Relationships between aquaporins gene expression and nutrient concentrations in melon plants (Cucumis melo L.) during typical abiotic stresses

Melon (Cucumis melo L.), a member of the Cucurbitaceae, in Mediterranean regions is usually affected by abiotic stresses like salinity, nutrients deficiency or high temperature. These abiotic stresses have been shown to produce the modulation of gene expression as a response to the altered conditions. Among these genes, aquaporins (transmembrane proteins) stand out due to their vital function as transporters of water and different solutes. For this reason, the aim of this work was to study the expression levels of all (31) aquaporins of melon plants (CmAQPs) after exposure to salinity (50 mM NaCl), nutrient deficiency (10% Hoagland solution) or high tem-perature (40 oC for 1 h/day) and relate them with nutrient content, water relations and hydraulic conductance. There were general decreases in plant nutrient concentrations, especially in the root (Fe, K, Mn or Zn), while the concentrations of some elements for each stress (B, Ca, Mg, Mo or Si) increased. Physiological parameters were regulated depending on the treatment, showing the important role of hydric physiology regulation in the whole melon plant response to the different stresses. For most of the aquaporins, their expression decreased in the root (PIP2;1, PIP2;5 and PIP2;6 within the PIPs; most of the TIPs; NIP6;1, NIP7;1; SIP1;1) in all three treatments, while other aquaporins were over-expressed, such as the PIP1s (high temperature treatment), PIP2;2 (nutrient deficiency and high temperature treatments) and TIP1;1 (salinity and high temperature treatments) and NIP5;1 (nutrients deficiency treatment). The leaf aquaporin expression levels were less affected. This study shows that CmAQPs expression is modified differently in response to distinct abiotic stresses and that this is related to plant water relations and nutrients levels.