Salt excretion: a new function of lenticels on pneumatophores of the mangrove Avicennia marina

Summary The mangrove Avicennia marina thrives in high‐salinity intertidal habitat and possesses pneumatophores with lenticels. The roles of pneumatophores in photosynthesis and lenticels in gas exchange are well established. However, their functions in salt excretion remain unclear. This study divided pneumatophores into three zones: aboveground portion (PA) with lenticels, belowground portion (PB), and feeding root (FR). Scanning electron microscopy with energy dispersive X‐ray spectroscopy (SEM‐EDS) analysis showed sodium (Na) and chlorine (Cl) were the predominant elements in crystals on lenticels, indicative of NaCl. Inductively coupled plasma mass spectrometry and spectrophotometry revealed significant Na + , Cl − , and K + accumulation in the PA. SEM‐EDS and non‐invasive micro‐test technology (NMT) revealed a salt transport pathway: ions are absorbed through FRs, followed by longitudinal transport via xylem (PB → PA) and lateral translocation through cortical cells to lenticels. Real‐time quantitative polymerase chain reaction showed predominant expression of Na + transporter genes ( SOS1 , NHX1 , and HKT1 ) in the PB, facilitating upward transport. Salt‐excretion efficiency increased with the degree of lenticel maturation and habitat salinity. PA‐specific expressions of aquaporin genes ( TIP1:3 , PIP2:2 , and PIP1:2 ) and salt‐transport‐related genes ( AKT1 and CLC‐c ) suggest their roles in maintaining water‐salt relation during salt excretion via lenticels. This work establishes a coordinated salt management model in A. marina pneumatophores, integrating root uptake, transport, and lenticel‐mediated excretion, redefining the excretory function of lenticels.