PROTECTION AGAINST ACTIVATED OXYGEN FOLLOWING RE-AERATION OF HYPOXICALLY PRETREATED WHEAT ROOTS - THE RESPONSE OF THE GLUTATHIONE SYSTEM

This paper shows the effects of re-aeration on the glutathione pool fo llowing a prolonged period of root hypoxia. An increased content of to tal glutathione has been measured in roots of wheat seedlings (Triticu m aestivum L. cv. Alcedo), grown in a nitrogen-flushed nutrient soluti on (HI) with their shoots in air compared with roots of aerobically gr own plants (C). Re-aeration of hypoxically pretreated roots causes oxi dative injury indicated by the oxidation of reduced glutathione (GSH), decrease of total thiol groups and increased formation of TBA reactiv e material (lipid peroxidation). Re-admission of oxygen results in a 5 0% rise in oxygen uptake over the whole 16 h re-aeration period compar ed with the control. During this time the overall glutathione pool of HI treatment increases to almost double that of the control, essential ly reflected in the amount of oxidized glutathione (GSSG). Hypoxically pretreated roots showed lower glutathione reductase activity (GR) tha n the control. Immediately following re-aeration the activity was furt her decreased to a limiting value which seems to prevent full reductio n of the newly formed glutathione. Therefore, the capacity to reduce t he GSSG pool is below the capacity for net glutathione synthesis. This results in a decline of the GSH/GSSG ratio which reflects oxidative s tress. The enzyme activity recovers slowly after re-aeration exceeding the values of aerobically grown roots only after 16 h correlating wit h a high reduction state of the glutathione pool. Copper, known to ind uce the formation of reactive oxygen species, strengthened the effect of re-aeration and enhanced the post-anoxic injury irreversibly. The i mportance of the glutathione system in roots to cope with varying oxyg en tension is discussed.