Summary
Cytosolic glutamine synthetase (GS1) plays a central role in nitrogen (N) metabolism. The importance of GS1 in N remobilization during reproductive growth has been reported in cereal species but attempts to improve N utilization efficiency (NUE) by overexpressing
GS1
have yielded inconsistent results. Here, we demonstrate that transformation of barley (
Hordeum vulgare
L.) plants using a cisgenic strategy to express an extra copy of native
HvGS1‐1
lead to increased
HvGS1.1
expression and GS1 enzyme activity.
GS1
overexpressing lines exhibited higher grain yields and NUE than wild‐type plants when grown under three different N supplies and two levels of atmospheric CO
2
. In contrast with the wild‐type, the grain protein concentration in the
GS1
overexpressing lines did not decline when plants were exposed to elevated (800–900 μL/L) atmospheric CO
2
. We conclude that an increase in GS1 activity obtained through cisgenic overexpression of
HvGS1‐1
can improve grain yield and NUE in barley. The extra capacity for N assimilation obtained by
GS1
overexpression may also provide a means to prevent declining grain protein levels under elevated atmospheric CO
2
.
The increasing use of cupric oxide nanoparticles (CuO NPs) has raised concerns about their potential environmental toxicity. Aerobic granular sludge (AGS) is a special form of microbial aggregates. In this study, the removal efficiencies of nitrogen and phosphorus, enzyme activities and microbial community of AGS under long-term exposure to CuO NPs (at concentrations of 5, 20, 50 mg/L) in aerobic/oxic/anoxic (A/O/A) sequencing batch reactors (SBRs) were investigated. The results showed the chronic toxicity caused by different concentrations of CuO NPs (5, 20, 50 mg/L) resulted in increases in the production of ROS of 110.37%, 178.64%, and 188.93% and in the release of lactate dehydrogenase (LDH) of 108.33%, 297.05%, 335.94%, respectively, compared to the control. Besides, CuO NPs decreased the activities of polyphosphate kinase (PPK) and exophosphatase (PPX), leading to lower phosphorus removal efficiency. However, the NH-N removal rates remained stable, and the removal efficiencies of TN increased due to the synthesis of nitrite and nitrous oxide (NO) reductases. In addition, CuO NPs at concentrations of 0, 5, 20 mg/L increased the secretion of protein (PN) to 90, 91, 105 mg/gVSS, respectively, which could alleviate the toxicity of CuO NPs. High-throughput sequencing showed that CuO NPs increased the abundance of nitrogen-removal bacteria and reduced the abundance of phosphorus-removal bacteria, which is consistent with the results of pollutant removal upon long-term exposure to CuO NPs.
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