On the involvement of non-phosphorylating glyceraldehyde-3-phosphate dehydrogenase in the response to oxidative stress in plants

IGLESIAS AA, BUSTAMANTE CA, BUSTOS DM

San Diego, California. USA.

Congreso; The annual meeting of the American Society of Plant Physiologists; 2000

The American Society of Plant Physiologists

            Non-phosphorylating glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.9; abbrev. GAPN) catalyzes the irreversible oxidation of glyceraldehyde-3P to 3-phosphoglycerate coupled to the reduction of NADP to NADPH. It has been suggested that higher plant GAPN is involved in a system for the transfer of photo-generated NADPH from the chloroplast to the cytosol. We evaluated the levels of GAPN in wheat and maize plants subjected to oxidative stress induced by methyl viologen (MV, also known as paraquat), a superoxide radical propagator. When added in the assay medium, MV (up to 5 mM) produced no inhibition of GAPN activity, which is a distinctive feature of the reagent after its inhibitory effect on other NADPH producer enzymes. Plants were sprayed with different concentrations of MV and then GAPN was characterized in leaf extracts. Specific activity of the enzyme increased 1.3-fold (average of 5 independent experiments) in the leaves of treated plants, respect to the control. The increase in activity was also observed at 0.1 mM MV, which is remarkable when compared with other enzymes that are highly affected by the reagent. Levels of GAPN mRNA, using the eukaryotic initiation factor of translation A4 as a control, were not modified by the treatment with the oxidant. Results suggest the involvement of GAPN in a plant response mechanism to oxidative stress. It is proposed that the enzyme actively supply NADPH necessary to protect the cytosol of leaf cells against the oxidative conditions.