Comparative Phytochrome Immunochemistry as Assayed by Antisera against Both Monocotyledonous and Dicotyledonous Phytochrome

Preparation and characterization of antisera against lettuce (Lactuca sativa L., cv. Grand Rapids) and pea (Pisum sativum L., cv. Alaska) phytochrome is described. These antisera, together with previously obtained antisera against zucchini (Cucurbita pepo L., cv. Black Beauty) and oat (Avena sativa L., cv. Garry) phytochrome, were used to compare by Ouchterlony double immunodiffusion phytochrome isolated from etiolated lettuce, pea, bean (Phaseolus vulgaris L., cv. Taylor Horticultural Bush), zucchini, oat and rye (Secale cereale L., cv. Balbo) seedlings. Cross reactivity between monocotyledonous phytochrome and antidicotyledonous-phytochrome serum and between dicotyledonous phytochrome and antimonocotyledonous-phytochrome serum was always weak or not perceptible by this assay. Among the four dicotyledonous phytochromes examined, pea and bean were the most similar immunochemically as anticipated. Pea and lettuce phytochrome somewhat unexpectedly also exhibited similar immunochemical reactivity. Zucchini phytochrome by contrast was immunochemically distinct from pea, bean, and lettuce phytochrome, although it did react with all three antidicotyledonous-phytochrome sera. Initial attempts to identify immunoglobulins that would recognize phytochrome regardless of its source indicated that they may exist. Such immunoglobulins are of interest because they might react with one or more determinants that could be part of an active site of phytochrome. These immunoglobulins, once isolated, could thus serve as a potential probe for the active site of phytochrome.