Alternaria cassiae alters phenylpropanoid metabolism in sicklepod (Cassia obtusifolia)
1990
Hoagland, R.E. (U.S. Department of Agriculture, Stoneville (USA). Southern Weed Science Lab. Agricultural Research Service)
Phenylpropanoid metabolism has been implicated in plant defence mechanism(s) against pathogen attack. In this study, phenylpropanoid metabolism was examined over a 72 h time course in the weed sicklepod (Cassiabtusifolia) in relation to pathogenic effects of the fungus Alternaria cassiae. When 3- to 4-week old seedlings were challenged by the pathogen, extractable phenylalanine ammonia-lyase (PAL, E.C. 4.3.1.5) activity was dramatically increased above that in uninfected plants several hours after inoculation and exposure to dew. Greatest increases of enzyme activity (3-fold, specific activity basis) occurred at ca 15-23h after treatment with fungal spores. After this peak of activity, P activity declined with time in infected tissue, but remained greater infected plants through 65 h after treatment. Total methanol-soluble hydryphenolic compound levels (PAL products) were higher in shoots (stems and leaves) of infected plants at 48-72 h. Leaves contained a higher concentration (per gram fresh weight) of hydroxyphenolic compounds than did stems, and infected leaves exhibited a phenolic content greater than that of uninfected leaves at ca 27-72 h. Increased soluble phenolic compound production correlated with the appearance of lesions and necrotic spots on leaves and stems. UV irradiation examination and spectrofluorometric analysis of thin layer chromatographic separations of methanolic extracts revealed a substantial increase of several thin layer chromatographic separations of methanolic extracts revealed a substantial increase of several components in infected tissue 48 h after inoculation. Results support the view that PAL activity increases correlate with increased phenolic compound production in this host/pathogen interaction
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