Effect of far-red light pulse on induction and production of flowers in Lemna paucicostata 6746 in darkness

A short-day duckweed, Lemna paucicostata 6746, was exposed tocontinuous darkness at 26^?C, and the changes in the floral parameters(3) due to far-red and/or red light pulse given at various timesof the dark period were studied. Parameters a (vegetative growth rate) and (flowering ratio)were respectively decreased and increased with a far-red lightpulse given at the outset of the dark period. The decreaseda and the increased remained almost unchanged until the 7thhour, but returned to their initial levels thereafter. The far-redlight actions on a and were reversed by subsequent exposureto red light. Parameter P₁ (pre-flower induction period) wasextended by 1 day when far-red and/or red pulse was given atabout the 7th hour of the dark period. A far-jed pulse givenat the outset of the dark period only affected parameter P₂(flower induction period). Although the sensitivity of P₂ tored light increased with time, its sensitivity to far-red lightremained constant and at about the 7th hour was equally sensitiveto far-red and red lights. Both red and far-red pulses givenlater than the 7th hour were increasingly ineffective on P₂.The red/far-red reversibility occurred only for the action onP₂ of the far-red pulse applied during the early dark period.Parameter P₄ (flower production period) varied rhythmicallyin length with a far-red puke, the maximum shortening and extensionbeing induced by the pulse given at about the 7th and 19th hours,respectively. The sensitivity of P₄ to red light also changedrhythmically with an inverse phase angle to the rhythmic responseto farred light, and the far-red and red light actions werereversed respectively by subsequent red and far-red lights. These findings suggested that multiple timing devices includingan hourglass-type clock and a circadian clock are involved induckweed flowering. (Received October 25, 1978; )