Microautoradiographic localisation of a glucosinolate precursor to specific cells in Brassica napus L. embryos indicates a separate transport pathwayinto myrosin cells

The in-situ localisation of a desulpho-glucosinolate precursor has been stu died by microautoradiography of cryo-sections from immature seeds and pods of the high-glucosinolate Brassica napus L. cv. Argentine collected 23 days after pollination. After feeding with the tritium-labelled glucosinolate p recursor [4,5-H-3](beta -D-glucopyranosyl)-4-pentenethiohydroxamic acid, em bryo radicles, cotyledons and pod-wall were frozen in liquid nitrogen. Cryo tome sections were freeze-dried and coated with nuclear emulsion autoradiog raphic film. A distinct pattern of radioactivity derived from the glucosino late precursor was found in specific cells in both radicle and cotyledons. In contrast, the labelling in pod walls was not cell specific, but general at the inner side of the pod wall. The results show that the glucosinolate/ desulphoglucosinolate was localised in specific cells, in a pattern resembl ing that of myrosin cells known to contain myrosinase (EC 3.2.3.1). In addi tion [4,5-H-3](beta -D-glucopyranosyl)-4-pentenethiohydroxamic acid was fed to immature seeds and pods of B. napus and a quantitative incorporation in to 2-hydroxy-3-butenylglucosinolate and 3-butenyl-glucosinolate was observe d. When [4,5-H-3](beta -D-glucopyranosyl)-4-pentenethiohydroxamic acid was fed to 4-day-old seedlings the label was taken up by all tissues. We propos e a model in which glucosinolate/desulphoglucosinolates are transported to myrosin cells to participate in the myrosinase-glucosinolate multifunctiona l defence system.