Endogenous light-on rhythm in respiration of a long-day duckweed, Lemna gibba G3 II. On basic and rhythmic components of the rhythm

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Effects of respiratory substrates (glucose, malate, citrate and pyruvate) and inhibitors (fluoride, iodoacetate, azide and DNP) on the O_2-uptake rhythm in a long-day duckweed, Lemna gibba G3 in continuous light period were examined. Rates of O_2-uptake at the starting point (6 hr after the beginning of a continuous light period) and at the time of the first peak of the rhythm (18 hr after the beginning of a continuous light period) were equally increased by exogenous substrates. Sensitivity of respiration to fluoride or iodoacetate was almost the same at the 6th and 18th hr. The O_2-uptake (at the 6th, 18th, 30th and 42nd hr) was increased by DNP by the same amount. Azide at lower concentrations than 5×10^<-4> M did not affect O_2-uptake at the 6th hr, but inhibited uptake at the 18th hr. In the presence of 5×10^<-4> M of azide the rates of O_2-uptake at the 18th, 30th or 42nd hr were down to the rate at the 6th hr, which was insensitive to azide. These results suggest that the O_2-uptake rhythm consists of two components, i.e. the basic respiration which is promoted by exogenous substrate, sensitive to DNP and insensitive to azide; and rhythmic respiration, which is sensitive to azide, but is not influenced by exogenous substrate and DNP.
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