The role of peroxiredoxin antioxidant and calmodulin in ABA-primed seeds ofBrassica napusexposed to abiotic stresses during germination

Both peroxiredoxin and calmodulin have been demonstrated previously to be involved in the early stages of seed germination. We believe that the peroxiredoxin antioxidant proteins may play a role in protecting seed from oxidative damages and maintaining seed dormancy, and that calmodulins in regulating metabolic enzymes in the early stages of seed germination. To test this hypothesis two cDNA clones BnPER1 and BnCAM1, encoding peroxiredoxin antioxidant and calmodulin respectively, were isolated from seed of Brassica napus cv. Quest. In dry control seeds, a high level of BnPER1 transcript was present while that of BnCAM was low. Priming with 100 μmol/L ABA, where seeds underwent complete imbibition prior to radicle protrusion then dried back to their original moisture content, reduced the transcript level of BnPER1 and induced the expression of BnCAM1. Coincidentally, ABA-primed seeds exhibited earlier (2-7 days) germination and higher final percent radicle protrusion than non-primed control seeds, under salt (100 mmol/L NaCl) or water stress (20 % PEG 8000) at a low temperature (8 °C). For both ABA-primed and non-primed seeds, the decreased expression of BnPER1 and increased expression of BnCAM1 transcripts was highly correlated to the degree of seed germination. These results suggest that peroxiredoxins are down regulated during seed germination in B. napus, probably due to a reduction in oxidative stresses. On the other hand, elevated calmodulin levels was indicative of increased enzymatic activities required for germination. ABA-priming affected the expression of these genes.