Allometric relationships between axial and radial stem growth in rice plants

Allometric relationships between axial and radial stem growth in rice plants (cvs. Nipponbare, Musashikogane and Dobashi 1) were examined based on developmental studies on successive stem segments (=frusta) composing the main stem. During the vegetative phase of the plants, the development of each stem segment followed an uniform pattern represented by an allometric regression of its diameter v. length. At the beginning of the reproductive phase, however, most of immature stem segments shifted from this allometric to more elongating side. Such abrupt change in segment shape was mainly caused by the concurrent activity of intercalary meristem located in the lower part of stem segments whose corresponding leaf had just emerged. However, in the upper stem segments, which also exhibited the same tendency to elongate though less pronounced, the growth prevailed throughout the whole organs and definite intercalary meristems were not yet recognized. These results suggest that the characteristic stem development associated with the transition from vegetative to reproductive phase of the plants does not necessarily depend upon activities of their intercalary meristems alone.