Comparison between Induction of Flowering by Nitrogen Deficiency and that by Short Days or Continuous Irradiation with Blue or Low-Intensity White Light in Lemna paucicostata 6746

Flowering of Lemna paucicostata 6746, a short-day plant, isinduced by nitrogen deficiency or by the suppression of nitratereductase activity under continuous light. The plant also flowersunder continuous blue or low-intensity white light. However,the nitrate reductase activity and levels of endogenous nitrogenof the plants did not decrease under these conditions. Glutaminesynthetase activity decreased slightly in darkness, but daylength-independentflowering was not induced by the suppression of the enzymaticactivity by methionine sulfoximine. Endogenous nitrogen levels of plants grown on nitrogen-deficientmedium at 30°C fell more rapidly than those of plants grownat 25°C, and thus difference was expressed as an enhancementof flowering at 30°C. Photoperiodic flowering was greatlysuppressed by exposure of plants to a high temperature (30°C)during the dark period, whereas the flowering induced undercontinuous blue or low-intensity white light was enhanced onlyslightly by high temperature during culture. (Received April 24, 1989; Accepted September 20, 1989)