Phytochrome Pelletability in Barley

Phytochrome pelletability in the 1000 g and 20,000 g pellet from crude homogenates of etiolated Hordeum vulgare L. cv. Ark Royal primary leaves is enhanced by red light in vivo and in vitro. Red enhanced phytochrome pelletability appears different in the 1000 g and 20,000 g pellets after red light in vivo, being irreversible by subsequent far red light in the latter. Mg²⁺ concentration in the range 1–20 mM has no effect on red enhanced phytochrome pelletability. The enhancement of pelletability is reduced by low pH and high 2‐mercaptoethanol concentration, conditions which lead to a high level of pelletability of the far red absorbing form of phytochrome. Washing these pellets at high pH or low 2‐mercaptoethanol concentration reveals the red enhancement of pelletability. The results are discussed in terms of a possible two point attachment of phytochrome to membranes.