Nitric Oxide Induces Flowering in the Duckweed Lemna aequinoctialis Welw. (Syn. L. paucicostata Hegelm.) Under Noninductive Conditions

Nitric oxide (NO) plays diverse roles in the growth and development of plants and in their responses to various abiotic and biotic stresses. It has also been reported to repress flowering in Arabidopsis thaliana. In the present study, NO donors sodium nitroprusside (SNP), S-nitroso-N-acetyl penicillamine (SNAP), and 3-morpholinosydnonimine (SIN-1) induced flowering in Lemna aequinoctialis 6746 (a short-day strain) and in L. aequinoctialis LP6 (a photoperiod-insensitive strain) under noninductive conditions. Nitrate and nitrite, two stable metabolites of NO, did not induce flowering. On the other hand, cyanide donors potassium ferricyanide {K-3[Fe(CN)(6)]} and potassium cyanide (KCN) induced flowering in both strains under noninductive conditions. The flowering induced under a 8-h daily photoperiod regime in the short-day strain L. aequinoctialis 6746 was inhibited by NO and cyanide donors. Vegetative multiplication of both strains was adversely affected by NO and cyanide donors, irrespective of the photoperiod conditions. The observed effects of NO donors on flowering were substantially negated by NO scavengers c-PTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide] and methylene blue. This confirmed the role of NO in induction of flowering. The inductive effect of CN- also appeared to be partly mediated through NO as NO scavengers partially negated the effect of CN-.