The Effect of Oxygen on Endogenous Cytokinin Levels and Germination of Leucadendron daphnoides Seed

The soybean callus assay was used to study the effect of high oxygen tensions on the cytokinin levels of Leucadendron daphnoides Meisn. seed, where dormancy is apparently due to the restricting effect of the seed coat on oxygen diffusion to the embryo. High oxygen tensions led to a six-fold increase in germination compared to seed incubated in air and resulted in significant increases in butanol soluble cytokinins prior to visible germination. It is suggested that the primary effect of oxygen is to increase the rate of respiration and thus, to provide the energy required for the synthesis of butanol soluble cytokinins which leads to cotyledon expansion and subsequent radicle elongation. Present indications are that untreated seeds remain dormant due to low concentrations of butanol soluble cytokinins in their embryos.