Chemical Defense of Leguminosae. Are Quinolizidine Alkaloids Part of the Antimicrobial Defense System of Lupins?

Growth of 6 bacteria (Serratia marcescens, Bacillus megaterium, Bacillus subtilis, Streptococcus viridis, Micrococcus luteus, and Mycobacterium phlei) was inhibited by 50% if the growth medium contained sparteine at concentrations between 0 .5 -1 0 m M . Total growth inhibition, which was bacteriostatic in nature, was achieved at 20 m M . The growth o f 6 phytopathogenic fungi was also affected: at a sparteine concentration o f 15 m M the growth o f Alternaria porri was reduced by 40% as compared to the untreated control. Respective values were 18% inhibition for Piricularia oryzae, 33% for Helminthosporium carbonum, 15% for Rhizoctonia solani, 5% for Fusarium oxysporum, and 42% for Asperquillus oryzae. Since the concentrations o f quinolizidine alkaloids range from 1 -2 0 0 m M (roots, leaves, or stems) or 1 0 -2 0 0 m m ol/kg (seeds) in Leguminosae, it is discussed whether quinolizidine alkaloids are involved in the antimicrobial defense o f lupins, in addition to their potential role as allelopathic or herbivore repellent defense compounds.