Plant Physiol, September 2001, Vol. 127, pp. 194-201
Long-Distance Phloem Transport of Glucosinolates in
Arabidopsis1
Sixue
Chen,2
Bent Larsen
Petersen,2
Carl Erik
Olsen,
Alexander
Schulz, and
Barbara Ann
Halkier*
Plant Biochemistry Laboratory and Center for Molecular Plant
Physiology (S.C., B.L.P., B.A.H.), Department of Plant Biology,
Department of Chemistry (C.E.O.), and Plant Anatomy and Physiology
Laboratory (A.S.), The Royal Veterinary and Agricultural University,
Thorvaldsensvej 40, DK-1871 Frederiksberg C, Copenhagen,
Denmark
Glucosinolates are a large group of plant secondary metabolites
found mainly in the order Capparales, which includes a large number of
economically important Brassica crops and the model plant Arabidopsis. In the present study, several lines of evidence are
provided for phloem transport of glucosinolates in Arabidopsis. When
radiolabeled p-hydroxybenzylglucosinolate
(p-OHBG) and sucrose were co-applied to the tip of
detached leaves, both tracers were collected in the phloem exudates at
the petioles. Long-distance transport of
[14C]p-OHBG was investigated in wild-type
and transgenic 35S::CYP79A1 plants, synthesizing high amounts
of p-OHBG, which is not a natural constituent of
wild-type Arabidopsis. In both wild-type and 35S::CYP79A1 plants, radiolabeled p-OHBG was rapidly transported from
the application site into the whole plant and intact
p-OHBG was recovered from different tissues. The pattern
of distribution of the radioactivity corresponded to that expected for
transport of photoassimilates such as sucrose, and was consistent with
translocation in phloem following the source-sink relationship.
Radiolabeled p-OHBG was shown to accumulate in the seeds
of wild-type and 35S::CYP79A1 plants, where
p-OHBG had been either exogenously applied or
endogenously synthesized from Tyr in the leaves. p-OHBG
was found in phloem exudates collected from cut petioles of leaves from
both wild-type and 35S::CYP79A1 plants. Phloem exudates were
shown to contain intact glucosinolates, and not desulphoglucosinolates,
as the transport form. It is concluded that intact glucosinolates are readily loaded into and transported by the phloem.
1
This work was supported by the Danish Scientific
Research Council (to S.C.) and by the Danish National Research Foundation.
2
These authors contributed equally to this work.
*
Corresponding author; e-mail bah{at}kvl.dk; fax 45-3528-3333.
© 2001 American Society of Plant Physiologists
