Browsing by Author "Bligny, Richard"
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- Effects of a sub-lethal copper exposure on non-green Acer pseudoplatanus cell lipidsPublication . Pádua, Mário; Aubert, Serge; Casimiro, Adalcina; Bligny, Richard; Block, Maryse ANon-green sycamore cells (Acer pseudoplatanus L.) treated with 50 μM Cu2+ showed a reversible arrest of cell growth after 5 d, indicating that the concentration used was sub-lethal for the cells. Growth arrest was accompanied by hexose and nucleotide-phosphate accumulation and, in contrast with previous reports, no polar-lipid degradation was found. Sub-lethal Cu2+ exposure resulted in an increase in phospholipid amounts, mostly due to an increase of phosphatidylethanolamine. Although the total amount of glycolipids was not significantly changed, Cu2+ exposure changed the relative concentrations of monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) and sulphoquinovosyldiacylglycerol (SQDG). There was a marked increase of DGDG whereas MGDG and SQDG declined. Our results suggest an increase of DGDG synthesis through a pathway similar to the recently described DGD2 pathway and an inhibition of SQDG synthesis. Furthermore, we observed modifications of the fatty acid composition of the plastid synthesized lipids. A significant increase in linoleate (18:2) and a decrease in linolenate (18:3) were found in MGDG, DGDG, SQDG and phosphatidylglycerol (PG), reflecting a deficient desaturation of plastid-located 18:2 fatty acids. In SQDG and PG, Cu2+ treatment also induced a strong enrichment of palmitate (16:0). The effects of Cu2+ on DGDG synthesis and fatty acid desaturation are discussed.
- Effects of copper on the photosynthesis of intact chloroplasts: interaction with manganesePublication . Pádua, Mário; Cavaco, Ana M.; Aubert, Serge; Bligny, Richard; Casimiro, AdalcinaHighly purified, intact chloroplasts were prepared from pea (Pisum sativum L.) and spinach (Spinacia oleracea L.) following an identical procedure, and were used to investigate the cupric cation inhibition on the photosynthetic activity. In both species, copper inhibition showed a similar inhibitor concentration that decreases the enzyme activity by 50% (IC(50) approximately 1.8 microM) and did not depend on the internal or external phosphate (Pi) concentration, indicating that copper did not interact with the Pi translocator. Fluorescence analysis suggested that the presence of copper did not facilitate photoinhibition, because there were no changes in maximal fluorescence (F(m)) nor in basal fluorescence (F(o)) of copper-treated samples. The electron transport through the photosystem II (PSII) was also not affected (operating efficiency of PSII-F'v/F'm similar in all conditions). Yet, under Cu(2+) stress, the proportion of open PSII reaction centers was dramatically decreased, and the first quinone acceptor (Q(A)) reoxidation was fully inhibited, as demonstrated by the constant photochemical quenching (q(P)) along experiment time. The quantum yield of PSII electron transport (Phi(PSII)) was also clearly affected by copper, and therefore reduced the photochemistry efficiency. Manganese, when added simultaneously with copper, delayed the inhibition, as measured by oxygen evolution and chlorophyll fluorescence, but neither reversed the copper effect when added to copper-inhibited plastids, nor prevented the inhibition of the Hill activity of isolated copper-treated thylakoids. Our results suggest that manganese competed with copper to penetrate the chloroplast envelope. This competition seems to be specific because other divalent cations e.g. magnesium and calcium, did not interfere with the copper action in intact chloroplasts. All results do suggest that, under these conditions, the stroma proteins, such as the Calvin-Benson cycle enzymes or others are the most probable first target for the Cu(2+) action, resulting in the total inhibition of chloroplast photosynthesis and in the consequent unbalanced rate of production and consumption of the reducing power.