The photosystem II-associated Cah3 in Chlamydomonas enhances the O2 evolution rate by proton removal

In sugar beet (Beta vulgaris L.) iron deficiency decreased not only the photosynthetic rate but also the actual photosystem II efficiency at steady-state photosynthesis. In moderate iron deficiency, the decrease in actual photosystem II efficiency under illumination was related to closure of photosystem II reaction centers, whereas in severe iron deficiency it was associated to decreases of intrinsic photosystem II efficiency. The O2 evolution, on an absorbed light basis, decreased more than the actual photosystem II efficiency, suggesting the presence of a significant fraction of electron transport to molecular oxygen or the existence of some form of cyclic electron flow. Iron-deficient leaves reduced the excess of light absorbed that cannot be used in photosynthesis not only by decreasing absorptance, but also by dissipating a large part of the light absorbed by the photosystem II antenna. This mechanism, that protects the photosystem II reaction centers through the enhancement of energy dissipation, was related to the de-epoxidation of violaxanthin (V) to antheraxanthin (A) and zeaxanthin (Z) in iron-deficient leaves. These data provide additional support for a role of Z+A in photoprotection under conditions of excess photosynthetic light absorption.

Download Full-text

The effect of Cl− depletion and X− reconstitution on the oxygen-evolution rate, the yield of the multiline managanese EPR signal and EPR Signal II in the isolated Photosystem-II complex

Biochimica et Biophysica Acta (BBA) - Bioenergetics ◽

10.1016/0005-2728(86)90214-8 ◽

1986 ◽

Vol 848 (3) ◽

pp. 378-391 ◽

Cited By ~ 37

Author(s):

Reddy Damoder ◽

V.V. Klimov ◽

G.Charles Dismukes

Keyword(s):

Photosystem Ii ◽

Oxygen Evolution ◽

Evolution Rate ◽

Oxygen Evolution Rate ◽

Epr Signal ◽

Epr Signal Ii

Download Full-text

The effects of high concentrations of salts on photosynthetic electron transport in spinach (Spinacia oleracea) chloroplasts

Biochemical Journal ◽

10.1042/bj2040705 ◽

1982 ◽

Vol 204 (3) ◽

pp. 705-712 ◽

Cited By ~ 6

Author(s):

A C Stewart

Keyword(s):

Electron Transport ◽

Photosystem Ii ◽

Photosystem I ◽

Spinacia Oleracea ◽

Photosynthetic Electron Transport ◽

Potassium Citrate ◽

O2 Evolution ◽

Hofmeister Series ◽

Reaction Centre ◽

High Concentrations

1. Photosynthetic electron transport from water to lipophilic Photosystem II acceptors was stimulated 3-5-fold by high concentrations (greater than or equal to 1 M) of salts containing anions such as citrate, succinate and phosphate that are high in the Hofmeister series. 2. In trypsin-treated chloroplasts, K3Fe(CN)6 reduction insensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea was strongly stimulated by high concentrations of potassium citrate, but there was much less stimulation of 2,6-dichloroindophenol reduction in Tris-treated chloroplasts supplied with 1,5-diphenylcarbazide as artificial donor. The results suggest that the main site of action of citrate was the O2-evolving complex of Photosystem II. 3. Photosystem I partial reactions were also stimulated by intermediate concentrations of citrate (up to 2-fold stimulation by 0.6-0.8 M-citrate), but were inhibited at the highest concentrations. The observed stimulation may have been caused by stabilizaton of plastocyanin that was complexed with the Photosystem I reaction centre, 4. At 1 M, potassium citrate protected O2 evolution against denaturation by heat or by the chaotropic agent NaNO3. 5. It is suggested that anions high in the Hofmeister series stimulated and stabilized electron transport by enhancing water structure around the protein complexes in the thylakoid membrane.

