Characterization of theStriga asiatica(Witchweed) Germination Stimulant fromZea maysL.

Abstract

Isolation and characterization experiments were conducted on the Striga germination stimulant produced by corn (Zea mays L.). Preliminary studies showed the stimulant to be relatively stable to heating for short periods, but very labile in a basic medium and somewhat less labile in acid. The stimulant was not detected in ungerminated corn seeds, but appeared a few hours after germination began. Roots of corn seedlings grown in the dark appeared to exude more stimulant than those of seedlings grown in the light. Shoots and roots of corn seedlings grown in the light contained the stimulant, but none was detected in the shoots of dark-grown seedlings. The stimulant in root exudates of corn seedlings was adsorbed on activated charcoal, eluted, and partially purified by charcoal-column and paper chromatography. Electrophoretic studies indicated the stimulant to be neutral, and by use of an agar-block diffusion procedure a molecular weight of slightly over 100 was estimated. The stimulant showed a bluish-white fluorescence under ultraviolet light. Reactions with classification reagents indicated that the stimulant possessed one or more hydroxyl or potential hydroxyl groups and possibly an ester or lactone bond. It appeared to be a nonacidic compound with no free amino or carbonyl groups. Results with Ehrlich and Salkowski reagents were characteristic of indole compounds, but none of the commonly occurring indoles were active in promoting germination. Final stimulant preparations did not give meaningful ultraviolet or infra-red spectra. Several of the findings in this study indicated the possibility that the stimulant from com seedlings may be similar to certain coumarin-like derivatives or related compounds.