Effect of benzyladenine and hydroxybenzyladenosine on gas exchange of beanand sugar beet leaves

Using bean seedlings, the effects of benzyladenine (BA) on stomatal conduct ance transpiration rate (E), and net photosynthetic rate (P-N) were examine d in order to find out dose and time responses. In bean seedlings, BA appli ed to roots in concentrations of 1, 5, 10, and 20 muM increased g, and P-N of leaves already 1 h after application. E was not markedly affected and wa ter use efficiency (WUE) was increased. However, the effects were mostly tr ansient and after 24 h P-N only at 1 and 5 muM BA was increased, and other parameters were not affected or even decreased. In sugar beet seedlings, th e effects of hydroxybenzyladenosine (HBA) in addition to those of BA on the same parameters were determined. The both cytokinins were applied in 1, 5, 10, and 20 muM concentrations either to roots or sprayed on leaves. Howeve r, the effects were inconsistent and the positive effect was observed only after 24 h on P-N in plants with roots immersed in 5 and 10 M BA, or 10 muM HBA, and on E in plants sprayed with 5 PM BA or 10 muM HBA. Thus the stimu lation of gas exchange by exogenously applied cytokinins is rather exceptio nal than general.