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Biomedical subjects

R L Satter

Publications and source records attributed to R L Satter.

At least 37 records · Page 2Linked to original sources
PubMed1979

A circadian rhythm in oxygen uptake by samanea pulvini.

The rate of O(2) uptake by excised Samanea pulvini oscillates with a circadian rhythm during 52 hours of darkness. Rates of respiration increase during pulvinar opening and decrease prior to and during closure, consistent with the concept that opening requires a greater expenditure of energy. Externally supplied sucrose, necessary for perpetuation of the leaflet movement rhythm, has a small promotive effect on the rate of respiration.

Journal Article↗
PubMed1979

Effect of vanadate on rhythmic leaflet movement in albizzia julibrissin.

Vanadate (Na(3)VO(4)) selectively and reversibly affects the rhythmic movement of Albizzia julibrissin leaflets. Leaflets floated on 1 millimolar vanadate open at the same rate or more rapidly than controls, but closure is inhibited. After 6 to 24 hours incubation, the inhibition can be reversed by a 24-to 48-hour period on water or control buffer. Recovery is complete in light-dark cycles, and it is almost complete under free-running conditions (prolonged darkness). Leaflets floated on 10 millimolar vanadate do not open in darkness, but they open at a reduced rate in light. Concentrations of 100 micromolar or less are ineffective.

Journal Article↗
PubMed1977

Phytochrome and Circadian Clocks in Samanea: Rhythmic Redistribution of Potassium and Chloride within the Pulvinus during Long Dark Periods.

Previous investigations with the electron microprobe reveal that the movements of Samanea leaflets are correlated with massive redistribution of K within the pulvinus. Evidence is now presented that Cl moves with K, whether plants are in white light or darkness, whether or not the amplitude of free running oscillations has damped, and whether or not the rhythm has been rephased by phytochrome photoconversion. The mid-extensor to mid-flexor ratio of K + Cl is correlated with leaflet angle under all conditions. Total Cl in both inner cortex and motor region is approximately 0.6 as high as K. The stoichiometry between Cl and the migratory fraction of K is close to, but not precisely 1:1 in all regions of the pulvinus, suggesting that other ions or systems may also be involved in the balancing of electrical charges.

Journal Article↗
PubMed1976

Potassium-linked Chloride Fluxes during Rhythmic Leaf Movement of Albizzia julibrissin.

Transverse sections of Albizzia pulvinules were examined with an electron microprobe to determine ion fluxes associated with turgorcontrolled leaflet movements. K(+) and Cl(-) concentrations are high in the flexor and low in the extensor region of closed pulvini. Both ions migrate out of the flexor and into the extensor during opening as previously described for K(+). The distribution of these elements is significantly correlated in each phase of the rhythmic cycle examined, but only 50 to 60% of the ionic charge of potassium is balanced by chloride. This value increases to 65 to 85% if one considers only the mobile fraction of the potassium.The increase in concentration of both ions in the extensor region precedes the decrease in the flexor, thus indicating that there must be a storage reservoir for K(+) and Cl(-). The inner cortex is suggested as such a reservoir, and plasmodesmata are discussed as a probable pathway for ion movement.

Journal Article↗
PubMed1976

Circadian rhythmicity in excised samanea pulvini: I. Sucrose-white light interactions.

The rhythmic movement of excised Samanea saman pulvini incubated in H(2)O 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). In continuous white light, the rhythm damps at an intermediate angle after only one cycle, whether pulvini are incubated in sucrose or H(2)O. The rhythm also damps after the first cycle when darkened pulvini are incubated in H(2)O, but it persists for several cycles if sucrose is available. Sucrose depresses the mesor (average angle) during extended dark periods in Samanea, as in Albizzia julibrissin, but it increases the mesor if supplied during white light-dark cycles. With the latter irradiation schedule, oscillations persist for several cycles whether pulvini are supplied with H(2)O or sucrose, but closure is incomplete when pulvini are incubated in sucrose.

