Role of aquaporins in root water transport of ectomycorrhizal jack pine (Pinus banksiana) seedlings exposed to NaCl and fluoride

Effects of ectomycorrhizal (ECM) fungus Suillus tomentosus on water transport properties were studied in jack pine (Pinus banksiana) seedlings. The hydraulic conductivity of root cortical cells (L_pc) and of the whole root system (L_pr) in ECM plants was higher by twofold to fourfold compared with the non‐ECM seedlings. HgCl₂ had a greater inhibitory effect on L_pc in ECM compared with non‐ECM seedlings, suggesting that the mercury‐sensitive, aquaporin (AQP)‐mediated water transport was largely responsible for the differences in L_pc between the two groups of plants. L_pc was rapidly and drastically reduced by the 50 mm NaCl treatment. However, in ECM plants, the initial decline in L_pc was followed by a quick recovery to the pre‐treatment level, while the reduction of L_pc in non‐ECM seedlings progressed over time. Treatments with fluoride reduced L_pc by about twofold in non‐ECM seedlings and caused smaller reductions of L_pc in ECM plants. When either 2 mm KF or 2 mm NaF were added to the 50 mm NaCl treatment solution, the inhibitory effect of NaCl on L_pc was rapidly reversed in both groups of plants. The results suggest that AQP‐mediated water transport may be linked to the enhancement of salt stress resistance reported for ECM plants.