From mature needles of white spruce, Picea glauca (Moench) Voss we isolated thylakoids capable of high rates of oxygen evolution. Oxygen-evolving activity of spruce thylakoids was labile in the absence of osmoticum and declined by 40 % during 1 h on ice, compared to a 9 % dechne observed in spinách thylakoids. We compared the relative activity in spruce and spinách of the oxygen evolving complex (OEC) and the reaction centre in Triton X-100 fractionated membranes prepared and stored for 20 or 240 h at 0 or -80 °C in media with different combinations of sucrose (0.3, 0.5 and 1.0 M) and two pH values (6.0 and 7.6). In membranes detergent- fractionated and stored at pH 7.6, photosystem 2 (PS2) activity (H2O -> DCIP) was sensitive to sucrose concentration of the medium. Spruce and spinách membranes prepared and stored in 0.3 M sucrose and pH 7.6, showed 22 and 48 % activity of their respective control membranes, freshly prepared in 1 M sucrose at pH 6.0. In contrast, in membranes prepared and stored at pH 6.0, PS2 activity was less sensitive to sucrose concentration: spruce and spinách membranes in 0.3 M sucrose showed 73 and 88 % (respectively) of the activity of membranes freshly prepared in 1 M sucrose. In both species, the degree of stimulation of DCIP photoreduction by diphenylcarbazide suggested minimal damage to the reaction centre (RC) except during preparation in 0.3 M sucrose, pH 7.6. Since the spruce RCs were not more labile than those of spinách, the extra sensitivity of spruce thylakoids in media of low sucrose concentration was likely due to extra lability of the OEC.
Membrane-bound bicarbonate is believed by some to act as an essential activator of photosystem 2 (PS2) electron transport. Formáte and other inhibitory monovalent anions act by removing bound-bicarbonate. This belief relies to a great extent on the observation that formáte (100 mM) pretreated thylakoids exhibit a non- proportionality between Hill activity (HAR) and chlorophyll (Chl) concentration when preirradiated with bright radiation in reaction mixture that contains only 5 mM formáte. The non-linearity was attributed to a supposed loosening of residual bicarbonate still present after formáte treatment and which would be more abundant at higher Chl concentrations. In repeating this experiment, we observed an increase in HAR at higher Chl concentrations in preirradiated, but also in non-preirradiated samples, the latter were simply left in the dark for 3 min before measurements were made. Therefore, preirradiation is not needed to restore some HAR in formáte pretreated samples; a 3 min wait in the electrode chamber at low formáte concentration is sufficient to partially relieve the formáte inhibition of PS2 activity. Moreover, HAR in samples preirradiated by weak radiation, or not preirradiated at all, was directly proportional to Chl concentration. We can attribute the increase in activity to a dissociation of bound formáte, not necessarily to the effect of residual bicarbonate. Non-linearity in HAR with Chl concentration was found only in high- irradiance pretreated samples. We can attribute this to a greater amount of photoinhibition occurring in the dilute samples, where the effective irradiance was greater. There is no need to postuláte the existence of residual bound bicarbonate to explain these results.
Glycinebetaine, a compatible osmolyte of halotolerant plants and bacteria, partially protected photosystem (PS) 1 and PS2 electron transport reactions against thermal inactivation but with different efficiencies. In its presence, the temperature for half-maximal inactivation (t1/2) was generally shifted downward by 3-12 °C. Glycinebetaine stabilized photoinduced oxygen evolving reactions of PS2 by protecting the tetranuclear Mn cluster and the extrinsic proteins of this complex. A weaker, although noticeable, stabilizing effect was observed in photoinduced PS2 electron transport reactions that did not originate in the oxygen-evolving complex (OEC). This weaker protection by glycinebetaine was probably exerted on the PS2 reaction centre. Glycinebetaine protected also photoinduced electron transport across PS1 against thermal inactivation. The protective effect was exerted on plastocyanin, the mobile protein in the lumen that carries electrons from the integral cytochrome b6f complex to the PS1 complex. and Y. M. Allakhverdieva ... [et al.].
