MICROTUBULES AND MORPHOGENESIS IN ORDINARY EPIDERMAL-CELLS OF VIGNA-SINENSIS LEAVES

Undifferentiated ordinary epidermal cells (ECs) of Vigna sinensis leav es possess straight anticlinal walls and cortical microtubules (Mts) s cattered along them. At an early stage of EC differentiation cortical Mts adjacent to the above walls form bundles normal to the leaf plane, loosely interconnected through the cortical cytoplasm of the internal periclinal wall. At the upper ends of the Mt bundles, Mts fan out tow ards the external periclinal wall and form radial arrays. Mt bundles a nd radial arrays exhibit strict alternate disposition between neighbou ring ECs. An identical reticulum of cellulose microfibril (CM) bundles is deposited outside the Mt bundles. Local wall pads rise at the junc tions of anticlinal walls with the external periclinal one, where the CM bundles terminate. They display radial CMs fanning towards the exte rnal periclinal wall. The CM bundles and radial CM systems prevent loc al cell bulging, but allow it in the intervening wall areas. In partic ular, the radial CM systems dictate the pattern of EC waviness by favo uring local tangential expansion of external periclinal wall. As a res ult, ECs obtain an undulate appearance. ''Constrictions'' in one EC co rrespond with protrusions of adjacent ECs. ECs affected by colchicine entirely lose their Mts and do not develop wavy walls, an observation substantiating the role of cortical Mts in EC morphogenesis.