Photophosphorylation in Chloroplasts

Avron, and M; Neumann, J.

doi:10.1146/annurev.pp.19.060168.001033

Cited by 137 publications

(58 citation statements)

References 107 publications

(161 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…2). This observation is contrary to the generally held view that DCMU does not inhibit cyclic photophosphorylation (24) but is in agreement with the findings of Kaiser and Urbach (25) that in far-red light endogenous cyclic photophosphorylation in isolated chloroplasts was inhibited by low concentrations of DCMU.…”

Section: Resultssupporting

confidence: 76%

Regulation of ferredoxin-catalyzed photosynthetic phosphorylations.

Arnon¹,

Chain²

1975

Proc. Natl. Acad. Sci. U.S.A.

134

View full text Add to dashboard Cite

Under aerobic conditions that are likely to prevail in chloroplasts in vivo, the optimal concentration of ferredoxin for cyclic photophosphorylation was found to be equal to that required for NADP reduction and about onetenth of that needed for cyclic photophosphorylation under anaerobic conditions. In the presence of ferredoxin and NADP, cyclic photophosphorylation operated concurrently with noncyclic photophosphorylation, producing an ATP: NADPH ratio of about 1.5. The effective operation of ferredoxin-catalyzed cyclic photophosphorylation by itself required a curtailment of the electron flow from water which was accomplished experimentally by the use of either an inhibitor or far-red monochromatic light. An unexpected discovery was that the operation of cyclic photophosphorylation by itself was also regulated by a back reaction of NADPH and ferredoxin with two components of chloroplast membranes, component C550 and cytochrome b559. The significance of these findings to photosynthesis in vivo is discussed.Solar energy is first converted into biologically useful chemical energy by photosynthetic phosphorylation (photophosphorylation), the process by which the photosynthetic apparatus transforms the electromagnetic energy of sunlight into phosphate bond energy of ATP, the universal energy carrier of living cells. The energy of the photochemically generated ATP and reducing power is conserved through the biosynthesis of organic compounds from CO2. When these are later degraded by fermentation and respiration, reducing power and ATP are regenerated to drive the multitude of endergonic reactions and activities of living cells.Chloroplasts, the photosynthetic organelles of green plants, have two types of photophosphorylation, cyclic and noncyclic, names devised to denote the coupling of ATP formation to a light-induced electron flow that is either of a closed (cyclic) type that yields only ATP or of a unidirectional (noncyclic) type that yields not only ATP but also NADPH as reducing power (1). Ferredoxin plays a key role in both. In cyclic photophosphorylation ferredoxin is the endogenous catalyst (2, 3) and in noncyclic photophosphorylation ferredoxin is the electron acceptor (4) that in turn reduces NADP by an enzymatic reaction that is independent of light (5).In this paper we report the concurrent operation of ferredoxin-dependent cyclic and noncyclic photophosphorylation under conditions that are likely to exist in chloroplasts in vivo. These experiments led to the discovery that noncyclic electron flow provides a regulatory mechanism that permits cyclic photophosphorylation to operate either concurrently with the noncyclic type (and thereby to increase the ratio of ATP to NADPH as needed for photosynthetic CO2 assimilation) or to operate by itself and produce only ATP for those endergonic reactions that do not require photochemically generated reducing power. Illumination. Incident monochromatic illumination was provided by a 250 W tungsten-halogen lamp (General Electric type EHN) and appropriate inte...

show abstract

Section: Resultssupporting

confidence: 76%

Regulation of ferredoxin-catalyzed photosynthetic phosphorylations.

Arnon¹,

Chain²

1975

Proc. Natl. Acad. Sci. U.S.A.

134

View full text Add to dashboard Cite

show abstract

“…Hence, both respiration and photosynthesis could support the uptake of this amino acid. Adding 10 /uM DCMU (1) to the incubation solution in the light under anaerobiosis did not affect the observed glycine uptake; however, adding 0.3 mm DNP together with the DCMU under anaerobiosis eliminated the glycine uptake in the light (Table I). The presence of 10 juM PMS increased glycine uptake in the light under anaerobiosis to 72% of the control value, while uptake in the dark remained unaffected (Table I).…”

mentioning

confidence: 93%

“…The present studies used this technique to investigate the uptake of amino acids into the mesophyll cells of pea leaves. The effects of light, anaerobiosis, metabolic inhibitors, and uncouplers of phosphorylation were employed in order to identify the energy source for the ob- 1 This investigation was supported in part by United Fully expanded leaves from 14-day-old plants were removed and chopped into pieces of random size with no dimension exceeding 2 mm (12, 13). The leaf fragments were then rinsed for 1 hr at 30 C in the dark.…”

mentioning

confidence: 99%

Amino Acid Uptake by Pea Leaf Fragments

Cheung

Nobel²

1973

Plant Physiol.

