Circadian Rhythmicity in Excised Samanea Pulvini

Abstract

pulvini received R and the other FR in all experiments comparing these two light treatments. Light sources for phytochrome photoconversion (R = 3-or 5-min exposure at 2.2 J m-2, 600 to 690 nm, and FR = 1.5-min exposure at 9 J m-2, 710 to 750 nm) and the dim green light used during the measurements and experimental manipulations are described in reference 15. The beginning of the dark period, DD = 0, coincides with the regular lights off signal. RESULTSExcised pulvini incubated in H20 during DD oscillate for only one cycle before the rhythm damps in the open position (18). R or FR administered at regular intervals (Fig. 1) permit the rhythm to persist for two to three cycles, although the amplitude of the oscillations and R-FR differences tend to decrease with time, and oscillations cease after 72 hr darkness. Since sucrose is required for sustained rhythmicity in DD (18), all pulvini were supplied with 50 mm sucrose in the remaining experiments. As will become apparent (see Figs. 5 and 6), R and FR have very different effects on the phase, period, and amplitude of the movement, when sucrose is available.Two types of experiments were performed. To investigate phase response, one R or FR light pulse was presented at different times of the rhythm. To test for rhythmic entrainment, pulses of R or FR light were presented every 24 hr. In all cases, the effects of light treatments were compared to free running dark controls.Phase Shifting with One Red Light Flash. The effects of R presented at 25 different times during a long dark cycle were analyzed; Figure 2 indicates the results of eight such treatments, while Figure 3 compares the effects of all 25 treatments. One R pulse presented during the second two-thirds of pulvinal opening or the first half of closure reduces the duration of the next cycle, thereby producing a phase advance, while one pulse presented during the second half of pulvinal closure, or the first third of the opening movement increases the duration of the next cycle, thereby causing a phase delay. R presented at the middle of closure has no effect on the phase; we have designated this as the ZPST.Phase and Amplitude Response Curves. The amount-of phase shift was determined by comparing the time of the first maximum after the R light treatment with that of the same maximum in the dark control. R produces a maximum phase shift of about 12 hr when presented during pulvinal opening, 12 hr from ZPST. The amount of phase shift depends primarily upon the interval between the light pulse and ZPST and is remarkably independent of the cycle in which the R treatment is presented, except for the first 8 hr of DD. R at this time is much less effective than if presented at an equivalent part of a later cycle, as also reported in other plants (5,22

A circadian clock regulates transcription of the wheat Cab-1 gene

“…These results together indicate that phytochrome is involved in regulating the level of Cab-1 transcript within the periodicity of the clock. The interplay between phytochrome and the circadian clock is reminiscent of a similar interaction reported for higher plant photoperiodism (Vince-Prue 1983J and nyctinastic leaf movements in some legumes (Simon et al 1976;Satter et al 1977). However, it does differ in the fact that phytochrome is exerting a quantitative effect on the Cab-1 gene, whereas in the physiological systems it also affects the clock directly by altering the periodicity and phase.…”

Circadian Rhythmicity in Excised Samanea Pulvini

“…We were surprised to find more leakage with sucrose than with H20, although K+ losses in all cases were too small to account for the large decrease in amplitude noted in Figure 1. Damping can be prevented by conversion of Pr to Pfr at an appropriate part of each rhythmic cycle (21).…”

Apoplastic transport of ions in the motor organ of Samanea

“…These motor cell-volume changes are reversed when leaves reopen in the morning. The leaflet movements and the causal ion migrations are controlled by an endogenous clock and its interaction with light absorbed by the photo-convertible pigment phytochrome (1,3,(6)(7)(8)(9).…”

“…These motor cell-volume changes are reversed when leaves reopen in the morning. The leaflet movements and the causal ion migrations are controlled by an endogenous clock and its interaction with light absorbed by the photo-convertible pigment phytochrome (1,3,(6)(7)(8)(9).The shuttling of K+ and Cl-between the extensor and flexor regions of pulvini has been documented by the use of an electron microprobe (1-3). However, the technique lacked the spatial resolution necessary to assess the pathway of this solute redistribution.…”