Inhibitor effects on photosynthesis, respiration and active ion transport inHydrodictyon africanum

Abstract

The effects of various inhibitors on photosynthesis, respiration, and active influx of K and Cl in light and dark inHydrodictyon africanum is reported. The inhibitors used were arsenate (uncouples electron-transport phosphorylations), dicyclohexylcarbodiimide (energy-transfer inhibitor in electron-transport phosphorylation), quinacrine (uncouples photophosphorylation and inhibits oxidative phosphorylation), and ethionine (traps adenylates as S-adenosyl ethionine). The action of these inhibitors, and of those previously used onHydrodictyon africanum, suggests that K influx requires ATP, while Cl influx requires some earlier manifestation of the ATP synthesizing process. Possible reasons for the greater sensitivity of K influx than of CO2 fixation to treatments which interfere with photophosphorylation are discussed.

Energy‐dependent Processes in Chara Corallina: Absence of Light Stimulation When Only Photo‐system One Is Operative

“…This implication of cyclic photophosphorylation as an energy source for cation transport was confirmed when Raven (1967), showed in H. africanum that cation transport has an increased quantum efficiency in far-red light (the 'red-rise') whereas Cl~ transport and CO2 fixation show a decreased efficiency ('reddrop'). Cation transport is much more sensitive to uncoupling agents and other energytransfer inhibitors than is Cl~ transport (MacRobbie, 1965(MacRobbie, , 1966Raven, 1968aRaven, , 1969Raven, , 1971bRaven, MacRobbie and Neumann, 1969). This indicates a linkage of Clt ransport to a reduced product of photosynthesis or (in the dark) respiration, or a direct coupling with electron transfer reactions.…”

The effects of triphenyltin chloride on respiration and photosynthesis in the green algae Enteromorpha intestinalis and Ulothrix pseudoflacca

“…vegetative tissue of the two algae (compare Figs 1 and 2, 3 and 4), only in E. intestinalis was the difference between a pair of values significant (at 95% confidence limits). This situation, that is the greater sensitivity of photosynthesis rather than respiration shown by E. intestinalis, is well-known in the response of mitochondria and chloroplasts to inhibitors in vivo (Raven, 1969(Raven, , 1971Gnanan, Govindarajan & Vivekanandan, 1975;Hawxby et al, 1977; see also Table 1) and indicates the greater sensitivity of the chloroplast to perturbation.…”

“…The uncouplers CCCP and quinacrine had little effect on respiration or photosynthesis (Table 1) and only the slight (23%) stimulation of photosynthesis by quinacrine was significant at 90% confidence limits, CCCP has been reported to uncouple both oxidative and photophosphorylation in vitro (Heyttler, 1963;Bamberger et al, 1963) while Gould & Bassham (1965) concluded that it would also uncouple photophosphorylation in Chlorella cells, Quinacrine has been reported to uncouple photophosphorylation (Avron & Shavit, 1965) and to inhibit oxidative phosphorylation in vitro. Additionally, Raven (1971) showed that active K+ influx in the light in Hydrodietyon africanum was more sensitive than K+ influx in the dark or photosynthesis in this alga. The lack of effect of these compounds on respiration may be related in some way to the relative insensitivity of this process to inhibitors.…”

“…Additionally, Raven (1971) showed that active K+ influx in the light in Hydrodietyon africanum was more sensitive than K+ influx in the dark or photosynthesis in this alga. The lack of effect of these compounds on respiration may be related in some way to the relative insensitivity of this process to inhibitors.…”

The energetics of Cl− active transport inChara

“…There are, however, many observations of reduction in ion transport rates when phosphorylation is inhibited. In many cases the inhibition of transport can be quite large for a relatively slight inhibition of energy transduction (Raven, 1969(Raven, , 1971Lin & Hanson, 1974;Wildes, Pitman & Schaefer, 1976). This could mean that the rates of active transport processes are acutely sensitive to the values of AG for the driving reactions; but it could equally mean that sensitive regulatory systems reduce the demand for ATP when its production is upset.…”