Studies to influence the carbon metabolism of the C 3 plant Nicotiana tabacum by expressing heterologous enzymes involved in C 4 -like CO 2 fixation
In the present study, heterologous enzymes were overexpressed in the C3 plant Nicotiana tabacum in order to establish a C4-like metabolic pathway ("C4-cycle"). These enzymes include phosphoenolpyruvate carboxylase (PC), NADP-malic enzyme (ME), pyruvate, orthophosphate dikinase (DK), phosphoenolpyruvate synthase (PS), phosphoenolpyruvate carboxykinase (CK) and phosphoenolpyruvate translocator (PT). By individual gene transformations and subsequent stepwise crosses, a series of transgenic tobacco plants were regenerated, in which all the enzymes required for the "C4-cycle" of the NADP-ME-type (PC/ME/DK or PS/PT) and PCK-type (PC/CK/PT) were introduced. As a consequence, biochemical and physiological changes occurred in these plants with respect to endogenous enzyme activities, metabolite contents, photosynthetic characteristics and growth parameters. The activity of endogenous cytosolic ME was increased in single PC overexpressors. There were significant increases in the activities of endogenous cytosolic PK and mitochondrial NAD-ME in single PC, and double PC/ME or PC/CK overexpressors. Endogenous NADP-MDH was inhibited in double PC/CK overexpressors. The leaf content of malate was distinctly increased in single PC overexpressors. Such change was diminished with an additional overexpression of ME. A decline in the leaf content of flavonoids (UV protectants) resulted from an overexpression of PC. Attenuation of the oxygen- and/or temperature-dependent inhibition of apparent CO2 assimilation (A) and enhancement of electron requirement for A (e/A ratio) were observed in single PC, and/or double PC/CK or PC/ME overexpressors. A decline in the apparent CO2 compensation point ((), and a short-term inhibition of photorespiration were observed in the multiple PC/ME/PS and PC/ME/DK/PS/CK/PT overexpressors, respectively. Higher growth rates and earlier formation of reproductive organs were found for single PC, double PC/ME and multiple PC/ME/PS/PT, PC/ME/DK/PT, PC/ME/DK/PT/CK, PC/ME/CK/PT or PC/ME/PT overexpressors, whereas double PC/CK and triple PC/ME/CK overexpressors had retarded growth. The growth parameters of a large number of progenies from various crosses between transgenic tobacco plants were statistically analysed.
info:eu-repo/classification/ddc/580, Tabak, Kohlenstoffstoffwechsel, Überexpression, Enzym, C4-Pflanzen, Pflanzen (Botanik), Nicotiana tabacum, heterologous enzymes, C4-like CO2 fixation
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