DEVELOPMENTAL AND LIGHT-DEPENDENT CHANGES OF THE CYTOSOLIC CHAPERONINCONTAINING TCP-1 (CCT) SUBUNITS IN MAIZE SEEDLINGS, AND THE LOCALIZATION IN COLEOPTILES

The cytosolic chaperonin containing TCP-1 (CCT) is known to keep fold cytoskeletal proteins and is involved in the proper organization of th e cytoskeleton, These studies are based on the assumption that growth responses linked to structural rearrangement of the plant cytoskeleton include the action of CCT and the need for newly synthesized tubulin. The presence of the alpha- and epsilon- subunits of CCT was investiga ted in soluble fractions of protein extracts from maize mesocotyls and coleoptiles at distinct growth stages. The CCT-subunits, tubulins and actin decreased in the coleoptile in response to far-red light. In ad dition, independent from light treatment, the amount of CCT epsilon ab undance declined with age in coleoptiles and mesocotyls between 2 and 4.5 days after sowing. In contrast to CCT epsilon, no significant ligh t regulation of CCT alpha was found in the mesocotyl. In two day old, light-grown rapidly elongating coleoptiles part of the CCT alpha subun it and the bulk of actin and tubulin was found shifted into fractions of high molecular weight complexes when compared to slowly elongating, dark grown coleoptiles. In 4.5 day old, etiolated and elongating cole optiles, part of both CCT-subunits and cytoskeleton proteins were foun d in fractions of high molecular weight. A complete disappearance of t hese polypeptides was observed in old far-red irradiated growth-arrest ed coleoptiles. CCT epsilon was found to be colocalized to microtubula r structures and to the nucleus. We conclude from our data that abunda nce of CCT-subunits in soluble extracts is dependent on age and light treatment, but independent from the growth stage of mesocotyl and cole optile.