Cell death, 6-methoxymellein accumulation, and induced resistance to Botrytis cinerea in carrot root slices

The carrot phytoalexin 6-methoxymellein (6-MM) accumulated in carrot root slices in response to several treatments which caused cell death. Maximal concentrations (360 μg g ^‑1 fresh weight) 24 h after inoculation, were induced using a noninvasive level of live inoculum of spores of Botrytis cinerea (1 × 10 ⁵ spores ml ^‑1). Optimal freezing times for 6-MM accumulation were between 2 and 10 s (approx. 45 μg g ^‑1 fresh weight at 24 h). Increasing spore concentrations which led to invasion, or lengthening freezing periods, increased the number of cell layers killed below the surface, but resulted in decreased levels of 6-MM accumulation. Ethylene (101 μl l ^‑1) did not cause cell death or induce resistance, although it caused a similar rate of 6-MM accumulation over a 24 h period as partial freezing. It is concluded that cell death is not a necessary prerequisite for 6-MM accumulation.