Nodulation of bean plants, Phaseolus vulgaris L., in water culture was poor during hot sunny weather in the greenhouse. It did not improve when indoleacetic acid, kinetin, gibberellic acid, purines and pyrimidines, yeast and soil extract were added. Nodulation was enhanced by adding used culture solution of nodulated pea or bean plants or an extract of root nodules. The active substance was soluble in water and ether and was inactivated by heating at 80°C. During purification it was observed that the active fractions strongly absorbed ultraviolet light at about 260 mμ.Light quality also influenced nodulation of plants grown in light cabinets: nodulation was good in red and poor in blue light. If the shoot was radiated with far- red light (about 730 mμ) for a few minutes at the end of the photoperiod, there were fewer nodules and this effect could be counteracted by subsequent radiation with red light (about 660 mμ). These results suggested that nodulation was controlled by the phytochrome system.The hypothesis was put forward that a kinetin-like substance was involved in the formation of root-nodules.
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