When rice seeds germinate under complete submergence, only the coleoptile elongates efficiently. It has been reported previously that coleoptile elongation is reduced in the rice alcohol dehydrogenase 1 (ADH1)-deficient mutant, reduced adh activity (rad). The aim of this study was to elucidate how expressions of genes responsible for coleoptile elongation are affected by the ADH1 deficiency in the rad mutant under submergence. To identify genes whose expressions are changed in the rad coleoptile at an early stage in germination (i.e. 1 d after imbibition), coleoptiles of the rad mutant and its wild type (WT) were isolated by laser microdissection, and their mRNA levels were examined with a microarray. The microarray analysis identified 431 genes whose transcript levels were different between rad and WT. Interestingly, among the down-regulated genes in the rad coleoptile, 17·5 % were cell division-related genes and 5·1 % were cell elongation-related genes. It was found that cell division started at 1 d after imbibition and then gradually ceased, whereas in the WT coleoptile cell elongation started between 1 d and 2 d after imbibition and then continued. However, neither cell division nor cell elongation actively occurred in the rad coleoptile, in which the amounts of ATP were reduced. These results indicate that cell division, as well as cell elongation, occur during coleoptile elongation in rice under complete submergence, and that the reduced ATP levels caused by the ADH1 deficiency repress both of them, thereby impairing coleoptile elongation in the rad mutant under submerged conditions.
