Mortierella volatiles promote plant growth
Plants reduce the CO2 concentration in closed systems which has to be considered in experimental designs with volatiles (Nazninet al. , 2013; Piechulla et al. , 2017). In preliminary experiments, we co-cultivated Arabidopsis seedlings with 5 different Mortierella strains with comparable growth rates and metabolite features. Since the three fungi with distinctive garlic-like smells (M. hyalina , M. alpina , M. turficolalis ) induced a stronger growth promotion compared to two non-smelling strains (M. vinacea , M. longicollis ; Figure S1), we hypothesized that the sulfur-containing volatiles from the fungi might be involved in the growth regulation. The major volatile in the headspace of one of these fungi, M. hyalina , was TMTM, and its abundance prompted us to investigate it in this study. The stronger growth of seedlings which are growing in the presence of the fungus compared to those treated with TMTM demonstrates that the investigated volatile is not the only factor involved in the growth promoting effect. However, it is difficult to design experimental set-ups which allow a quantitative comparison of fungal and volatile effects on plant growth and performance. We assume that the stabilizing effect of TMTM on the sulfur homeostasis allows better plant performance under sulfur stress.