Exogenous proline and glycinebetaine suppress apoplastic flow to reduce Na⁺ uptake in rice seedlings

The application of exogenous proline and glycinebetaine (betaine) confers salt tolerance on plants undersalt stress. The e?ects of exogenous proline and betaine on apoplastic ?ow in rice plants under saline conditions were investigated using trisodium-8-hydroxy-1,3,6-pyr-enetrisulphonic acid (PTS), an apoplastic tracer. Rice plants took up more PTS under light conditions than under dark conditions. Salt stress increased PTS uptake and Nap content of rice leaves, but did not a?ect Kp content, resulting in a lower Kp/Nap ratio. Addition of proline or betaine to the saline medium suppressed Napinduced PTS uptake and Nap accumulation, while the Kp content was slightly increased, which led to a high Kp/Nap ratio under saline conditions. These results suggest that exogenous proline and betaine suppressed Nap-enhanced apoplastic ?ow to reduce Nap uptake in rice plants.