Instantaneous and Developmental Effects of Low Temperature on the Catalytic Properties of Antioxidant Enzymes in Two Zea 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 (V_max,K_m,V_max/K_m) were determined inextracts from Z. mays and compared with extracts fromits low temperature tolerant relative, Z. diploperennisIltis, Doebley & Guzman. The kinetic power(V_max/K_m) was determinedbecause the K_m 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 thaninZ. mays. This suggests that theZ. 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.