View full text Add to dashboard Cite

Amino acid uptake into leaf fragments of Pisum sativum depended on metabolism. Glycine uptake was optimal at 30 C and could be supported by respiration and by photosynthesis. Based on studies with an electron flow cofactor, inhibitors, and uncouplers, the energy source for glycine uptake was apparently ATP.The energy-dependent transport of glycine was mediated by a carrier that had a broad specificity for neutral and positively charged L-amino acids. It readily translocated 15 such L-amino acids into the cells, but had a very low affinity for L-aspartate, L-glutamate, D-amino acids, and a-aminoisobutyrate. The Ki for competitive inhibition of glycine uptake by another amino acid was equal to the Km for the uptake of that competing species.

show abstract

“…CMU has been shown to be a potent inhibitor of photosynthetic oxygen evolution in living plants, as well as an inhibitor of light-mediated electron transport associated with the production of reducing equivalents, known as photosystem II, in isolated chloroplasts (1). Chlorella was inoculated into dilute suspensions (0.5 ml of packed cells per liter) and was placed in 8000 lux of light in the normal manner.…”

Section: Resultsmentioning

confidence: 99%

Chlorophyll Synthesis in Chlorella

Beale

Appleman

1971

Plant Physiol.

View full text Add to dashboard Cite

The degree of light limitation of growth is the primary controlling factor of chlorophyll synthesis during photoautotrophic growth of Chlorella. The chlorophyll content of the cells increases when light is limiting for growth as occurs in dense cultures, or in cultures under low incident light, or when the light is used less efficiently through partial inhibition of photosynthesis by 3-(p-chlorophenyl)-1, 1-dimethylurea. Most algae, Chlorella included, do not require light in order to carry out chlorophyll synthesis, and therefore, the regulation of chlorophyll synthesis in algae appears to be quite different from that involved in the greening of etiolated higher plants. There are, however, some common features of chlorophyll synthesis in algae and higher plants: 8-aminolevulinic acid synthetase, the putative first enzyme of chlorophyll synthesis, has not been detected in extracts of any green plant, including algae (3); chlorophyll synthesis in Chlorella appears to be dependent upon protein synthesis (2), as it is in higher plants (4, 5); mutants of Chlorella exist which behave like higher plants with respect to a light requirement for protochlorophyllide reduction and chlorophyll formation (7,8).Sargent (14) and Myers (10, 11) reported that Chlorella produced more chlorophyll under low light conditions than under high light conditions. This is perhaps related to the observations of Sestak (15) specifically suppressed when dilute cultures of Chloreilla were exposed to high light intensity, the effect being designated the lag phase of chlorophyll synthesis. The duration of the lag phase could be altered by changing the incident light intensity on the culture or the initial cell population density, and by the presence of certain sugars in the culture medium. A number of possible explanations were put forward concerning the physiological basis of the lag phase. First, the lag could be due to some intrinsic induction period required before the enzymes necessary for chlorophyll biosynthesis are produced within the cells. When a newly inoculated culture is placed in the light, perhaps some component of the chlorophyll biosynthetic system is destroyed and then resynthesized during the induction period. Second, perhaps light suppresses chlorophyll synthesis directly. Then the lag phase might reflect the time required for the cells to overcome the light-induced suppression of chorophyll synthesis, i.e., to adapt to the new light environment. Third, the lag phase might represent a feedback control exerted by a product of photosynthesis over another process, chlorophyll biosynthesis, which provides a key component of the photosynthetic apparatus, namely, chlorophyll. The cells might adjust their chlorophyll content in response to the light available for carrying ouLt photosynthesis. Fourth, inasmuch as growth rate and chlorophyll biosynthetic rate appear to be inversely related, perhaps there is a competition for a common precursor of chlorophyll and other cellular components.The experiments described in this pap...

show abstract

Photophosphorylation in Chloroplasts

Cited by 137 publications

References 107 publications

Regulation of ferredoxin-catalyzed photosynthetic phosphorylations.

Regulation of ferredoxin-catalyzed photosynthetic phosphorylations.

Amino Acid Uptake by Pea Leaf Fragments

Chlorophyll Synthesis in Chlorella

Contact Info

Product

Resources

About