Destruction and possible de novo synthesis of phytochrome in subcellular fractions of laminae from Avena sativa L.

Phytochrome was determined in etiolated laminae of Avena sativaL. either without pretreatment or after 5 min of red irradiation followed by different periods of darkness (0-24 h). At given intervals laminae were homogenized and phytochrome was determined spectrophotometrically in the total homogenate and in purified etioplasts and mitochondria. Enhanced specific activity of phytochrome was found in all fractions after the irradiation in comparison to dark controls. Phytochrome destruction was observed in all fractions at the beginning of the subsequent dark period. Whereas the homogenate and the mitochondrial fraction showed a continuous destruction so that phytochrome reached a level far below that in etiolated plants, the phytochrome level in the plastid fraction reacheda minimum at 2 h with a subsequent increase beyond the dark level. This increase was most pronounced between 4 and 8 h after the red irradiation. The results are discussed in terms of the destruction and possible de novo synthesis of phytochrome that may be different in mitochondria and plastids.