Effect of Gibberellic Acid and Kinetin on Growth of the Primary Leaf of Dwarf Bean (Phaseolus vulgaris)

Abstract

IN the course of experiments on the effect of gibberellic acid on leaf area it was found that this substance accelerated expansion of the primary leaf of dwarf bean (var. Canadian Wonder); but the final area attained was identical with that of leaves receiving no treatment. Kinetin (6-furfurylaminopurine), on the other hand, depressed the rate of leaf expansion. Areas were estimated by use of a regression equation relating to the product of length × breadth calculated from measurements of more than 100 leaves. This equation is: area (cm.²) = 0.8682 (± 0.0196) × p + 3.19, where p is length × breadth in cm.². The application of the allometry formula indicated that treatment produced no change in shape of leaf, so it is justifiable to apply this regression equation irrespective of treatment. The leaves were sprayed as soon as they had unfolded and assumed a horizontal position (length about 5.0 cm.), and were kept in darkness for about 16 hr. in case kinetin was destroyed by light. The average daily increments in area plotted for the mean period are shown in Fig. 1. Leaves sprayed with gibberellic acid (50 p.p.m.) or gibberellic acid + kinetin (0.1 p.p.m.) at first increased in area at a greater rate than the control. Kinetin alone slightly depressed the rate of leaf expansion. About six days after spraying, the position was reversed and the control and kinetin-sprayed plants increased in area at a greater rate. The final area of the leaves sprayed with gibberellic acid was the same as that of the controls, but kinetin alone depressed final area (Table 1).