Nitrogen (N) and potassium (K) are key elements for crop growth, yet studies on the impact of N–K interactions on plant N and K status and yield are lacking.  This study aimed to develop effective indicators for diagnosing N and K nutrition and predicting the yield of wheat under N–K interactions based on the theoretical framework of a critical nutrient dilution curve.  A 4-year N–K interaction experiment involving three wheat cultivars was employed for building and validating nutrient indices (NIs) based on the critical N dilution curve (CNDC) and the critical K dilution curve (CKDC).  In addition, relevant data from the literature were collected for supplementary validation.  The results revealed that changes in parameter A1 of the critical K dilution curves (CKDCs) can reflect the impact of nitrogen application on K absorption and utilization.  However, the difference in K nutrition index (KNI) values calculated by CKDC under different N levels was not significant.  Based on the aboveground biomass (AGB), a universal CKDC was established and defined as K_c=3.63AGB^–0.37 under N–K interactions.  The results showed that the direct effects of N or K deficiency on crops could be quantified by the N–K interaction index (NKI) calculated by integrating CNDC and CKDC, and the changes in crop growth in response to proportional N and K concentrations could be determined by NKI as well.  In addition, topdressing N fertilizer at the jointing stage significantly improved the N–K interaction effect on the N nutrition index (NNI) and NKI at the booting stage (P<0.05), but it had no significant N–K interaction effect on the KNI.  All indicators at the heading stage demonstrated the best predictive capability for relative yield (RY) compared to other stages.  Compared with NNI and KNI, the prediction accuracy of yield with NKI improved by 11.63 and 17.44%, respectively.  The NKI has better performance in diagnosing N and K nutrition and predicting yield under N–K interactions than either NNI or KNI.  This result enhances our understanding of the effects of N–K interactions on wheat growth and has important applications for improving the accuracy of N and K nutrition diagnosis and yield prediction.

Low-density lipoprotein receptor-related protein 2 (LRP2) is a multifunctional endocytic receptor expressed in epithelial cells.  In mammals, it acts as an endocytic receptor that mediates the cellular uptake of cholesterol-containing apolipoproteins to maintain lipid homeostasis.  However, little is known about the role of LRP2 in lipid homeostasis in insects.  In the present study, we investigated the function of LRP2 in the migratory locust Locusta migratoria (LmLRP2).  The mRNA of LmLRP2 is widely distributed in various tissues, including integument, wing pads, foregut, midgut, hindgut, Malpighian tubules and fat body, and the amounts of LmLRP2 transcripts decreased gradually in the early stages and then increased in the late stages before ecdysis during the nymphal developmental stage.  Fluorescence immunohistochemistry revealed that the LmLRP2 protein is mainly located in cellular membranes of the midgut and hindgut.  Using RNAi to silence LmLRP2 caused molting defects in nymphs (more than 60%), and the neutral lipid was found to accumulate in the midgut and surface of the integument, but not in the fat body, of dsLmLRP2-treated nymphs.  The results of a lipidomics analysis showed that the main components of lipids (diglyceride and triglyceride) were significantly increased in the midgut, but decreased in the fat body and hemolymph.  Furthermore, the content of total triglyceride was significantly increased in the midgut, but markedly decreased in the fat body and hemolymph in dsLmLRP2-injected nymphs.  Our results indicate that LmLRP2 is located in the cellular membranes of midgut cells, and is required for lipid export from the midgut to the hemolymph and fat body in locusts.

    H9N2 avian influenza virus (AIV) infection is a major problem in poultry industry worldwide. In this study, molecular characterizations and phylogenetic relationships of hemagglutinin (HA) gene sequences of H9N2 AIV of 5 Chinese isolates in 2014 recently available in GenBank, 3 widely used vaccine strains, and 52 novel isolates in China from 2013 to 2015 were analyzed. The homology analysis showed that the nucleotide sequences of HA gene of these recent Chinese H9N2 AIV isolates shared homologies from 94.1 to 99.9%. Phylogenetic analysis showed that all isolates belonged to AIV lineage h9.4.2.5. Fifty-six out of the 57 recent Chinese H9N2 AIV isolates had the motifs PSRSSR↓GLF at the cleavage sites within the HA protein, while one isolate PWH01 harbored LSRSSR↓GLF. Remarkably, all of the recent Chinese H9N2 AIV strains had the Q216L substitution in the receptor binding site, which indicated that they had potential to infect humans. Most of recent Chinese H9N2 AIV isolates lost the potential N-linked glycosylation site at residues 200–202 compared with vaccine strains. This present study demonstrated that AIV lineage h9.4.2.5 was more predominant in China than other lineages as it harbored all the H9N2 AIV isolated between 2013 and 2015. Also we showed the importance of continuous surveillance of emerging H9N2 AIV in China and update of vaccine formulation accordingly in order to prevent and control H9N2 AIV.