Motik, L. S., Fagerstedt, K. V. and Crawford, R. M.M. 1989. Oxygen toxicity and superoxide dismutase as an antioxidant in physiological stress. -Physiol. Plant, 76: 456-459.Although oxygen is vital for all aerobic life forms, excessive levels of oxygen free radical production can lead to potentially lethal oxidative reactions. The role of superoxide dismutase is examined as an integral part of the defence against oxidative injury resulting from various physiological stresses.

Mont, L. S., Braendle, R. and Crawford, R. M. M. 1987. Catalase activity and post-anoxic injury in monocotyledonous species.-J. exp. Bot. 38: 233-246. Three anoxia-intolerant species, Glyceria maxima, Juncus effusus and Iris germanica (var. Quechei), and three anoxia-tolerant species Schoenoplectus lacustris, Acorus calamus and Iris pseuaacorus were chosen for investigation. Rhizomes of anoxia-intolerant species show increased catalase activities when returned to air after periods of prolonged anoxia. Levels of catalase remained fairly constant in anoxia-tolerant species under the same conditions. In the anoxia intolerant G. maxima, the postanoxic increase in catalase activity was reduced by circulating the anaerobic atmosphere. This treatment also reduced the ethanol content of the tissue under incubation, and increased the survival of the rhizomes as seen in their ability to resume growth in the post-anoxic phase. Exposure of anaerobic G. maxima rhizomes to ethanol vapour increased post-anoxic levels of catalase activity and when this produced a 5-fold increase always resulted in death of the rhizomes. Acetaldehyde vapour applied in the same way gave rise to increases in catalase activity followed by rapid death of the rhizomes.It is suggested that post-anoxic oxidation of anaerobically accumulated ethanol may result in a surge of acetaldehyde production, which could exert a toxic effect on the recovering tissues. The possible role of catalase in an ethanol-oxidation reaction, which is well documented in animals, is discussed in the light of the association between the natural accumulation of large concentrations of ethanol and subsequent post-anoxic death in some plant tissues.

Although oxygen is vital for all aerobic life forms, excessive levels of oxygen free radical production can lead to potentially lethal oxidative reactions. The role of superoxide dismutase is examined as an integral part of the defence against oxidative injury resulting from various physiological stresses.

The perennating organ, the rhizome, was chosen for examination of response to anoxia in the species Iris pseudacorus L., Iris germanica L. var Quechei, and Glyceria maxima (Hartm.) Holmberg. These monocots are known to differ in their tolerance of anoxia. Intact rhizomes were subjected to periods of prolonged anoxia of up to 28 days and superoxide dismutase (SOD) activity was determined in a 48 hour postanoxic recovery phase. Tests were performed to ensure the accuracy of the measured enzyme activities. In the most anoxia tolerant species, I. pseadaorus, SOD activity rose continuously during the period of imposed anoxia, and levels were maintained in the postanoxic recovery phases: 28 days brought about a 13-fold increase to 1576 U SOD per milligram protein. Small increases were found in the less anoxia tolerant I. germanica during anoxic/postanoxic phases, while a drop in activity was recorded in the least anoxia tolerant G. maxima. However, initial levels in G. maxima were more than twice as high as in the other two species. Experiments applying cycloheximide to anoxic rhizome slices of I. pseudacorus inhibited the increase in SOD activity. This indicates that SOD is, paradoxically, induced under anoxia and we suggest that in this species SOD is one of the enzymes identified as anaerobic polypeptides. The significance of the induction ofan 'oxygen-protecting' enzyme during complete oxygen deprivation is discussed with regard to a possible critical role duning recovery from anoxic stress.

The antioxidant status of potato (Solanum tuberosum L.) tubers of two genotypes, cv. Désirée and clone 10337de40 was investigated in relation to susceptibility to internal rust spot (IRS), a Ca2+‐related physiological disorder. Concentrations of total calcium within the perimedulla tissue of tubers, grown with a restricted (1 mM CaCl2) Ca2+ supply, were similar in cv. Désirée (IRS resistant) and clone 10337de40 (IRS susceptible). A range of antioxidants was assayed in order to assess antioxidant status in both genotypes under the two Ca2+ treatments. Although no appreciable differences were detected between low Ca2+ and control treatments, certain antioxidants were present at significantly higher levels in the IRS resistant genotype, cv. Désirée. These included dehydroascorbate reductase (EC 1.8.5.1) activity (more than 100% higher), total glutathione content (ca 40% higher), glutathione reductase (EC 1.6.4.2) activity (almost 50% higher), peroxidase (EC 1.11.1.7) activity (ca 60% higher) and superoxide dismutase (EC 1.15.1.1) activity (almost 80% higher). There was no difference in ascorbate content, ascorbate free radical reductase activity (EC 1.6.5.4), α‐tocopherol levels and catalase activity (EC 1.11.1.6) between the two genotypes. The possible relationship between resistance to IRS and a superior antioxidant status, found in cv. Désirée, is discussed.