Re-Aeration following Hypoxia or Anoxia Leads to Activation of the Antioxidative Defense System in Roots of Wheat Seedlings

Abstract

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.

Figure 1

Effect of hypoxic or anoxic conditions on growth of wheat shoots and roots. The data are given as mean dry weights per plant and are from at least three independent experiments, each with 10 seedlings. sds are (in the range of) ≤10%.

Figure 2

Activities of APX, MDAR, DHAR, and GR in roots of wheat seedlings under hypoxia (H) followed by re-aeration for 20 min, 2 h, and 16 h (H+20′C, H+2hC, and H+16hC, respectively) compared with aerated control (C). Each data point represents the mean of five separate experiments. Bars, ± sd; asterisks, the significance of differences at the 5% level between control and hypoxia and between hypoxia and re-aeration.

Figure 3

Activity of APX and GR after 2, 4, and 8 d of anoxia (C+2dA, C+4dA, and C+8dA, respectively) compared with aerated controls (C). Each data point represents the mean of three or 10 (for control) separate experiments. Bars, ± sd; asterisks, the significance of differences at 5% level between control and anoxically grown plants.