Amelioration of the Salt-stressed Root Growth of Rice and Normalization of the Na⁺ Distribution between the Shoot and Root by (S)-α-Methylbenzyl-2-fluoro-4-methylphenylurea

Abstract

  Optically active α-methylbenzyl phenyl ureas (MBPUs) show diverse plant physiological properties. Experiments were conducted to evaluate the salt-stress response of just-germinated rice seedlings supplemented with the S-enantiomer of MBPUs by assessing the growth and Na⁺ content. This study indicates that S-MBPUs served as a unique stress reliever for just- germinated young seedlings of rice injured by salinity. NaCl severely affected the root growth of rice seedlings. Concomitant treatment with S-MBPUs effectively ameliorated the growth inhibition of rice by NaCl. Glycine betaine (GB) did not act as a reliever of the NaCl stress. The addition of S-α-methylbenzyl 2-fluoro-4-methylphenyl urea (7, denoted as S-FM) to the saline medium ameliorated not only the root growth but also the protein content and dry weight of roots depending upon its concentration. The protein content, Na⁺ content and growth rate were correlated to each other with a positive relationship. The Na⁺ distribution ratio (S/R_(Na⁺)) between the shoot and root increased with increasing concentration of NaCl when added alone, viz. with increasing growth reduction. A concomitant treatment with S-FM (7), however, resulted in the S/R_(Na⁺) value becoming smaller with growth amelioration. This indicates that S-FM (7) controlled the translation of Na⁺ from the roots to shoots. S-FM (7) would have influenced some inherent functions connected with the Na⁺ behavior in the rice plant, although details of the mechanism for normalization of the S/R_(Na⁺) ratio are still not clear.