Plant second metabolites
momilactone A and B, which act as potent
phytoalexins and
allelochemicals, have been found thus far only in rice and the moss Hypnum plumaeforme, although both plants are taxonomically quite distinct. The concentrations of
momilactone A and B, respectively, in rice plants were 4.5-140 and 2.9-85μg/g, and those in H. plumaeforme were 8.4-58.7 and 4.2-23.4μg/g.
Momilactone A and B concentrations in rice and H. plumaeforme plants were increased by UV irradiation, elicitor and
jasmonic acid treatments. Rice and H. plumaeforme plants secrete
momilactone A and B into the rhizosphere, and the secretion level was also increased by UV irradiation, elicitor and
jasmonic acid treatments. In addition, although endogenous concentrations of
momilactone A in rice and H. plumaeforme were greater than those of
momilactone B, the secretion levels of
momilactone B were greater than those of
momilactone A in rice and H. plumaeforme, which suggests that
momilactone B may be selectively secreted by both rice and H. plumaeforme. As
momilactone A and B exert potent antifungal and growth inhibitory activities,
momilactone A and B may play an important role in the defense responses in H. plumaeforme and rice against pathogen
infections and in allelopathy. The secretion of
momilactone A and B into the rhizosphere may also prevent bacterial and
fungal infections and provide a competitive advantage for nutrients through the inhibition of invading root systems of neighboring plants as
allelochemicals. Therefore, both plants, despite their evolutionary distance, may use same defense strategy with respect to the
momilactone A and B production and secretion, which resulting from convergent or parallel evolutionary processes. In the case of parallel evolution, there may be plant species providing the missing link in molecular evolution of momilactones between H. plumaeforme and rice.