Salt tolerance of the chloroplast thylakoid membrane in wild Oryza species, Oryza latifolia desv.

In our previous report, the wild Oryza species O. latifolia showed higher salt-tolerance than the standard salt tolerant rice species, SR26B. To elucidate the mechanism of salt tolerance in O. latifolia, we compared the activity of photosynthetic machinery in thylakoid membrane in O. latifolia with that in a salt-susceptible wild Oryza species, O. rufipogon under high salinity condition. In O. rufipogon photosynthetic rate declined by 75 % and 30 % of that in non-stress leaves under 300 mM and 655 mM NaCl, respectively. Whereas in O. latifolia it was unchanged under 300 mM NaCl, and decreased under 655 mM NaCl by 60 % of that in non-stress leaves. Thylakoid membrane of O. latifolia also showed salt tolerance. The oxygen evolution rate from isolated thylakoid membrane in O. latifolia decreased only 13 % under 655 mM NaCl. On the other hand, in O. rufipogon, it decreased 10 % and 30 % under 300 mM and 655 mM NaCl, respectively. The peptide compositions of thylakoid membranes examined by SDS-PAGE showed that O. latifolia has species-specific proteins with 20.3 kDa and 22,4 kDa of molecular weight. Two-dimensional electrophoresis (2-DE) of thylakoid membrane proteins showed that the 20.3 kDa and 22.4 kDa proteins contained at least two or three proteins with different isoelectric points. Some of them were novel proteins that had not been published in the database. These results suggest that thylakoid membrane of O. latifolia has high salt tolerance and this plant can maintain photosynthetic activity under high NaCl condition. The results of SDS-PAGE and 2-DE showed that the thylakoid membrane of O. latifolia had specific proteins which may be partially responsible for the salt-tolerance.