Journal of Experimental Botany, Vol 50, 805-812, Copyright © 1999 by Oxford University Press
C Atkins
Like some of the Mediterranean members of the genus
Lupinus, the New World lupin, Lupinus
mutabilis (Sweet; cv. Inti), exhibits prolonged (20-40 min)
exudation of phloem sap from incisions made in stems, in the raceme and at
the tips and sutures of developing fruits. Just prior to or immediately
following abscission of flowers of L. mutabilis there
was also spontaneous exudation from the proximal face of the abscission
zone at the base of the pedicel. This is not a recorded feature of other
lupins. Analysis of solutes in this exudate was consistent with its having
been derived directly from phloem. The major solutes were sucrose
(0.94
ARTICLES
Spontaneous phloem exudation accompanying abscission in Lupinus mutabilis (Sweet)
Department of Botany, The University of Western Australia, Nedlands, WA 6907, Australia; Fax: +6 18 93801001; E-mail: catkins@cyliene.wua.edu.au
0.04 M), amino acids (18811 mM, 45% as asparagine and 15% as glutamine), K
ion (52 mM), and total phosphorus (17 mM). Microscopic examination of the
proximal face of the pedicel abscission zone at or following abscission
showed little or no breakage of the cells at the zone. The major solutes of
spontaneous exudate were similar to those in exudates collected from
incisions made in the supporting raceme, upper stem and branches, at the
tips and sutures of developing fruits and in the mid- and basal stem
regions. However, there were significant compositional differences among
minor constituents. The spontaneous exudate had a higher level of Ca ion
and, consequently, a narrower Mg/Ca ratio (2.8) than exudate from incisions
in the adjacent raceme (9.3) or fruits (15.7). There were also higher
concentrations of trace elements (Mn, Zn and Cu) but lower concentrations
(3 ng m-1) of cytokinins compared to exudates
collected from incisions (20 ng ml-1). The relative
contents of K and Na ions in exudates from incisions at different sites on
the plant showed evidence of selective phloem loading and downward
translocation of Na ion and selective loading and upward translocation of K
ion.Keywords: Cytokinin, legumes, lupin, phloem,
translocation
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