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

Abstract

A gene encoding aminolevulinate synthase (ALA-S) in yeast (Saccharomyces cerevisiae YHem1) was introduced into the genome of tobacco (Nicoliana tabacum) under the control of Arabidopsis thaliana HemA1 gene promoter (AtHemA1 P). All transgenic lines transcribed the YHem1 gene, especially under light condition. The capacity to synthesize ALA and therefore chlorophyll was increased in transformed plants. Determination of gas exchange suggested that transgenic plants had significantly higher level of net photosynthetic rate (P ( n )), stomatal conductance (G ( s )) and transpiration rate (T ( r )), compared to the wild type (WT). Analysis with a modulated chlorophyll fluorometer demonstrated that the genetic transformation also caused a significant increase in photochemical efficiency of PSII ([Formula: see text]), actual photochemical efficiency (Ф ( PSII )), photochemical quenching (qP), electron transfer rate (ETR) and the energy proportion in photochemistry (Pc), but decrease in proportion in heat dissipation (Hd). Chlorophyll-a fast fluorescence measurement and JIP-test indicated that photosynthetic performance index on cross section basis (PI ( CS )) and electron transport flux (ET ( o ) /CS) of transgenic tobacco were increased remarkably. And the probability that a trapped exciton can move a electron into the electron transport chain beyond Q ( A ) (-) (Ψ ( o )) and the density of active reaction centers (RC/CS) were also increased obviously in transgenic tobacco. These results imply that transgenic tobacco plants expressing YHem1 gene had higher photosynthetic capacity and energy conversion efficiency than the WT plants.