Response of cytokinin concentration in the xylem exudate of bean (Phaseolus vulgaris L.) plants to decapitation and auxin treatment, and relationship to apical dominance

Abstract

Response of cytokinin concentration in the xylem(Phaseolus vulgaris L.) plants to decapitation and and relationship to apical dominance exudate of bean auxin treatment, Abstract. When xylem exudate of previously untreated Phaseolus vulgaris plants was analysed for cytokinins by radioimmunoassay, a low concentration (about 5 ng-ml-L) 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 after decapitation this increase even reached 4000% compared to control plants. Applying naphthaleneacetic acid (NAA) to the shoot of decapitated plants almost eliminated the effect of shoot tip removal on cytokinin concentration, suggesting that cytokinins in the xylem exudate of intact plants are under the control of the polar auxin transport system. 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 apical dominance but in many other correlative events as well.

Functional Analysis of the Tandem-Duplicated P450 Genes SPS/BUS/CYP79F1 and CYP79F2 in Glucosinolate Biosynthesis and Plant Development by Ds Transposition-Generated Double Mutants

“…Even though the exact mechanisms that regulate these hormone interactions are not fully understood, it has been shown that auxin can stimulate oxidative breakdown of active cytokinin (Palni et al, 1988;Zhang et al, 1995). In addition, it has been proposed that auxin levels may influence cytokinin biosynthesis, because removal of the endogenous source of auxin by decapitation leads to an increase in the cytokinin content of xylem exudates (Bangerth, 1994). Unlike the effect of auxin that results in decreased cytokinin levels, the effect of cytokinin on auxin levels is less well understood.…”

“…Therefore, the outcome appears to depend on the ratio of the two hormones (for review, see Tamas, 1995;Li and Bangerth, 1992). The two plant hormones not only play opposite roles in controlling plant growth and development, but also influence each other hormone homeostasis (Binns et al, 1987;Palni et al, 1988;Bangerth, 1994;Zhang et al, 1995;Makarova et al, 1996). We and others have described Arabidopsis mutants called supershoot (sps) or bushy (bus), which are disrupted in the gene encoding the cytochrome P450 CYP79F1 (Reintanz et al, 2001;Tantikanjana et al, 2001).…”

The BUD2 mutation affects plant architecture through altering cytokinin and auxin responses in Arabidopsis

“…Although an antagonistic role of auxin and cytokinin in the regulation of apical dominance has been postulated for decades, little is known about the underlying molecular mechanisms. Recent studies have shown that auxin can regulate the expressions of IPT genes and that cytokinin biosynthesis is directly affected by auxin in local shoots [32,33], suggesting that auxin may modulate cytokinin concentration and thus represses AM outgrowth [31,[34][35][36].…”

“…Although an antagonistic role of auxin and cytokinin in the regulation of apical dominance has been postulated for decades, little is known about the underlying molecular mechanisms. Recent studies have shown that auxin can regulate the expressions of IPT genes and that cytokinin biosynthesis is directly affected by auxin in local shoots [32,33], suggesting that auxin may modulate cytokinin concentration and thus represses AM outgrowth [31,[34][35][36].Recent studies on a series of branching mutants, such as more axillary growth (max) of Arabidopsis [37][38][39][40], ramosus (rms) mutants of pea [41][42][43], decreased apical dominance (dad) mutants of petunia [44,45] and dwarf (d) mutants of rice [46][47][48][49][50][51], have revealed strigolactone as a second messenger of auxin action on the control of AM outgrowth [52,53]. Strigolactones, a group of terpenoid lactones that have been found in root exudates of diverse plant species, are synthesized from carotenoids in roots and transported acropetally or synthesized locally to repress the outgrowth of shoot branches [38,[54][55][56].…”

Branching in Pea (Action of Genes Rms3 and Rms4)

“…Furthermore, phytohormones may influence gene action at some or a11 of these stages. Recent studies involving decapitation, auxin application, and cytokinin assays have indicated that a dynamic interaction may exist between the shoot and roots in terms of auxin and cytokinin levels (Bangerth, 1994;Li et al, 1995). It is widely accepted that IAA and cytokinin, but not ethylene (Romano et al, 1993), are the primary factors that control apical dominance (Klee and Estelle, 1991;Cline, 1994).…”