Studies on the limitations to photosynthesis in leaves of the atrazine-resistant mutant ofSenecio vulgaris L. |
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Authors: | C. R. Ireland A. Telfer P. S. Covello N. R. Baker J. Barber |
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Affiliation: | (1) Department of Biology, University of Essex, CO4 3SQ Colchester, Essex, UK;(2) AFRC Photosynthesis Research Group, Department of Pure and Applied Biology, Imperial College of Science and Technology, Price Consort Road, SW7 2BB London, UK |
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Abstract: | In leaves of an atrazine-resistant mutant ofSenecio vulgaris the quantum efficiency of CO2 assimilation was reduced by 21% compared to the atrazine-susceptible wild type, and at a light level twice that required to saturate photosynthesis in the wild type the CO2 fixation rate in the mutant was decreased by 15%. In leaves at steady-state photosynthesis there was a measurable increase in the reduction state of the photosystem II (PSII) primary quinone acceptor,QA. Although this would lead to a decreased rate of PSII electron transport and may thus explain the decrease in quantum efficiency, this cannot account for the fall in the maximum rate of CO2 fixation. The atrazine-resistant mutant showed an appreciably longer photosynthetic induction time which indicates an effect on carbon metabolism; however, the response of CO2-fixation rate to intercellular CO2 concentration revealed no differences in carboxylation efficiency. There were also no differences in the ability to perform a State 1–State 2 transition between the atrazine-resistant and susceptible biotypes and no difference in the profiles of phosphorylated thylakoid polypeptides. It is concluded that the alteration of the redox equilibrium between PSII quinone electron acceptors in the atrazine-resistant biotype limits appreciably the photosynthetic efficiency in non-saturating light. Additionally, there is a further, as yet unidentified, limitation which decreases photosynthesis in the resistant mutant under light-saturating conditions.Abbreviations and symbols DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - Fmax maximum fluorescence emission - Fo2 minimal fluorescence emission upon exposure to saturating light flash - Fv variable fluorescence emission - Fv2 variable fluorescence emission upon exposure to saturating light flash - kDa kilodalton - PSI, II photosystems I, II - QA primary quinone acceptor of PSH - QB secondary quinone acceptor of PSII - RuBP ribulose-1,5-bisphosphate |
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Keywords: | Atrazine Carbon assimilation Chlorophyll fluorescence Herbicide resistance Mutant (atrazine resistant) Photosynthesis in atrazine resistant mutant Senecio (atrazine, mutant) |
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