White light requirements for stimulation of plant growth by malformin.

Over a 3-day period, the minimum white fluorescent light intensity required for malformin-induced growth stimulation of etiolated and green cuttings of Phaseolus aureus was approximately 2.6 x 10(3) and 0.4 x 10(3) ergs/cm(2) . sec, respectively. High light intensities were unable to inhibit the ability of malformin to stimulate growth. Over 3 days, the minimum photoperiod for malformin-induced growth stimulation using etiolated and green cuttings and a light intensity of 13.5 x 10(3) ergs/cm(2) . sec was 4 hours and 1 hour, respectively. Malformin must be present in the area of growth stimulation during the time of light treatment. Those changes induced by light and required for malformin-induced growth stimulation were estimated to undergo almost complete decay within 1 hour in the dark. By manipulating the experimental technique, it was possible to stimulate the growth of green cuttings with malformin with a 10-min light treatment (13.5 x 10(3) ergs/cm(2) . sec). Although low light intensities and short photoperiods did not allow growth stimulation by malformin using etiolated cuttings, they prevented or alleviated growth inhibition induced by malformin in the dark.