Rubisco activity in guard cells compared with the solute requirement for stomatal opening. [Pisum sativum]

Journal Article · Mon Jan 01 04:00:00 EST 1990 · Plant Physiology; (USA)

DOI:https://doi.org/10.1104/pp.92.1.246· OSTI ID:6867810

Reckmann, U; Scheibe, R; Raschke, K ^[1]

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1. Universitaet Goettingen (Germany, F.R.)

We investigated whether the reductive pentose phosphate path in guard cells of Pisum sativum had the capacity to contribute significantly to the production of osmotica during stomatal opening in the light. Amounts of ribulose 1,5-bisphophate carboxylase/oxygenase (Rubisco) were determined by the ({sup 14}C) carboxyarabinitol bisphosphate assay. A guard cell contained about 1.2 and a mesophyll cell about 324 picograms of the enzyme; the ratio was 1:270. The specific activities of Rubisco in guard cells and in mesophyll cells were equal; there was no indication of a specific inhibitor of Rubisco in guard cells. Rubisco activity was 115 femtomol per guard-cell protoplast and hour. This value was different from zero with a probability of 0.99. After exposure of guard-cell protoplasts to {sup 14}CO{sub 2} for 2 seconds in the light, about one-half of the radioactivity was in phosphorylated compounds and <10% in malate. Guard cells in epidermal strips produced a different labelling pattern; in the light, <10% of the label was in phosphorylated compounds and about 60% in malate. The rate of solute accumulation in intact guard cells was estimated to have been 900 femto-osmol per cell and hour. If Rubisco operated at full capacity in guard cells, and hexoses were produced as osmotica, solutes could be supplied at a rate of 19femto-osmol per cell and hour, which would constitute 2% of the estimated requirement. The capacity of guard-cell Rubisco to meet the solute requirement for stomatal opening in leaves of Pisum sativum is insignificant.

• OSTI ID: 6867810
• Journal Information: Plant Physiology; (USA), Journal Name: Plant Physiology; (USA) Vol. 92:1; ISSN 0032-0889; ISSN PLPHA
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES
BIOLOGICAL PATHWAYS
CARBON 14 COMPOUNDS
CARBON COMPOUNDS
CARBON DIOXIDE
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CARBON-CARBON LYASES
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ENZYME ACTIVITY
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OPENINGS
OXIDES
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PLANT CELLS
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RIBULOSE DIPHOSPHATE CARBOXYLASE
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TRACER TECHNIQUES