Effects of Respiratory Inhibitors on Red Light and Lumiflavin Induced Betacyanin Formation in Amaranthus caudatus L. Seedlings

Abstract

Summary The effects of respiratory inhibitors were monitored in red light- and lumiflavin-induced betacyanin formation, using etiolated, three-day-old Amaranthus caudatus L. seedlings, derooted and decoated under green safelight. The responses to red light (5 min to 4 h) and to a cytokinin (50 nM 6-benzylaminopurine) were resistant to 1 mM KCN, while the promoting effect of lumiflavin (4 ¼M) was sensitive to 0.1 and 1 mM cyanide. Safelight control and betacyanin induction by 5 min far-red light were only partly reduced in 1 mM cyanide, which dramatically increased the far-red reversibility of red light action. These effects of cyanide, which were also observed in 0.01 mM NaN3, were apparently cancelled by 4 ¼M lumiflavin. In contrast to cyanide, 0.1 mM SHAM decreased the far-red reversibility of the red light-mediated response, while the same compound at 2 mM concentration severely suppressed the net inductive effect of prolonged red and, to a lesser extent, brief far-red light. The effects of respiratory inhibitors and lumiflavin on the rate of oxygen uptake in darkness and during 4 h illumination with red light were different in comparison to betacyanin photoregulation, but some similarity was observed during the postillumination period of 30 min darkness. These results suggest that a metabolic pattern involved in betacyanin photoregulation is restricted to a limited cell fraction in the seedlings. The relevance of such metabolic pattern for the mechanism of phytochrome action is discussed.