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Articles

Phytochrome Stability in Vitro

I. Effect of Metal Ions ¹

^a Department of Biology, Yale University, New Haven, Connecticut 06520

Photoreversible phytochrome disappears from etiolated tissue upon actinic irradiation. Such disappearance, of possible physiological importance, involves several processes, at least one of which is accelerated by metals in vivo. Purified phytochrome from oat (Avena sativa L. cv. Garry) coleoptiles is greatly stabilized in vitro by scrupulous removal of metal impurities via chelating agents. Such stabilized phytochrome decays rapidly upon the addition of about 10 µM Hg²⁺, Cd²⁺, Cu²⁺, and Zn²⁺, all of which probably act on sulfhydryl groups. Other tested metals and growth factors were much less active or inactive. The metals effective in promoting decay do not affect the Pfr Pr reversion process. This supports other evidence indicating the possible physiological importance of phytochrome "decay."

³ Present address: Philip Lyle Memorial Research Laboratory, University of Reading, RG6 2BX, England.

¹ This work was aided by a National Science Foundation grant to A.W.G.