Characterization of the alternative respiratory pathway in soybean
The alternative respiratory pathway may be important in the energy economy of higher plants. The objective of this study was to characterize the alternative pathway in soybean and to gain a better understanding of the importance of this respiratory pathway to soybean productivity;Capacity for the alternative pathway was assessed in leaf and root tissue of male-sterile and fertile soybean plants and in leaf, embryonic axis and epicotyl tissue, as well as isolated mitochondria, of pea (Pisum sativum L.) by measurement of oxygen uptake in the presence and absence of KCN and salicylhydroxamic acid (SHAM). Male-sterile and fertile soybean tissues showed similar responses to the inhibitors and both possessed a capacity for alternative respiration. Tissues and isolated mitochondria from 'Progress No. 9' pea, contrary to published information, possessed alternative respiratory pathway capacity similar to that of 'Alaska' pea;The effects of the respiratory inhibitors, KCN and SHAM, on dark CO[subscript]2 evolution in soybean leaves were examined to test the hypothesis that KCN stimulation of O[subscript]2 uptake in this tissue is due to decontrol of glycolysis, caused by a diversion of electrons into the alternative pathway. Both KCN and SHAM, when used individually, caused a 30% increase in CO[subscript]2 evolution. When both inhibitors were present together, the resulting rate was approximately equal to the control. Due to the unexpected stimulatory effect of SHAM on CO[subscript]2 evolution, conclusions about the cause of KCN stimulation of O[subscript]2 uptake in this tissue could not be drawn;In soybean axis tissue and cotyledons 3 to 9 days of age, increasing amount of alternative oxidase, as determined by immunoblots probed with alternative oxidase antibodies, corresponded with the increasing alternative pathway capacity of isolated mitochondria from these tissues. In older cotyledons, however, little or no change in amount of alternative oxidase occurred even though there were substantial changes in capacity. This suggests that, whereas alternative oxidase content is likely to be important in determining the capacity of the alternative pathway in axis tissue and young cotyledons, other factors regulate the capacity in older cotyledons.