Plant and Cell Physiology, 1990, Vol. 31, No. 2 179-185
© 1990
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Effect of Salicylhydroxamic Acid on Respiration, Photosynthesis, and Peroxidase Activity in Various Plant Tissues
1Department of Agronomy, Iowa State University Ames, IA 50011, U.S.A.
2Departments of Botany and of Plant Pathology, Iowa State University Ames, IA 50011, U.S.A.
5To whom correspondence should be sent.
Earlier reports from our laboratory described salicylhydroxamic acid (SHAM) stimulation of O2 uptake by expanded soybean leaves or older green cotyledons. This stimulation could not be interpreted in terms of engagement or capacity of the cytochrome and alternative respiratory pathways. In this report, we tested the possibility that a soluble peroxidase, which can be easily eluted from soybean leaves and cotyledons, might be responsible for SHAM stimulation in whole tissue. The peroxidase catalyzes oxidation of NADH by O2, is strongly stimulated by SHAM and benzhydroxamic acid (BHAM) and inhibited by KCN, propyl gallate and gentisic acid. This peroxidase, however, does not seem to be responsible for SHAM-stimulated O2 uptake in whole, green tissue.
In our earlier work reporting SHAM-stimulated respiration in green tissue, the samples had not been shielded from room light (10–20 µmol photons m–2.s–1). In this report, we show that O2-uptake rates of controls measured in darkness were always greater than those measured in room light. SHAM stimulation was not observed in the dark or in tissue without chlorophyll. We also found that CO2 uptake of whole leaflets in saturating light was completely inhibited by SHAM fed through the transpiration stream. SHAM, therefore, is a potent inhibitor of photosynthesis. We conclude that the SHAM-stimulated respiration of green tissues we reported earlier likely was due to very low rates of photosynthesis occurring under room light.
3Present address: SANDOZ Ltd., Agrobiological Research Station, 4108 Witterswil, Switzerland
4Present address: WTC 1A3, Weyerhaeuser Co., Tacoma, WA 98477, U.S.A.
(Received June 23, 1989; Accepted October 20, 1989)
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