RESPONSE OF CYTOKININ CONCENTRATION IN THE XYLEM EXUDATE OF BEAN (PHASEOLUS-VULGARIS L) PLANTS TO DECAPITATION AND AUXIN TREATMENT, AND RELATIONSHIP TO APICAL DOMINANCE
F. Bangerth, RESPONSE OF CYTOKININ CONCENTRATION IN THE XYLEM EXUDATE OF BEAN (PHASEOLUS-VULGARIS L) PLANTS TO DECAPITATION AND AUXIN TREATMENT, AND RELATIONSHIP TO APICAL DOMINANCE, Planta, 194(3), 1994, pp. 439-442
When xylem exudate of previously untreated Phaseolus vulgaris plants w
as analysed for cytokinins by radioimmunoassay, a low concentration (a
bout 5 ng.ml(-1)) was found. However, when the plants were decapitated
about 16 h before the xylem exudate was collected, an almost 25-fold
increase in cytokinin concentration was observed. Twenty-four hours af
ter decapitation this increase even reached 4000% compared to control
plants. Applying naphthaleneacetic acid (NAA) to the shoot of decapita
ted plants almost eliminated the effect of shoot tip removal on cytoki
nin concentration, suggesting that cytokinins in the xylem exudate of
intact plants are under the control of the polar auxin transport syste
m. Other xylem constituents, such as potassium or free amino acids did
not show this strong increase after decapitation and did not respond
to NAA application. It is concluded that the observed auxin/cytokinin
interaction has an important regulatory role to play, not only in apic
al dominance but in many other correlative events as well.