Natural petroleum acids of naphthenic type such as carboxylic acids from petroleum basins of Vojvodina are interesting because of diverse possibilities for their use, most importantly for their biological activity and the potential use as plant growth stimulators. The paper is concerned with biological activity of natural petroleum acids isolated form "Velebit", oil commercial fraction (168-290 °C). Petroleum acids were isolated by alkaline extraction and turned into methylesters with diazomethane. Subsequently, group-structure n-d-M-analyses and GC-MS-analysis have been used to determine individual acid structures. Structures of aliphatic. mono and bicyclic acids of average molecular mass 144-326 have been determined. Biological activity of auxine type has been assessed in the K-naphthenate form, and distinct activity was detected in the solutions of 10-7 mol dm-3

Petroleum acids can be obtained from oil and oil derivatives by alkaline extraction. The aim of this work was to optimize the process of alkaline extraction of petroleum acids from light commercial oil fractions of Vojvodina "Velebit" oil by changing the contact time of oil fraction with strong alkali and by changing the reaction temperature. Optimal conditions for isolation of petroleum acids have been determined to be 9 hours of contact time and reaction temperature of 90°C. Under these conditions the obtained petroleum acids yield was 88.38%. Identification of isolated acids was performed by GC-MS analysis

The paper describes a study of the effect of salts of natural naphthenic acids on the rooting of young sunflower cuttings and latteral branching of interspecies sunflower hybrids. Naphthenic acids were obtained by alkaline extraction from atmospheric gas oil fraction of Vojvodina crude oil "Velebit" and purified by column chromatography on alumina. Their sodium salts in concentrations of 1×10-7 mol/dm 3 stimulated the formation of adventitious roots in sunflower cuttings even by a factor of 40 compared with control, the effect being also observed in lateral branches of interspecies sunflower hybrids. The obtained results suggest the possibility of using naphthenic acids as a means for rooting of plant cuttings.

The investigated petroleum acids have been isolated from middle oil fractions (b.p. 270-380°C) of Vojvodina crude oil "Kelebija." Group-structural analysis was performed with low resolution mass spectrometry using Field Ionization and Chemical Ionization. The identified carboxylic acids, CnH2n+zO2, belong to the series of monocyclic, bicyclic, tricyclic and tetracyclic carboxylic acids. Physiological activity of isolated petroleum acids was determined using aqueous solutions of potassium salts. High auxin activity was determined using the coleoptile test (20.5% increase in coleoptile) with petroleum acid concentration of 10-7M, and very high biological activity of gibberellin type was determined using the endosperm test (31.6% increase in concentration of reducing sugars) with petroleum acid concentration of 10-7M

The objective of this work was to study the effect of treatment of young soybean plants with cholic acid of different concentrations on their oxidative status. Young soybean plants, grown hydroponically for two weeks, were treated by adding cholic acid to the nutrient solution at the concentrations 20, 40, 60 and 80 mg/L, the control being without cholic acid. After one week, several parameters of the oxidative status were determined in the leaves and roots of the plants: contents of superoxide (-O?2 ), hydroxyl radicals (?OH) and glutathione (GSH), lipid peroxidation (LP), the superoxide dismutase (SOD) activity and the soluble protein accumulation, as well as the contents of chlorophylls and carotenoids. Treatments with cholic acid increased - O?2, LP, ?OH and GSH in the leaves of the treated plants, while only the OH content increased in the roots at higher cholic acid concentrations. The obtained results support the idea that cholic acid, as an elicitor of defense responses in plants, might act through the generation of an oxidative burst.