Journal Article

Effects of Carbohydrate Accumulation on Photosynthesis Differ between Sink and Source Leaves of <i>Phaseolus vulgaris</i> L.

Takao Araya, Ko Noguchi and Ichiro Terashima

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 47, issue 5, pages 644-652
Published in print May 2006 | ISSN: 0032-0781
Published online May 2006 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcj033
Effects of Carbohydrate Accumulation on Photosynthesis Differ between Sink and Source Leaves of Phaseolus vulgaris L.

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Accumulation of non-structural carbohydrate in leaves represses photosynthesis. However, the extent of repression should be different between sink leaves (sugar consumers) and source leaves (sugar exporters). We investigated the effects of carbohydrate accumulation on photosynthesis in the primary leaves of bean (Phaseolus vulgaris L.) during leaf expansion. To increase the carbohydrate content of the leaves, we supplied 20 mM sucrose solution to the roots for 5 d (sugar treatment). Plants supplied only with water and nutrients were used as controls. The carbohydrate contents, which are the sum of glucose, sucrose and starch, of the sugar-treated leaves were 1.5–3 times of those of the control leaves at all developmental stages. In the young sink leaves, the photosynthetic rate at saturating light and at an ambient CO2 concentration (A360) did not differ between the sugar-treated and control leaves. The A360 of sugar-treated source leaves gradually decreased relative to the control source leaves with leaf expansion. The initial slope of the A–Ci (CO2 concentration in the intercellular space) curve, and the Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) content per leaf area showed trends similar to that of A360. Differences in Amax between the treatments were slightly smaller than those in A360. These results indicate that the effect of carbohydrate accumulation on photosynthesis is significant in the source leaves, but not in the young sink leaves, and that the decrease in Rubisco content was the main cause of the carbohydrate repression of photosynthesis.

Keywords: Bean (Phaseolus vulgaris L.); Carbohydrate repression of photosynthesis; Depletion of orthophosphate; Mesophyll conductance (gi); Rubisco; Sugar treatment; A360, photosynthetic rate at a PPFD of 1,000 µmol m–2 s–1 and CO2 concentration of 360 µmol mol–1; Amax, photosynthetic rate at a PPFD of 1,000 µmol m–2 s–1 and CO2 concentration of 1,500 µmol mol–1; Ca, ambient CO2 concentration; Ci, CO2 concentration in the intercellular space; Fv/Fm, maximum quantum yield of PSII; gi, CO2 conductance between the intercellular space and the catalytic site of Rubisco; LHCII, light-harvesting chlorophyll binding protein of PSII; LMA, leaf mass per area; LSU, large subunit of Rubisco; PPFD, photosynthetic photon flux density; Rubisco, ribulose-1,5-bisphosphate carboxylase/oxygenase; RuBP, ribulose-1,5-bisphosphate

Journal Article.  5950 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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