Contribution of the Arbuscular Mycorrhizal Symbiosis to the Regulation of Radial Water Transport in Roots of Maize Plants Under Drought

Radial water and solute transport across the root cylinder was described by the composite model and consists in three major pathways: apoplastic, symplastic and transcellular. The last two are known as the cell-to-cell pathway. The flux of water through them depends on the species, root developmental states and environmental conditions. While in transpiring conditions water is mainly flowing following the apoplastic pathway due to the hydrostatic pressure, under drought stress, when transpiration is reduced, water moves driven by the osmotic gradient, through the cell-to-cell path.

The association between arbuscular mycorrhizal (AM) fungi and plant roots can modify root water transport. Indeed, recent studies found that AM are able to differently modulate the switching between water transport pathways in roots.

In the present study we shed light on the effect of this symbiosis on radial root water transport in maize under well-watered and drought stress conditions. For that, we used sodium azide (2 mM), an inhibitor of aquaporin activity and water flux through the cell-to-cell pathway. Osmotic and hydrostatic root hydraulic conductivities (Lpr) were analyzed, as well as the percentage of water flowing through the apoplast.

Additionally, anatomical differences between the roots of the different treatments were investigated by using berberine hemisulphate for the staining of suberized and lignified structures.

Results showed that the application of sodium azide differently affected hydrostatic and osmotic Lpr and % of water flowing through the apoplast in non-AM and AM plants, depending on the watering conditions. Deposition of suberin in the apoplastic barriers also differed between plants of the different treatments.