Abstract
Two kinds of bioactive gibberellins (GAs), 13-hydroxy and non 13-hydroxy GAs are frequently found in a given plant tissue. However, physiological meaning of GA 13-hydroxylation is still unclear. We have previously found two cytochrome P450 genes whose products have GA 13-hydroxylation activity from rice. Moreover, GA measurements in seedlings of a rice double mutant of these genes have indicated that the levels of 13-hydroxy GAs including GA1 were significantly decreased, whereas those of non 13-hydroxy GAs including GA4 were increased in the double mutant. In this study, we further analyzed the GA 13-hydroxylase mutants. GA measurements of each single mutant indicated that neither single mutation is sufficient to inhibit the GA 13-hydroxylation pathway. GA measurements of heading stage of the double mutant showed that the levels of 13-hydroxylated GAs are significantly decreased as seen for the double mutant seedlings. Our results strongly suggested that these two cytochrome P450 genes play a major role in GA 13-hydroxylation in rice.
