Profile of Basic Carbon Pathways in Guard Cells and Other Leaf Cells of Vicia faba L.

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Abstract
Guard cells and three other cell types from Vicia faba L. `Longpod' leaflets were assayed for enzymes that catalyze one step in each of five major carbon pathways in green plants: the photosynthetic carbon reduction pathway (ribulose-bisphosphate carboxylase, EC 4.1.1.39), the photosynthetic carbon oxidation pathway (hydroxypyruvate reductase, EC 1.1.1.81), glycolysis ([NAD] glyceraldehyde-P dehydrogenase, EC 1.2.1.12), the oxidative pentose-P pathway (6-P-gluconate dehydrogenase, EC 1.1.1.44), and the tricarboxylic acid pathway (fumarase, EC 4.2.1.2). Neither ribulose-bisphosphate carboxylase nor hydroxypyruvate reductase could be detected in guard cells or epidermal cells; high levels of these activities were present in mesophyll cells. The specific activity of fumarase (protein basis) was about 4-fold higher in guard cells than in epidermal, palisade parenchyma or spongy parenchyma cells. (NAD) glyceraldehyde-P and 6-P-gluconate dehydrogenases also were present at high protein specific activities in guard cells (2- to 4-fold that in meosphyll cells).
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