Mechanism of salt tolerance in wild Oryza species.

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The dry matter production and physiological response of wild Oryza species(O. latifolia and O. officinalist) to salinity stress were investigated by comparing with check varieties of O. sativa L. cv. Pokkali(salt-tolerant) and O. rufipogon(salt-susceptible). O. officinalis showed resistance to salinity as high as O. latifolia. The degree of decline in dry matter production of each part(root, leaf sheath, leaf blade) was different among the varieties after NaCl treatment. Top leaf Na^+ content per unit of dry-matter under 100mM NaCl condition in O. latifolia and O. officinalis increased 6.0 times and 5.2 times, respectively, as compared with Pokkali. Accumulation pattern of leaf blade Na^+ content in salt tolerant wild Oryza species were different from that in salt tolerance varieties, Pokkali. The wild Oryza species accumulated more Na^+ in lower leaf blade than in upper leaf blade. Carbon assimilation and oxygen evolution rate was examined under salinity conditions. The carbon assimilation rate of the wild Oryza species hardly decreased at 21 day after salt treatment. On the other hand, the oxygen evolution rate increased by salinity stress. The result of photosynthetic activity indicates that wild Oryza species has notable salt tolerance ability.