Compared with sole nitrate (NO₃^–) or sole ammonium (NH₄⁺) supply, mixed nitrogen (N) supply may promote growth of maize seedlings.  Previous study suggested that mixed N supply not only increased photosynthesis rate, but also enhanced leaf growth by increasing auxin synthesis to build a large sink for C and N utilization.  However, whether this process depends on N absorption is unknown.  Here, maize seedlings were grown hydroponically with three N forms (NO₃^– only, 75/25 NO₃^–/NH₄⁺ and NH₄⁺ only).  The study results suggested that maize growth rate and N content of shoots under mixed N supply was little different to that under sole NO₃^– supply at 0–3 d, but was higher than under sole NO₃^– supply at 6–9 d.  ¹⁵N influx rate under mixed N supply was greater than under sole NO₃^– or NH₄⁺ supply at 6–9 d, although NO₃^– and NH₄⁺ influx under mixed N supply were reduced compared to sole NO₃^– and NH₄⁺ supply, respectively.  qRT-PCR determination suggested that the increased N absorption under mixed N supply may be related to the higher expression of NO₃^– transporters in roots, such as ZmNRT1.1A, ZmNRT1.1B, ZmNRT1.1C, ZmNRT1.2 and ZmNRT1.3, or NH₄⁺ absorption transporters, such as ZmAMT1.1A, especially the latter.  Furthermore, plants had higher nitrate reductase (NR) glutamine synthase (GS) activity and amino acid content under mixed N supply than when under sole NO₃^– supply.  The experiments with inhibitors of NR reductase and GS synthase further confirmed that N assimilation ability under mixed N supply was necessary to promote maize growth, especially for the reduction of NO₃^– by NR reductase.  This research suggested that the increased processes of NO₃^– and NH₄⁺ assimilation by improving N-absorption ability of roots under mixed N supply may be the main driving force to increase maize growth.

Organic acids are one of the most important factors influencing fruit flavors. The predominant organic acid in most pear cultivars is malic acid, but the mechanism controlling its accumulation remains unclear. In this study, by comparing gene expression levels and organic acid content, we revealed that the expression of PbPH5, which encodes a P_3A-ATPase, is highly correlated with malic acid accumulation in different pear species, with correlation coefficients of 0.932^**, 0.656^*, 0.900^**, and 0.518^* (^*, P<0.05 or ^**, P<0.01) in Pyrus bretschneideri Rehd., P. communis Linn., P. pyrifolia Nakai., and P. ussuriensis Maxim., respectively. Moreover, the overexpression of PbPH5 in pear significantly increased the malic acid content. In contrast, silencing PbPH5 via RNA interference significantly decreased its transcript level and the pear fruit malic acid content. A subcellular localization analysis indicated that PbPH5 is located in the tonoplast. Additionally, a phylogenetic analysis proved that PbPH5 is a PH5 homolog gene that is clustered with Petunia hybrida, Malus domestica, and Citrus reticulata genes. Considered together, these findings suggest PbPH5 is a functionally conserved gene. Furthermore, the accumulation of malic acid in pear fruits is at least partly related to the changes in PbPH5 transcription levels.

Leaf area index (LAI) is used for crop growth monitoring in agronomic research, and is promising to diagnose the nitrogen (N) status of crops.  This study was conducted to develop appropriate LAI-based N diagnostic models in irrigated lowland rice.  Four field experiments were carried out in Jiangsu Province of East China from 2009 to 2014.  Different N application rates and plant densities were used to generate contrasting conditions of N availability or population densities in rice.  LAI was determined by LI-3000, and estimated indirectly by LAI-2000 during vegetative growth period.  Group and individual plant characters (e.g., tiller number (TN) and plant height (H)) were investigated simultaneously.  Two N indicators of plant N accumulation (NA) and N nutrition index (NNI) were measured as well.  A calibration equation (LAI=1.7787LAI₂₀₀₀–0.8816, R²=0.870**) was developed for LAI-2000.  The linear regression analysis showed a significant relationship between NA and actual LAI (R²=0.863**).  For the NNI, the relative LAI (R2=0.808**) was a relatively unbiased variable in the regression than the LAI (R²=0.33**).  The results were used to formulate two LAI-based N diagnostic models for irrigated lowland rice (NA=29.778LAI–5.9397; NNI=0.7705RLAI+0.2764).  Finally, a simple LAI deterministic model was developed to estimate the actual LAI using the characters of TN and H (LAI=–0.3375(TH×H×0.01)²+3.665(TH×H×0.01)–1.8249, R²=0.875**).  With these models, the N status of rice can be diagnosed conveniently in the field.

