The phloem mobility of glucosinolates |
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Authors: | Brudenell A; Griffiths H; Rossiter J; Baker D |
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Institution: | Department of Agricultural and Environmental Science, University of Newcastle, Newcastle upon Tyne NE1 7RU, UK; Department of Biological Sciences, Wye College, University of London, Wye, Ashford, Kent TN25 5AH, UK; Present address and Corresponding author: Department of Entomology and Nematology, IACR-Rothamsted, Harpenden, Hertfordshire AL5 2JQ, UK; Fax: +44 1582 760981; E-mail: alistair.brudenell@bbsrc.ac.uk |
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Abstract: | The transport properties of glucosinolates within Brassica
napus are of interest as identification of the mechanism of
transport could lead to lower levels being obtained in specific tissues
such as the seeds. The phloem mobility of
35S-gluconapin (but-3-enylglucosinolate) and
35S-desulphogluconapin in oilseed rape plants has
been inferred from tissue distribution patterns, as well as from observed
coincident phloem mobility of 3H-gluconapin and
14C-sucrose. The measured relative phloem mobilities
for sinigrin (2-propenylglucosinolate),
3H-gluconapin,
35S-desulphogluconapin,
35S-desulphosinigrin,
14C-tryptophan, 3H-AIB
(-aminoisobutyric acid), and literature
values for a reduced 3H-oligogalacutonide elicitor
(degree of polymerization 6) and 14C-IAA
(indolylacetic acid), have been compared with the predicted values obtained
using the Kleier model for phloem mobility of xenobiotics. All the above
compounds show phloem systemicity, demonstrated using the
Ricinus assay, as predicted by the model. Log
Kow (octanol-water partition coefficient) values for
glucosinolates and desulphoglucosinolates measured at pH 4 and pH 7, and
the effect of pH on uptake by oilseed rape embryos are provided as evidence
against a weak acid trap mechanism acting in either the phloem mobility or
the accumulation of glucosinolates in oilseed rape embryos. The phloem
mobility of glucosinolates is explained by the intermediate permeability
hypothesis. In conclusion, it would appear that glucosinolates like other
groups of endogenous compounds have physicochemical properties allowing
phloem mobility as predicted by the Kleier model.Keywords:
Brassica napus, Ricinus communis, phloem
mobility, glucosinolates, Kleier model.
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