Transcripts of sunflower antioxidant scavengers of the SOD and GPX families accumulate differentially in response to downy mildew infection, phytohormones, reactive oxygen species, nitric oxide, protein kinase and phosphatase inhibitors

Messenger RNA accumulation of two previously characterized sunflower glutathione peroxidases (GPXha-1 and GPXha-2) was monitored in response to pathogen attack. The accumulation of GPXha-1 and GPXha-2 mRNAs was also followed after stimulation with various signalling molecules including stress related phytohormones, reactive oxygen species, nitric oxide and protein phosphatase or kinase inhibitors. To have a more complete view of the response of the plant enzymatic antioxidant system when challenged by these various stimuli, the accumulation of superoxide dismutase (SOD) mRNAs was monitored too. To do so, partial sunflower SOD cDNAs (SODha-1 and SODha-2) were cloned in the course of the study. We show here that sunflower GPX mRNA accumulated differently in leaves of plants infected with either a virulent or an avirulent race of pathogen (Plasmopara halstedii). We also observed that any of the stimuli used translated in a stronger accumulation of both GPX mRNAs. These data suggest that GPX enzymes are involved in the hypersensitive and stress responses in sunflower. When compared to each other, GPX and SOD messenger steady state levels behaved differently following biotic stress or treatments with stress signalling factors. This suggests that the antioxidant enzymes GPX and SOD are likely to play different functions in stress responses.