PbrSLAH3b mediates nitrate-dependent regulation of pollen tube growth in pear

Pollen tube growth represents a critical process in plant sexual reproduction, governed by the highly coordinated activities of ion channels that regulate polarized cell expansion. Among them, the slow anion channel (SLAC/SLAH) family plays a central role in mediating transmembrane anion fluxes, particularly nitrate (NO₃⁻). However, the identity and function of SLAH family members involved in pear pollen tube development remain largely unexplored. In this study, we identified and characterized PbrSLAH3b as a candidate nitrate-permeable anion channel highly expressed in pear pollen tubes. Expression profiling revealed that PbrSLAH3b is markedly induced by NO₃⁻ and peaks at the middle stage of pollen tube elongation. Subcellular localization analysis confirmed that PbrSLAH3b is targeted to the plasma membrane. Electrophysiological assays using a two-electrode voltage-clamp system demonstrated that PbrSLAH3b functions as an anion channel with high permeability to NO₃⁻ relative to other anions including Cl⁻ and SO₄²⁻. Notably, PbrSLAH3b mediated substantial nitrate-dependent currents in Xenopus laevis oocytes without the requirement for exogenous kinase co-expression. Moreover, antisense oligodeoxynucleotide (AS-ODN)-mediated knockdown of PbrSLAH3b significantly suppressed its transcript abundance and inhibited pollen tube elongation. Taken together, these results demonstrate that PbrSLAH3b is a NO₃⁻-permeable and NO₃⁻-activated anion channel that mediates NO₃⁻ transport to support pollen tube growth.