Botany Department, University of Auckland, Auckland, New Zealand.
The composition of wall alterations and appositions (reaction material) and their role in the resistance of onion bulb scale epidermis to colonization by Botrytis allii
Article first published online: 5 APR 2007
Volume 34, Issue 1, pages 25–37, March 1985
How to Cite
STEWART, A. and MANSFIELD, J.W. (1985), The composition of wall alterations and appositions (reaction material) and their role in the resistance of onion bulb scale epidermis to colonization by Botrytis allii. Plant Pathology, 34: 25–37. doi: 10.1111/j.1365-3059.1985.tb02756.x
- Issue published online: 5 APR 2007
- Article first published online: 5 APR 2007
Ultrastructural examination of deposits of reaction material (RM) showed them to be composed of paramural granules (osmiophilic to varying degrees) lying within amorphous electron–dense material. Epidermal cell walls per se became increasingly electron–dense around the short infection hyphae produced by Botrytis allii. Fluorescence microscopy, histochemical tests and microautoradiography showed the accumulation of phenolic compounds at infection sites. Use of phenylalanine and cinnamate for E.M. autoradiography demonstrated the accumulation of phenolics within paramural granules, amorphous aggregates and within the penetrated cell wall, Paramural deposits were soluble in organic solvents and probably represented reservoirs of low MW phenolics which were progressively incorporated into insoluble polymers within the cell wall. Initial synthesis or accumulation of phenolics appeared to take place in rough endoplasmic reticulum during the first 2 h after cuticle penetration. Suppression of RM deposition and wall alterations was achieved by treatment of bulb scales with cycloheximide. Tissues treated with the protein synthesis inhibitor became susceptible to colonization by B. allii. Accumulation of phenolics at infection sites rendered the onion cell walls resistant to attack by a mixture of cell wall–degrading enzymes, Methanolic extracts of epidermal strips containing RM deposits contained very weakly active inhibitors of B. allii germ–tube growth. The role of RM deposits and wall alterations in the resistance of onion epidermis to colonization by Botrytis is discussed.