Alteration of gene expression in Pisum sativum tissue cultures caused by the free radical‐generating agent 2,2′‐azobis (2‐amidinopropane) dihydrochloride

Root‐differentiated tissue cultures (PS‐R) from Pisum sativum (cv. Greenfeast) were exposed to a 5 mM solution of the free radical‐generating compound 2,2′‐azobis (2‐amidinopropane) dihydrochloride (AAPH). The levels of mRNA transcripts for two genes were examined: chs2, encoding a chalcone synthase isozyme, and cab, encoding the chlorophyll a/b‐binding protein of the light‐harvesting antenna complex. In light‐grown PS‐R, cab mRNA transcript levels decreased to 14% of controls after 6 h of exposure, whereas chs2 mRNA levels increased 50‐fold. In dark‐grown PS‐R, chs2 mRNA transcripts increased by 40‐fold compared with the controls. Glutathione determination in light‐grown PS‐R showed no substantial difference in total glutathione (GSHtot), whereas oxidized glutathione (GSSG) increased by 66% after 12 h of exposure. However, in dark‐grown PS‐R a decrease in both GSHtot and GSSG after 6 h was followed by an increase of about 70%, as compared with the controls, after 12 h of exposure. In conclusion, AAPH generated oxidative stress, reflected in changed glutathione levels and induced expression of the chs2 gene of the flavonoid biosynthetic pathway and also caused a decreased level of mRNA for the photosynthetic cab gene.