Regulation of water transport in Arabidopsis by methyl jasmonate

Following a stress event, jasmonate-dependent signaling pathway triggers a shift from growth to defense responses that are accompanied by the cessation of growth in many plants. However, the processes leading to this growth inhibition remain obscure. In this study, we provide evidence for a rapid inhibition of cell hydraulic conductivity (L_p) by methyl jasmonate (MeJA) in the roots of wild-type Arabidopsis within 0.5 h of 20 and 50 μM MeJA treatments. We also demonstrate that MeJA did not affect L_p in fad3-2 and fad7-2 Arabidopsis mutants that are deficient in jasmonate precursor, linolenic acid. The reductions of L_p in wild-type plants were accompanied by the down-regulation of several plasma membrane intrinsic protein (PIP) isoforms, and dephosphorylation. Treatments with HgCl₂ did not further reduce L_p in the wild-type plants, but significantly reduced L_p in the fad3-2 and fad7-2 that had been first treated with MeJA. Continuous prolonged exposure to exogenous 50 μM MeJA inhibited the relative growth rates (RGR) of shoots and net photosynthesis (P_n) in the Arabidopsis wild-type and fad7-2 plants, but had no effect on the RGR of roots. The results demonstrated that a reduction of aquaporin (AQP)-mediated water transport was the initial target of MeJA exposure, and may contribute to the processes of growth inhibition by MeJA.