PubMed · 6316396
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P Gabriele. 1983. The Keyes technique.. https://pubmed.ncbi.nlm.nih.gov/6316396/
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Effect of paraquat (methylviologen) was investigated on photosynthetic electron transport activity of a submerged aquatic angiosperm Hydrilla verticillata following polarographic and fluorimetric techniques. The plant showed resistance for electron acceptance by paraquat both in isolated chloroplasts and in intact leaves. The in vitro (isolated chloroplasts) and in vivo (intact leaf) electron transport analysis indicated that the failure of paraquat to intercept electrons from photosynthetic electron transport chain is for the existence of some rate limiting steps at the acceptor side of photosystem I complex. Hydrilla verticillata, as reported here for the first time, is a true paraquat resistant bio-type where the resistance for the herbicide paraquat can be observed both in isolated chloroplasts and also in intact leaf.
Salvage and de novo purine and pyrimidine nucleotide syntheses were studied in H9 (a human lymphoid cell line) and H9-AZT cells (chronically zidovudine-exposed H9 cells). H9-AZT cells incorporated 18% and 27% more hypoxanthine and uridine, respectively, than H9 cells. The incorporation of the formate and bicarbonate was similar in both cell lines. Purine and pyrimidine de novo synthesis was inhibited by hypoxanthine and uridine, respectively. Hypoxanthine and uridine salvage pathways, however, were not affected by formate or bicarbonate. Short-term AZT exposure of cells had no effect on nucleotide synthesis. Some of the problems encountered in the studies of purine and pyrimidine synthesis are also discussed.
Suppression of electron flow (and its subsequent restoration with 3-10 mM NaHCO3) on the donor side of photosystem II is shown upon either a partial depletion of pea subchloroplast membranes in bicarbonate or the addition of 5-20 microM formate. At higher concentrations (5 mM) formate induces the known 'bicarbonate effect' on the acceptor side of photosystem II. In preparations depleted of manganese the restoration of electron flow with 0.1-0.2 microM MnCl2 (2-4 Mn per photosystem II reaction center) occurs only in the presence of bicarbonate and it is accompanied by an increased functional binding of manganese. Restoration of electron flow with diphenylcarbazide or NH2OH does not require the addition of NaHCO3. It is suggested that bicarbonate participates in the formation of the Mn-cluster capable of water oxidation or serves as a substrate for the water-oxidizing center.