GLUCOSINOLATE RESPONSES OF OILSEED RAPE, MUSTARD AND KALE TO MECHANICAL WOUNDING AND INFESTATION BY CABBAGE STEM FLEA BEETLE (PSYLLIODES-CHRYSOCEPHALA)

Mechanical wounding of the petioles of six laboratory-grown rapeseed (Brassica napus) cultivars induced physiological changes in the plant, markedly affecting the levels of individual glucosinolates. Greatest increases were observed for the indole glucosinolates, glucobrassicin and neoglucobrassicin. Such changes were usually associated with large decreases in the levels of aliphatic glucosinolates. The total glucosinolate content of the wounded plant was thus a reflection of these two opposing trends and wounding produced a greater relative indole glucosinolate content in this total figure. Thus increasing wounding was associated with an increase in indole glucosinolates and a decrease in aliphatic compounds. Infestation of field- and laboratory-grown rapeseed with cabbage stem flea beetle (Psylliodes chrysocephala) produced similar effects, which were observed in various parts of the plant. Differences in response between field- and laboratory-grown infested plants are attributed to the different physiological ages of the harvested material. Laboratory-grown kale and mustards also showed wound-induced glucosinolate changes. The kale, cv. Fribor, produced elevated levels of both indoles and aliphatics after wounding. Total glucosinolate content in the mustards, which, unlike rape and kale, normally contain only traces of indole glucosinolates in the unstressed state, was increased following wounding. This was, however, not associated with elevated levels of indole glucosinolates, but with accumulation of aliphatic (Brassica nigra, B. juncea) and aromatic (Sinapis alba) glucosinolates. The significance of these findings is discussed.