Differentiation of stomatal meristemoids and guard cell mother cells into guard-like cells in Vigna sinensis leaves after colchicine treatment : An ultrastructural and experimental approach.

The temporary development of Vigna sinensis seedlings in the presence of colchicine results in the inhibition of stomata generation and the formation of numerous persistent stomatal meristemoids (P-SM) and guard cell mother cells (P-GMC). Before dividing differentially or becoming GMC, the untreated meristemoiidsundergo a 'preparatory' differentiation, during which a synthesis of new densely ribosomal cytoplasm, an increase of nuclear size, and a detectable proliferation of all the organelles are observed. The same process appears depressed and delayed in treated meristemoids; the cells have usually undergone only part of it when they reach the C mitosis. After the inhibition of their division, the bulged meristemoids II and GMC increase further in size, synthesize new nonribosomal cytoplasm, and start vacuolating slowly. The plastids also increase in size, change in shape, and become able to synthesize large quantities of starch. The cells retain a ribosomal cytoplasm, rough ER membranes, and active dictyosomes for a long time. At the advanced stages of differentiation, the microtubules reappear in the cells even when the plant remains under colchicine treatment. When mature, the P-GMC and P-SM are quite similar to the guard cells and possess considerably thickened periclinal walls, numerous mitochondria, and small vacuoles, while the nucleus, the plastids, and the cytoplasm occupy significant parts of the cell volume. In the epidermis displaying open stomata in light, significant K(+) quantities are detectable in guard cells and P-GMC or P-SM, while they are almost absent from their surrounding cells. When the stomata close in darkness, K(+) is accumulated primarily in the subsidiary or typical epidermal cells surrounding these idioblasts and only minimally inside them. Besides, the P-GMC and P-SM, like the guard cells, retain the starch for a long time and build up considerable starch quantities from exogenously supplied sugars.