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The agrobacterial isopentenyltransferase (ipt) gene, under the control of its native promoter, was transferred to poplar (Populus tremula x P. alba) by an Agrobacterium co-cultivation method. The ipt-transformed stem explants developed calli that regenerated many buds in the absence of exogenous cytokinins. Microcuttings of the ipt transformants exhibited frequently branching shoots with short internodes that were unable to root. In this material, the concentrations of zeatin, zeatin riboside and isopentenyladenosine, determined by an indirect enzyme-linked immunosorbent assay (ELISA), were 4.8-. 17.1- and 14.6-fold higher, respectively, than in non-transformed shoots. Results are discussed with regard to cytokinin metabolism.

Leaf conductance, water relations, growth, and abscisic acid (ABA) concentrations in xylem sap, root apices and leaves were assessed in oak seedlings (Quercus robur L.) grown with a root system divided between two compartments and subjected to one of four treatments: (a) well watered, WW; (b) half of root system exposed to soil drying and half kept well watered, WD; (c) whole root system exposed to drought, DD; and (d) half of root system severed, RE. Sharp decreases in plant stomatal conductance, leaf water potential, hydraulic conductance and leaf growth were observed during DD treatment. No significant differences in plant leaf water potential and stomatal conductance were detected between the WW and WD treatments. Nevertheless, the WD treatment resulted in inhibition of leaf expansion and stimulation of root elongation only in the well-watered compartment. Abscisic acid concentrations did not change in leaves, root tips, or xylem sap of WD- compared to WW-treated plants. Increased concentrations of ABA were observed in xylem sap from DD-treated plant roots, but the total flux of ABA to shoots was reduced compared to that in WW-treated plants, because of decreases in transpiration flux. Similar plant responses to the WD and RE treatments indicate that the responses observed in the WD-treated plants were probably not triggered by a positive signal originating from drying roots.

25 ref.; High-performance liquid chromatography, immunochromatography, and radioimmunoassay were used to identify cytokinin-like bases and glycosides in xylem sap of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Isopentenyladenosine-type (isopentenyladenine and isopentenyladenosine) and zeatin-riboside type (zeatin, zeatin riboside, and dihydrozeatin riboside) cytokinins were detected during springtime. A glucosyl conjugate of zeatin riboside was also present in small amounts. Levels of cytokinin-like compounds varied throughout the spring but were generally highest in late April to early May.