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In addition to circadian changes in the membrane potential and leaf movement, light applied to the pulvinus causes changes in both the membrane potential and the pulvinar movement in Phaseolus vulgar is L. Even after a short pulse of light, a transient depolarization of the membrane occurs and leaf movement is observed. Decreases of turgor pressure of the motor cells are always preceded by the depolarization. The direction of the leaf movement can be explained by the decrease of turgor pressure in the motor cells on the irradiated side of the pulvinus. Using the Okazaki Large Spectrograph at the National Institute for Basic Biology, we determined the action spectrum of the membrane depolarization induced by light pulses (30 s) in motor cells of Phaseolus. The pulvinus was left exposed to air during measurement of the membrane potential with microelectrodes. The action spectrum obtained was in the range of 300 to 730 nm. It had the highest peak at 460 nm with lower peaks at 380 nm and 420 nm. Almost no sensitivity was observed at wavelengths shorter than 360 nm and longer than 520 nm. Red and far-red light had no effect on the depolarization of the motor cell. The features of the action spectrum are almost the same as those of the Blue-Type response in plants.

Pulvinar motor cells ofPhaseolus vulgaris L display transient depolarization of the membrane potential and a turgor pressure decrease when exposed to a pulse of blue light. To analyze the mechanism of the transient depolarization, the effects of some factors such as anoxia, metabolic inhibitors and specific inhibitors of H+-ATPase have been examined. The findings have led to the conclusion that blue light inactivates the electrogenic H+-pumping ATPase in the plasma membrane of the motor cells. This inactivation seems to suppress ion uptake and decrease the turgor pressure of the motor cells.

Blue light was found to induce shrinkage of the protoplasts isolated from first-leaf lamina pulvini of 18-day-old Phaseolus vulgaris. The response was transient following pulse stimulation, while it was sustainable during continuous stimulation. No apparent difference was found between flexor and extensor protoplasts. Protoplasts of the petiolar segment located close to the pulvinus showed no detectable response. In the plants used, the pulvinus was fully matured and the petiole was ceasing its elongation growth. When younger, 12-day-old, plants were used, however, the petiolar protoplasts did respond to blue light. The pulse-induced response was similar to that in pulvinar protoplasts, although the response to continuous stimulation was transient and differed from that in pulvinar protoplasts. No shrinkage was induced in pulvinar protoplasts when the far-red-light-absorbing form of phytochrome was absent for a period before blue-light stimulation, indicating that the blue-light responsiveness is strictly controlled by phytochrome. Inhibitors of anion channels and H(+)-ATPase abolished the shrinking response, supporting the view that protoplasts shrink by extruding ions. The response of pulvinar protoplasts is probably involved in the blue-light-induced, turgor-based movement of pulvini. The blue-light responding system in pulvini is suggested to have evolved from that functioning in other growing organs.

A pulse of blue light induced both a transient increase in activity of apoplastic K+ and membrane depolarization in laminar pulvinus of Phaseolus vulgaris L. This shows that blue-light-induced net efflux of K+ from motor cells is closely related to membrane depolarization.

This paper describes the effects of anoxia and RL on the BL-induced changes in the membrane potential of the motor cells and in the leaf movement. BL-induced depolarization of the membrane was found to be closely related to the electrogenic component of the membrane potentiel

KCl-induced luminescence in relation to slow delayed light emission (> 3 s) and pH shift-triggered luminescence was studied in preilluminated chloroplasts. An activation pathway for KCl-induced luminescence similar to that for acid-base-triggered luminescence but different from that for delayed light emission is suggested. When the chloroplasts were subjected to a small amount of pH transition together with a simultaneous addition of KCl, a synergistic enhancement of triggered luminescence was observed. The synergism was not observed when the pH transition was increased. The results are interpreted according to the protonation model for stimulated luminescence.

