FIGURE 1.

A schematic diagram of water transport pathways and aquaporin involvement in ectomycorrhizal (EcM) association. (A) A conceptual model of water pathways through EcM hypha-root continuity. The diagram was drawn based on the composite model of root water transport (Steudle and Peterson, 1998), with reference to that of the EcM root water transport suggested by Lehto and Zwiazek (2011). (B) Involvement of fungal and plant aquaporins in water transport at the hypha-root interface in EcM. The simplified model is postulated according to a study on the roles of fungal aquaporin Laccaria bicolor JQ585595 in EcM interaction and root hydraulic dynamics of the host plant Picea glauca (Xu et al., 2015). (B1) Water is transported in apoplastic space and cell-to-cell pathways in cortical cells in non-mycorrhizal root tips; (B2) In mycorrhizal root tips, root water transport in apoplastic, and cell-to-cell pathways is altered by the presence of mycorrhizal hyphae, as water released from mycorrhizal hyphae increases the hydration in the intercellular space of cortical cells, and the root aquaporins are engaged for transmembrane water transport; (B3) When transcript abundance of the fungal aquaporins is up-regulated, a moderate increase in fungal aquaporins contributes to the increase in water efflux from hyphal cells and in hydration of root intercellular space, which leads to further enhancement of apoplastic water availability to root; (B4) Conditionally, increased abundance of fungal aquaporins may cause more water influx into hyphal cells and less water in intercellular space available for root transport. The diagrams were modified from Xu (2015) with the author’s permission.