An NADP/thioredoxin system (NTS), consisting of NADPH, NADP-thioredoxin reductase (NTR), and thioredoxin h (Trxh) plays a posttranslational regulatory role by reducing disulfide bonds in target proteins involved in different cellular processes. In contrast with prokaryotic and mammalian cells, plants have a complex NTR/Trx system comprising several Trx h and NTR isoforms. Therefore, one important question to be addressed is whether there is specificity in the interactions between different NTR and Trxh isoforms. Through search in rice ( oryza sativa L.) genome database we identified nine potential genes encoding Trxh and four potential genes encoding NTR. The recombinant forms of two isoforms of OsNTR (OsNTR1 and OsNTR2) and three isoforms of Trx h (OsTrx1, OsTrx20 and OsTrx23) were heterologously produced in E. coli as His-tag proteins in considerable amounts and then purifed using affinity chromatography. This enabled us to analyze in vitro interaction between different isoforms of NTR and Trxh from the same organism. To this end the kinetic parameters of OsNTRs towards three isoforms of OsTrx were determined using DTNB assay. The results of this assay showed that in contrast to OsTrx1 and OsTrx23, the isoform OsTrx20 was not reduced by OsNTR. Both OsNTR1 and OsNTR2 had five times more affinity towards OsTrx1 than OsTrx23. The amount of k cat however was almost similar towards both OsTrx isoforms. These results indicate that there is specificity in interaction of NTR and Trx isofroms in NTS .Furthermore, to test whether OsTrx isoforms can be reduced by glutathione (GSH), the reduction of insulin, was measured in the presence of GSH and each Trx isoform. OsTrx20 was efficiently reduced by GSH indicating that glutathione system may be responsible for reduction of OsTrx20. In addition, in the present study the tolerance of cells expressing recombinant proteins in response to oxidative stresses such as H 2 O 2 and ethanol were compared with control by plotting their growth curve. In comparison to OsNTR2, the expression of OsNTR1 yielded more growth in the presence of H 2 O 2 and ethanol. Moreover, the strains overexpressing OsTrx23 and OsTrx1 showed higher tolerance compared to OsTrx20 in the presence of H 2 O 2 , respectively, whereas the tolerance to ethanol did not differ significantly among these strains. We also for first time prepared the strains which were able to co-express OsNTR1 with each OsTrx isoform after induction with IPTG. To this end, the PCR products including promoter, ribosome binding site and the gene encoding each OsTrx isoform were ligated to plasmid pET-28a containing gene OsNTR1. Therefore three constructs containing genes encoding OsNTR1/OsTrx1, OsNTR1/OsTrx20 and OsNTR1/OsTrx23 were produced and transferred to E. coli . The preparation of these starins enabled us to analyze the interaction of OsNTR1 with each OsTrx isoform in vivo . Among these strains, tolerance of strain coexpressing OsNTR1/OsTrx1 in response to H 2 O 2 was higher than the strains expressing OsNTR1 or OsTrx1 solely. This result indicates that OsNTR1 has higher interaction towards OsTrx1 in vivo which corresponds to the results of in vitro assay. Key Words: Rice, NTR/Thioredoxin System, Kinetic Parameters, Glutathione, Oxidative Stress, Co-expression.