Improved Waterlogging Tolerance in Roots of Cucumber Plants after Inoculation with Arbuscular Mycorrhizal Fungi

Abstract

Mycorrhizal symbiosis enhances host plant resistance to various unfavorable environmental stresses, but whether and how it also enhances waterlogging tolerance in cucumber plants is not known. The objective of this study was to analyze the effect of Paraglomus occultum inoculation on biomass production, osmolyte levels, and the expression of 12 heat shock protein 70 (Hsp70) genes and 14 plasma membrane intrinsic protein (PIP) genes in the roots of cucumber plants under a short-term waterlogging stress (WS) (5 days) condition. Although the short-term WS treatment significantly inhibited the arbuscular mycorrhizal fungal colonization of roots, the inoculation with arbuscular mycorrhizal fungi (AMFs) significantly increased leaf, stem, and root biomass under WS. AMF inoculation also significantly increased root glucose, sucrose, betaine, and proline contents, along with decreased fructose levels, compared with the uninoculated control. More CsHsp70 and CsPIP genes were up-regulated in AMF-inoculated plants than in AMF-uninoculated plants in response to WS. AMF inoculation showed no significant effect on the expression of any of the examined CsHsp70 genes under no-waterlogging stress, but it did raise the expression of 11 of 12 CsHsp70 genes under WS. AMF colonization also down-regulated or had no effect on CsPIP expression under no-waterlogging stress, whereas it up-regulated the expression of 12 of the 14 CsPIP genes under WS. It is concluded that AMF inoculation enhances waterlogging tolerance in cucumber plants by increasing osmolyte levels and stress-responsive gene (CsPIP and CsHsp70) expression.