Poster: Vegetative Development

Abs # 416: ANGUSTIFOLIA3 mediates cell proliferation in leaf morphogenesis of Arabidopsis

Presenter:	Horiguchi, Gorou , ghori@nibb.ac.jp
Authors	Horiguchi, Gorou  (A)   Tsukaya, Hirokazu  (A)
Affiliations:	(A): National Institute for Basic Biology

Leaf is a flat organ and two-dimensional growth mechanisms should play a key role in the leaf morphogenesis. In this study, contribution of cell-division orientation in the determination of leaf shape was evaluated. As a first step, cell proliferation in wild type leaves was characterized in terms of distance of a dividing cell from the base of a primordium, angle of a cell division plane, cell numbers along leaf-length and leaf-width directions, and cell area. These data showed that horizontal cell division plane was predominant at an early stage of leaf primordium formation, while frequency of vertical division plane increased at a later stage in wild type. Based on the observation, the cell proliferation profiles were analyzed in a novel narrow leaf mutant, angustifolia3 (an3), that had been isolated as a mutant with fewer number of leaf cells. While no defect was detected in the early stage of the an3 leaf primordium, the number of dividing cells was fewer in the later stage of the an3 leaves than in wild-type leaves. On the other hand, distribution of cell division planes showed a similar trend in both genotypes. As a result, the reduction of cell number in an3 leaf was more prominent in leaf-width direction than in leaf-length direction. Interestingly, the decrease in cell number in an3 leaves was compensated by increases of cell size. This compensation was enough to fully restore leaf length but not width. These findings indicate that cell proliferation in leaf morphogenesis consists of two phases, namely the early mono-directional and the later multi-directional phases. AN3 is considered to play a role in two-dimensional extension of the leaf blade by keeping cell division competence high in the multi-directional phase.