Physiological Function of Night Interruption in Lemna paucicostata 6746: Action of Light as a Phaser on the Photoperiodic Clock

Flowering of Lemna paucicostata 6746 under short-day conditionsis completely inhibited by daily night interruption given tothe "inhibition zone" that starts at Zeitgeber time (ZT) 14,i.e., 14 h after dawn, and ends 14 h before the next dusk Oota(1983a) Plant & Cell Physiol. 24: 327]. With a modifiedmin-SD method, most of these night interruptions were foundto signal the false dawn (false ZT 0) after one entraining cycle.Thus, on and after day 2 the interruption was associated withthe next main photoperiod to form a noninductive skeleton photoperiod.However, a light pulse applied at the start of the inhibitionzone, caused no phase shift in the photoperiodic clock, andformed a noninductive skeleton photoperiod in association withthe preceding main photoperiod. The complete floral inhibition due to the night interruptionwas ascribed to the illumination of both the LI-phase (realor false ZT 0) and L2-phase (real or false ZT 14), or the twolight-sensitive fractions of the original or shifted criticalphotoperiod, by the thus formed skeleton photoperiod, just aswas the case for the floral inhibition by complete photoperiodslonger than the critical daylength, 14 h Oota (1983a), Oota(1983b) Plant & Cell Physiol. 24: 1503]. (Received October 20, 1983; Accepted January 7, 1984)