Mr. Hull et al., INSTANTANEOUS AND DEVELOPMENTAL EFFECTS OF LOW-TEMPERATURE ON THE CATALYTIC PROPERTIES OF ANTIOXIDANT ENZYMES IN 2 ZEA SPECIES, Australian journal of plant physiology, 24(3), 1997, pp. 337-343
When Zea mays cv. LG11 plants were grown 14 degrees C (close to the lo
wer thermal limit for leaf expansion), three of the five enzymes of th
e active oxygen scavenging cycle (Halliwell-Asada Pathway) showed chan
ges in total leaf activity compared with growth at 25 degrees C. Two o
f these enzymes, ascorbate peroxidase (APX) and glutathione reductase
(GTR), were selected for further investigation. The effects of assay t
emperature on three kinetic parameters (V-max, K-m, V-max/K-m) were de
termined in extracts from Z. mays and compared with extracts from its
low temperature tolerant relative, Z. diploperennis Iltis, Doebley & G
uzman. The kinetic power (V-max/K-m) was determined because the Km alo
ne may not be a useful predictor of an enzyme's effectiveness in situ.
The decrease in the kinetic power of APX on lowering the temperature
to 5 degrees C was much smaller in Z. diploperennis than in Z. mays. T
his suggests that the Z. diploperennis APX is better able to remove H2
O2 at severely reduced temperatures than is APX from Z. mays. Z. diplo
perennis had a twofold greater ascorbate pool than the chilling-suscep
tible Z. mays. Only minor differences were seen in the kinetic propert
ies of GTR and the size of the glutathione pool between the genotypes.