The response of the ascorbate-
glutathione cycle was investigated in roots of young wheat (Triticum aestivum L.) seedlings that were deprived of
oxygen either by subjecting them to root
hypoxia or to entire plant
anoxia and then re-aerated. Although higher total levels of ascorbate and
glutathione were observed under
hypoxia, only the total amount of ascorbate was increased under
anoxia. Under both treatments a significant increase in the reduced form of ascorbate and
glutathione was found, resulting in increased reduction states. Upon the onset of re-aeration the ratios started to decline rapidly, indicating oxidative stress.
Hypoxia caused higher activity of
ascorbate peroxidase, whereas activities of
monodehydroascorbate reductase,
dehydroascorbate reductase, and
glutathione reductase were diminished or only slightly influenced. Under
anoxia, activities of
ascorbate peroxidase and
glutathione reductase decreased significantly to 39 and 62%, respectively. However, after re-aeration of hypoxically or anoxically pretreated roots, activity of
enzymes approached the control levels. This corresponds with the restoration of the high reduction state of ascorbate and
glutathione within 16 to 96 h of re-aeration, depending on the previous duration of
anoxia. Apparently,
anoxia followed by re-aeration more severely impairs entire plant metabolism compared with
hypoxia, thus leading to decreased viability.