Functional analysis of the role of tomato (Solanum lycopersicum L.) fruit photosynthesis in metabolism and development

该项目特别关注改变果实光合作用对果实生长、代谢和成熟等方面的影响。为此，在绿果特异性启动子的控制下，产生了对Rubisco小亚基具有独立反义抑制的磷酸烯醇丙酮酸羧化酶（PEPC）和谷氨酸-1-半醛转氨酶（GSA），以及后者的过表达的转基因番茄植株。迄今为止的研究结果表明，GSA的过表达和PEPC的反义抑制对青果的性能和成熟的影响不大，特别是对气体交换和叶绿素荧光参数的影响。在PEPC活性较低的植株中，淀粉和几种有机酸含量略有下降，而在过表达GSA的转基因果实中，己糖-磷酸盐含量有所增加。相反，GSA在果实中的反义抑制导致果实叶绿素缺乏表型，并对果实同化速率和叶绿素量子产率有明显影响。水果的特点是叶绿素a（高达90%）和类胡萝卜素含量急剧减少。然而，最初的观察结果并没有揭示叶绿素含量下降与果实成熟行为的光合性能受损之间的相关性。这方面和其他方面的水果代谢仍有待在未来的实验中进行详细的研究，包括广泛的生理、分子生物学和生化（包括代谢物分析的气相色谱、液相色谱、质谱和通量分析）方法的应用。

Particular attention in the project is paid to the effect that altering fruit photosynthesis has on aspects of fruit growth, metabolism and ripening. To this end transgenic tomato plants, under the control of a green fruit specific promoter, exhibiting independent antisense inhibition of the small subunit of Rubisco, Phosphoenolpyruvate carboxylase (PEPC) and Glutamate-1-semialdehyde aminotransferase (GSA), as well as overexpression of the latter enzyme, were generated.Results to date have revealed that overexpression of GSA and antisense inhibition of PEPC had little effect on green fruit performance or ripening in general, in particular on gas-exchange and chlorophyll fluorescence parameters. There were slight decreases in starch and several organic acid contents in plants with lower PEPC activity, and increases in hexose-phosphates in transgenic fruits overexpressing GSA.In contrast, antisense inhibition of GSA in fruits led to chlorophyll-deficient fruit phenotype and had distinct effect on fruit assimilation rate and chlorophyll quantum yield. Fruits were characterised by drastic reduction in chlorophyll a (up to 90%) and carotenoids content. However, first observations did not revealed a correlation between the decreased chlorophyll content and consequently compromised photosynthetic performance with ripening behaviour of the fruits. This and other aspects of fruit metabolism remain to be studied in detail in forthcoming experiments including application of a broad range of physiological, molecular biological and biochemical (including metabolite profiling by gas chromatography- and liquid chromatography – mass spectrometry and flux analysis) methods.