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Feedback regulation of xylem cytokinin content is conserved in pea and Arabidopsis

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Foo, E and Morris, SE and Parmenter, K and Young, Naomi and Wang, H and Jones, A and Rameau, C and Turnbull, CGN and Beveridge, CA (2007) Feedback regulation of xylem cytokinin content is conserved in pea and Arabidopsis. Plant Physiology, 143. pp. 1418-1428. ISSN 0032-0889

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Abstract

Increased-branching mutants of garden pea (Pisum sativum; ramosus [rms]) and Arabidopsis (Arabidopsis thaliana; more axillary
branches) were used to investigate control of cytokinin export from roots in relation to shoot branching. In particular, we tested
the hypothesis that regulation of xylem sap cytokinin is dependent on a long-distance feedback signal moving from shoot to
root. With the exception of rms2, branching mutants from both species had greatly reduced amounts of the major cytokinins
zeatin riboside, zeatin, and isopentenyl adenosine in xylem sap compared with wild-type plants. Reciprocally grafted mutant
and wild-type Arabidopsis plants gave similar results to those observed previously in pea, with xylem sap cytokinin downregulated
in all graft combinations possessing branched shoots, regardless of root genotype. This long-distance feedback
mechanism thus appears to be conserved between pea and Arabidopsis. Experiments with grafted pea plants bearing two
shoots of the same or different genotype revealed that regulation of root cytokinin export is probably mediated by an inhibitory
signal. Moreover, the signaling mechanism appears independent of the number of growing axillary shoots because a suppressed
axillary meristem mutation that prevents axillary meristem development at most nodes did not abolish long-distance regulation
of root cytokinin export in rms4 plants. Based on double mutant and grafting experiments, we conclude that RMS2 is essential
for long-distance feedback regulation of cytokinin export from roots. Finally, the startling disconnection between cytokinin
content of xylem sap and shoot tissues of various rms mutants indicates that shoots possess powerful homeostatic mechanisms
for regulation of cytokinin levels.

Item Type: Article
Journal or Publication Title: Plant Physiology
Publisher: American Society of Plant Biologists
Page Range: pp. 1418-1428
ISSN: 0032-0889
Identification Number - DOI: 10.1104/pp.106.093708
Additional Information:

© 2007 American Society of Plant Biologists

Date Deposited: 07 Apr 2008 14:36
Last Modified: 18 Nov 2014 03:35
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