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.

Seed biopriming with plant growth promoting rhizobacteria: a review.

Beneficial microbes are applied to the soil and plant tissues directly or through seed inoculation, whereas soil application is preferred when there is risk of inhibitors or antagonistic microbes on the plant tissues. Insufficient survival of the microorganisms, hindrance in application of fungicides to the seeds and exposure to heat and sunlight in subsequent seed storage in conventional inoculation methods force to explore appropriate and efficient bacterial application method. Seed priming, where seeds are hydrated to activate metabolism without actual germination followed by drying, increases the germination, stand establishment and stress tolerance in different crops. Seed priming with living bacterial inoculum is termed as biopriming that involves the application of plant growth promoting rhizobacteria. It increases speed and uniformity of germination; also ensures rapid, uniform and high establishment of crops; and hence improves harvest quality and yield. Seed biopriming allows the bacteria to enter/adhere the seeds and also acclimatization of bacteria in the prevalent conditions. This review focuses on methods used for biopriming, and also the role in improving crop productivity and stress tolerance along with prospects of this technology. The comparison of methods being followed is also reviewed proposing biopriming as a promising technique for application of beneficial microbes to the seeds.

4,4'-DDE and Endosulfan Levels in Agricultural Soils of the Çukurova Region, Mediterranean Turkey.

Mediterranean Turkey has long been at the forefront of Turkish agriculture and the use of organochlorinated pesticides (OCPs) in this area rose considerably between the 1940s and 1980s. This study aimed to determine OCP residue levels in agricultural soils collected from the Mersin and Adana Districts, Çukurova Basin in Mediterranean Turkey. Most soil samples were contaminated with one, or both, of two OCP metabolites; 4,4'-dichlorodiphenyldichloroethylene (4,4'-DDE) and endosulfan sulfate. 4,4'-DDE occurred in 27 of the 29 samples and ranged from 6 to 1090 µg kg(-1)-dry soil (ds)(-1), while six samples contained endosulfan sulfate ranging between 82 and 1226 µg kg(-1)-ds(-1). Generally, horticultural and corn-planted soils contained only 4,4'-DDE, whereas greenhouse cultivation appeared to accumulate both residues. This study indicated that 4,4'-DDE occurred above acceptable levels of risk in agricultural soils of Mersin District and further studies on the qualitative and quantitative assessment of OCPs in other agricultural regions with intensive pesticide use are necessary to fully understand the impact of OCPs on agricultural soil in Turkey.

Isolation and characterization of metal resistant-tolerant rhizosphere bacteria from the serpentine soils in Turkey.

Despite the number of studies describing metal hyper-accumulating plants and their associated bacteria in various regions and countries, there is no information on rhizosphere microbial potential of the Turkish serpentine soils. This study aimed to explore the rhizosphere microbial diversity of Ni-resistant, hyper-accumulating plants grown on Ni-rich soils and their metal tolerance-resistance characteristics. One hundred ninety-one locations were visited to collect soil and plant samples from different serpentine regions of Western Turkey. Following bioavailable and total Ni analysis of collected samples, the seeds of the selected plants with higher Ni content were taken to the growth/germination test in a range of serpentine soils in a growth chamber condition. In order to investigate the rhizosphere microbial diversity, Isatis pinnatiloba and Alyssum dasycarpum which were able to germinate and grow well in the preliminary tests, were introduced to 6-month greenhouse experiment in the range of three serpentine soils with higher bioavailable Ni content. I. pinnatiloba had a better stimulatory effect on the rhizosphere microbial diversity. A total of 22 bacterial isolates were identified from different soil conditions in the end of experiment. Following microbial identification and confirmation tests, 11 isolates were found to be resistant and tolerant to the increasing concentrations of Ni, Pb, Cd and Zn in the range of 50-2,000 mg L( - 1), which was considerably higher than those indicated by earlier studies. The strains isolated and identified from the Turkish serpentine soils were the members of genera Arthrobacter, Bacillus, Microbacterium and Staphylococcus.

Effect of humic deposit (leonardite) on degradation of semi-volatile and heavy hydrocarbons and soil quality in crude-oil-contaminated soil.

In order to investigate the bioremedial potential of humic deposit (leonardite), the effects of the treatments of leonardite and a commercial bioaugmentation agent on the degradation of a variety of petroleum hydrocarbons (C13-C31) and soil enzyme activities (urease acid-alkaline phosphatase and dehydrogenase) were tested within a soil incubation experiment lasting 120 days. Experimentally crude-oil-contaminated soil (2.5%) was regulated to a C:N:P ratio (100:15:1; Oilcon), amended with 5% of leonardite and regulated to the same C:N:P ratio (Oilcon-L) or mixed with a commercial bioaugmentation product (Oilcon-B), respectively. In the short period of incubation (60 days), Oilcon and Oilcon-B treatments showed higher hydrocarbon degradations, whereas Oilcon-L showed higher hydrocarbon degradation over Oilcon and Oilcon-B treatments in the long-term (120 days). Applying contaminated soil with leonardite increased urease (LSD, 4.978, *P<0.05) and dehydrogenase (LSD, 0.660, *P<0.05) activities. However, acid and alkaline phosphatase activities showed no certain inclination between different treatments. Dehydrogenase seemed to be more related to hydrocarbon degradation process. Overall results showed that leonardite enhanced biodegradation of petroleum hydrocarbons and also stimulated soil ecological quality measured as soil enzyme activities.