Cell kinetics, development of stomata and some effects of colchicine in barley.

The developmental sequence of the formation of stomatal complexes in the leaf epidermis of barley was studied. Cell-kinetic parameters were obtained from two genotypes - "Early Bonus" and eceriferum-g, a mutant with an abnormal stomatal pattern. The distribution of mitotic frequencies as a function of position in the stomatal rows was analyzed at each stage of development leading to mature stomata. Regression curves obtained for each stage showed that the distributions were stage-specific. Thus, the mitotic frequencies presented similar values throughout the portion of the file where the first asymmetrical divisions take place, had a parabolic distribution for the stage of subsidiary formation, and showed a linear shape, with a negative slope, for the stage of guard-mother-cell divisions. The mutant genotype differed from the normal by having a faster rate of ordinary guard-mother-cell divisions as a function of position in the row. The higher level of subsidiary cell formation in the mutant was interpreted as a consequence of a displacement of the used markers, suggesting a precocious initiation of subsidiary-cell formation in eceriferum-g. Time estimations of the length of the cell cycles were obtained by cell-population studies after a pulse with colchicine. Eceriferum-g appeared to have slower cell cycles. The leaves treated with colchicine showed a shift in the elongation axis of the cells. Autoradiography after treatment with (3)H-thymidine showed ineorporation of the label in the portions of the row proximal to all three peaks of divisions indicating that all mitoses were preceded by the usual period of DNA synthesis. Labelling of lateral cells at a mature stage suggested DNA synthesis leading to endoploidy.