Effects of Growth Substances on Frond and Flower Production in Lemna Gibba G3

Frond and flower production in a long-day duckweed, Lemna gibba G3, growing under different photoperiodic conditions in presence and absence of varied concentrations of applied IAA, KIN and GA was investigated. The predominant actions of IAA, KIN and GA were revealed to be respectively the depression of flowering, the promotion of frond multiplication and the enhancement of flowering. The rate of increase in FL % as an index of the concentration of floral stimulus in the tissues was curtailed greatly by IAA, to a lesser extent by KIN and little by GA. GA at 10−5 M apparently reduced the critical day length (12 hr) and the induction period (48 hr) by 2 and 4 hr, respectively. No vegetative growth was promoted by KIN in the light. On the basis of these and relevant findings the sites of action of the growth substances examined in the flowering process of the duckweed were suggested.