Changes in Cell Wall Carbohydrates Composition and Ca Distribution of Brassica campestris ssp. pekinesis in Relation to Erwinia Polygalacturonase Production during Soft Rot Development

Abstract

Relatively resistant and susceptible lines of Chinese cabbage were selected among dihaploids populations derived from microspore culture and their composition of cell wall polysaccharides and Ca content were determined during soft rot infection by Erwinia carotovora ssp. carotovora in concert with disease development and bacterial polygalacturonase (PG) production. PG was purified by one step, histidine-affinity column chromatography, after produced in Escherichia coli expression vector. Western blot analysis showed that PG from the bacteria inoculated into the susceptible line was expressed actively between 6 to 12 h after infection, whereas no visible immuno-reactivity was observed in the resistant line. The composition of cell wall polyuronides decreased predominantly after bacterial inoculation in both genotypes, but cellulose and non-cellulosic neutral sugars (NCNS) remained fairly constant. Initial contents of NCNS in the cell wall of the resistant line maintained 71% higher than those of the susceptible one. More than 95% of cellular Ca was found as cell wall-associated form and loss in wall bound Ca progressed mostly 12 h after infection. Thus, development of NCNS in pectin backbone as observed in the resistant line of Chinese cabbage may provide one of the mechanism responsible for being resistant to soft rot disease, by refraining the Erwinia PG production upon invasion.