Physiological characterization of the response of excised etiolated cucumber cotyledons to benzyladenine: expansion begins at 30 minutes.

摘要

Benzyladenine (BA) and other cytokinins are known to induce a three-part physiological response in excised, dark-grown cucumber cotyledons consisting of (a) increased size and fresh weight, (b) more prominent veins, and (c) increased yellowing due to carotenoid biosynthesis. Based upon an analysis of long-term kinetics, the three elements of this response occurred roughly in parallel rather than sequentially. KCl (20 mmol.L-1 optimum) promoted all three elements, especially when supplied with BA, but RbCl had no effect. As measured by increase in cotyledon width, BA-induced expansion was extrapolated to begin at approximately 30 min. with linear kinetics for at least the first 2 h. KCl promoted the growth rate (1.7-fold at 2 h) but failed to decrease the lag time. This lag time, far shorter than any previous determination using cytokinin-treated cotyledons, is in the range reported for auxin- and gibberellin-responsive elongating systems. Fusicoccin promoted growth even more quickly and with greater initial rate than BA (2.9-fold at 2 h). As found in many plant tissues responsive to auxin and gibberellin, but in contrast to cytokinin-treated radish cotyledons, cell wall synthesis in cucumber cotyledons was promoted by BA (1.5-fold at 48 h). 2,6-dichlorobenzonitrile, a potent inhibitor of cellulose biosynthesis, had no effect on overall BA-induced cotyledon growth as measured at 24 h but completely abolished vein enlargement. As discussed, these results indicate that auxin-, gibberellin-, and cytokinin-induced cell expansion have apparent physiological similarities in terms of early kinetics and cell wall synthesis.