Study of influence of heterologous HMG1 gene on leaf mesostructure and resistance of the transgenic tobacco plants to Pseudomonas syringae

Isoprenoids are one of the most numerous classes of natural plant compounds. Cytoplasmicsynthesis of isoprenoids begins from the formation of mevalonic acid by the enzyme3-hydroxy-3-methylglutaryl-CoA reductase encoded by the hmg1 gene. Transgenictobacco plants Nicotiana tabacum L. variety Samsun, containing the heterologous hmg1gene from Arabidopsis thaliana (L.) Heynh. in forward (lines C1, C2, C4) and reverse(lines A1, A2) orientations towards double constitutive cauliflower mosaic virus promoterCaMV 35S were obtained. The effects of heterologous hmg1 gene expression onleaf mesostructure and resistance of transgenic tobacco plants to Pseudomonas syringaewere studied. There was a change in total amount of leaf sterols in transgenic tobaccoplants associated with the proposed modification of isoprenoid compounds synthesis inthese plants. Before plant flowering leaves of transgenic plants with sense hmg1 genecontained significantly more sterols compared to control. Reducing of sterol amount inleaves of antisense transgenic tobacco lines compared to control was observed duringflowering. Study of leaf mesostructure has shown that mesophyll cells package in antisenseplant lines is more dense than in control due to the reducing of leaf thickness andincrease in cells number. More dense leaf cells package in leaves of plant sense lines C2and C4, but not in line C1, compared to control was found. Reducing of leaf thickness inC2 and C4 plant lines was accompanied by an increase in palisade cell volume. Meanwhile,the leaf thickness of C1 plants line did not change. The leaf tissue of these plantswas more porous than in control. The density of leaf cells package may affect the rate ofpathogens' spreading under biotic stress. After exposure of leaf disks to phytopathogenPseudomonas syringae the level of lipid peroxidation in plants of lines C2 and C4 wasnot changed, indicating that they have no stress. It increased by 40-70% in controlplants, antisense lines and line C1. There was an increase in proline level after stress inall plants, but most significantly - in sense plant lines (up to 300%). In addition, the increaseof guaiacol peroxidase activity indicated increase of stress in antisense plants andin plants of C1 line. As the enzyme activity didn't change in control plants and in plantsof sense lines C2 and C4 under the stress, testifying the absence of peroxide accumulationin them.Correlation between leaf tissue structure and resistance to biotic stress in sensetransgenic hmg1 gene plant lines was revealed. The resistance of transgenic tobaccoplants depended on the hmg1 gene expression level.

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