Key Proliferative Activity in the Junction between the Leaf Blade and Leaf Petiole of Arabidopsis

Yasunori Ichihashi,Takeshi Usami,Taku Takahashi,Hirokazu Tsukaya,Kensuke Kawade,Gorou Horiguchi

doi:10.1104/pp.111.185066

Yasunori Ichihashi, Takeshi Usami + Show 4 more

Open Access

https://doi.org/10.1104/pp.111.185066

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Abstract

Leaves are the most important, fundamental units of organogenesis in plants. Although the basic form of a leaf is clearly divided into the leaf blade and leaf petiole, no study has yet revealed how these are differentiated from a leaf primordium. We analyzed the spatiotemporal pattern of mitotic activity in leaf primordia of Arabidopsis (Arabidopsis thaliana) in detail using molecular markers in combination with clonal analysis. We found that the proliferative zone is established after a short interval following the occurrence of a rod-shaped early leaf primordium; it is separated spatially from the shoot apical meristem and seen at the junction region between the leaf blade and leaf petiole and produces both leaf-blade and leaf-petiole cells. This proliferative region in leaf primordia is marked by activity of the ANGUSTIFOLIA3 (AN3) promoter as a whole and seems to be differentiated into several spatial compartments: activities of the CYCLIN D4;2 promoter and SPATULA enhancer mark parts of it specifically. Detailed analyses of the an3 and blade-on-petiole mutations further support the idea that organogenesis of the leaf blade and leaf petiole is critically dependent on the correct spatial regulation of the proliferative region of leaf primordia. Thus, the proliferative zone of leaf primordia is spatially differentiated and supplies both the leaf-blade and leaf-petiole cells.

Highlights

Leaves are the most important, fundamental units of organogenesis in plants
In this study, using Arabidopsis leaves, we found a unique proliferative zone within the leaf primordium marked by promoter of AN3 (pAN3) (Fig. 8)
We showed that cell proliferation activity in the leaf primordium was established, being spatially independent and isolated from that of the TA cells of the shoot apical meristem (SAM), indicating that it has the nature of an intercalary meristem (Esau, 1977)

Summary

Introduction

Leaves are the most important, fundamental units of organogenesis in plants. the basic form of a leaf is clearly divided into the leaf blade and leaf petiole, no study has yet revealed how these are differentiated from a leaf primordium. We found that the proliferative zone is established after a short interval following the occurrence of a rod-shaped early leaf primordium; it is separated spatially from the shoot apical meristem and seen at the junction region between the leaf blade and leaf petiole and produces both leaf-blade and leaf-petiole cells. Classical morphological and histological observations and recent molecular developmental analyses suggest that a series of organogenesis steps in the leaf primordium depends on several distinct meristematic activities that are established after the initiation of leaf primordia. The meristems described above would be recognized, in a broad sense, as intercalary meristems: they are meristematic tissues some distance away from the SAM and reside in a differentiating organ (Esau, 1977) If so, these tissues in leaf primordia may have a different nature from TA cells. Exist between classic and modern viewpoints on the organogenesis of leaf primordia

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