Accumulation of phenolic compounds in cells and formation of lignin-like polymers in cell walls of young tomato fruits after inoculation with Botrytis cinerea

Abstract

Total of phenolic acids, including p-coumaric and ferulic acid, increased in young tomato fruits during the first few days after inoculation with conidia of Botrytis cinerea. The activity of phenylalanine ammonia lyase also increased during this period, indicating a de novo synthesis of these compounds. The phenolic acids inhibited neither fungal growth nor the fungal enzyme endo-polygalacturonase in vitro, so it is unlikely that these compounds are fungitoxic. Both cis- and trans-p-coumaric acid increased in the cell walls of the epidermal layers during the first few days after inoculation. Ferulic acid, undetectable in cell walls of healthy fruits, also increased in quantity with time. Ionization difference spectra of the alkali soluble fraction of cell walls showed an increased absorption with increased incubation indicating lignification of the cell walls. Alkaline oxidative nitrobenzene degradation of the cell walls of infected tissues, revealed increasing amounts of p-hydroxybenzaldehyde and vanillin with time, while 4 weeks after inoculation syringaldehyde was detected. These results indicate, that lignin-like materials are synthesized by young tomato fruits after infection by B. cinerea. This lignification of the cell walls may explain why mycelium of B. cinerea remains restricted to a few epidermal cells.