P fr PHYTOCHROME AND SUCROSE REQUIREMENT FOR RHYTHMIC LEAFLET MOVEMENT IN ALBIZZIA

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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

Section: Discussionsupporting

confidence: 58%

Circadian Rhythmicity in Excised Samanea Pulvini

Simón

Satter²,

Galston³

1976

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“…Comparative Analysis of the Effects of Sucrose during DD, LD, and LL. The effect of sucrose in maintaining rhythmicity during DD resembles that already reported for petal and leaf movements (6,9,17). Sucrose probably substitutes for a product formed in the light during photosynthesis, and necessary for expression of the rhythm.…”

Section: Discussionsupporting

confidence: 50%

“…Sucrose probably substitutes for a product formed in the light during photosynthesis, and necessary for expression of the rhythm. Sucrose-dependent metabolic events such as synthesis of ATP and organic anions, have been discussed in relation to Albizzia experiments (17).…”

Section: Discussionmentioning

confidence: 99%

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Circadian Rhythmicity in Excised Samanea Pulvini

Simón¹,

Satter²,

Galston³

1976

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The rhythmic movement of excised Samanea saman pulvini incubated in H20 or 50 mm sucrose was monitored during extended periods of white light (cool white fluorescent, 2,000 ft-c), darkness, or alternating white Light (16 hr) and darkness (8 hr [18][19][20] possibly related to changes in transmembrane potential (15). Samanea is a particularly useful plant for studies of light-rhythmic interactions, since each pulvinus is an autonomous system whose rhythmic and photoregulated turgor changes persist after the pulvinus has been excised and laminar tissue removed (18,19). The photoreceptors and the oscillating system, including the clock and the ions that regulate motor cell turgor and pulvinar movements, must be located in the pulvinus or attached rachilla section.In Samanea, as in Albizzia (17) MATERIALS AND METHODS Samanea saman (Jacq.) Merrill4 plants grown from seed in the greenhouse, were transferred to controlled chambers at least 1 week before experimental use. The chambers provide a 16-hr photoperiod (about 2,000 ft-c cool white fluorescent light with about 10% incandescent supplement) at 24 C + 2 C, and relative humidity of 60% ± 10%. These chambers and light sources were used for experiments in LL and LD. The beginning of the dark period (DD = 0) coincided with the regular "lights off" signal; thus, continuous darkness represents an extension of the usual 8-hr dark period. Experiments continued for 120 to 150 hr. All measurements and experimental manipulations during the dark periods were done under a dim green safelight.Secondary pulvini from the third to eighth youngest fully expanded leaves were used in all experiments. The rachis, cut transversely 1.5 cm below pulvini to separate the paired pinnae from the plant, was then split along its longitudinal axis to separate the two paired pulvini, which became experimental and control partners. Laminar tissue was removed, but a small (2.5 cm) section of rachilla was left attached to the pulvinus for immersion in water or 50 mM sucrose (see reference 18 for further details). Solutions were changed daily to minimize bacterial contamination. Six to eight pairs of pulvini were used for each treatment. Angles between the rachis and rachilla were estimated at 2-hr intervals by comparison with angles on a chart.Preliminary experiments, conducted to determine the effect of cutting, revealed that leaflets tend to close for a short time following excision. This causes a slight disturbance in the maximum of the first cycle but it does not affect subsequent behavior. To avoid variability, pinnae were always excised at DD = 2.5 hr. Figure 1 shows the movement of pulvini supplied with water or sucrose during prolonged DD. The rhythm of pulvini supplied with H20 damps in the open position after two cycles. By contrast, oscillations persist for at least 1 week if sucrose is available, although both the amplitude of the oscillation and the mesor or median angle (11), decrease with time. To determine whether loss of K+ from the pulvinus to the bathing solution might...

“…One bank was positioned above the leaflets and one below, so that both pulvini in a closed leaflet pair would be irradiated similarly. Red irradiation establishes a high level of Pfr in the tissue, as required for persistence of rhythmicity during DD2 (17). The leaflet pairs were maintained in physiological darkness immediately following the red irradiation.…”

mentioning

confidence: 99%

Chronobiology of Aging in Albizzia julibrissin

Chen

Lee²,

Satter³

1984

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We are using leaflet movements in Albizzia julibrissin as a model system for investipting the chronobiology of aging. To monitor leaflet movements during long dark periods with adequate temporal and spatial resolution, we designed an automated, computerized photoelectric monitoring system. Each of 12 leaflet pairs was positioned in an individual light-proof container, with one leaflet immobilized. The angle of the mobile leaflet was monitored by a photosensor array using a low intensity infrared beam. Leaflet position was determined by custom-developed software, using information on the shading patterns of the sensors. Data on leaflet angle as a function of time were collected and stored on a floppy disc and then printed in numerical and graphical form.OsciDations of young, middle-aged, and old leaflets persist during 7 d of darkness with a periodicity close to 24 h. Period length appears to be age-independent, but rhythmic wave form is age-dependent. The older the leaflet, the earlier and more completely it opens and the less completely it closes.