Abstract
Phytochrome has been shown to be the major photoreceptor involved in photomorphogenetic and physiological responses in plants, and there are three rice genes for them. Our previous study showed that one of the genes encoding ethylene biosynthetic enzymes, ACO1, was highly expressed in phytochrome triple mutants compared to the wild-type (WT). To examine the role of ACO1 in internode elongation at the heading stage, ACO1-deficient (aco1) and overexpressing (ACO1-OX) mutants were characterized and used for study. The first internode of ACO1-OX mutants showed no significant difference in length compared to that of WT plants, but lower elongated internodes were longer in ACO1-OX mutants than in WT plants. On the other hand, the first internode of aco1 mutants was shorter than that of WT plants, whereas the lower elongated internodes were similar in length. We further examined expression of ethylene biosynthesis/signaling genes and found that some of them were upregulated in aco1 mutants. From these results, we discuss about the molecular mechanism of internode elongation mediated by ACO1.
