This method enables the distinction between the three SOD isoen zymes found in Arabidopsis by using inhibitors of specific SODs. Gels inhibitor JQ1 were preincubated with KCN, which inhibits CuZn SOD, as well as H2O2, which inhibits both CuZn SOD and Fe SOD. MnSOD is resistant to both inhibitors. Plants were harvested from control plates containing no arsenate and treated plates containing 100M arsenate at seven. ten. and thirteen days post germination. Irrespec tive of harvest date, CuZnSOD activity was strongly induced by arsenate treatment, whereas FeSOD activity was repressed, and MnSOD showed no change in activity, therefore providing sufficient evidence to confirm our microarray results. Transcription of other antioxidant genes were indicated by our microarray experiment as affected by arsenate stress, however these genes were not included in our qRT PCR validation.

Inhibitors,Modulators,Libraries Transcription factors Our microarray experiment indicated that eight different genes encoding proteins with known transcription factor Inhibitors,Modulators,Libraries activity all displayed lower expression levels in As stressed plants. One of these transcription fac tors encodes a member of the DREB sub family A 1 of the ERF AP2 transcription factor family. One other AP2 domain containing transcription factor that encodes a member of the ERF subfamily B 3 of the ERF AP2 transcription factor family was also repressed in response to As. Two zinc finger genes encoded a ZAT7 and a protein similar to ZAT7, respectively. Also exhibiting lower expression in As treated plants were three members of the WRKY fam ily of transcription factors respec Inhibitors,Modulators,Libraries tively as well as one gene encoding NAC domain contain ing protein 81.

As represses Inhibitors,Modulators,Libraries genes involved in phosphate starvation response A notable transcriptional trend is that As stress results in repression of some genes involved in the Pi starvation response. Of particular interest, a P type cyclin that was affected by As stress shares sig nificant homology to the PHO80 gene from yeast. We per formed qRT PCR for this gene and found that its expression was actually Inhibitors,Modulators,Libraries strongly repressed at both day 3 and day 10. Three genes that were repressed by As in this study have also been reported to be repressed by Pi starvation. Interestingly, the three highest ranking differentially expressed genes found to be strongly induced by Pi starvation. were also repressed by As in our study. These genes are of partic buy inhibitor ular interest on account of their unknown function. Quantitative RT PCR confirmed that transcription of these genes was strongly repressed at both 3 day and 10 day time points. Additionally, the qRT PCR data indicate that these genes were more repressed at day 3 than at day 10.