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Effects of Elevated CO2 on Antioxidative Enzymes in Soybean
Pritchard, S.G., Ju, Z., van Santen, E., Qiu, J., Weaver, D.B., Prior, S.A. and Rogers, H.H.  2000.  The influence of elevated CO2 on the activities of antioxidative enzymes in two soybean genotypes.  Australian Journal of Plant Physiology 27: 1061-1068.

What was done
The authors grew two genotypes of soybean (Glycine max (L.) Merr.) for 61 days in pots placed within open-top chambers receiving atmospheric CO2 concentrations of 365 and 720 ppm to determine the effects of elevated CO2 on the activities of several foliar antioxidative enzymes.  One of the genotypes studied typically displays resistance to the fungal pathogen Cercospora sojina, which causes frogeye leaf spot disease in this species; while the other genotype is generally susceptible to this pathogen.

What was learned
Irrespective of genotype, elevated CO2 decreased foliar rubisco activity and concentration by about 30 and 25%, respectively.  Similarly, leaf chlorophyll and carotenoid contents were reduced by 23 and 37% by atmospheric CO2 enrichment, respectively.

The activities of all antioxidative enzymes studied were significantly reduced by elevated CO2.  Of special interest were 15 and 24% CO2-induced reductions in the activities of superoxide dismutase and catalase, respectively, in leaves of the fungal pathogen-resistant soybean.  In leaves of the susceptible soybean genotype, atmospheric CO2 enrichment led to even greater reductions of 30 and 54% in these same respective enzymes.  Thus, it would appear that elevated CO2 reduces the activity, and probably the amount, of antioxidative enzymes in leaves of soybeans of both genotypes.

What it means
As the air's CO2 content continues to rise, it is likely that plants will experience reductions in the amounts of harmful reactive oxygen compounds they typically encounter, due to the amelioration of various types of stresses (which produce the deleterious reactive oxygen compounds) that is generally provided by atmospheric CO2 enrichment.  Thus, as demonstrated here, plants should not have to produce as many antioxidative enzymes as they currently do under ambient CO2 concentrations, which should therefore allow even greater amounts of resources to be used elsewhere in the plant to support further growth and development.

Reviewed 27 December 2000