A Semidian Rhythm in the Flowering Response of Pharbitis nil to Far-Red Light

Abstract

ABSTRACT?Evidence is presented of an endogenous rhythm in flowering response to far-red (FR) irradiation, with a period of about 12 h (hence semidian rhythm), which persists through at least three cycles in constant conditions of continuous light at 27°C and has a marked influence on the flowering response in Pharbitis nil to a subsequent inductive dark period. The phase of the rhythm is not influenced by real time nor by the time from imbibition or from the beginning of the light period. Rather, it is fed forward from the beginning of the FR interruption to the beginning of the inductive dark period. The period of the rhythm is not affected by irradiance but is longer at cooler temperature. When there are two FR interruptions during the preceding light period, it is primarily the later one which determines the phase of the rhythm, although some interactions are evident. There appears to be an abrupt rephasing of the rhythm at the beginning of the inductive dark period. No overt rhythms which could be used as "clock hands" for the semidian rhythm were detected in photosynthesis, stomatal opening, or translocation.Although the effects ofR2 and FR interruptions during a single inductive dark period on flowering in Pharbitis nil Chois. seedlings have been widely examined (16,18), less attention has been given to the effect of R and FR interruptions of light preceding the inductive dark period.

The semidian rhythm in flowering response ofPharbitis nilin relation to dark period time measurement and to a circadian rhythm

“…The results of a third experiment, in which FR pretreatments were given either 2, 8, 15 or 22 h before a dark period of 13,5 h are shown in Fig, 2b, The close similarity of the two FR -2 h curves in Fig, 2a the two FR -8 h curves, indicates how highly reproducible these responses are. FR pretreatments at -2 and -15 h promote flowering whereas those at -8 and -22 h are inhibitory as shown by Heide et al (1986) and . The data in Fig.…”

“…The fact that the rhythm was less advanced after FR -15 h than after FR -2 h could have been due to a small shift in the penultimate semidian peak in this experiment (cf. Heide et al 1986; Fig. 3).…”

“…The irradiance in the growth cabinet was 20() jimol m"^ s~' at plant height, from fluorescent lamps (Philips 140 W/TLMF). A description of the R and FR sources was given by Heide et al (1986). Immediately prior to the inductive dark period all seedlings were exposed to a saturating R dose (1-5 min) to allow the period in darkness to be accurately timed from a standard initial setting of phytochrome.…”

Involvement of cyclic GMP in phytochrome-controlled flowering of Pharbitis nil

“…The exposure of plants to white light of low intensity resulted in lightlabile phytochrome degradation. This model was described and used previously (Heide et al, 1986;Kopcewicz, 1994, 1995;Łukasiewicz-Rutkowska et al, 1997;Kulikowska-Gulewska and Kopcewicz, 2002;Maciejewska et al, 2004). P. nil grown in these special photoperiodic conditions formed four axillary flower buds and one terminal flower bud per plant.…”

The Photoperiodic Control of Flowering: Progress Toward Understanding the Mechanism of Induction

“…The complicated nature of the timing mechanism is illustrated by the short-day plant, Pharbitis nil, for which endogenous rhythms are well characterized Hamner, 1964, 1965;Spector and Paraska, 1973;Evans et al, 1986;Heide et al, 1986Heide et al, , 1988Lumsden et al, 1982;VincePrue, 1975). For this short-day plant, physiological experiments have shown that the timing of the CNL and response to NB is controlled mainly by an endogenous rhythm initiated or reset at the onset of the main light period.…”