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Plant Physiology 82:443-447 (1986)
© 1986 American Society of Plant Biologists

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Articles

Effects of KCN and Salicylhydroxamic Acid on Respiration of Soybean Leaves at Different Ages 1

Abu Sesay2, Cecil R. Stewart and Richard M. Shibles

Department of Agronomy, Iowa State University, Ames, Iowa 50011, Department of Botany, Iowa State University, Ames, Iowa 50011, Department of Plant Pathology, Seed and Weed Sciences, Iowa State University, Ames, Iowa 50011

Measurements of respiration were made on leaf discs from glasshouse-grown soybean (Glycine max [L.] Merr. cv `Corsoy') plants in the presence and absence of cyanide (KCN) and salicylhydroxamic acid (SHAM). O2 uptake by mature leaves measured at 25°C was stimulated by 1 millimolar KCN (63%) and also by 5 millimolar azide (79%). SHAM, an inhibitor of the alternative oxidase and a selection of other enzymes, also stimulated O2 uptake by itself at concentration of 10 millimolar. However, in combination, KCN and SHAM were inhibitory. The rate of O2 uptake declined consistently with leaf age. The stimulation of O2 uptake by KCN and by SHAM occurred only after a certain stage of leaf development had been reached and was more pronounced in fully expanded leaves. In young leaves, O2 uptake was inhibited by both KCN and SHAM individually. The uncoupler, p-trifluoromethoxy carbonylcyanide phenylhydrazone, stimulated leaf respiration at all ages studied, the stimulation being more pronounced in fully expanded leaves. The uncoupled rate was inhibited by KCN and SHAM individually. The capacity of the cytochrome path declined with leaf age, paralleling the decline in total respiration. However, the capacity of the alternative path peaked at about full leaf expansion, exceeding the cytochrome capacity and remaining relatively constant. These results are consistent with the presence in soybean leaves of an alternative path capacity that seems to increase with age, and they suggest that the stimulation of O2 uptake by KCN and NaN3 in mature leaves was mainly by the SHAM-sensitive alternative path. The stimulation of O2 uptake by SHAM was not expected, and the reason for it is not clear.

2 Permanent address: Department of Biological Sciences, Njala University College, University of Sierra Leone, P.M.B. Freetown, Sierra Leone, West Africa.

1 Journal Paper No. J12207 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Projects No. 2496 and 2682. Supported in part by United States Department of Agriculture Cooperative State Research Service Special Grant 59-2191-1-2-010-0 and by Pioneer Hybrid International.






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