| Research Abstract |
The leaf is the fundamental unit of shoot morphogenesis and the leaf shepe is controlled physiologically (Nakaya et al. 2002 ; Tsukaya et al. 2002 ; 2000). We have accumulated much evidence that a decrease in the number of leaf cells can be compensated for by an increase in the volume of each cell. Such compensation is known only for leaf morphogenesis (reviewed in Tsukaya 2002 ; 2003). The presence of such a compensatory system does not necessarily invalidate Cell Theory ; it requires only a slight modification of Cell Theory. The modified Neo-Cell Theory fully explains the morphogenesis of leaves.
Focusing on the genetic analysis of leaf morphogenesis, in the course of this research project, we have proven that the polarized growth of leaves is regulated via genetic control of polar cell elongation and polar cell proliferation in Arabidopsis thaliana (L.) Heynh. Two genes act independently to regulate the polar cell elongation process in leaves : ANGUSTIFOLIA (AN), a homolog of animal CtBP, regulates leaf width and ROTUNDIFOLIA3 (ROT3), a cytochrome P450 gene, regulates leaf length (Tsukaya et al. 1994, Tsuge et al. 1996, Kim et al 1998, 1999, 2002). Based on molecular genetic data on AN and ROT3, we have revealed that polar leaf expansion is regulated by plant-specific gene families. We also revealed new plant-specific regulatory genes of KNOX expression, namely, AS2 and BOP (Ha et al. 2003 ; Iwakawa et al. 2002 ; Semiarti et al. 2001).
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