Adenine and Pyridine Nucleotide Status of Isolated Vicia Guard Cell Protoplasts During K^+-Induced Swelling

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The levels of ATP, ADP, and reduced and oxidized pyridine nucleotides were determined in guard cell protoplasts of Vicia faba during their swelling in 10 mM potassium iminodiacetate. Upon addition of K^+, the ATP/ADP ratio dropped from 9 to about 6 (0 to 1 min of incubation), followed by a steep increase up to 15 between 1 and 3 min. After 3 min, the protoplasts began to increase in diameter from about 15μm to nearly 17 μm after 5 min of incubation, accompanied by a rapid decrease of the ATP/ADP ratio to about 7. During this time, NAD and NADPH showed oppositely directed oscillations, while the pools of NADH and NADP stayed rather constant. As the sum of all pyridine nucleotides did not change, an interconversion of NAD and NADPH must have occurred during the swelling. The levels of glucose-6-P dehydrogenase activity, which were assayed under the same conditions, showed oscillations parallel to those of the ATP/ADP ratios and opposite to those of the NADPH/NAD ratios. The results are discussed with respect to the regulatory mechanisms during guard cell swelling.
日本植物生理学会の論文