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R Popovic

Publications and source records attributed to R Popovic.

40 records · Page 3Linked to original sources
PubMed1983

Evolution of o(2) in brown algal chloroplasts.

A METHOD IS DESCRIBED FOR THE ISOLATION OF PHOTOSYNTHETICALLY ACTIVE CHLOROPLASTS FROM FOUR SPECIES OF BROWN ALGAE: Fucus vesiculosis, Nereocystis luetkeana, Laminaria saccharina, and Macrocystis integrifolia. When compared to lettuce and spinach chloroplasts, the algal chloroplasts all showed lower activities for both photosystems II and I. Chloroplasts from all the plants produced H(2)O(2), with photosystem I functioning as the O(2) reductant in the light. In contrast to the green plants, however, brown algal chloroplasts strongly reduced O(2) under conditions where both photosystems II and I remain active. Relative variable fluorescence values were lower both in intact plants and chloroplasts of the brown algae than for either spinach or lettuce. It is suggested that although light harvesting activities appear similar in all the plants, details of electron transport in brown algae may differ from those of green plants.

Journal Article↗
PubMedDate not supplied

Electron donation to photosystem II by diphenylcarbazide is inhibited both by the endogenous manganese complex and by exogenous manganese ions.

Diphenylcarbazide (DPC) is an efficient electron donor to the inactive oxygen-evolving complex of photosystem II (PSII). We investigated the role of manganese on the rate of electron donation from DPC to PSII in both Mn-depleted (Tris washed) and Mn-retaining (NaCl washed) PSII preparations. The rate of electron donation from DPC to PSII was significantly higher in Mn-depleted than in Mn-retaining preparations, indicating a negative role of native Mn complex on DPC electron donation. The apparent Km values for DPC were found to be 0.11 and 0.17 mM for Mn-depleted and Mn-retaining PSII preparations, respectively. This difference in the Km values also indicates an antagonistic effect of endogenous Mn cluster on electron donation from DPC, which was markedly inhibited by exogenous Mn2+. However, the magnitude of inhibition was greater in Mn-depleted than in Mn-retaining PSII preparations. This indicates a higher accessibility to DPC to PSII in the absence of native Mn complex. Our results suggest (i) that Mn, either endogenous or added, acts as an accessibility barrier for DPC to donate electrons to PSII and (ii) that the native Mn complex not only functions as an accumulator of oxidizing equivalents but may also protect PSII from exogenous reductants.

Diphenylcarbazide↗
PubMedDate not supplied

Rapid chlorophyll a fluorescence transients of Lemna minor leaves as indication of light and exogenous electron carriers effect on photosystem II activity.

By using saturating flash, we investigated the change in the rapid fluorescence rise when Lemna minor leaf was exposed to different light conditions and treated with exogenous electron acceptors (methyl viologen and duroquinone) and electron donor (hydroxylamine). Investigation was carried out by using combined pulse amplitude modulated fluorometer and plant efficiency analyzer system, which were employed simultaneously to provide different light conditions and to induce rapid fluorescence rise respectively. We have shown that when leaf of L. minor was exposed to different conditions of illumination, rapid fluorescence rise was greatly influenced by the electron transport functions beyond quinone A-plastoquinone reduction. This was indicated by the change in both fluorescence yield and appearance time of the different transients. When exogenous electron donor (hydroxylamine) and acceptors (methyl viologen and duroquinone) were applied in in vivo condition, we showed that rapid fluorescence rise represented a reliable indicator of PSII-PSI electron transport state and energy dissipation process.

Chlorophyll↗