Cations such as Mg2+ regulate spillover of absorbed excitation energy mainly in favour of photosystem (PS) 2. Effect of low concentration (<10 mM) of the monovalent cation Na+ on chlorophyll (Chl) a fluorescence was completely overridden by divalent cation Mg2+ (5 mM). Based on Chl a fluorescence yield and 77 K emission measurements, we revealed the role and effectiveness of anions (Cl-, SO42-, PO43-) in lowering the Mg2+-induced PS2 fluorescence. The higher the valency of the anion, the lesser was the expression of Mg2+ effect. Anions may thus overcome Mg2+ effects up to certain extent in a valency dependent manner, thereby diverting more energy to PS1 even in the presence of MgCl2. They may do so by reversing Mg2+-induced changes. and Anjana Jajoo, Sudhakar Bharti.
Typical chestnut thylakoid extracts isolated by mechanical disruption of leaf tissues had an equivalent of 0.28 kg m-3 chlorophyll (Chl) which is six times less than in thylakoids obtained from spinach, although Chl content in leaves was only half as small. According to optical microscopy, the vesicles showed a good integrity, exhibiting at 21 °C a high capacity of photon-induced potential membrane generation, which was demonstrated by the almost full 9-amino-6-chloro-2-methoxyacridine fluorescence quenching in a hyper-saline medium containing 150 mM KCl and having osmotic potential of -1.5 MPa. The half-time of the thylakoid potential generation was 11.7 s with the time of dissipation around 8.9 s. In such conditions, spinach thylakoids showed an increased swelling and also differences in the half-time generation which was almost four times faster than was observed in chestnut. However, when spinach thylakoids were incubated in a typical hypo-saline medium without KCl with osmotic potential -0.8 MPa, no additional swelling was observed. Consequently the half-time of potential dissipation was 35 s. Studies with nigericin suggested a chestnut thylakoid ΔpH significantly smaller than that observed in spinach, which was confirmed by the measurements of the ATP driven pumping activity. and J. Gomes-Laranjo ... [et al.].
Kinetics of non-photochemical reduction of the photosynthetic intersystem electron transport chain by exogenous NADPH was examined in osmotically lysed spinach chloroplasts by chlorophyll (Chl) fluorescence measurements under anaerobic condition. Upon the addition of NADPH, the apparent F0 increased sigmoidally, and the value of the maximal slope was calculated to give the reduction rate of plastoquinone (PQ) pool. Application of 5 µM antimycin A lowered significantly both the ceiling and the rate of the NADPH-induced Chl fluorescence increase, while the suppressive effect of 10 µM rotenone was slighter. This indicated that dark reduction of the PQ pool by NADPH in spinach chloroplasts under O2-limitation condition could be attributed mainly to the pathway catalysed sequentially by ferredoxin-NADP+ oxidoreductase (FNR) and ferredoxin-plastoquinone reductase (FQR), rather than that mediated by NAD(P)H dehydro-genase (NDH). and Ming-Xian Jin, Hualing Mi.
We analyzed the effect of NaCl stress on photorespiration of spinach leaves by calculating the rate of carboxylation/oxygenation of ribulose-1,5-bisphosphate carboxylase/oxygenase, and by measuring the content of amino acids produced through photorespiration. After 20 d of NaCl stress the carboxylation rate was reduced while the oxygenation rate was not affected. The contents of serine, glycine, and alanine increased relevantly. The amount of glutamine also increased after 20 d but the amount of glutamate did not. Hence photorespiration may be stimulated under moderate NaCl stress. A relevant electron transport rate was observed under CO2-free air, which may indicate refixation of photorespiratory CO2. When NaCl accumulation proceeded for more than 20 d, photosynthesis was reduced and the content of photo-respiratory amino acids started to decrease, but the oxygenation rate did not change. and C. di Martino ... [et al.].
The stimulating effect of 1-alkyl-1-ethyl piperidinium bromides on the oxygen evolution rate in spinách chloroplasts was caused by rearrangement of thylakoid membrane.
Three extrinsic polypeptides and manganese cluster were sequentially released from the membrane when photosystem 2 (PS2) membranes were kept under high hydrostatic pressure. The 17 kDa polypeptide was the most sensitive, while the 33 kDa polypeptide was the most reluctant to the treatment with high pressure. The release of manganese was not simply correlated with the loss of 33 kDa polypeptide. The losing of oxygen-evolving activity of PS2 was synchronised with the releasing of extrinsic polypeptides and manganese. and Y. Yu ... [et al.].