Background-free imaging of cold atoms in optical traps.

Optical traps, including those used in atomic physics, cold chemistry, and quantum science, are widely used in the research on cold atoms and molecules. Owing to their microscopic structure and excellent operational capability, optical traps have been proposed for cold atom experiments involving complex physical systems, which generally induce violent background scattering. In this study, using a background-free imaging scheme in cavity quantum electrodynamics systems, a cold atomic ensemble was accurately prepared below a fiber cavity and loaded into an optical trap for transfer into the cavity. By satisfying the demanding requirements for the background-free imaging scheme in optical traps, cold atoms in an optical trap were detected with a high signal-to-noise ratio while maintaining atomic loading. The cold atoms were then transferred into the fiber cavity using an optical trap, and the vacuum Rabi splitting was measured, facilitating relevant research on cavity quantum electrodynamics. This method can be extended to related experiments involving cold atoms and molecules in complex physical systems using optical traps.

An eukaryotic elongation factor 2 from Medicago falcata (MfEF2) confers cold tolerance.

BACKGROUND: An eukaryotic translation elongation factor-2 (eEF-2) plays an important role in protein synthesis, however, investigation on its role in abiotic stress responses is limited. A cold responsive eEF2 named as MfEF2 was isolated from yellow-flowered alfalfa [Medicago sativa subsp. falcata (L.) Arcang, thereafter M. falcata], a forage legume with great cold tolerance, and transgenic tobacco (Nicotiana tabacum L.) plants overexpressing MfEF2 were analyzed in cold tolerance and proteomic profiling was conducted under low temperature in this study. RESULTS: MfEF2 transcript was induced and peaked at 24 h and remained at the high level during cold treatment up to 96 h. Overexpression of MfEF2 in trasngenic tobacco plants resulted in enhanced cold tolerance. Compared to the wild type, transgenic plants showed higher survival rate after freezing treatment, higher levels of net photosynthetic rate (A), maximum photochemical efciency of photosystem (PS) II (Fv/Fm) and nonphotochemical quenching (NPQ) and lower levels of ion leakage and reactive oxygen species (ROS) production after chilling treatment. iTRAQ-based quantitative proteomic analysis identified 336 differentially expressed proteins (DEPs) from leaves of one transgenic line versus the wild type after chilling treatment for 48 h. GO and KEGG enrichment were conducted for analysis of the major biological process, cellular component, molecular function, and pathways of the DEPs involving in. It is interesting that many down-regulated DEPs were grouped into "photosynthesis" and "photosynthesis-antenna", such as subunits of PSI and PSII as well as light harvesting chlorophyll protein complex (LHC), while many up-regulated DEPs were grouped into "spliceosome". CONCLUSIONS: The results suggest that MfEF2 confers cold tolerance through regulating hundreds of proteins synthesis under low temperature conditions. The elevated cold tolerance in MfEF2 transgenic plants was associated with downregulation of the subunits of PSI and PSII as well as LHC, which leads to reduced capacity for capturing sunlight and ROS production for protection of plants, and upregulation of proteins involving in splicesome, which promotes alternative splicing of pre-mRNA under low temperature.

Increased abscisic acid levels in transgenic tobacco over-expressing 9 cis-epoxycarotenoid dioxygenase influence H2O2 and NO production and antioxidant defences.

Abscisic acid (ABA) regulates the plant's adaptive responses to abiotic stresses. Over-expression of the 9-cis-epoxycarotenoid dioxygenase gene (SgNCED1) in the transgenic tobaccos increased ABA content and tolerance to drought and salt stresses. H2O2 and nitric oxide (NO) contents were enhanced in guard cells and mesophyll cells of the transgenic plants, accompanied with increased transcripts and activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR). The enhancements of H2O2 and NO and transcripts and activities of antioxidant enzymes in the transgenic plants were blocked by pre-treatments with inhibitor of ABA biosynthesis, scavengers of H2O2 and NO, and inhibitors of NADPH oxidase and NO synthase-like (NOS-like). The elevated production of NO in the transgenic plants was blocked by scavenger of H2O2 and inhibitors of NADPH oxidase, whereas H2O2 level was not affected by scavenger of NO and inhibitor of NOS-like, indicating that H2O2 is essential for the elevated production of NO. The results demonstrate that the increased drought and salt tolerance in the transgenic plants is associated with ABA-induced production of H2O2 via NADPH oxidase and NO via NOS-like, which sequentially induce transcripts and activities of SOD, CAT, APX and GR.