Involved in the regular timing (plastochron) of lateral organs formation. May regulate the rate of leaf initiation and the duration of vegetative phase. Seems to be redundant to the function of PLASTOCHRON2, but to act in an independent pathway. Expressed in seedlings, shoot apices and young panicles, but not in mature leaves, calli and roots. Expressed in plastochron 0 (P0) leaf founder cells, and leaf plastochrons P1, P2 and P3 primordia, but not beyond. Expressed in developing bract leaves and their incipient primordia of young inflorescence apices. Down-regulated in developing spikelets. Plants double the number of leaves, and leaf size and plant height are reduced to about the half that of the wild-type. Some inflorescence branches are converted into vegetative shoots (PubMed:14711998, PubMed:9724697). Late flowering and excessive vegetative growth (PubMed:19337211). Plastochron is defined as the time interval between leaf initiation events. Belongs to the cytochrome P450 family.