Instantaneous and Developmental Effects of Low Temperature on the Catalytic Properties of Antioxidant Enzymes in Two <i>Zea</i> Species

Abstract

When Zea mays cv. LG11 plants were grown 14˚C(close to the lower thermal limit for leaf expansion), three of the five enzymes of the active oxygen scavenging cycle (Halliwell-Asada Pathway) showed changes in total leaf activity compared with growth at 25˚C. Two of theseenzymes, ascorbate peroxidase (APX) and glutathione reductase (GTR), were selected for further investigation. The effects of assay temperature on threekinetic parameters (Vmax,Km,Vmax/Km) were determined inextracts from Z. mays and compared with extracts fromits low temperature tolerant relative, Z. diploperennis Iltis, Doebley &amp; Guzman. The kinetic power(Vmax/Km) was determinedbecause the Km alone may not be a useful predictor of anenzyme’s effectiveness in situ . The decrease inthe kinetic power of APX on lowering the temperature to 5ºC was muchsmaller in Z. diploperennis thanin Z. mays . This suggests that the Z. diploperennis APX is better able to removeH2O2 at severely reducedtemperatures than is APX from Z. mays . Z. diploperennis had a twofold greater ascorbate poolthan the chilling-susceptible Z. mays . Only minordifferences were seen in the kinetic properties of GTR and the size of theglutathione pool between the genotypes.