ANALYTICAL STUDIES OF THE GROWTH OF THE ETIOLATED SEEDLING OF AVENA SATIVA

Abstract

SummaryThe increased final length of the mesocotyls of intact, etiolated oat seedlings which have been treated with carbon dioxide, sucrose or ethanol, results from the maintenance of cell division in the nodal meristem. Sucrose and ethanol initially retard the overall rate of mitosis but carbon dioxide, at the concentration used, does not. In contrast with these external effects on the growth of the mesocotyl, variation in cell length with treatment is negligible, hence the extra growth is due directly to the increased number of cells.Illumination or high temperature each reduces mesocotyl length by means of two inhibitory effects, on mitosis and on cell elongation. The cells that respond are of a particular length when treated and they show maximum sensitivity when 0.12 mm long, at which length mitosis normally ceases.The retardation of coleoptile growth by sucrose, or by ethanol, is associated with the presence of fewer cells; carbon dioxide appears not to modify the overall rate of cell division. A subsequent stimulation of mitosis, however, does not occur. The cells of the coleoptile, unlike those in the mesocotyl, increase in length after either illumination or heating. Since the same treatments applied to mesocotyl and coleoptile cells elicit different consequences, cell extension in the two organs is most probably controlled by different processes.