Expression ofα-Amylase Isoforms and theRAmylAGene in Rice (Oryza sativaL.) during Seed Germination, and its Relationship with Coleoptile Length in Submerged Soil

SummaryA significant difference in the seed germinability was observed between the two rice cultivars, ‘Nipponbare’ and ‘Suweon 287’, under anoxia (i.e., during germination in submerged soil at 18°C), although little difference was seen under aerobic (in air) or hypoxic (in water) conditions. The number of α-amylase isoforms synthesized in germinating seeds was inversely proportional to the O2 concentrations at the early germination stage. The formation of isoform B was promoted by oxygen supply, while isoform H was undetectable if the seeds were unable to germinate. The activity of isoform H was highly correlated with the coleoptile length in the submerged soil at 18°C, indicating that isoform H is a critical factor for seed germination under anoxia. The expression of the rice α-amylase RAmylA gene was repressed when the seeds germinated under hypoxia or anoxia. The interactions between oxygen stress, gibberel-lin, and carbon metabolites on the expression of α-amylase in rice are discussed.