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Plant and Cell Physiology Advance Access published online on March 31, 2008
Plant and Cell Physiology, doi:10.1093/pcp/pcn052
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© The Author 2008. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Apical wilting and petiole xylem vessel diameter of the rms2 branching mutant of pea are shoot controlled and independent of a long-distance signal regulating branching

Ian C. Dodd1, Brett J. Ferguson2 and Christine A. Beveridge2,3

1 The Lancaster Environment Centre Lancaster University, LA1 4YQ United Kingdom
2 ARC Centre of Excellence for Integrative Legume Research, The University of Queensland St Lucia, 4072 Australia
3 School of Integrative Biology The University of Queensland St Lucia, 4072, Australia

Corresponding author: Dr. Ian C. Dodd, The Lancaster Environment Centre, Lancaster University, LA1 4YQ, United Kingdom, E-mail: I.Dodd{at}lancaster.ac.uk, Phone: +44 1524 510 227, Fax: +44 1524 593 192


  Abstract

RMS2 (RAMOSUS2) affects the level or transport of a graft-transmissible signal produced in the shoot and root that controls axillary bud outgrowth in pea (Pisum sativum L.). The shoot apex of rms2 transiently wilts under high evaporative demand. The origin of this phenotype was investigated to determine whether it was involved in the regulation of branching. Wild-type (WT) and rms2 leaves showed a similar stomatal conductance at both low and high evaporative demand in vivo, indicating normal stomatal function. Leaves of both genotypes had similar abscisic acid (ABA) content and response to ABA. Although root hydraulic conductance (determined by pressure-induced flow) of rms2 plants was normal, more xylem vessels per vascular bundle were identified in cross-sections of fully-expanded rms2 petioles compared with those of the WT. However, the diameter of these vessels was nearly half that of the WT. Since the conductance of each vessel is proportional to the fourth power of vessel radius (according to the Hagen-Poiseulle Law), theoretical (calculated) petiole hydraulic conductance of rms2 was greatly decreased compared to WT plants. Under high evaporative demand, this would cause a temporary imbalance between water supply to, and demand from, rms2 shoots, directly resulting in the wilting phenotype of the mutant. Reciprocal grafting showed that xylem vessel development in rms2 shoots is strictly shoot controlled, likely via elevated auxin levels. This altered xylem vessel development, though causing wilting in rms2 shoot tips, does not appear to affect shoot branching.

Keywords: auxin - branching - Pisum sativum - rms mutant - wilting - xylem vessel development -

(Received January 25, 2008; Accepted March 26, 2008)
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