Endogenous light-on rhythm in respiration of a long-day duckweed,Lemna gibbaG3 II. On basic and rhythmic components of the rhythm

摘要

Effects of respiratory substrates (glucose, malate, citrate and pyruvate) and inhibitors (fluoride, iodoacetate, azide and DNP) on the O2-uptake rhythm in a long-day duckweed,Lemna gibbaG3 in continuous light period were examined.Rates of O2-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 O2-uptake (at the 6th, 18th, 30th and 42nd hr) was increased by DNP by the same amount. Azide at lower concentrations than 5X10−4M did not affect O2-uptake at the 6th hr, but inhibited uptake at the 18th hr. In the presence of 5 X 10−4M of azide the rates of O2-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 O2-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