The role of cytokinins in the development and metabolism of barley leaves. I. The effect of cytokinins on leaf senescence

The loss of chlorophyll during dark-induced ageing of barley leaves was prevented to a similar extent by kinetin and the natural cytokinin, 6-Δ2-iso-pentenylarninopurine (2iP). A concentration of 400 μM appeared to be optimal in both cases. In the presence of 2iP the structure of mesophyll cells in dark-incubated leaves was maintained unchanged. A distinct correlation has been found between the retardation by 2iP of the chlorophyll loss, the rate of S2P-incorporation into nucleic acids and the maintaining of the RNase activity at a low level. The importance of the RNA synthesis and the rate of its de-gradation in the cytokinin action in barley leaf senescence will be subjected to future experiments.