Abstract:

Aims The fungal vacuole plays a key role in nutrient transportation and storage, especially in ectomycorrhizal symbionts. Our objective was to explore the effects of fungal activity and vacuole structure changes on host plant growth to further understand the mechanism of growth-promotion of mycorrhizal fungi and coevolution between host plant and mycorrhizal fungi.

Methods Hyphae of ectomycorrhizal fungi Rhizopogen luteous (Rl), Pisolithus tinctorius (Pt₂), and Boletus edulis(Be) cultured in vitro were stained with 6-CFDA, and the morphologies of fungal vacuoles and their activities were examined. Frozen sections of the ectomycorrhizal symbiont formed by the three fungi and Pinus thunbergii seedlings were stained and observed in the same way.

Important findings Dispersive large vacuoles in hyphae of Pt₂ and Rl and many small dense vacuoles in the hyphae of Be were observed in fungi cultured in vitro, and some vacuoles of Rl and Be linked into tubular vacuole systems. The activity of Be hyphae was higher than Pt₂ and Rl, and Be grew faster than the other two. After ectomycorrhizal formation, P. thunbergii seedlings with Pt₂ or Rl grew better than those with Be, and the fungal activities vacuole morphologies had changed greatly. Hyphae in mantles and Hartig nets of ectomycorrhiza formed by Pt₂ and Rl showed higher activities than those formed by Be, which were hard to label, and tubular vacuole systems were observed sometimes in the hyphae of Hartig nets of Pt₂ and Rl symbionts. It appears that fungal activity and tubular vacuole systems are related to the growth of P. thunbergii seedlings.

Key words: Pinus thunbergii, ectomycorrhiza, tubular vacuole systems, fungal activity, 6-CFDA