Suppression of Na+ Uptake Via Apoplastic Flow by Chitosan in Rice

Abstract Purpose: Chitosan enhances tolerance to salinity in rice. Apoplastic flow plays a crucial role in the accumulation of sodium (Na + ) in rice under salinity. This study investigated the effects of exogenous chitosan on apoplastic flow and Na + uptake in NaCl-treated rice seedlings. Methods: We employed an apoplastic tracer, trisodium salt of 8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS), in order to evaluate apoplastic flow in rice ( Oryza sativa L., cv. Nipponbare) seedlings that were hydroponically grown in the solution containing NaCl (0 and 25 mM), and chitosan (0 mg L − 1 , 10 mg L − 1 , and 50 mg L − 1 ). Results: Application of 25 mM NaCl significantly increased PTS uptake and Na + content in shoots but did not affect K + content, resulting in a lower K + /Na + ratio although 25 mM NaCl did not affect the seedling growth. The application of chitosan suppressed Na + -enhanced PTS uptake and Na + accumulation in shoots without affecting the K + content, which led to a higher K + /Na + ratio. Moreover, chitosan did not affect the reducing sugar content or electrical conductivity in the solution containing NaCl. Conclusions: These results suggest that application of chitosan suppressed Na + -enhanced apoplastic flow to reduce Na + uptake in rice seedlings.