Metabolites released by illuminated stomatal chloroplasts originated predominantly from starch breakdown

Vicia faba – Manual of the Alien Plants of Belgium

Metabolite export of isolated guard cell chloroplasts of Vicia faba

by Ritte G., Raschke K. (2003)

Gerhard Ritte, Klaus Raschke,

University of Göttingen, Germany


In New Phytologist 159: 195–202 – –


  • •Stomatal opening is caused by guard cell swelling due to an accumulation of osmotica. We investigated the release of carbon from guard cell chloroplasts as a source for the production of organic osmotica.
  • •Photosynthetically active chloroplasts were isolated from guard cell protoplasts of Vicia faba. Export of metabolites into the surrounding medium was analyzed by silicone oil filtering centrifugation and spectrophotometrically by coupled metabolite assays. Effects of external oxaloacetate and 3‐phosphoglycerate on photosynthetic electron transport were examined by recording chlorophyll fluorescence.
  • •In the light, guard cell chloroplasts exported triose phosphates, glucose, maltose and hexose phosphates. The presence of phosphate in the medium was essential for the release of phosphorylated compounds and also strongly enhanced the export of glucose and maltose. Total efflux of carbon from illuminated guard cell chloroplasts was on average 486 µatom C (mg Chl)−1 h−1, which was significant with respect to the carbon requirement for stomatal opening.
  • •Metabolites released by illuminated guard cell chloroplasts originated predominantly from starch breakdown. Photosynthetic electron transport provided redox power for the reduction of oxaloacetate and 3‐phosphoglycerate.

Published by

Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.

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