperm at the time of germination.