Functional Plant Biology Functional Plant Biology Society
Plant function and evolutionary biology
RESEARCH ARTICLE

Rhizobium-induced elevation in xylem cytokinin delivery in pigeonpea induces changes in shoot development and leaf physiology

Jean W. H. Yong A C , D. Stuart Letham B , S. Chin Wong B and Graham D. Farquhar B

A Singapore University of Technology and Design, 20 Dover Drive, Singapore.

B Research School of Biology, Australian National University, Acton, ACT 0200, Australia.

C Corresponding author. Email: jwhyong@gmail.com

Functional Plant Biology 41(12) 1323-1335 http://dx.doi.org/10.1071/FP14066
Submitted: 27 February 2014  Accepted: 11 June 2014   Published: 14 August 2014

Abstract

Inoculation with Rhizobium strain IC3342 induces in pigeonpea (Cajanus cajan (L) Millsp.) a leaf curl syndrome and elevated cytokinin levels in the xylem sap. High nitrogen (N) nutrition was found to inhibit onset of the syndrome which could then be induced by N-free nutrient after development of seven trifoliate leaves. This provided a new system to study the role of xylem cytokinin in shoot development and yielded plants suitable for determining the rate of delivery of xylem cytokinin to the shoot which for IC3342-inoculated plants was found to be three times that of control plants. Relative to leaves of control plants, the non-curled leaves of these IC3342 plants exhibited higher nitrogen and chlorophyll content and greater photosynthetic rate and stomatal conductance. Induction of the syndrome increased leaf thickness in developing leaves but not in expanded leaves already formed. Diameter of stems and number of laterals were also increased markedly by IC3342 inoculation which in addition induced leaf hyponasty. Exogenous cytokinins when applied directly to control leaves induced leaf curl and increased leaf thickness. The present studies are discussed in relation to the role of xylem cytokinins in plant development and especially the release of lateral buds from apical dominance.

Additional keywords: apical dominance, legume, plant-microbe interactions, root-shoot communication.


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