Effects of Ca2+/Mg2+ chelators, SKF 525‐A and rotenone on phytochrome‐mediated betacyanin formation in Amaranthus seedlings

Abstract

The effects of EDTA, EGTA, SKF 525‐A (a selective inhibitor of cytochrome P‐450) and rotenone were studied in betacyanin induction by 6 h red and 5 min far‐red light, using etiolated, three‐day‐old Amaranthus caudatus L. half‐seedlings. With 0.1 mM EDTA, EGTA and rotenone, and with 10 μM SKF 525‐A, mainly the far‐red reversible betacyanin induction by red light was suppressed. Only in 0.1 mM rotenone was about 50% of that effect compensated by an increased far‐red irreversible betacyanin induction. An unspecific inhibition was obtained with 0.1 mM SKF 525‐A in both control and illuminated plants.These results are consistent with the view that red light, but not far‐red, causes Ca2+ efflux from both mitochondria and cytoplasm, whereas Ca2+ uptake is indicated mainly after illumination. The resulting switch in the coupling of the mitochondrial electron transport to a Ca2+ dependent one in cytochrome P‐450 system via respiratory complex 1, appears to be responsible for the far‐red reversibility. However, the bulk of the high irradiance reaction seems to be related to another secondary messenger, alternative to Ca2+.