Release of calcium and other ions from various plant host tissues infected by different necrotrophic pathogens with special reference to Botrytis cinerea Pers
Kaile, A. | Pitt, D. | Kuhn, P.J.
Substantial amounts of calcium ions were released to the external medium from Brassica napus (Swede) storage organs (bulbs) heavily infected with Botrytis cinerea, whilst lower amounts were released from lightly infected and uninfected regions of the tissue. Mg2+, K+ and Na+ followed the same pattern of release, which has also been observed in a number of other plant-pathogen interactions. The theoretical concentration of free calcium ions arising in the apparent free space of diseased swede bulbs consequent upon release from the pectic fraction of host cell walls was calculated to be 42.39 +/- 2.65 mM. Significantly higher release of Ca2+ was observed from healthy excised swede seedling hypocotyls incubated in an osmoticum containing cell wall degrading enzymes than from those incubated without enzymes. The extra calcium (approximately 46.48 +/- 2.89 mM) represented that component of wall bound Ca2+ mobilized during degradation. Transmission electron microscopy of diseased swede bulbs showed extensive disruption of host cell walls in the vicinity of hyphae of B. cinerea. Polygalacturonase and pectin lyase were detected in B. cinerea infected zones of swede bulbs and when the pathogen was grown in vitro. This suggested that B. cinerea had the potential to release a high level of Ca2+ normally bound to pectic substances in the middle lamella during host tissue maceration by secreted pectolytic enzymes and that these ions may be implicated in host cytotoxicity during necrotrophic pathogenesis.
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