Effect of NaCl on the Photosynthesis, Water Relations and Free Proline Accumulation in the Wild Oryza Species

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The physiological responses of wild Oryza species (Oryza latifolia Desv., a salt-tolerant species and O. rufipogon Griff., a salt-susceptible species) to salinity stress were investigated by comparing with check varieties of cultivated rice (O. sativa L.), SR26B (salt-tolerant) and IR28 (salt-susceptible). As the Nacl concentration of water culture solution was raised to 12 dS m^<-1> (about 113mM), leaf Na^+ content per dry matter in wild Oryza species increased from 4 to 17 times as compared with the control (no NaCl treatment), whereas the accumulation was lower in cultivated rice varieties. The increased concentration of leaf Na^+ resulted in the decrease in leaf water potential (Ψ_w) in all rice species, although the degree of decline in photosynthetic rate was different among the varieties. It was notable that the photosynthetic rate was almost constant in O. latifolia though Ψ_w decreased to - 2.0 MPa with the increased NaCl concentration in the water culture solution. A significant negative correlation between free-proline content and osmotic potential (Ψ_s) of leaf blade was found in both salt tolerant entries, SR26B and O. latifolia. In spite of higher leaf Na^+ storage, the survival rate of O. latifolia was higher than that of SR26B, indicating that the mechanism of salt tolerance in O. latifolia may be different from that in SR26B.
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