Effects of maize and soybean intercropping on soil phosphorus bioavailability and microbial community structure in rhizosphere

To investigate the effect of maize/soybean intercropping on rhizosphere soil microbial communities and phosphorus (P) bioavailability, we examined the changes of soil bioavailable P fractions and microbial community characteristics in the monoculture and intercropping systems based on high-throughput sequencing. The results showed that maize/soybean intercropping increased the contents of rhizosphere soil organic matter (SOM), available phosphorus (AP), microbial biomass phosphorus (MBP), and aboveground biomass. The increase of AP was mainly related to the increasing enzyme extracted phosphorus (Enzyme-P) and hydrochloric acid extracted phosphorus (HCl-P) contents. The dominant bacterial phyla under each treatment were Proteobacteria, Actinobacteria, Acidobacteria and Chloroflexi, while the dominant bacterial genera were Nocardioides, Solirubacter, Sphingomonas and Arthrobacter, with Proteobacteria and Sphingomonas having the highest relative abundance. The relative abundance of Proteobacteria and Sphingomonas in intercropping maize rhizosphere soil was significantly higher than that in monoculture, and that of Proteobacteria in intercropping soybean rhizosphere soil was significantly higher than monoculture. Soil properties and P fractions were closely related to the rhizosphere soil microbial composition. In all, maize/soybean intercropping could affect the rhizosphere soil P bioavailability by altering the structure of rhizosphere microbial communities.

First Report of Rice stripe virus in Vietnam

Rice stripe virus (RSV) is the type member of the genus Tenuivirus, and one of the prevalent viruses infecting rice. The disease was first recorded in central Japan in 1903, and is currently present in many Asian countries, including South Korea and China in the Far East (1,2). In May of 2012, a disease outbreak in Indica rice (Oryza satira L.) caused losses in a field in Huaifu, Hungyen, Vietnam (20°53'N, 106°02'E). Infected plants showed yellowing stripe symptoms on leaves. A survey indicated that disease incidence was about 10%. Six leaf samples were randomly collected and four were found positive in dot-ELISA using RSV-specific monoclonal antibodies (provided by Dr. X. Zhou, Institute of Biotechnology, Zhejiang University) (3). To confirm RSV infection, total RNA was extracted from dot-ELISA positive and asymptomatic control samples. RT-PCR was performed using RSV-specific primers (CP(+): 5'-GAGGATCCATGGGTACCAACAAGCCAG-3', CP(-): 5'-TCGTCGACCTAGTCATCTGCACCTTCTG-3'; SP(+): 5'-TGGGATCCATGCAAGACGTACAAAGGAC-3', SP(-): 5'-CTGTCGACCTATGTTTTATGAAGAAGAGGT-3'; NS2(+): 5'-GAGGATCCATGGGTACCAACAAGCCAG-3', NS2(-): 5'-CCGTCGACTCATACATCTGAATTTG-3'; NS3(+): 5'-ACCGGATCCATGACTATCAAATACAAC-3', NS3(-): 5'-CCGTCGACTCATACATTAGCTATTGTC-3') that amplify the coat protein, disease-specific protein, and NS2 and NS3 genes of RSV, respectively. Amplicons of the expected size were obtained from the four symptomatic but not the asymptomatic plants. Amplicons obtained from one of the positive samples were cloned into the vector pMD18-T (TaKaRa, Dalian, China) and sequenced (GenBank Accession Nos. KC197055 to KC197058). Sequence comparisons indicated that the complete sequences of the CP, SP, NS2, and NS3 of the Vietnamese isolate shared 97.1%, 97.5%, 96.8%, and 97.3% sequence identity at the nucleotide level with the corresponding genes of RSV isolate T (NC_003776, NC_003753, and NC_003754, respectively). These results indicate that the virus associated with yellowing stripe disease of rice in Vietnam is an isolate of RSV. To our knowledge, this is the first report of RSV in Vietnam. This finding redefined the distribution of RSV in the world. Research on whole-genome sequencing of the Vietnamese isolate is continuing and is being expanded to compare the genetic diversity of the virus, assisting in the study of the evolution of the virus. References: (1) S. Toriyama. Microbiol. Sci. 3:347, 1986. (2) Q. Y. Lin et al. J. Fujian. Agric. Univ. 20:24, 1991. (3) G. Z. Wang et al. Acta Phytopathol. Sinica 34:302, 2004.

