Expression of yeast Hem1 controlled by Arabidopsis HemA1 promoter enhances leaf photosynthesis in transgenic tomato

A gene encoding 5-aminolevulinic acid synthase (ALA-S) in Saccharomyces cerevisiae (Hem1) under the control of an Arabidopsis thaliana HemA1 promoter (HemA1 promoter) was introduced into the genome of tomato (Solanum lycopersicum). All transgenic tomato plants were able to transcribe the Hem1 gene and the capacity to synthesize ALA was increased. The transgenic plants had 18% higher levels of chlorophylls, as compared to wild-type plants, indicating that part of the additional ALA from yeast ALA-S was metabolized to chlorophylls. Determination of gas exchange suggested that the net photosynthetic rate (Pn) in the transgenic tomato was about 60% higher than that of wild type. The apparent quantum yield (AQY) in the transgenic plants was 0.0363, significantly higher than 0.0313 of wild type. The Chlorophyll-a fast fluorescence measurement and JIP-test at continuous intensities of excitation light (90-2100 μmol m-2 s-1) showed that the genetic transformation caused a significant reduction in Vj (the relative variable fluorescence at the J-step) but addition in Vi (the relative variable fluorescence at the I-step). The maximum photochemical efficiency (φPo=Fv/Fm) did not vary with the light intensity, which demonstrated that φPo was a stable index for leaf photosynthesis. ψo (the probability that a trapped exciton moves an electron into the electron transport chain beyond QA-) and φEo (the quantum yield of electron transport) decreased with the light intensity increased, especially in wild type. Furthermore, the photosynthetic performance index on absorption basis (PIABS) or cross section basis (PICS) in the transgenic plants was also increased obviously in transgenic tobacco. Thus, the results obtained in this work approved that ALA improved photosynthetic capacity and the activity of PSII reaction center.