Yong, JeanLetham, D StuartWong, Suan ChinFarquhar, Graham2015-12-101445-4408http://hdl.handle.net/1885/56011Root restriction experiments on cotton plants were conducted under conditions where water and nitrogen supplies were not limiting. Xylem sap and leaf tissues were obtained before significant biomass reduction as a result of root restriction. Xylem-derived cytokinins (CTKs) entering a leaf and the CTK levels in the same excised leaf were measured, thus, enabling xylem sap and foliar CTKs to be compared concurrently under root-restrictive and control conditions. Abscisic acid (ABA) was also measured simultaneously in the same xylem sap samples. Root restriction reduced photosynthesis and18O of leaf matter showed that leaves of root-restricted plants generally had lower stomatal conductances. Root-restriction significantly decreased (37%) the delivery rate per unit leaf area of CTK bases (dihydrozeatin (DZ) and N6-(2-isopentenyl)adenine (iP)) to the leaf but did not alter the export of CTK O-glucosides and ABA from the roots to leaf 4. Root-restriction also did not alter significantly the levels of total CTK bases in the leaves but increased (54-57% higher) the CTK O-glucosides (especially zeatin O-glucosides). Root restriction also slowed down the apparent CTK turnover rates in the leaves. The slow down in CTK turnover rate can be interpreted as a reduction in leaf CTK metabolism during root restriction.Keywords: Abscisic acid; root pressure chamber; root-shoot signalling; Stable isotopes; trans-zeatin; Xylem sap; Acids; Carbohydrates; Ecology; Endocrinology; Hormones; Isotopes; Plants (botany); Cotton; abscisic acid; cotton; growth rate; growth response; hormone; abscisic acid; hormones; root pressure chamber; root-shoot signalling; stable isotopes; trans-zeatin; xylem sap201010.1071/FP100092016-02-24