Arbuscular mycorrhizas modulate carbohydrate, phenolic compounds and hormonal metabolism to enhance water deficit tolerance of olive trees (Olea europaea)

Abstract

Olive trees (Olea europaea L.) in natural environments are increasingly being subjected to abiotic stresses, such as water deficit. Arbuscular mycorrhizal (AM) symbioses can improve olive tolerance to water deficit. In the current study, to elucidate the role of AM fungi in regulating water deficit resistance in olive, the effects of AM fungi Rhizophagus irregularis DAOM 197198 on gas exchange, stem water potential, phytohormones, carbohydrates and individual phenolic compounds were studied in potted culture under well-watered and water deficit-stressed conditions. Results showed a negative impact of mycorrhizal fungi on abscisic acid (ABA) and salicylic acid (SA) contents in roots. On the other hand, many intermediaries in primary and secondary were among the compounds accumulating more in AM leaves, mainly sugar alcohols (mannitol), flavan 3-ols (catechin), flavones (luteolin 7-O-glucoside), secoiridoid (oleuropein). These enhancements were higher under water deficit-stressed conditions. Maintaining high phenolic (especially oleuropein) and sugars (especially mannitol) levels in mycorrhizal stressed olive plants prevented stem water potential to decline to critical value, which did not exceed − 2 MPa, compared to their relative non-mycorrhizal stressed plants (−3.8 MPa). We showed that colonization of olive roots by Rhizophagus irregularis DAOM 197198 significantly reduced the deleterious effect of water deficit stress by up-regulating the primary and secondary metabolism and preserving a high stem water potential level.