Download Full-text

Relationship between O2 evolution capacity and cytochrome b-559 high-potential form in Photosystem II particles

Biochimica et Biophysica Acta (BBA) - Bioenergetics ◽

10.1016/0005-2728(85)90019-2 ◽

1985 ◽

Vol 808 (2) ◽

pp. 348-351 ◽

Cited By ~ 38

Author(s):

Jean-Marie Briantais ◽

Claudie Vernotte ◽

Mitsue Miyao ◽

Norio Murata ◽

Martine Picaud

Keyword(s):

Photosystem Ii ◽

Cytochrome B ◽

High Potential ◽

O2 Evolution ◽

Potential Form ◽

Photosystem Ii Particles

Download Full-text

Fast enzymatic HCO3- dehydration supports photosynthetic water oxidation in Photosystem II from pea

10.1101/2021.09.30.462629 ◽

2021 ◽

Author(s):

Alexandr V. Shitov ◽

Vasily V. Terentyev ◽

Govindjee Govindjee

Keyword(s):

Photosystem Ii ◽

Pisum Sativum ◽

Water Oxidation ◽

Photochemical Reactions ◽

O2 Evolution ◽

Donor Side ◽

Psii Photochemistry ◽

Similar Dependence ◽

Enzymatic Nature ◽

Photosynthetic Water Oxidation

Carbonic anhydrase (CA) activity, associated with Photosystem II (PSII) from Pisum sativum, has been shown to enhance water oxidation. But, the nature of the CA activity, its origin and role in photochemistry has been under debate, since the rates of CA reactions, measured earlier, were less than the rates of photochemical reactions. Here, we demonstrate high CA activity in PSII from Pisum sativum, measured by HCO3- dehydration at pH 6.5 (i.e. under optimal condition for PSII photochemistry), with kinetic parameters Km of 2.7 mM; Vmax of 2.74·10-2 mM·sec-1; kcat of 1.16·103 sec-1 and kcat/Km of 4.1·105 M-1 sec-1, showing the enzymatic nature of this activity, which kcat exceeds by ~13 times the rate of PSII, as measured by O2 evolution. The similar dependence of HCO3- dehydration, of the maximal quantum yield of photochemical reactions and of O2 evolution on the ratio of chlorophyll/photochemical reaction center II demonstrate the interconnection of these processes on the electron donor side of PSII. Since the removal of protons is critical for fast water oxidation, and since HCO3- dehydration consumes a proton, we suggest that CA activity, catalyzing very fast removal of protons, supports efficient water oxidation in PSII and, thus, photosynthesis in general.

Download Full-text

Mangrove Photosynthesis: Response to High-Irradiance Stress

Functional Plant Biology ◽

10.1071/pp9880043 ◽

1988 ◽

Vol 15 (2) ◽

pp. 43 ◽

Cited By ~ 55

Author(s):

O Bjorkman ◽

B Demmig ◽

TJ Andrews

Keyword(s):

Energy Dissipation ◽

Photosystem Ii ◽

Energy Conversion ◽

O2 Evolution ◽

Photon Yield ◽

Mangrove Species ◽

Reaction Centres ◽

Fluorescence Characteristics ◽

Shade Leaves ◽

Sun Leaves

Efficiencies of photosynthetic energy conversion were determined in sun and shade leaves of several mangrove species, growing in an open intertidal habitat in North Queensland, by measuring the maximum photon yield of O2 evolution and 77K chlorophyll fluorescence characteristics. Preliminary meas- urements confirmed that mangrove leaves have low water potentials, low stomatal conductances and low light-saturated CO2 exchange rates. Mangrove sun leaves therefore received a very large excess of excitation energy. Mangrove shade leaves had as high a photon yield of O2 evolution as non-mangrove leaves and their fluorescence characteristics were normal, showing that the energy conversion efficiency was unaffected by the high salinity. Mangrove sun leaves had markedly depressed photon yields and fluorescence was severely quenched showing that the efficiency of the photochemistry of photosystem II was reduced. The efficiency of energy conversion decreased with an increased radiation receipt. No such depression was detected in sun leaves of non-mangrove species growing in adjacent non-saline sites. Shading of man- grove sun leaves resulted in an increase in the efficiency of energy conversion but, in most species, more than 1 week was required for these leaves to reach the efficiency of shade leaves. Leaves exposed to direct sunlight had somewhat higher efficiencies in mangrove plants cultivated in 10% seawater as compared with full-strength seawater but the salinity of the culture solution had little effect on the increase in the efficiency upon shading. Field and laboratory fluorescence measurements indicated that the reduced efficiency of energy conversion in mangrove sun leaves resulted from a large increase in the rate constant for radiationless energy dissipation in the antenna chlorophyll rather than from damage to the photosystem II reaction centres. We propose that this increase in radiationless energy dissipation serves to protect the reaction centres against damage by excessive excitation.

Download Full-text