Photo reversible calcium dependent aggregation of purified phytochrome from etiolated pea pisum sativum cultivar alaska and rye secale cereale cultivar cougar seedlings
Yamamoto, K.T.; Smith, W.O.Jr; Furuya, M.
Photochemistry and Photobiology 32(2): 233-240
ISSN/ISBN: 0031-8655 Accession: 006109352
The aggregation of phytochrome purified from etiolated pea (Pisum sativum 'Alaska') and rye (Secale cereale 'Cougar') tissues was investigated by centrifugation and turbidimetry. Purified pea phytochrome (A669/A280 = 0.88), if irradiated with red light, became precipitable in the presence of CaCl2. The precipitation upon red-light irradiation was optimal at a Ca2+ or Mg2+ concentration of 10-20 mM, was greater at increased phytochrome concentration or lower pH values, and was inhibited by 0.1 M KCl. The precipitated phytochrome slowly became soluble after far-red light exposure. Turbidity of pea phytochrome solutions after red-light irradiation also increased rapidly in the presence of either Ca2+ or Mg2+. Far-red light exposure after the red light canceled the turbidity increase. Rye phytochrome showed less turbidity increase than pea phytochrome and occurred only in the presence of Ca2+. Partially degraded pea phytochrome produced by endogenous proteases in the extract did not show the turbidity increase. Undegraded pea phytochrome also associated with microsomal fractions under conditions similar to those described above, but the partially degraded phytochrome did not.