Water availability affects photosynthetic gene expression in the desert plant Ammopiptanthus mongolicus

Abstract

Two habitats of Ammopiptanthus mongolicus growing in the desert regions of Northwest China, one with watering (IR) and one without watering (DR), were investigated simultaneously for gas exchange patterns and the expression of photosynthetic genes. Stomatal conductance (gs) and intracellular CO2 concentration (ci) were markedly lower in A. mongolicus in the natural desert habitat (DR) compared to IR, paralleling a similar depression observed in the net photosynthetic CO2 assimilation rate (Pn). The steady-state levels of photosystem II (PS II) reaction center protein D1, light-harvesting complex II (LHCII), photosystem I (PS I) reaction center protein PsaA/B, and light-harvesting complex I (LHC I) were reduced in DR compared to IR. Our results indicate that both stomatal and nonstomatal factors contribute to the low carbon assimilation rate in DR. Moreover, the contents of PsaA/B and LHC I are more reduced than those of D1 and LHC II, indicating that PS I is more susceptible to photoinhibition under natural desert environment stresses. The cab transcripts for nuclear-encoded LHC II were decreased in DR compared with those in IR, while the psbA transcripts for chloroplast-encoded D1 protein remain largely unchanged between DR and IR. These results indicate that the nuclear-encoded photosynthetic gene is regulated, at least at the transcriptional level, and that the chloroplast-encoded gene is regulated mainly posttranscriptionally.