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Plant and Cell Physiology Advance Access originally published online on March 31, 2008
Plant and Cell Physiology 2008 49(5):791-800; 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 email: 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

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

*Corresponding author: E-mail, I.Dodd{at}lancaster.ac.uk; 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 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 the vessel radius (according to the Hagen–Poiseulle law), the theoretical (calculated) petiole hydraulic conductance of rms2 was greatly decreased compared with 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, probably 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

Abbreviations: RWC, relative water content; VPD, vapor pressure deficit; WT, wild type.

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