When totally etiolated pea epicotyls were cut into segments and incubated with potassium phosphate buffer, pH 6.0, in the dark at 25 C, an instantaneous loss of photoreversible absorbance change, Δ (ΔA) between 660 and 730 nm, was observed after the first irradiation with actinic red light in the spectrophotometric measurement of phytochromein vivo. The shorter the epicotyl segments, and the longer the period of dark incubation, the greater was the loss detected in the measurement.
A remarkable decline of Δ(ΔA) in the far-red region was seen inin vivo difference spectra for phytochrome, after the epicotyl segments were incubated in the dark at 25 C. As the period of dark incubation was prolonged, the ratio of the maximal change of Δ(ΔA) in the far-red region to that in the red region was reduced. It decreased to ca. one third of the initial value after incubation for 8 hr.
The evidence indicates that Pfr killer activity and P* denaturation, both of which have so far been known onlyin vitro, can also occur in segments of etiolated pea epicotyls.
Potassium Phosphate Buffer Rapid Loss Dark Incubation Apical Hook Epicotyl Segment
red light absorbing form of phytochrome
far-red light absorbing form of phytochrome
denaturation, protein denaturation of phytochrome resulting in decrease of Δ Afr/Δ Ar
the first actinic far-red light
the second actinic far-red light
the first actinic red light
a 4 mm-long stem region cut from 1 mm below the apcial hook of an etiolated pea epicotyl, equivalent to the S1 of Purves and Hillman (1958) except that the latter was 5 mm long
mg fr wt
mg fresh weight
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