Summary

SUMMARY of Ph.D. thesis entitled:

''Antioxidants of growing-wild plants’’

by Dragoljub Miladinovic

This Ph.D. thesis presents the results of determination of oxygen radicals (superoxide and hydroxyl radicals), malonyl-dialdehyde, antioxidant enzymes (superoxide dismutase, catalase, peroxidase and glutathione peroxidase), nonenzymatic antioxidants (reduced glutathione, carotenoids), chlorophyll and soluble proteins in: Astragalus onobrychis L. Var. Chlorocarpus (Gris.) Stoj. et Stef. (Leguminosae) , Oxytropis pilosa (L.) DC and Salvia officinalis L. from locations near Nis, during their vegetative period. Season variation in content of magnesium, iron, manganese, zinc, cupper and selenium in soil, as well as that accumulation in plant was researched too. At the same time the dominant flavonoid-glycosides were isolated from all researched plants, as was the essential oil from S. officinalis L. The antibacterial activity of essential oil and plant extracts were estimated. According to the obtained results the following conclusions were reached:

In all stages of plant development a defence antioxidative system operates, consisting of enzymatic and nonenzymatic compounds. The mode of antioxidant action depends of plant's growth, developmental stage and sample specificity.

Low activity of antioxidant enzymes and low contents of nonenzymatic antioxidants in the initial vegetation stage indicate that plants were not exposed to high oxidative stress. That was confirmed by low quantities of superoxide and hydroxyl radicals, as well as low quantities of malonyl-dialdehyde.

In the blooming stage with intensification of photosynthesis and photorespiration the quantities of superoxide and hydroxyl radicals were significantly higher, which conditioned a high level of lipid peroxidation. All enzymatic systems (except for superoxide dismutase) exhibit the highest activity, catalase specially. In these conditions nonenzymatic antioxidants' contents apparently increase. High content of carotenoids pointed at its possibilities to absorb activated oxygen generated under UV light.

A characteristic of seed forming stage was a decrease of enzymatic activity, confirmed by high quantities of superoxide and hydroxyl radicals, and higher oxidative damage. Oxygen radicals influenced the increase of membrane's permeability and initiate lipid membrane peroxidation. In that stage of plant development only superoxide dismutase affects maximum activity and prevents oxidative damages caused by drought. S. officinalis L. exhibited significant adaptation to drought stress.

Examined soils (at an average) have optimal content of researched metals, except for magnesium and selenium especially. In seed forming stage the high content of manganese and iron specially were established. In this stage plants were exposed to drought stress and exhibited different dynamics of element accumulation. From all elements, iron exhibited the highest variability in accumulation during vegetative period. Extremely high content of this element was found in A. onobrychis L.

Older plants contained both lower concentrations of antioxidants and activities of antioxidative enzymes and exhibited a lower ability to adequately respond to enhanced oxidative stress than younger plants. Obtained results indicate that enhanced plant protection from oxidative stress will probably require concurrent and balanced increase in several components of the antioxidative systems.

The total flavonoids content in examined plants ranged from 33,23 mg/100 g, to 624,53 mg/100 g respectively. In all researched plants the highest content of total flavonoids was in the blooming stage of growth.

The content of essential oil in S. officinalis L. was 2,00%. In the essential oil 26 compounds were detected from which 18 were identified. Dominant compounds were: a-thujone (24,88%), camphor (16,03%) and 1,8-cineole (9,76%). These components represent a chemotype of S. officinalis L.

The best antioxidant characteristics of all examined plants had sage, S. officinalis L. from the location Sicevo gorge; therefore it can be used for the preparation of natural antioxidants.

The ethyl acetate extract of A. onobrychis L. exhibited a strong antimicrobial activity on all tested microorganisms. Buthanoyl and methanoyl extracts of O. pilosa (L.) DC. exhibited activities on three cultures of the bacteria. The essential oil of sage had inhibitory effect on most of microorganisms. Ethyl acetate extract of A. onobrychis L. and the essential oil of sage (S. officinalis L.) had similar antibacterial activities as ampicilin, a reference antibiotic. For that reason they can be used as a potential antimicrobial agent.