Effects of divalent cations and EDTA [ethylendiaminetetraacetic acid] on spectral properties of phytochrome in particulate fractions from etiolated pea [Pisum sativum] epicotyls

• Published in: Plant and cell physiology 1980-01, Vol.21 (5), p.855-863
• Main Authors: Shimazaki, Y, Furuya, M
• Format: Article
• Language: English
• Subjects: Divalent cations; EDTA; Pelletable phytochrome; Pisum sativum; plant biochemistry; plant physiology; Spectral distortion
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/oxfordjournals.pcp.a076059

The photoreversible absorbance change of phytochrome in suspensions of a 20,000×g particulate fraction (20kP) prepared from a 1,000×g supernatant (1kS) of etiolated pea epicotyl extracts decreased remarkably in the presence of 5 mM Cu2+, Zn2+ and Co2+, but remained unchanged in 5 mM Ca2+, Mg2+, Fe2+ or Mn2+. This spectral distortion of phytochrome was more evident in soluble preparations and in suspensions of pellets prepared from red light (R)-irradiated tissues than it was in suspensions of pellets prepared in the dark from etiolated tissues that received no actinic irradiation. When Cu2+ was added to the red-light-absorbing form of phytochrome (Pr) in resuspended pellets prepared from R-irradiated tissues, the distortion of its difference spectrum took place after irradiation with the first actinic R. In contrast, when Cu2+ was added to the far-red-light-absorbing form of phytochrome (Pfr) in the same resuspended pellet, no distortion was seen, unless the Pfr in the pellet was first photoconverted to Pr and then photoconverted back to Pfr. Spectral distortion of Pr remained small during dark incubation at 25°C when suspensions of 20kPs were prepared and incubated with a buffer containing EDTA, whether the 20kP was prepared from nonirradiated tissue or from R-irradiated tissues. But, when EDTA was added to a suspension of 20kP prepared from 1kS, after the 1kS was irradiated with R in the presence of 10 mM CaCl2, the spectral distortion of Pr in 20kP occurred instantaneously.