Ribulose-1,5-bisphosphate carboxylase-oxygenase,other Calvin-cycle enzymes,and chlorophyll decrease when glucose is supplied to mature spinach leaves via the transpiration stream |
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Authors: | Anne Krapp W Paul Quick Mark Stitt |
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Institution: | (1) Lehrstuhl für Pflanzenphysiologie, Universität Bayreuth, W-8580 Bayreuth, Germany;(2) Present address: Department of Molecular Biology and Biotechnology, University of Sheffield, UK;(3) Present address: Botanisches Institut, Im Neuenheimerfeld 360, W-6900 Heidelberg, Germany |
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Abstract: | The inhibition of photosynthesis after supplying glucose to detached leaves of spinach (Spinacia oleracea L.) was used as a model system to search for mechanisms which potentially contribute to the sink regulation of photosynthesis. Detached leaves were supplied with 50 mM glucose or water for 7 d through the transpiration stream, holding the leaves in low irradiance (16 mol photons · m–2 · s–1) and a cycle of 9 h light/15 h darkness to prevent any endogenous accumulation of carbohydrate. Leaves supplied with water only showed marginal changes of photosynthesis, respiration, enzyme levels or metabolites. When leaves were supplied with 50 mM glucose, photosynthesis was gradually inhibited over several days. The inhibition was most marked when photosynthesis was measured in saturating irradiance and ambient CO2, less marked in saturating irradiance and saturating CO2, and least marked in limiting irradiance. There was a gradual loss of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) protein, fructose-1,6-bisphosphatase, NADP-glyceraldehyde-3-phosphate dehydrogenase and chlorophyll. The inhibition of photosynthesis was accompanied by a large decrease of glycerate-3-phosphate, an increase of triose-phosphates and fructose-1,6-bisphospate, and a small decrease of ribulose-1,5-bisphosphate. The stromal NADPH/NADP ratio increased (as indicated by increased activation of NADP-malate dehydrogenase), and the ATP/ADP ratio increased. Chlorophyll-fluorescence analysis indicated that thylakoid energisation was increased, and that the acceptor side of photosystem II was more reduced. Similar results were obtained when glucose was supplied by floating leaf discs in low irradiance on glucose solution, and when detached spinach leaves were held in high light to produce an endogenous accumulation of carbohydrate. Feeding glucose also led to an increased rate of respiration. This was not accompanied by any changes of pyruvate kinase, phosphofructokinase, or pyrophosphate: fructose-6-phosphate phosphotransferase activity. There was a decrease of phosphoenolpyruvate, glycerate-3-phosphate and glycerate-2-phosphate, an increase of pyruvate and triose-phosphates, and an increased ATP/ADP ratio. These results show (i) that accumulation of carbohydrate can inhibit photosynthesis via a long-term mechanism involving a decrease of Rubisco and other Calvin-cycle enzymes and (ii) that respiration is stimulated due to an unknown mechanism, which increases the utilisation of phosphoenolpyruvate.Abbreviations and Symbols Ci
CO2 concentration in the air space within the leaf
- Fm
fluorescence yield with a saturating pulse in dark-adapted material
- Fo
ground level of fluorescence using a weak non-actinic modulated beam in the dark
- Fru1,6bisP
fructose-1,6-bisphosphate
- Fru1,6Pase
fructose-1,6-bisphosphatase
- Fru2,6bisP
fructose-2,6-bisphosphate
- IRGA
infrared gas analyser
- NAD-MDH
NAD-dependent malate dehydrogenase
- NADP-MDH
NADP-dependent malate dehydrogenase
- NADP-GAPDH
NADP-dependent glyceraldehyde-3-phosphate dehydrogenase
- PEP
phosphoenolpyruvate
- PFK
phospho-fructokinase
- PFP
pyrophospate: fructose-6-phosphate-phosphotransferase
- 3-PGA
glycerate-3-phospate
- Pi
inorganic phosphate
- Ru1,5bisP
ribulose 1,5-bisphosphate
- Rubisco
ribulose-1,5-bisphosphate carboxylase-oxygenase
- triose-phosphates
sum of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate
This research was supported by the Deutsche Forschungsgemeinschaft (SFB 137). |
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Keywords: | Glucose Photosynthesis (sink regulation) Ribulose-1 5-bisphosphate carboxylase-oxygenase Sink regulation Spinacia (photosynthesis) |
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