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Swollen chloroplasts, suspended in succinic or other acids at pH 4 were mixed with alkali in a stopped-flow apparatus to permit observation of the pH of the medium following an acid-base transition. Immediately after mixing the observed pH values were as much as 0.6 units more alkaline than the final equilibrium pH, then dropped to the equilibrium value over a period of several seconds. Experimental results support the idea that most of the slowly appearing acidity represented diffusional loss from the thylakoids of organic acid molecules, previously absorbed from the initial acid medium. Time-courses for the approach to equilibrium pH showed apparent first-order kinetics, with two distinct components: (a) the major portion of acid loss, having a Q 10 of 2, and (b) a minor residual portion of the acid loss, having a Q 10 of 1.2. Component (a) could be distinguished by faster kinetics only at 20° or above. Uncouplers had relatively little effect on (b), but diminished the extent and duration by accelerating the velocity of initial acid loss (a). The combined results of several diverse experiments showed a correlation between the ability to make ATP, and the existence of large and relatively slow initial acid loss (a). Kinetics of this initial phase are similar to those of the post illumination pH drop studied previously, under equivalent conditions. The very slow response times of the glass pH electrode in unbuffered solutions described previously was found here to limit the observed rate constants for the chloroplast light-induced pH rise, thereby calling into question the accuracy of some previously published kinetic studies.

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書誌情報のみ, Bibliographic data Only

書誌情報のみ, Bibliographic data Only

1. The potential difference (P. D.) between the two ends of one and the same internodial cell of Nitella was measured when water enters the cell at one end and goes out at the other under the osmotic gradient of 0.2M sucrose.2. When the cell is in contact with the KCl solution in the concentration range of 0.05M-0.01M, the potential at the part where water comes out of the cell becomes always higher than that where water enters.3. This phenomenon is explained by the uneven distribution of KCI in the cell sap in terms of diffusion potential.4. When very diluted KCl solutions (0.001M-0.0001M) are applied to the external medium, the P. D. between the two parts of the cell shows discrepancies which are not apprehensible on the basis of diffusion potential unless changes in the mobility of K+ in the protoplasmic layer are postulated in the cell part where water flows out.The author wishes to express his most cordial thanks to Professor N. Kamiya for his helpful advice and directions throughout this work.

The kinetics of proton release in chloroplast suspensions by acid-base transition were studied by means of a stopped-flow spectrophotometer. The time courses of pH change show two-phase kinetics, fast and slow. The fast phase suggests the rapid release of protons from the thylakoid membranes, and the slow phase the efflux through the membranes of organic acid (and/or protons) previously absorbed from the initial acid medium.

Acid-base triggered luminescence in relation to slow delayed light emission (> 3 s) was studied in chloroplasts. After analyzing their time courses, the acid-base induced luminescence curve was found to return to the original curve of delayed light emission. Peaks of the acid-base triggered luminescence induced after various darkness periods following preillumination decreased parallel to the time course of delayed light emission without base treatment. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea enhanced both the delayed light emission and acid-base induced luminescence, while carbonyl cyanide m-chlorophenylhydrazone inhibited both. Several photophosphorylation uncouplers inhibited the acid-base induced luminescence without any substantial effect on the delayed light emission. It is concluded that the acid-base triggered luminescence is not caused by the reversion of electrons from remote intermediates on the reducing side of Photosystem II. The possibility of the presence of an activation pathway for the acid-base triggered luminescence which differs from that of the delayed light emission is also discussed.

The relationship between the kinetics of ATP formation and proton release in chloroplast suspensions by acid-base transition were studied by means of a stopped-flow spectrophotometer. The time course of ATP synthesis shows two-phase kinetics, fast and slow, corresponding to the two-phase efflux of protons from the chloroplasts. Under certain conditions of the experiments, about 50% of the H+ gradient is constantly utilized for ATP formation in both phases. However, the ratio of ATP formed to the amount of protons leaked out, changes depending on the rate constants of proton efflux.