Morphological and metabolic responses to salt stress of rice (Oryza sativa L.) cultivars which differ in salinity tolerance

Salinization is one of the most important abiotic stressors for crop growth and productivity. Rice (Oryza sativa L.), as the major food source around the world, is very sensitive to salt, especially at seedling stage. In order to examine how salt stress influences the metabolism of rice, we compared the levels of a range of sugars and organic acids in three rice cultivars with different tolerance under salt stress over time. According to the morphological result, the shoot length and root fresh weight were only affected by salinity in the salt sensitive cultivar (Nipponbare). The responses of metabolites to salinity were time-, tissue- and cultivar-dependent. Shikimate and quinate, involved in the shikimate pathway, were dramatically decreased in the leaves of all three cultivars, which was regarded as a response to salinity. Many sugars in the leaves of the salt tolerant cultivar (Dendang and Fatimawati) showed earlier increases to salt stress compared to Nipponbare leaves. Moreover, only in the leaves of tolerant cultivars (Dendang and Fatimawati), malate was significantly decreased while sucrose was significantly increased. In Dendang roots, mannitol levels were significantly higher than in Nipponbare roots after 14 days of salt treatment, which may be attributed to its higher salt tolerance. It is proposed that these responses in the more tolerant cultivars are involved in their resistance to high salt stress which may lay the foundation for breeding tolerant rice cultivars.