title: Hormonal control of second flushing in Douglas-fir shoots.
abstract: Spring-flushing, over-wintered buds of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) produce new buds that may follow various developmental pathways. These include second flushing in early summer or dormancy before flushing during the following spring. Second flushing usually entails an initial release of apical dominance as some of the current-season upper lateral buds grow out. Four hypotheses concerning control of current bud outgrowth in spring-flushing shoots were tested: (1) apically derived auxin in the terminal spring-flushing shoot suppresses lateral bud outgrowth (second flushing); (2) cytokinin (0.5 mM benzyladenine) spray treatments given midway through the spring flush period induce bud formation; (3) similar cytokinin spray treatments induce the outgrowth of existing current lateral buds; and (4) defoliation of the terminal spring-flushing shoot promotes second flushing. Hypothesis 1 was supported by data demonstrating that decapitation-released apical dominance was completely restored by treatment with exogenous auxin (22.5 or 45 mM naphthalene acetic acid) (Thimann-Skoog test). Hypothesis 2 was marginally supported by a small, but significant increase in bud number; and Hypothesis 3 was strongly supported by a large increase in the number of outgrowing buds following cytokinin applications. Defoliation produced similar results to cytokinin application. We conclude that auxin and cytokinin play important repressive and promotive roles, respectively, in the control of second flushing in the terminal spring-flushing Douglas-fir shoot.
authors.affiliation: Department of Plant Cell and Molecular Biology, Ohio State University, Columbus, OH 43210, USA. cline.5@osu.edu
authors.forename: Morris
authors.initials: M
authors.lastname: Cline
authors.forename: Mark
authors.initials: M
authors.lastname: Yoders
authors.forename: Dipti
authors.initials: D
authors.lastname: Desai
authors.forename: Constance
authors.initials: C
authors.lastname: Harrington
authors.forename: William
authors.initials: W
authors.lastname: Carlson
mesh_terms: D003583:Cytokinins / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism; D010937:Plant Growth Regulators / Q000378:metabolism* / Q000494:pharmacology; D018515:Plant Leaves / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D028224:Pseudotsuga / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D012621:Seasons; D014197:Trees / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*
chemical_list: D003583:Cytokinins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators