Inhibition of root elongation and modification of membrane properties are sensitive responses of plants to aluminium. The present paper reports on the effect of AI on lipid peroxidation and activities of enzymes related to production of activated oxygen species. Soybean seedlings (Glycine max L. cv. Sito) were precultured in solution culture for 3–5 days and then treated for 1–72 h with Al (AICI3) concentrations ranging from 10 to 75 μM at a constant pH of 4.1. In response to Al supply, lipid peroxidation in the root tips (< 2 cm) was enhanced only after longer durations of treatment. Aluminium-dependent increase in lipid peroxidation was intensified by Fe2+ (FeSO4). A close relationship existed between lipid peroxidation and inhibition of root-elongation rate induced by Al and/or Fe toxicity and/or Ca deficiency. Besides enhancement of lipid peroxidation in the crude extracts of root tips due to Al, the activities of superoxide dismutase (EC 1.15.1.1) and peroxidase (EC 1.11.1.7) increased, whereas catalase (EC 1.11.1.6) activity decreased. This indicates a greater generation of oxygen free radicals and related tissue damage. The results suggest that lipid peroxidation is part of the overall expression of Al toxicity in roots and that enhanced lipid peroxidation by oxygen free radicals is a consequence of primary effects of Al on membrane structure.

Effect of aluminium on lipid peroxidation, superoxide dismutase, catalase, and peroxidase activities in root tips of soybean (Glycine max)

Zinc deficiency is one of the most widespread micronutrient deficiencies in plants and causes severe reductions in crop production. There are a number of physiological impairments in Zn-deficient cells causing inhibition of the growth, differentiation and development of plants. Increasing evidence indicates that oxidative damage to critical cell compounds resulting from attack by reactive O2 species (ROS) is the basis of disturbances in plant growth caused by Zn deficiency. Zinc interferes with membrane-bound NADPH oxidase producing ROS. In Zn-deficient plants the iron concentration increases, which potentiates the production of free radicals. The Zn nutritional status of plants influences photooxidative damage to chloroplasts, catalysed by ROS. Zinc-deficient leaves are highly light-sensitive, rapidly becoming chlorotic and necrotic when exposed to high light intensity. Zinc plays critical roles in the defence system of cells against ROS, and thus represents an excellent protective agent against the oxidation of several vital cell components such as membrane lipids and proteins, chlorophyll, SH-containing enzymes and DNA. The cysteine, histidine and glutamate or aspartate residues represent the most critical Zn- binding sites in enzymes, DNA-binding proteins (Zn-finger proteins) and membrane proteins. In addition, animal studies have shown that Zn is involved in inhibition of apoptosis (programmed cell death) which is preceded by DNA and membrane damage through reactions with ROS. contents Summary 185 I. introduction 186 II. effect of zinc on production of reactive oxygen species 186 III. membrane damage by reactive oxygen species 193 III. membrane damage by reactive oxygen species 193 V. involvement of zinc in plant stress tolerance 199 VI. conclusions 199 Acknowledgements 200 References 200.

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Tansley Review No. 111: Possible roles of zinc in protecting plant cells from damage by reactive oxygen species.

Purification and characterization of an extracellular Mn(II)-dependent peroxidase from the lignin-degrading basidiomycete, Phanerochaete chrysosporium

INTRODtTCTION ... .. .... . . ........ . . . . ....... . . . ... .. .. . .. . . .... . . . .. ... ....... .. . .. .. . . .... .. . .. .. . . ... . . . . 74 OXYGEN ACTIVATION AND REACTIVE OXYGEN SPECIES ... ..... . . . . . ..... . .. ... 75 Reductive Activation ........ . . ......... ... . . . ..... . ..... .. ....... . . . . .. ....... . . . . 75 Oxygen Addition to Organic Radicals or Reduced Metal Complexes 75 Photodynamic Reactions ,.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...... . . . . . . . 76 REACTIVITY AND DETECTION OF ACTIVE OXYGEN SPECIES 77 Superoxide . . . . . ... . . . . ....... . . . . . . . . ....... . . . . . . . . ..... ......... ..... 77 Hydrogen Peroxide (H20JJ 77 The OR Radical ....... . . 78 Singlet Oxygen 78 Organic Peroxides and Peroxy Radicals ......... . . . . . 79 OXYGEN ACTIVATION IN DIFFERENT COMPARTMENTS AND ORGANELLES OF PLANT CELLS 79 Peroxides in Cell Walls . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Microsomal Oxygen Activation .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Peroxisomes ........ . . . . . . . . . . . . . . . . . . . . . . ....... . . . . . . . . . . . . . ..... ...... 80 Oxygen Activation and Detoxification in Mitochondria . ...... 80 Chloroplasts ....... .... ...... ..... .. . . . ..... . . . ...... . . . . . . . . ..... . . . . . ......... . ... 81 Physiological observations and the biological significance of oxygen reduction 8 1 Mechanisms o f oxygen activation in the chloroplast .... ..... 82 Functions of activated oxygen species in chloroplasts . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . 84 ENDOGENOUS MECHANISMS OF PROTECTION AGAINST DELETERIOUS OXYGEN SPECIES ...... 84 PATHOLOGICAL, ENVIRONMENTAL, AND COMMERCIAL ASPECTS OF OXYGEN TOXICITy 86 CONCLUDING REMARKS AND FUTURE TRENDS 88

Oxygen activation and oxygen toxicity

Mechanisms for the generation of reactive oxygen species in plant defence – a broad perspective

Peroxidase associated with isolated horseradish cell walls catalyzes the formation of H2O2 in the presence of NADH The reaction is stimulated by various monophenols, especially of coniferyl alcohol NADH can be provided by a bound malate dehydrogenase This system is capable of polymerizing coniferyl alcohol yielding an insoluble dehydrogenation polymer NADH was found to be oxidized by two different mechanisms, one involving Mn2+, monophenol, and the superoxide radical O2·- in a reaction that is not affected by superoxide dismutase, and another one depending on the presence of free O2·- and probably of an enzyme-NADH complex A scheme of these reaction chains, which are thought to be involved in the lignification process, is presented

Involvement of malate, monophenols, and the superoxide radical in hydrogen peroxide formation by isolated cell walls from horseradish (Armoracia lapathifolia Gilib.).

C. Janse

Papers

Involvement of malate, monophenols, and the superoxide radical in hydrogen peroxide formation by isolated cell walls from horseradish (Armoracia lapathifolia Gilib.).