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Photosynthetic Depression in Beans After Exposure to Cold for One Night¹

Phaseolus vulgaris L. plants exposed to 5 C for a single night exhibited severe reductions in photosynthesis the following day. However, the response was manifest only if the roots as well as the shoots were cooled. Photosynthetic reductions were accompanied by a parallel drop in transpiration, a rise in stomatal and mesophyll resistance to CO₂ uptake, and a decrease in leaf water potential. Activities of ribulose diphosphate carboxylase and malate dehydrogenase were unaffected. Starch retention within chloroplasts of cold-treated leaves accompanied a drop in photosynthesis, but the presence of starch did not reduce photosynthesis. The data suggest that rather than feedback inhibition, the photosynthetic reduction of potted bean plants following an exposure to cold is due to stomatal resistance brought on by temporary water stress.

Key Words: Leaf resistance • Water stress • Photosynthate accumulation • Enzyme activity

² Research Associate, Graduate Research Assistant, Research Technician, and Professors, Vegetable Crops Department, Cornell University, Ithaca, NY 14850.

Received for publication November 12, 1973.