The specific sense (S) and antisense (AS) primers (5′-3′) were designed using Primer3 (http:www-genome.wi.mit.educgi-binprimerprimer3http:www.cgi) and used to amplify the different AtMRPs by RT-PCR. The nomenclature of AtMRPs was according to Martinoia et al. (2002): (AC025295, T4K22.12, AtMRP1) AtMRP1-S, ccgc agaaatcctcttggtcttgatg and AtMRP1-AS, gtgaatcatcaccgt tagcttctctgg; (AC003096, T29F13, AtMRP2) AtMRP2-S, ccgcagaaatcctcttggtcttgatg and AtMRP2-AS, ccttgtaagtggt gtgagtcatctttgg; (AP000375, MJG19.3, AtMRP3) AtMRP3-S, ccactgcttctgttgacactg and AtMRP3-AS, gaggtgtactcagcc acaagc; (AC005309, F17A22.19, AtMRP4) AtMRP-4S, ctgg aacggtgtcaactcaaggatgttg and AtMRP4-AS, attccggcagatcg gagagcgtactctt; (AC002411, F20D22.11, AtMRP5) AtMRP-5S, cacttggacgagcattactga and AtMRP5-AS, tcttctaatagccgt gcagga; (AP000375, MJG19.4, AtMRP6) AtMRP6-S, ggtca gagacaattggtgtgc and AtMRP6-AS, accttggtctaggagcaggac; (AP000375, MJG19.5, AtMRP7) AtMRP-7S, aactggtgtgtct tggacgag and AtMRP7-AS, tcttgaatccgaacttgctgt; (AB023045, MXL8.11, AtMRP8) AtMRP-8S, ctctgcaagg gagctgattaggatca and AtMRP8-AS, tggagctatgtagcccttgg gaataa; (AL138658, T209.140, AtMRP9) AtMRP9-S, gccactgcttctgttgattct and AtMRP9-AS, gagccggcaaagtgat tagat; (AL163527, F17J16.190, AtMRP10) AtMRP10-S, ccacggcatcgatagataatg, and AtMRP10-AS; gccgagttgtaat gagaccaa; (AC025295, T4K22.1, AtMRP11) AtMRP-11S, tcgctcacagattgaatacca and AtMRP11-AS, ccaccttgactcattc cattc; (AC025295, T4K22.13, AtMRP12) AtMRP12-S, attcgcgaggaattcaagtct and AtMRP12-AS, cacccacactcattc cattct; (AC006225, T5E7.1, AtMRP13) AtMRP13-S, tca gagcccttttctgtttca and AtMRP13-AS, tcgtgttgtggagtagg gaag; (AL162651, F26K9.130, AtMRP14) AtMRP14-S, cgagcgatgtcaacttaagga and AtMRP14-AS, gcaaacaacgact gtctctcc. For this study, the selected housekeeping genes were S16 (At5g18380, this 40S ribosomal protein of Arabidopsis thaliana belongs to the S9P family of ribosomal proteins) and actin2 (At3g18780), the primers were S16-S: ggcgactcaaccagctactga; S16-AS: cggtaactcttctggtaacga; actin2-S, tggaatccacgagacaaccta; actin2-AS, ttctgtgaacgattc ctggac, respectively. The primers for PR1 (M90508) were, respectively, PR1-S: ggccttacggggaaaacttag; PR1-AS: cgttcacataattcccacgag. The PCR reactions were performed in a final volume of 25 µL containing the following mixture: PCR buffer, 0·2 mm dNTPs, 1 µm of both 5′- and 3′- primers, 1 U Taq DNA polymerase (Promega, Catalys, Wallisellen, Switzerland) and adjusted amounts of cDNA. Total RNA was purified from plants using the RNeasy Plant Mini Kit (Qiagen, Basel, Switerland) and stored at −80 °C after quantification by spectrophotometry. After DNAse treatment (DNase, RQ1, RNase free, Promega, Catalys), cDNAs were prepared using M-MLV reverse transcriptase, RNase H minus, point mutant (Promega, Catalys) as indicated by the manufacturer and stored at −20 °C. The cDNAs used in the PCR reaction were between a 1/10 and 1/100 dilution. After 2 min denaturation at 95 °C, 35 PCR cycles (94 °C for 45 s, 58 °C for 45 s and 72 °C for 1 min) were run. The PCR products for all 14 AtMRPs were sequenced to confirm that they corresponded to the right amplified fragments.