Specific and Non-specific Markers of Stress in Tobacco

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.