Ecophysiology of energy budget of higher plant respiration with special reference to involvement of the cyanide-resistant pathway

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Mitochondria in higher plants possess the alternative pathway in addition to cytochrome pathway. Because the alternative pathway does not translocate proton, engagement of the alternative pathway decreases the ATP/O_2 ratio. Thus, estimation of engagement of the alternative pathway is important to understand energy budget of the plants. We have already constructed a system that separately determines the rate of electron flow through these two pathways. The purpose of this study is to conduct ecophysiological studies using this system. Four main results are as follows.1. Differences in respiratory regulation mechanisms between sun and shade plants were clarified. Although there is potential activity of the alternative pathway, it is little used.2. ATP production rate in the leaf is estimated based on the rates of electron flow in the two pathways. We also estimated how ATP is used.3. Nitrogen nutrition stress was shown to enhance the engagement of the alternative pathway.4. Effects of growth temperature on root respiration rate were studied for four Allium species. Root respiration rate were well correlated with nitrogen uptake rate.