Transgenic NfFeSOD Sedum alfredii plants exhibited profound growth impairments and better relative tolerance to long-term abiotic stresses.

Transgenic research was preformed by transferring a cyanobacterial ( Nostoc flagelliforme) iron superoxide dismutase gene ( NfFeSOD) into heavy metal hyperaccumulator Sedum alfredii via Agrobacterium-mediated method. Beyond expectation, NfFeSOD-overexpressing S. alfredii plants exhibited profound impairments, including plant growth retardation, abnormal root architecture, and reduced leaf greenness, photosynthetic efficiency and metal accumulation efficiency. Although transgenic plants appeared physiologically sensitive to high temperature, a higher relative biomass growth was still observed under long-term high temperature and osmotic stresses. Further investigation found that reactive oxygen species (ROS) homeostasis of transgenic plants was significantly affected, being ~50 % reduction of HO level relative to wild-type plants. Gene transcription including ROS responsive genes was overall attenuated in transgenic plants, being more significant at normal temperature than at high temperature. In addition, ascorbate peroxidase (APX) activity was increased nearly twofolds in transgenic plants as compared to wild-type control. It may be inferred that ectopic NfFeSOD overexpression gives rise to a substantial increase of APX activity and leads to a sharp reduction of HO level, thus impairing basal ROS signaling and plant growth. Specific genetic background of S. alfredii may be responsible for this sharp reduction of HO level induced by NfFeSOD overexpression. S. alfredii plant has acclimated to elevated levels of ROS induced by heavy metals in native habitats and should require high ROS levels for basal signaling. We thus suppose that a sustained disturbance of high basal ROS signaling in metal hyperaccumulators may instead incur very sensitive response and thus result in profound growth impairments. [ABSTRACT FROM AUTHOR]