BUNDLE-SHEATH CELLS AND CELL-SPECIFIC PLASTID DEVELOPMENT IN ARABIDOPSIS LEAVES

Bundle sheath cells form a sheath around the entire vascular tissue in Arabidopsis leaves and constitute a distinct leaf cell type, as defin ed by their elongate morphology, their position adjacent to the vein a nd by differences in their chloroplast development compared to mesophy ll cells. They constitute about 15% of chloroplast-containing cells in the leaf. In order to identify genes which play a role in the differe ntial development of bundle sheath and mesophyll cell chloroplasts, a screen of reticulate leaf mutants of Arabidopsis was used to identify a new class of mutants termed dov (differential development of vascula r-associated cells). The dov1 mutant clearly demonstrates a cell-speci fic difference in chloroplast development. Mutant leaves are highly re ticulate with a green vascular pattern. The underlying bundle sheath c ells always contain normal chloroplasts, whereas chloroplasts in mesop hyll cells are abnormal, reduced in number per cell and seriously pert urbed in morphology at the ultrastructural level. This demonstrates th at differential chloroplast development occurs between the bundle shea th and mesophyll cells in the Arabidopsis leaf.