PHOTOSYNTHESIS AND WATER RELATIONS IN TRANSGENIC TOBACCO PLANTS WITH T-DNA CARRYING GENE 4 FOR CYTOKININ SYNTHESIS

Expression of the gene 4 for cytokinin synthesis in two clones of tran sgenic tobacco plants resulted in slightly higher (ca. 10 - 20 %) leve ls of endogenous cytokinins - zeatin, zeatin riboside and isopentenyla denosine. This was associated with changes in photosynthetic processes on chloroplast and leaf level. In comparison with non-transformed pla ntlets a higher degree of grana stacking was found in both clones of t ransgenic plants which indicated a higher proportion of photosystem 2 light-harvesting complex in thylakoids. This was supported by a decrea sed chlorophyll a/b ratio in the separated grana fraction. The rate of leaf net photosynthetic rate (measured as CO2 uptake) was ca. 25 % hi gher in both clones than in non-transformed plants. Also the rates of dark and light respiration, and CO2 compensation concentration were hi gher in transgenic plants. On the other hand, parameters of water rela tions (water, osmotic and pressure potentials, stomatal and cuticular transpiration rates) were not significantly affected in transgenic tob acco plants.