The phloem mobility of glucosinolates

The transport properties of glucosinolates within Brassica napus are of int erest as identification of the mechanism of transport could lead to lower l evels being obtained in specific tissues such as the seeds. The phloem mobi lity of S-35-gluconapin (but-3-enylglucosinolate) and S-35-desulphogluconap in in oilseed rape plants has been inferred from tissue distribution patter ns, as well as from observed coincident phloem mobility of H-3-gluconapin a nd C-14-sucrose, The measured relative phloem mobilities for sinigrin (2-pr openylglucosinolate), H-3-gluconapin, 35S-desulphogluconapin, S-35-desulpho sinigrin, C-14-tryptophan, H-3-AIB (alpha-aminoisobutyric acid), and litera ture values for a reduced H-3-oligogalacturonide elicitor (degree of polyme rization 6) and C-14-IAA (indolylacetic acid), have been compared with the predicted values obtained using the Kleier model for phloem mobility of xen obiotics. All the above compounds show phloem systemicity, demonstrated usi ng the Ricinus assay, as predicted by the model. Log K-ow (octanol-water pa rtition coefficient) values for glucosinolates and desulphoglucosinolates m easured at pH 4 and pH 7, and the effect of pH on uptake by oilseed rape em bryos are provided as evidence against a weak acid trap mechanism acting in either the phloem mobility or the accumulation of glucosinolates in oilsee d rape embryos. The phloem mobility of glucosinolates is explained by the i ntermediate permeability hypothesis, In conclusion, it would appear that gl ucosinolates like other groups of endogenous compounds have physicochemical properties allowing phloem mobility as predicted by the Kleier model.