Journal Article↗
PubMed1976

Circadian Rhythmicity in Excised Samanea Pulvini: II. Resetting the Clock by Phytochrome Conversion.

Excised Samanea saman pulvini were incubated in H(2)O or 50 mm sucrose in darkness for 100 to 152 hours except for brief exposures to red or far red light, and angles of opening measured periodically. When pulvini are incubated in H(2)O, the rhythm damps in the open position after two to three cycles irrespective of the light treatments, but when sucrose is available, the now persistent oscillations show large red, far red-regulated effects on phase, amplitude, mesor slope, and entrainment. Single red light pulses rephase the rhythm, with a phase response curve that resembles that reported for other plants and animals; such rephasing is prevented by immediately subsequent far red light, indicating that phytochrome is the photoreceptor. Red light pulses repeated every 24 hours entrain the rhythm, and also prevent damping if presented at an appropriate part of the cycle.

Journal Article↗
PubMed1974

Potassium flux and leaf movement in Samanea saman. I. Rhythmic movement.

Samanea leaflets usually open in white light and fold together when darkened, but also open and dose with a circadian rhythm during prolonged darkness. Leaflet movement results from differential changes in the turgor and shape of motor cells on opposite sides of the pulvinus; extensor cells expand during opening and shrink during closure, while flexor cells shrink during opening and expand during closure but change shape more than size. Potassium in both open and closed pulvini is about 0.4 N. Flame photometric and electron microprobe analyses reveal that rhythmic and light-regulated postassium flux is the basis for pulvinar turgor movements. Rhythmic potassium flux during darkness in motor cells in the extensor region involves alternating predominance of inwardly directed ion pumps and leakage outward through diffusion channels, each lasting ca 12 h. White light affects the system by activating outwardly directed K(+) pumps in motor cells in the flexor region.

Biological Transport, Active↗
PubMed1974

Potassium flux and leaf movement in Samanea saman. II. Phytochrome controlled movement.

Phytochrome, a membrane-localized biliprotein whose conformation is shifted reversibly by brief red or far-red light treatments, interacts with the rhythmic oscillator to regulate leaflet movement and potassium flux in pulvinal motor cells of Samanea. Darkened pinnae exposed briefly to red light (high P(fr) level) have less potassium in motor cells in the extensor region, more potassium in motor cells in the flexor region, and smaller angles than those exposed to far-red light (low P(fr) level). Increase in temperature from 24 degrees to 37 degrees increases the differential effect of the light treatments during opening (the energetic phase) but not during closure, implying that phytochrome controls an energetic process. It seems likely that phytochrome interacts with rhythmically controlled potassium pumps in flexor and extensor cells. During nyctinastic closure of white-illuminated pinnae, exposure to far-red light before darkening results in larger angles than does exposure to red. As in rhythmic opening, the angles of all pinnae and the differential effect of the light treatments increases with increasing temperature.

Bile Pigments↗
PubMed1974

Rhythmic potassium flux in albizzia: effect of aminophylline, cations, and inhibitors of respiration and protein synthesis.