First Report of Tomato yellow leaf curl virus in Acalypha australis in China

Whitefly-transmitted geminiviruses (WTGs) can cause serious damage to many crops in China, so an investigation of weed hosts of WTGs was carried out in Jiangsu Province, China, in 2012. Fifty-seven symptomless samples of Acalypha australis L., a common weed known as Asian copperleaf, were randomly collected from seven tomato fields in Nanjing and Lianyungang, Jiangsu Province, from July to September. Total DNA of each sample was extracted and PCR was performed using degenerate primers PA and PB to amplify a specific region covering the AV2 gene of DNA-A and part of the adjacent intergenic region (1). DNA fragments were successfully amplified from 27 out of 57 samples and PCR amplicons of 16 samples were sequenced. Alignment results showed that the nucleotide sequence identities ranged from 98 to 100% with Tomato yellow leaf curl virus (TYLCV) accessions. The full-length viral circular DNA genome was amplified using primer pair 1AbF (ATGTGGGATCCACTTCTAAATGAATTTCC) and 1AsR (GCGTCGACAGTGCAAGACAAACTACTTGGGGACC) which were designed based on the known sequences amplified by PA and PB. The complete genome sequence (GenBank Accession No. JX910534) was 2,781 nucleotides in length and had 99 to 100% sequence identity with TYLCV accessions (GU434142, GU111505). The dot immunobinding assay using monoclonal antibody against TYLCV confirmed the 27 weed samples positive by PCR were infected by TYLCV. These results demonstrated that A. australis is a host of TYLCV that might play an important role in viral epidemics in tomato fields in China. TYLCV-infected A. australis did not show typical symptoms like leaf curl, chlorosis, and stunting and thus appears to be a symptomless host. In our investigation, the infection rate ranged from 14 to 79% depending on the field sampled, suggesting that the weed may be an important reservoir of TYLCV, especially during the non-tomato planting period. To our knowledge, this is the first report of A. australis as a host of TYLCV in China. Reference: (1) D. Deng et al. Ann. Appl. Biol. 125:327, 1994.

Effects of β-glucan extracted from Saccharomyces cerevisiae on growth performance, and immunological and somatotropic responses of pigs challenged with Escherichia coli lipopolysaccharide1

Three experiments were conducted to investigate the effects of beta-glucan supplementation on pig performance and immune function. In Exp. 1, 100 weaned pigs (8.65 +/- 0.42 kg of BW and 28 +/- 2 d of age) were used in a 35-d experiment to determine the effects of graded levels of beta-glucan. Pigs were randomly allotted to 1 of 5 treatments containing beta-glucan supplemented at 0, 25, 50, 100, or 200 ppm. Each treatment was replicated using 5 pens containing 4 pigs per pen. The ADG of pigs between d 14 to 28 and d 0 to 28 responded to dietary beta-glucan in a quadratic fashion (P < 0.05), whereas beta-glucan had no effect on ADFI and G:F in any period. In Exp. 2, 80 crossbred pigs (8.23 +/- 0.56 kg of BW and 28 +/- 2 d of age) were used in a 35-d experiment. Pigs were allotted to 1 of 2 dietary treatments (0 or 50 ppm of beta-glucan in the diet) using 10 pens with 4 pigs per pen. Pigs treated with beta-glucan had greater ADG in the 14- to 28-d (P = 0.05) and 0-to 28-d (P = 0.035) periods. The ADFI of pigs receiving beta-glucan was increased (P < 0.05) in the periods from 0 to 14, 0 to 28, and 28 to 35 d. The lymphocyte proliferation index in response to phytohemagglutinin (P = 0.051) and concanavalin A (P = 0.052) tended to decrease on d 14 in pigs supplemented with beta-glucan compared with pigs without supplementation. In Exp. 3, 24 barrows (8.89 +/- 0.20 kg of BW and 28 d of age) were used to investigate the immunological and somatotropic responses of pigs challenged with lipopolysaccharide (LPS). Experimental treatments were arranged in a 2 x 2 factorial, with the main effects of LPS challenge (saline vs. LPS) and dietary addition of beta-glucan (0 vs. 50 ppm). Pigs were raised individually in metabolic cages. Pigs were fed 0 or 50 ppm of beta-glucan for 28 d and then challenged with LPS (25 microg/kg of BW) or saline. After LPS injection, blood was obtained at 0, 1.5, 3, 4.5, 6, and 7.5 h to determine cytokine production and the somatotropic response. Dietary beta-glucan increased plasma interleukin-6 at 1.5, 3, and 4.5 h and tumor necrosis factor-alpha at 3 and 4.5 h and increased plasma interleukin-10 from 3 to 7.5 h after LPS challenge. The beta-glucan treatments had no effect on growth hormone. In conclusion, beta-glucan can selectively influence performance and partially offer benefits on somatotropic axis and immune function in weaned piglets challenged with LPS.

