Inhibition of flower development in Chenopodium rubrum by a photosynthetic inhibitor

Cumming 1969 has demonstrated that the short-day plant Chenopodium rubrum (60°47′ N) is induced to flower if inductive darkness is substituted by a relatively long exposure to a low intensity light of a low red/far-red ratio (light emitted by BCJ lamps). DCMU (3(3,4-dichlorophenyl)-1,1-dimethyl urea), a photosynthetic inhibitor, inhibited flowering if applied during this inductive BCJ light period.Our experiments show that ascorbic acid and dichlorophenol-indophenol (which have been used as reducing agents in photosynthesis by various workers) overcome the effect of DCMU on flowering. Sugars are also effective in overcoming the DCMU effect. This indicates that DCMU acts specifically on photosynthesis and that there are no side effects.In Cumming's experiments DCMU was supplied at the start of a BCJ inductive period and then washed off at the end of the BCJ period. However, there are indications that DCMU may persist in the plant for several days after the medium on which plants are growing has been thoroughly washed off. This raises the question whether the action of DCMU is on induction in BCJ light or on subsequent development in white light. By applying DCMU during the BCJ period and terminating its effect by ascorbic acid + dichlorophenol-indophenol or sugars at the time of transferring to white light, no inhibition of flowering was found. This suggests that inhibition of photosynthesis during the inductive BCJ light had no detrimental effect on flowering. The inhibition of flowering by DCMU might be a result of inadequate photosynthesis in white light for development of floral primordia.