Rhythmic leaflet movement in Albizzia is controlled by rhythmic K(+) flux in pulvinal motor cells. The angle assumed by darkened leaflets during the open phase of the rhythm can be altered by various compounds and changes in temperature; such treatments are ineffective during the closed phase. In all cases, effects on leaflet angle are correlated with and probably a consequence of K(+) flux in pulvinal motor cells. Incubation at low temperature (6C) or on sodium azide (1.0 mm) reduces K(+) in the ventral motor region and increases K(+) in the dorsal motor region, thereby decreasing leaflet angle. Incubation on cycloheximide (0.1 mm) or sodium acetate (0.05 m) inhibits protein synthesis; if the incubation period immediately precedes the opening phase, these compounds prevent both K(+) flux into the ventral motor cells and leaflet opening. Magnesium nitrate (0.05 m), supplied after leaflets have started to open, promotes K(+) secretion from the dorsal motor cells and increases the angle of opening.The data support the following hypothesis. Active K(+) transport into the ventral motor cells and out of the dorsal motor cells leads to opening; K(+) leakage in the opposite directions causes closure; and the interaction of these processes results in a rhythmic oscillation. Proteins in the ventral cell membranes that are required for active transport or membrane integrity turn over rhythmically and are resynthesized before opening. The availability of divalent cations determines the phase relationships between the K(+) rhythms in the dorsal and ventral motor cells.White light phases the rhythm. The "light on" signal turns on a K(+) secreting pump in the dorsal motor cells, while the "light off" signal initiates a period of protein synthesis which in turn leads to active K(+) transport into the ventral motor cells. Aminophylline (0.1-6.0 mm) inhibits white light-promoted opening and nyctinastic closure.

Journal Article↗
PubMed1973

Protein synthesis during endogenous rhythmic leaflet movement in Albizzia.

A rhythm was found in protein synthesis accompanying rhythmic leaflet opening and closing in the dark in the plant Albizzia. More protein was synthesized during the opening of the leaflets than during the closing. Furthermore, an inhibitor of protein synthesis, cycloheximide, prevented rhythmic opening of leaflets but had no effect on rhythmic closing. It is suggested that protein synthesis is involved in the movement across membranes of K(+) ions that cause turgor changes and leaflet movement.

Circadian Rhythm↗
PubMed1973

Rhythmic Leaflet Movement in Albizzia julibrissin: Effect of Electrolytes and Temperature Alteration.

The rhythmic movement of darkened Albizzia leaflets is accompanied by K(+) flux in pulvinule motor cells whose turgor changes control opening and closing. The azide-sensitive open phase is promoted by an increase in temperature from 16 to 33C (Q(10) = 3), implying active transport of K(+) ions during this period. The azide-insensitive closed phase is less temperature-sensitive and has a Q(10) less than 1, implying diffusion or some other physical process as the predominant pathway of K(+) flux at this time. Thus rhythmic leaflet movement is probably due to oscillation in active K(+) transport or membrane permeability or both. External electrolytes (0. 1 n) alter leaflet angle during the open, but not the closed, phase of the rhythm. All chlorides except NH(4) (+) promote opening, with divalent more effective than monovalent ions. Some anions promote and others inhibit opening; activity is not correlated with charge. It is likely that electrolytes alter leaflet movement by altering K(+) flux, accomplishing this by interacting with key macromolecules in motor cell membranes.Pfr phytochrome dampens the amplitude of rhythmic leaflet movement; this process is temperature sensitive (Q(10) = 2) and unaltered by 0.1 n salt solutions. Although K(+) flux is a common basis for phytochrome and rhythmic control of leaflet movement, different mechanisms are clearly involved.

Journal Article↗
PubMed1972

Phytochrome-controlled Nyctinasty in Albizzia julibrissin: IV. Auxin Effects on Leaflet Movement and K Flux.

Indole-3-acetic acid, alpha-naphthylacetic acid, and 2,4-dichlorophenoxyacetic acid (0.001 to 1.0 mm) inhibit the nyctinastic closure of excised Albizzia leaflet pairs; antiauxins and auxin analogs are ineffective, and the auxin effects seem not to be mediated by ethylene. Indoleacetic acid (0.001 to 0.1 mm) also promotes rhythmic opening in the dark, but is ineffective during that phase of rhythmic closure ("leaky phase") which is insensitive to azide. At these concentrations, all of the indoleacetic acid effects are reversible upon transfer of the tissue to water and are linked to alteration of potassium flux in pulvinule motor cells.A supraoptimal concentration of indoleacetic acid (1 mm) inhibits rhythmic opening as well as nyctinastic closure, although it has little or no effect on potassium flux in motor cells. These inhibitions cannot be completely reversed by transferring the leaflets to water.Although indoleacetic acid (0.01 to 1.0 mm) inhibits leaflet opening and potassium flux in dorsal and ventral motor cells when leaflets are transferred from darkness to light, it has no effect during other portions of the light period, implying that changes in endogenous auxin do not control leaflet angle in the light. Neither does auxin seem to be involved in the phytochrome-regulated process, since it does not alter phytochrome control of leaflet movement or potassium flux. However, endogenous auxin probably plays an important role in controlling potassium flux into ventral motor cells during the opening phase of rhythmic leaflet movement in the dark.

