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Cytokinins in Populus × robusta : Qualitative Changes during Development
Author(s) -
HEWETT E. W.,
WAREING P. F.
Publication year - 1973
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1973.tb04835.x
Subject(s) - cytokinin , xylem , shoot , botany , biology , elongation , sephadex , apical dominance , apex (geometry) , horticulture , auxin , biochemistry , materials science , ultimate tensile strength , gene , metallurgy , enzyme
Abstract Qualitative changes of cytokinins in leaves of different ages from Populus x robusta (Schneid.) have been determined, together with seasonal changes in cytokinin activity in mature leaves and xylem sap. Chromatography on Sephadex LH‐20 has shown that total cytokinin activity and diversity are at a maximum in expanding leaves. As leaves age, the amount and number of cytokinins decrease, with yellow senescent leaves having only one detectable cytokinin, thought to be a glucoside. Seasonal changes were followed by chromatography of the extracts on paper in butan‐2‐ol: 25 % NH 4 OH (4:1). Maximum cytokinin levels, due to Fraction Z (Rf 0.5–0.8), in leaves and xylem sap were found in mid‐summer. Prior and subsequent to cessation of shoot elongation growth, fraction Z decreased and fraction N (Rf 0–0.2) increased to predominate in senescent leaves. Removal of the apex resulted in an increase of fraction N in leaves from decapitated plants when compared to similar leaves from intact plants. It is suggested that, once apical sink activity has ceased, cytokinins in the xylem sap are diverted into leaves and converted to a cytokinin glucoside, possibly a storage form of the hormone.