Effects of mycorrhizas on physiological performance and root TIPs expression in trifoliate orange under salt stress

Arbuscular mycorrhizal fungi (AMF) enhance salt tolerance of host plants, while it is unclear whether aquaporins are involved in the AMF event. This study analyzed the effects of inoculation with an arbuscular mycorrhizal fungus Paraglomus occultum on plant physiological performance and relative expression of root tonoplast intrinsic proteins (TIPs, a kind of aquaporins) genes in potted trifoliate orange (Poncirus trifoliata) seedlings subjected to 0 and 100 mM NaCl concentrations. AMF inoculation significantly increased plant growth performance, leaf water status (relative water content and water potential) and gas exchange (photosynthetic rate, transpiration rate and stomatal conductance), irrespective of non-salt and salt stress. Mycorrhizal seedlings exhibited significantly higher root salicylic acid concentrations and lower leaf and root jasmonic acid concentrations than non-mycorrhizal seedlings under non-salt and salt stress. Transcript levels of PtTIP1;1, PtTIP1;2 and PtTIP1;3 were down-regulated by AMF inoculation under non-salt and salt stress. PtTIP2;1 and PtTIP2;2 expression was unchanged under non-salt stress whereas was down-regulated by AMF colonization under salt stress. AMF inoculation considerably enhanced PtTIP4;1 transcript levels under non-salt and salt stress and PtTIP5;1 expression under non-salt stress. It is concluded that mycorrhizas mitigated salt stress of trifoliate orange through improving physiological performance and regulating root PtTIPs expression.