    The effect of hot air (HA, 45°C, 3.5 h) treatment on reducing gray mold caused by Botrytis cinerea in strawberry fruit and the possible mechanisms were investigated. The results showed that HA treatment significantly reduced lesion diameter and enhanced activities of chitinase (CHI), β-1,3-glucanase and phenylalanine ammonia-lyase (PAL) in strawberry fruit. Total phenolic contents were also increased by HA treatment. The activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) were higher in HA treated strawberry fruit than those in control. Expression of three defense related genes such as CAT, CCR-1 allele and PLA6 was greatly induced in HA treated strawberry fruit with or without inoculation by B. cinerea. In addition, the in vitro experiment showed that HA treatment inhibited spore germination and tube growth of B. cinerea. These results suggested that HA treatment directly activated disease resistance against B. cinerea in strawberry fruit without priming response and directly inhibiting growth of B. cinerea.

Different nitrogen (N) forms may cause changes in the metabolic profiles of plants. However, few studies have been conducted on the effects of amino acid-N on plant metabolic profiles. The main objective of this study was to identify primary metabolites associated with amino acid-N (Gly, Gln and Ala) through metabolic profile analysis using gas chromatography- mass spectrometry (GC-MS). Plants of pakchoi (Brassica campestris L. ssp. chinensis L.), Huawang and Wuyueman cultivars, were grown with different nitrogen forms (i.e., Gly, Gln, Ala, NO3 --N, and N starvation) applied under sterile hydroponic conditions. The fresh weight and plant N accumulation of Huawang were greater than those of Wuyueman, which indicates that the former exhibited better N-use efficiency than the latter. The physiological performances of the applied N forms were generally in the order of NO3 --N>Gln>Gly>Ala. The metabolic analysis of leaf polar extracts revealed 30 amino acid N-responsive metabolites in the two pakchoi cultivars, mainly consisting of sugars, amino acids, and organic acids. Changes in the carbon metabolism of pakchoi leaves under amino acid treatments occurred via the accumulation of fructose, glucose, xylose, and arabinose. Disruption of amino acid metabolism resulted in accumulation of endogenous Gly in Gly treatment, Pro in Ala treatment, and Asn in three amino acid (Gly, Gln and Ala) treatments. By contrast, the levels of endogenous Gln and Leu decreased. However, this reduction varied among cultivars and amino acid types. Amino acid-N supply also affected the citric acid cycle, namely, the second stage of respiration, where leaves in Gly, Gln and Ala treatments contained low levels of malic, citric and succinic acids compared with leaves in NO3 --N treatments. No significant difference in the metabolic responses was observed between the two cultivars which differed in their capability to use N. The response of primary metabolites in pakchoi leaves to amino acid-N supply may serve an important function in pakchoi adaptation to amino acid-N sources.

The purpose of the present study was to survey contents of trace elements of Cu, Mn, Fe, and Zn in the surface layer (0-20 cm) in the soil, pasture and serum of sheep in Huangcheng area of Qilian mountain grassland, China. Also the soil-plant- animal continuum was analyzed. Soil (n=300), pasture (n=60), and blood serum samples from sheep (n=480) were collected from Huangcheng area of Qilian mountain grassland, China. The contents of trace element in the samples were analyzed by atomic absorption spectrophotometer after digestion. The soil trace elements density distribution shows a ladder-like pattern distribution. Equations developed in the present study for prediction of Fe (R2=0.943) and Zn (R2=0.882) had significant R2 values.

Plants need to be efficient in nutrient management, especially when they face the temporal nutrient defficiencies. Understanding how crops respond to nitrogen (N) starvation would help in the selection of crop cultivars more tolerant to N deficiency. In the present work, the physiological responses of two wheat cultivars, Yannong 19 (YN) and Qinmai 11 (QM), to N starvation conditions were investigated. The two cultivars differed in biomass and N rearrangement between shoots and roots during N starvation. QM allocated more N to roots and exhibited higher root/shoot biomass ratio than YN. However, tissue measurement indicated that both cultivars had similar nitrate content in leaves and roots and similar remobilization rate in roots. Microelectrode measurement showed that vacuolar nitrate activity (concentration) in roots of QM was lower than that in roots of YN, especially in epidermal cells. Nitrate remobilization rates from root vacuoles of two cultivars were also identical. Moreover, vacuolar nitrate remobilization rate was proportional to vacuolar nitrate activity. During N starvation, nitrate reductase activity (NRA) was decreased but there were no significant differences between the two cultivars. Nitrate efflux from roots reduced after external N removal and QM seemed to have higher nitrate efflux rate.