Journal of Experimental Botany, Vol 50, 1567-1576, Copyright © 1999 by Oxford University Press
P Hetherington, T Reynolds, G Marshall and R Kirkwood
Maize (Zea mays L. var. Bonnie) transformed with a
gene encoding a 5-enolpyruvylshikimate 3-phosphate synthase with altered
sensitivity showed over 100-fold greater resistance to the herbicide
glyphosate (N-[phosphonomethyl]glycine) in comparison
with its non-transformed progenitor (parental control) at the third-leaf
stage. Studies with [14C]-glyphosate at a dosage
lethal to the parental control, but sublethal to the transgenic, revealed
that a maximum of 45-65% of the applied dose was absorbed, with greater
absorption occurring in transgenic plants. Translocation of glyphosate was
closely related to its absorption (r value 0.956) with
approximately 15% more of the applied dose being mobilized in transgenic
plants than the parental controls. Analysis of electronic autoradiograms
along the treated leaf lamina found discrete internal regions of glyphosate
accumulation closely associated with the site of application. These regions
contained lower amounts of glyphosate present in the treated leaf lamina
was almost completely translocated in transgenic plants, while in the
parental controls more remained and the leaf became necrotic. In both types
of maize there was a small accumulation of herbicide in the tip region of
the leaf which was not mobilized. Younger shoot tissues and roots were
major sinks for translocated glyphosate accumulating approximately 25-40%
of the applied dose depending upon treatment. In the parental control,
equal amounts of glyphosate were found distributed between young shoot
tissues and roots; while in transgenic plants, the young shoot tissue
accumulated around three times more glyphosate than the roots. In both
plant types, glyphosate was localized in the meristems and young, actively
growing leaves. Specific glyphosate activity (the amount of glyphosate per
unit dry weight of tissue) in the major sinks of the transgenic declined
towards the end of the treatment period but remained relatively constant in
the parental control. In conclusion, enhancing glyphosate resistance by
genetic transformation influenced the absorption, translocation and
distribution of this herbicide in whole plants.Keywords:
Zea mays, glyphosate
(N-[phosphonomethyl]-glycine), transgenic, absorption,
translocation, source-sink.
ARTICLES
The absorption, translocation and distribution of the herbicide glyphosate in maize expressing the CP-4 transgene
Department of Plant Biology, Plant Science Division, SAC Auchincruive, Ayr KA6 5HW, UK; Monsanto Company, 800 N. Lindbergh Blvd, Mail Zone Q2D, St Louis MO 63167, USA; Corresponding author; Fax: +44 1292 525314; E-mail: G.Marshall@au.sac.ac.uk
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