An examination of two halophytes Spartina alterniflora and Phragmites australis for the production of phytoalexins

Studies in terrestrial systems have shown that abiotic and biotic stresses may induce the production of phytoalexins in many plants. However, the extent to which this defense mechanism occurs in the plant kingdom is unknown. This study examined the response of the halophytes Spartina alterniflora Loisl. and Phragmites australis Trin. to abiotic and biotic stresses.; Field studies indicated that natural populations of Spartina contained a compound which was active against the marine fungus Phaeosphaeria typharum in an in vitro bioassay. Several related antifungal metabolites were detected in field samples of Phragmites. These compounds were effective against P. typharum as well as the marine fungus Buergenerula spartinae when combined. However, none were effective when tested individually suggesting that the antifungal activity was a result of synergy.; The antifungal metabolites detected in the field samples of Phragmites were isolated and characterized. Spectral data suggest that the compounds may be terpenoid derivatives.; Laboratory studies undertaken to determine if these naturally occurring antifungal metabolites could be induced in sterile plant and callus cultures revealed that the abiotic stress of mechanical wounding was ineffective in inducing a detectable phytoalexin response in any of the laboratory cultures. The biotic stress of inoculation or wounding followed by inoculation with the fungi used in the bioassay did not elicit a detectable response in sterile Spartina plants. However, Phragmites sterile plants and callus cultures stressed biotically contained an antifungal metabolite not present in control cultures. Thin layer chromatographic analyses suggest that the metabolite produced in the sterile plant and callus cultures may be the same as that detected in the field samples.; Treatments which induced the production of the antifungal metabolite in sterile Phragmites plants were used to determine if pathogenesis related (PR) proteins, which have been correlated with phytoalexins production, were also produced. Results of total protein analyses and electrophoretic studies suggest that PR proteins were not induced in the response of Phragmites to biotic stress.; Results of the field survey and laboratory experiments suggest that a biotic stress such as microbial invasion may induce the formation of antifungal metabolites in Phragmites australis plants.