Abstract
Expression of the gene 4 for cytokinin synthesis in two clones of transgenic tobacco plants resulted in slightly higher(ca. 10 - 20 %) levels of endogenous cytokinins -zeatin, zeatin riboside and isopentenyladenosine. This was associated with changes in photosynthetic processes on chloroplast and leaf level. In comparison with nontransformed plantlets a higher degree of grana stacking was found in both clones of transgenic plants which indicated a higher proportion of photosystem 2 lightharvesting complex in thylakoids. This was supported by a decreased chlorophylla/b ratio in the separated grana fraction. The rate of leaf net photosynthetic rate (measured as CO2 uptake) wasca. 25 % higher in both clones than in nontransformed plants. Also the rates of dark and light respiration, and CO2 compensation concentration were higher in transgenic plants. On the other hand, parameters of water relations (water, osmotic and pressure potentials, stomatal and cuticular transpiration rates) were not significantly affected in transgenic tobacco plants.
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