Can meristematic activity determine variation in leaf size and elongation rate among four Poa species? A kinematic study

We studied inherent variation in final leaf size among four Poa spp. that l ive at different elevations. The average final length of leaf 7 of the main stem of the smallest species (Poa alpina) was only one-half that of the la rgest species (Poa trivialis); it was correlated with leaf elongation rate, but not with the duration of leaf elongation. A faster rate of leaf elonga tion rate was associated with (a) larger size of the zone of cell expansion , and (b) faster rates of cell production (per cell file) in the meristem, which in turn were due to greater numbers of dividing cells, whereas averag e cell division rates were very similar for all species (except Poa annua). Also we found that the proliferative fraction equaled 1 throughout the mer istem in all species. It was remarkable that rates of cell expansion tended to be somewhat higher in the species with slower growing leaves. We discus s the results by comparing the spatial and material viewpoints, which lead to different interpretations of the role of cell division. Although the pre sented data do not strictly prove it, they strongly suggest a regulatory ro le for cell division in determining differences in growth rate among the pr esent four Poa spp.