Foliar CO2photoassimilation and chloroplast linear electron transport rates in nitrogen-sufficient and nitrogen-limited soybean plants |
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Authors: | Robinson J Michael Burkey Kent O |
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Abstract: | Leaflets of soybean plants which are moderately inorganic nitrogen (N)-limited exhibit either no difference in the rate of net photosynthesis or as much as a 15–23% lower net photosynthesis rate per unit area than leaflets of N-sufficient plants Robinson JM (1996) Photosynth Res 50: 133–148; Robinson JM (1997a) Int J Plant Sci 158: 32–43]. However, mature leaflets of N-limited soybean plants have a higher CO2photoassimilation rate per unit chlorophyll than leaflets of N-sufficient soybean plants at both moderate light intensity ( 500 µmol m-2s-1) and saturating light intensity ( 1200 µmol m-2s-1) Robinson JM (1996) Photosynth Res 50: 133–148]. This study was undertaken to determine whether chloroplast thylakoids isolated from the leaflets of nitrogen-limited soybean plants displayed similar or higher linear electron transport rates (H2O ferredoxin NADP) per unit chlorophyll than thylakoids isolated from leaflets of N-sufficient plants. Chlorophyll concentration in reaction mixtures containing chloroplast thylakoids prepared from leaflets of N-limited plants was manipulated so that it was similar to the chlorophyll concentration in reaction mixtures of thylakoids prepared from leaflets of N-sufficient plants. Measurements of ferredoxin dependent, NADP dependent, O2photo-evolution in thylakoid isolates were carried out in saturating light ( 1500 µmol m-2s-1) and with
(an uncoupler) in the chloroplast reaction mixtures. Chloroplast thylakoids isolated from N-limited soybean plant leaflets routinely had a 1.5 to 1.7 times higher rate of uncoupled, whole chain electron transport per unit chlorophyll in saturating light than did chloroplast thylakoids isolated from leaflets of N-sufficient plants. The results suggest that the photosystems and photosynthetic electron transport chain components are more active per unit Chl in leaflet chloroplast thylakoids of N-limited soybean plants than in thylakoids of N-sufficient plants. |
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Keywords: | ferredoxin NADP photoreduction nitrogen limitation non cyclic electron transport photosynthesis Photosystem 1 and 2 |
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