Tryptophan dimer produced by water-stressed bahia grass is an attractant for Gigaspora margarita and Glomus caledonium

We isolated and elucidated the structure of several stimulants for arbuscular mycorrhizal fungi (AMF) in water-stressed bahia grass roots. We could isolate some compounds that promoted the growth of Gigaspora margarita Becker and Hall and Glomus caledonium (Nicol. and Gerd.) Trappe and Gerd. In these compounds, tryptophan dimer (Trp-Trp) was elucidated the structure. Trp-Trp was abundantly produced in water-stressed bahia grass roots and exuded to the soil, although it was scarcely detected in non-stressed root exudates. Interestingly, this peptide strongly attracted the hyphae of Gi. margarita and G. caledonium and promoted their hyphal growth in vitro (1.8 x longer than the control). Tryptophan, however, had no effect on hyphal growth and attraction. Thus, Trp-Trp exuded from water-stressed roots would play an important role as a major signal for AMF.