LAM1 is required for dorsoventrality and lateral growth of the leaf blade in Nicotiana

The role of LAM1 in dorsoventrality and lateral growth of the leaf blade wa s investigated in the 'bladeless' lam1 mutant of Nicotiana sylvestris and i n periclinal chimeras with lam1 and wild-type (N. glauca) cell layers. Muta nt lam1 primordia show normal dorsoventrality at emergence, but produce bla de tissue that lacks dorsal cell types and fails to expand in the lateral p lane. In leaves of a lam1-glauca-glauca (L1-L2-L3) chimera, we observed res toration of dorsal identity in the lam1 upper epidermis, suggesting non-cel l-autonomous movement of a dorsalizing factor between cell layers of the bl ade, A lam1-lam1-glauca chimera generated a leaf blade with lam1 cells in t he L1-derived epidermis and the L2-derived upper and lower mesophyll, An in situ lineage analysis revealed that N. glauca cells in the L3-derived midd le mesophyll restore palisade differentiation in the adjoining lam1 upper m esophyll. Movement of dorsalizing information appears short-range, however, having no effect on the upper lam1 epidermis in lam1-lam1-glauca. Clusters of lam1 mesophyll in distal or proximal positions show a localized default to radial growth, indicating that the LAM1 function is required for dorsov entrality and lateral growth throughout blade expansion.