Flowering Responses of the Long-day Plant Lemna gibba G3

Abstract

Lemna gibba L., strain G3,exhibits a qualitative long-day flowering response with a critical daylength on a 24-hr, cycle of about 10 hr. Evidence is presented that the onset of daughter frond formation in a given frond inhibits the activity of the flowering meristem. Consequently, flower induction can only occur in fronds smaller than about 0.05 to 0.07 mm long. Although a minimum of 1 long day seems to be sufficient to induce the formation of flower primordia, at least 6 long days are required to obtain mature flowers since long days are also required for the early stages of flower development. The critical night length on 24, 48 and 72-hr. cycles is respectively 14, 16, and 18 to 22 hr. The close similarity between the critical night length for the different cycle lengths is explained in terms of an inhibitory effect of darkness both on flower initiation and development. A 10-hr, dark period is more inhibitory to flowering on a 36-hr. cycle than on 24, 48, 60 or 72-hr. cycles. It is suggested that darkness inhibits flowering through the formation of a light-labile flower inhibitor which acts to inhibit the functioning of the flowering stimulus.