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

Effects of respiratory substrates (glucose, malate, citrateand pyruvate) and inhibitors (fluoride, iodoacetate, azide andDNP) 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 beginningof a continuous light period) and at the time of the first peakof the rhythm (18 hr after the beginning of a continuous lightperiod) were equally increased by exogenous substrates. Sensitivityof respiration to fluoride or iodoacetate was almost the sameat the 6th and 18th hr. The O₂-uptake (at the 6th, 18th, 30thand 42nd hr) was increased by DNP by the same amount. Azideat lower concentrations than 5X10^–4 M did not affect O₂-uptakeat the 6th hr, but inhibited uptake at the 18th hr. In the presenceof 5 X 10^–4 M of azide the rates of O₂-uptake at the 18th,30th or 42nd hr were down to the rate at the 6th hr, which wasinsensitive to azide. These results suggest that the O₂-uptakerhythm consists of two components, i.e. the basic respirationwhich is promoted by exogenous substrate, sensitive to DNP andinsensitive to azide; and rhythmic respiration, which is sensitiveto azide, but is not influenced by exogenous substrate and DNP. (Received February 19, 1971; )     

Endogenous light-on rhythm in respiration of a long-day duckweed, Lemna gibba G3 III. Relationship to frond production

Relationship between the C>2-uptake rhythm and frond productionin a long-day duckweed, Lemna gibba G3, was investigated. The rate of frond production and the amplitude of the rhythmwere dependent on light intensity. Photosynthetic inhibitors,CMU and DCMU, at concentrations effective in stopping frondproduction, abolished the O₂-uptake rhythm after a lag of 1day. In the presence of inhibitors of protein and RNA syntheses,ETH, CH and TU, at concentrations which brought about completeinhibition of frond production, the O₂-uptake rhythm disappeared.FUdR, an inhibitor of DNA synthesis, did not eliminate the rhythmalthough it suppressed frond production. This indicates a ratherindirect correlation between the rhythm and the rate of frondproduction which, in turn, is probably related to photosynthesis.The rhythm may be more directly correlated with the cell expansion. (Received July 27, 1971; )