Sedimentation du phytochrome: A propos de l'induction in vitro du phenomene

Abstract

In vivo irradiation-enhanced phytochrome pelletability, observed in extracts of several plants, was described as resulting from a direct binding between P fr and subcellular constituents. In Cucurbita pepo, the phenomenon can be also induced after red irradiation of crude extracts or supernatants. As proposed and largely documented recently, this binding could be due to an artificial association of the pigment with degraded ribonucleoprotein material. In the present paper, experiments have been designed in order to test the hypothesis of electrostatic adsorption which seems to arise non-specifically between P fr and some subcellular components like 31 S particles. Mixing of 20 000 g supernatants from etiolated corn and squash seedlings demonstrated that the corn phytochrome was unable to bind to particles from squash (Fig. 1). Association of partially purified squash phytochrome, or phytochrome separated from all pelletable material by high-speed centrifugation, was no more possible after re-combination with various freshly prepared extracts. These findings appear to preclude the hypothesis that the enhanced phytochrome pelletability results from any P fr-particulate components interaction which would occur spontaneously during or after disruption of the cellular organization.