The aim of this research was to investigate the microbial activity in forest soil from different sites under deciduous and coniferous trees in Serbia. One site on Stara planina was under beech trees (Fagus sp.) while another under mixture of spruce (Picea sp.) and Douglas fir (Pseudotsuga sp.). The site on Kopaonik was under mixture of beech (Fagus sp.) and spruce (Picea sp.) trees. The site on Tara was dominantly under fir (Abies sp.), beech (Fagus sp.) and spruce (Picea sp.). The total number of bacteria, the number of actinobacteria, fungi and microorganisms involved in N and C cycles were determined using standard method of agar plates. The activities of dehydrogenase and ß-glucosidase enzymes were measured by spectrophotometric methods. The microbial activity was affected by tree species and sampling time. The highest dehydrogenase activity, total number of bacteria, number of actinobacteria, aminoheterotrophs, amylolytic and cellulolytic microorganisms were determined in soil under beech trees. The highest total number of fungi and number of pectinolytic microorganisms were determined in soil under spruce and Douglas fir trees. The correlation analyses proved the existence of statistically significant interdependency among investigated parameters.
Factors of stress induce important alterations in gene expression of plants. In tobacco, new molecular species (absent in healthy plants) appear in stress conditions; they may result from both gene derepression and posttran-scriptional events. These molecules can be regarded as markers of stress. Two groups of markers are observed: non-specific, which are induced by various stresses of different origin (pathogens or abiotic factors), and specific, appearing as a response to a definite stress. We established that non-specific markers in tobacco leaves are lipid peroxides, pathogenesis-related (PR)-proteins, one acidic peroxidase isoenzyme (relative electrophoretic mobility (REM) 0.34), phenylamides, and chlorogenoquinones. In tobacco seedlings non-specific stress markers are three acidic peroxidase isoenzymes (REM 0.51, 0.60, 0.72), as well as PR-proteins. Peroxidase activity is also increased as a response to all stress factors studied in both tobacco leaves and seedlings. A specific marker of endoparasitic fungal pathogenesis (ex: P. tabacina) in tobacco leaves and seedlings is the dramatic increase of ss-glucosidase activity. This response was not induced by other pathogens (bacteria, viruses) and abiotic factors. Hence, the non-specific markers are informative for stress situation independently of the nature of stress factors, and can be suggested as components of a general defence system in tobacco. Specific markers may be used for diagnostic purposes, and as a basis for engineering of stress resistant genotypes.