THE EFFECT OF THE SLOW-TO-GREEN MUTATION ON CELL-DIVISION DURING LEAFINITIATION AND EARLY LEAF GROWTH IN LOLIUM-TEMULENTUM

Cell division was examined during leaf initiation in the slow-to-green mutant of Lolium temulentum L. to test the hypothesis that the cell c ycle in the leaf primordium is a key regulator of the well characteriz ed reduction in final leaf length in the mutant compared with that of the wild type. The cell doubling time (cdt, by colchicine method) was substantially longer in the youngest leaf primordium (YLP) of the muta nt (107 h) than in the wild type (43 h) although the duration of the m ost rapid cell cycle (cc, by percentage labelled mitoses method) was b etween 18-20 h in each. As a consequence, the proportion of rapidly pr oliferating cells was only 20% in the mutant compared with 47% in the wild type. The size of the shoot apical meristem and the plastochron w ere similar between genotypes which indicates that the shoot meristem was largely buffered from the effects of the mutation. Mitotic cell ar ea was also similar in the YLP of both genotypes. However, as the leaf elongated, mitotic cell area and interphase cell size were significan tly larger in the mutant compared with the wild type. This change was coupled with a reduced number of cells per unit length of leaf in the mutant. The data are consistent in showing that the proportion of rapi dly proliferating cells in the YLP (but not the rate of cell division) is a key parameter which influences growth of the leaf.