Phase Shifting Effects in the Photoperiodic Rhythm of Flowering in Dark-Grown Seedlings of Pharbitis nil Choisy

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Dark-grown seedlings of Pharbitis nil Choisy received an initial saturating fluence of red (R) light (R_1), followed at intervals by further R pulses (R_2 and R_s). R_2 was given at different times after R_1. R_s was used to scan the subsequent 72 h period. The initial exposure to R (R_1) initiated a circadian rhythm in the flowering response to the scanning R exposure (R_s). The phase of the rhythm was shifted by the second exposure to R (R_2) and the sensitivity of the phase-shifting response varied with the time of giving the R_2 pulse. The direct response to R_2 (i.e., the magnitude of flowering produced in the absence of a scanning R_2 exposure) also varied in sensitivity. When R_2 was given 4 h after R_1, the phase-shift was achieved by an exposure of 20 s (sufficient to establish 20-25% Pfr/P) but more than 80 s was required to saturate the direct flowering response at this time. When given 16 h after R_1, 80 s of R_2 (sufficient to establish 55% Pfr/P) was required for the phase-shift, whereas the maximum promotion of flowering was produced by only 5 s R. These differences in fluence-response relationships indicate that the direct flowering response to a dark interruption with R and the effect of such an interruption to phase-shift the underlying rhythm are distinct processes.
日本植物生理学会の論文