Effect of Light Quality on the Rhythmic Flowering Response of Biloxi Soybean

Abstract

The flowering response of Biloxi soybean (Glycine max) subjected to 48-hour cycles, initiated by an 8-hour photoperiod, shows a rhythm in response to perturbations of red and white light. No such rhythm is apparent when far-red is employed to interrupt the dark period. The action of both red and white light may be reversed to some extent by far-red given immediately after the initial perturbation and in addition, some reversal is observed when long dark periods are interspersed between the 2 perturbations. However, both red and white light are completely inhibitory to flowering when given at the 16-hour point in the total cycle and this inhibition cannot be overcome by far-red given any time after the 1st perturbation. These results suggest that the conversion of phytochrome from one form to another is not responsible for the time-measuring ability of Biloxi soybean but can influence the basic timing mechanism only within the framework of the endogenous rhythm. It also appears that neither form of the pigment acts solely to inhibit flowering in the short-day plant Biloxi soybean.