Metabolomics Analyses Reveal Metabolites Affected by Plant Growth-Promoting Endophytic Bacteria in Roots of the Halophyte Mesembryanthemum crystallinum.

Mesembryanthemum crystallinum L. (common ice plant) is an edible halophyte. However, if ice plants are used to phytoremediate salinity soil, there are problems of slow initial growth, and a long period before active NaCl uptake occurs under higher salinity conditions. Application of endophytic bacteria may improve the problem, but there remain gaps in our understanding of how endophytic bacteria affect the growth and the biochemical and physiological characteristics of ice plants. The aims of this study were to identify growth-promoting endophytic bacteria from the roots of ice plants and to document the metabolomic response of ice plants after application of selected endophytic bacteria. Two plant growth-promoting endophytic bacteria were selected on the basis of their ability to promote ice plant growth. The two strains putatively identified as Microbacterium spp. and Streptomyces spp. significantly promoted ice plant growth, at 2-times and 2.5-times, respectively, compared with the control and also affected the metabolome of ice plants. The strain of Microbacterium spp. resulted in increased contents of metabolites related to the tricarboxylic acid cycle and photosynthesis. The effects of salt stress were alleviated in ice plants inoculated with the endobacterial strains, compared with uninoculated plants. A deeper understanding of the complex interplay among plant metabolites will be useful for developing microbe-assisted soil phytoremediation strategies, using Mesembryanthemum species.

Profiling of proteasome activity in Alyssum species on serpentine soils in Turkey reveals possible insight into nickel tolerance and accumulation.

In crops and most plants, nickel induces oxidative stress resulting in oxidized and misfolded proteins. Proteasomes maintain cellular homeostasis during stress by removing these damaged proteins. Although mild stress tolerance is mediated by proteasomal proteolysis of misfolded and oxidized proteins, previous studies have observed that severe nickel stress decreases proteasome activity in nickel-sensitive plants. Whether or not proteasome function is impaired in nickel-tolerant plants is not know. Therefore, we tested the hypothesis that proteasome activity is elevated in nickel-tolerant Alyssum species capable of accumulating nickel to unusually high levels. Our field studies examined Alyssum sibiricum and Alyssum caricum, a moderate nickel accumulator and hyper-accumulator respectively, growing on their native serpentine soil in Turkey. A. sibiricum had higher proteasome activity on serpentine soil compared to non-serpentine soil; these plants also had elevated levels of nickel accumulation and higher proteasome activity compared to other low accumulating plants in the genus Festuca or Astragalus. In A. caricum, proteasome activity was very weakly correlated with nickel soil bioavailability or accumulation in leaf tissue, suggesting that proteasome function was not impaired in plants that accumulated the highest concentration of nickel. We discuss if maintained proteasome activity might underpin nickel tolerance and the unique ecophysiology of nickel hyper-accumulation in plants.