PENGARUH EKSTRAK Sargassum cristaefolium PADA MULTIPLIKASI Dendrobium antennatum Rchb.f SECARA IN VITRO

The purpose of this study was to determine the potential and concentration of Sargassum cristaefolium extract as a natural cytokinin in tissue culture media of Dendrobium antennatum Rchb.f. This study is experimental with a completely randomized design, using several extract concentrations compared with the positive control (BAP 1.5 ppm) and negative control (MS0 media). Extract concentrations used 5 ppm, 10 ppm, 15 ppm, 20 ppm, and 25 ppm. Based on analysis of variance (ANOVA), the effect of Sargassum cristaefolium extract on the growth media significant on all parameters. Sargassum cristaefolium extracts caused different responses at certain levels of concentration. Extract concentration of 10 ppm was able to initiate the highest number of shoots and leaves compared to other extract concentrations, where as the concentration 20 ppm was able to accelerate and increase root growth.

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.