抄録
Plants of the genera Striga and Orobanche are noxious root parasitic weeds on many food crops. Their life cycle is strongly cued to that of their hosts. To germinate the parasites need a moist pre-treatment (conditioning) at specified temperatures followed by exposure to an exogenous stimulant. On perception of a second signal the parasites produce haustoria that are the bridge for transfer of water, minerals and organic compounds from the hosts. I have been studying the interactions between the parasites and their hosts. Based on proposed structure of sorgolactone, the main germination stimulant isolated from sorghum root exudates, all eight stereoisomers were synthesized. Only those isomers possessing the same stereochemistry as the natural sorgolactone at two adjacent chiral centers exhibited significant germination stimulatory activity. The involvement of endogenous ethylene in germination of S. hermonthica was confirmed. Expression of ACC synthase and ACC oxidase genes was found to be responsive to germination stimulants and to conditioning, respectively. Lotus japonicus, a model legume for nodulation and mycorrhizal colonization, was compatible with O. aegyptiaca but not with O. minor, S. hermonthica and S. gesnerioides. O. aegyptiaca and S. hermonthica parasitism specifically induced the expression of genes involved in nodulation and phytoalexin biosynthesis, respectively. Reactions of the model legume and its mutants to O. aegyptiaca suggest that nodulation, mycorrhizal colonization and plant parasitism are modulated by similar mechanisms.