Journal Article↗
PubMed1971

Phytochrome-controlled Nyctinasty in Albizzia julibrissin: III. Interactions between an Endogenous Rhythm and Phytochrome in Control of Potassium Flux and Leaflet Movement.

Prolonged irradiation during appropriate parts of the diurnal cycle promotes the opening of Albizzia julibrissin leaflets. Leaflets also open without illumination, but such opening starts later and is slower and less complete. Opening in the dark is accompanied by lower potassium efflux from dorsal pulvinule motor cells but equal or greater potassium movement into ventral motor cells than occurs during opening in the light. Far red-absorbing phytochrome inhibits opening in the dark, indicating that its action is similar during endogenously controlled opening and nyctinastic closure; i.e., a high far redabsorbing phytochrome level is associated with low potassium content in ventral motor cells, high potassium content in dorsal motor cells, and a small angle between leaflets.When open leaflets are darkened, there is an immediate and large potassium flux into dorsal motor cells. This is initially independent of red and far red preirradiation, but prior red light appears to promote continued potassium movement into dorsal cells during the latter part of a 90-minute dark period. The situation in ventral motor cells is different; here the effect of prior red or far red irradiation on potassium efflux is evident after 10 minutes of darkness. Phytochrome controls the direction of potassium movement in ventral motor cells during the early part of the dark period (to 25 minutes); potassium moves out of ventral motor cells if leaflets are preirradiated with red light and into these same cells if leaflets are preirradiated with far red light. Kinetic data are consistent with the suggestion that potassium leaving ventral cells enters dorsal cells. However, there must be an additional source of potassium entering dorsal cells since this potassium movement precedes potassium efflux from ventral cells.Pulvinules excised from the lamina or rachilla open and close in response to light and darkness and also move during extended periods of constant intensity light or uninterrupted darkness. This shows that the photoreceptor controlling opening and the oscillator controlling endogenously rhythmic leaflet movement are localized in the pulvinule. In addition, all the potassium that enters expanding cells during leaflet movement and the energy for potassium transport must be available from within the pulvinule.If leaflets are darkened late in the photoperiod, they close more rapidly and show lower inhibition by far red preirradiation or anaerobic conditions. A rhythmic increase in potassium efflux from ventral motor cells appears to be the basis for rhythmic promotion of nyctinastic closure. We suggest this is due to a rhythmic increase in the leakiness of ventral motor cells.

Journal Article↗
PubMed1968

Photomorphogenesis in Sinningia speciosa, cv. Queen Victoria I. Characterization of Phytochrome Control.

The morphological development of Sinningia speciosa plants that were exposed to supplementary far red light was very different from that of plants receiving dark nights. After several nights of such irradiation, stems and petioles were elongated, petioles were angulated, leaf blade expansion was inhibited, plants were chlorotic and the accumulation of shoot dry weight was retarded.Red reversibility of the morphological changes potentiated by far red light indicated control by the phytochrome system. A high P(FR) level during the last half of the night inhibited stem elongation and promoted leaf blade expansion, but both of these processes were hardly affected by the P(FR) level during the first half of the night. Thus sensitivity to P(FR) was cyclic.The interpretation of our experiments was complicated by quantitative morphological differences resulting from long, as compared to short, far red irradiations.

Journal Article↗