Phyllochron dynamics during the course of late shoot development might be affected by reproductive development in rice (Oryza sativa L.).

Phyllochron, defined as the interval time between appearances of successive leaves on a shoot, is an important measurement to know the developmental state of a shoot apex in rice. Previous studies revealed that phyllochron dynamics during the course of shoot development of rice was divided into three stages, regardless of environment and genotype: (1) maintenance of short phyllochron in the early developmental stage, (2) drastic increase of phyllochron depending on leaf number from the base in the late stage, and (3) decrease of phyllochron before final-leaf stage. Recent studies of shoot development of rice suggested that the first and the second stage might reflect the internal state of juvenile and adult phase, respectively. The remaining question is what internal state is related to the third stage. In the present study, to give a suggestion for the question, we performed the two experiments using near-isogenic lines (NILs) for flowering-time genes. First, using new data from the previous study, we statistically showed that reproductive initiation significantly affected the decreasing point of phyllochron dynamics during the late shoot development. Second, we demonstrated that photoperiod-strongly sensitive NILs tended to maintain increase of phyllochron during the course of late development when reproductive initiation was inhibited by an extremely long day condition. Then, we suggest that reproductive initiation might trigger suppression of internal increase of phyllochron during the late development. Variation of pattern of the phyllochron dynamics between environments and between genotypes, which has been identified by the previous studies, was discussed based on the suggestion.