Secondary metabolism, enzymatic oxidants and antibacterial activities as signaling to some stress elicitors

Faba bean (Vicia faba, Giza 40) seedlings were subjected to some stress elicitors such as biotic due to infection with Botrytis cinerea (5x105 spores ml-1 ) and abiotic due to the herbicide metribuzin (1.0 kg ha-1 ) or sludge (150 g l-1 ). During the subsequent 11 days, there were differential decreases in fresh and dry weights and in protein content of faba shoots and roots; the magnitude of decrease augmented with the progress of time. The decreases were greatest with B. cinerea while sludge was the least reductive. At the same time, there were significant increases in anthocyanin content as well as in activities of phenylalanine ammonia lyase (PAL), tyrosine ammonia lyase (TAL) and chalcone isomerase (Cl). On the contrary, the activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX) and glutathione Stransferase (GST) were significantly increased in shoots and roots of treated seedlings. On the other hand, the crude extracts of treated seedlings exhibited an inhibitory action towards some bacterial species; the inhibition was most pronounced towards Bacillus cereus followed by Klebsiella pneumonia, Bacillus subtilis and finally Micrococcus roseus. Nonetheless, the antibacterial activities were more efficient for extracts derived from seedlings stressed with B. cinerea than sludge while metribuzin had a negative effect. These findings suggest that stress elicitors, particularly biotic stress, could induce faba bean to produce some metabolites with antibacterial activities to withstand these harsh conditions.