L-form bacteria of Pseudomonas syringae pv. phaseolicola induce chitinases and enhance resistance to Botrytis cinerea infection in Chinese cabbage

Induction of chitinases in Chinese cabbage (Brassica campestris L. ssp. pekinensis var. Granaat) plants treated with L-form bacteria of Pseudomonas syringae pv. phaseolicola during seed germination, was investigated using a fluorometric assay with 4-methylumbelliferyl substrates. The constitutive chitinase activities of seeds and seedlings were low and contrasted with much higher chitinase activities in seedlings treated with L-form bacteria. Maximum chitinase activities of seedlings treated with L-form bacteria was found 31 days after treatment. Extracts of the seedlings treated with L-form bacteria showed 4-fold and 1.5-fold endochitinase activities with, 4-methylumbelliferyl beta-D-N-triacetylchitotrioside and 4-methylumbelliferyl beta-D-N-tetraacetylchitotetraoside, respectively. Plant/L-form association was detected using a slide agglutination assay, enzyme linked immuno-sorbent assay and by re-isolation of bacteria from seedlings. L-form bacteria were also observed in root hairs using light microscopy. Re-isolation showed that L-forms were systemically distributed throughout the plant, with the highest population in room This was supported by ELISA results. Chinese cabbage seedlings treated with L-form bacteria had enhanced resistance to infection by the grey mould pathogen Botrytis cinerea. (C) 2003 Elsevier Ltd. All rights reserved.