Investigation of the Radish Leaf Bioassay for Kinetins, and Demonstration of Kinetin-like Substances in Algae

This study is part of an investigation into the occurrence ofplant growth substances in marine unicellular algae. Auxinsand gibberellins have previously been detected. This paper reportsthe occurrence of phytokinins in algae, using the radish leaftest. The technique of the test is described and a few modificationsexamined. Radish leaves were shown to be more responsive thanswede leaves. Some requirement for a minimum temperature below7? C during the growing period of the plants appeared to bea factor for maximum response. The size and age of the leafwere shown to influence kinetin activity. Chemicals tested includedbenzyl adenine, a 9-substituted benzyl adenine, and kinetin.Kinetin showed lower activity than the benzyl adenines. Kinetinkept in the solid state at –20? C for 2 years was as activeas freshly prepared kinetin. Gibberellic acid (GA₂) at 10^–5g/ml sometimes showed activity equivalent to 10^–5 g/mlkinetin. Indole-3-yl acetic acid at concentrations of 10^–4to 10^–6 g/ml was inactive. The radish leaf test was successfully used to demonstrate phytokininsin extracts of two species of unicellular marine algae, andin marine phytoplankton samples. Amounts found were within therange 0.1 to 1.0 mg/kg with one exception of 10 mg/kg. Phytokininactivity in these extracts decreased over a period of a fewweeks when stored at –20? C.