Effect of wounding and jasmonates on the physico-chemical properties and flea beetle defence responses of canola seedlings, Brassica napus L.

Abstract

Inducible defence responses of seedlings of Brassica napus were investigated after cotyledons were mechanically wounded or treated topically with methyl jasmonate (MeJA). Flea beetles (Phyllotreta cruciferae Goeze) fed less (twofold) on wounded or jasmonate-treated seedlings, probably because their cotyledons were tougher (1.4-fold), the protein content was lower (by half), and the level of cysteine proteinase inhibitor was higher (twofold) than in untreated controls. Wound-induced defences in the cotyledons of B. napus appear to be based on multiple mechanisms (all relatively weak) that may be mediated by jasmonates.Remarkable increases (up to 25-fold) were observed in the viscosity of cotyledon extracts after wounding or treatment with MeJA. Altered tissue water content, DNA, sugars or sugar alcohols did not account for the increase in viscosity. Heating extracts at 100 °C, trichloroacetic acid precipitation, chloroform extraction, and anion–cation–exchange chromatography removed protein and greatly lowered viscosity, indicating that jasmonate-induced proteins may be responsible for elevated viscosity. It is uncertain whether the high viscosity of extracts reflects actual physico-chemical conditions within cotyledons or reflects stress, defence or hydraulic responses to wounding and jasmonates. Key words: Wounding, jasmonate, resistance, Insecta, Brassica napus, Phyllotreta cruciferae, plant defence