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Effect of Salicylhydroxamic Acid on Respiration, Photosynthesis, and Peroxidase Activity in Various Plant Tissues
Authors:Diethelm  R; Miller  M G; Shibles  R; Stewart  C R
Institution: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.
Abstract:Earlier reports from our laboratory described salicylhydroxamicacid (SHAM) stimulation of O2 uptake by expanded soybean leavesor older green cotyledons. This stimulation could not be interpretedin terms of engagement or capacity of the cytochrome and alternativerespiratory pathways. In this report, we tested the possibilitythat a soluble peroxidase, which can be easily eluted from soybeanleaves and cotyledons, might be responsible for SHAM stimulationin whole tissue. The peroxidase catalyzes oxidation of NADHby 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 forSHAM-stimulated O2 uptake in whole, green tissue. In our earlier work reporting SHAM-stimulated respiration ingreen tissue, the samples had not been shielded from room light(10–20 µmol photons m–2.s–1). In thisreport, we show that O2-uptake rates of controls measured indarkness were always greater than those measured in room light.SHAM stimulation was not observed in the dark or in tissue withoutchlorophyll. We also found that CO2 uptake of whole leafletsin saturating light was completely inhibited by SHAM fed throughthe transpiration stream. SHAM, therefore, is a potent inhibitorof photosynthesis. We conclude that the SHAM-stimulated respirationof green tissues we reported earlier likely was due to verylow 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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