Effects of optic tract stimulation on baroreflex vagal bradycardia in rats

1. Arterial baroreflexes are suppressed in stressful conditions. Intense visual stimuli can cause a threatening sensation and produce defensive reactions. 2. The present study was designed to determine whether and how electrical stimulation of the optic tract (OT) affects arterial baroreflexes, especially the heart rate component, baroreflex vagal bradycardia (BVB), in rats. In chloralose- urethane anaesthetized, beta-adrenoceptor-blocked rats, BVB was evoked by electrical stimulation of the aortic depressor nerve. 3. Electrical stimulation of the OT was found to not only increase blood pressure and heart rate, but also to inhibit BVB. To determine whether these responses were mediated by the lateral genticulate body and/or the superior colliculus, which are major target sites to which the OT projects, each was activated with electrical and chemical stimulation. 4. The lateral genticulate body did not respond to either electrical or chemical stimulation, whereas the superior colliculus increased blood pressure and heart rate while suppressing BVB following electrical stimulation. Essentially similar responses were observed following microinjection of the GABA antagonist bicuculline methiodide. 5. Optic tract-induced inhibition of BVB was abolished by bilateral destruction of the superior colliculus. Furthermore, this inhibition was also largely attenuated by destruction of the midbrain periaqueductal grey (PAG). 6. In conclusion, electrical stimulation of the OT increases blood pressure, heart rate and inhibits BVB. These responses are not mediated by the lateral genticulate body but are mediated by the superior colliculus. The PAG may participate in the subsequent mediation of the responses to electrical stimulation of the OT and the OT-induced inhibition of BVB may contribute to expression of a light-induced defence reaction.

Inhibition of baroreflex vagal bradycardia by activation of the rostral ventrolateral medulla in rats

In stressful conditions, baroreflex vagal bradycardia (BVB) is often suppressed while blood pressure is increased. To address the role of the rostral ventrolateral medulla (RVL), a principal source of sympathetic tone, in inhibition of BVB, we microinjected DL-homocysteic acid (DLH, 6 nmol) into the RVL of chloralose-urethan-anesthetized, sinoaortic-denervated rats to examine the effect on BVB. The BVB was provoked by electrical stimulation of the aortic depressor nerve ipsilateral to the injection sites. DLH microinjection was found to suppress BVB while increasing blood pressure. The inhibition of BVB was observed even during the early phase in which DLH transiently suppressed central inspiratory activity. The inhibition was not affected either by upper spinal cord transection or suprapontine decerebration. Similar results were obtained by microinjection of bicuculline methiodide (160 pmol), a GABA antagonist, into the RVL of carotid sinus nerve-preserved rats due to withdrawal of a tonic GABA-mediated, inhibitory influence including the input from arterial baroreceptors. In conclusion, activation of the RVL inhibits BVB at brain stem level independently of central inspiratory drive.

Is the aortic depressor nerve involved in arterial chemoreflexes in rats?

Recent anatomical and physiological studies showed that chemoreceptor afferent fibers are present in the rat aortic depressor nerve (ADN), which has been considered to contain exclusively baroreceptor afferent fibers. However, it remains to be proven whether the chemoreceptor afferents of the ADN are practically involved in chemoreflexes. The present study was performed in chloralose/urethane-anesthetized rats of either Sprague-Dawley (SD) or Wistar strain to examine whether the ADN carries sufficient information regarding arterial hypoxia and hypercapnia, and whether the ADN indeed participates in chemoreflexes, the circulatory and respiratory components. It was found in either strain that afferent discharges of the ADN were not affected at all by hypoxia or hypercapnia, whereas those of the carotid sinus nerve (CSN) markedly increased due to these stimuli. Hypoxia produced hypertension, transient bradycardia followed by tachycardia, and respiratory facilitation, which characterize the chemoreflexes. Any of these responses was not affected at all by the ADN section, but all were abolished by the CSN section. Intraaortic injection of cyanide also induced transient bradycardia and respiratory facilitation, but any of them was not affected by the ADN section while all were abolished by the CSN section. Furthermore, electrical stimulation of the ADN produced solely baroreflex responses, i.e. hypotension and respiratory suppression, whereas that of the CSN provoked chemoreflex responses, i.e. early, transient hypertension and respiratory facilitation. In conclusion, the rat ADN does not contain a functionally significant number of chemoreceptor afferent fibers, if at all, and does not appreciably contribute to generation of chemoreflexes.

Inhibition of baroreflex vagal bradycardia by nasal stimulation in rats

Nasal stimulation provokes hypertension and bradycardia. We report here that such stimulation inhibits baroreflex vagal bradycardia (BVB). In chloralose- and urethan-anesthetized, beta-adrenergic receptor-blocked rats, the aortic depressor nerves were cut and electrically stimulated to induce BVB. Nasal application of smoke, warm distilled water, or cold or hot Ringer solution suppressed BVB, but application of warm Ringer solution did not. Smoke-induced inhibition was abolished by trigeminal but not olfactory denervation. Neither suprapontine decerebration nor C3 spinal cord transection affected the inhibition. Bradycardia induced by electrical stimulation of the peripheral cut end of the cervical vagus nerve (VIB) was suppressed by long-lasting smoke application. Intravenous prazosin, a proposed blocker of prejunctional inhibition of acetylcholine release from the vagus terminals, abolished VIB inhibition but attenuated BVB inhibition only slightly. Thus nasal stimulation inhibits BVB, and this inhibition is mediated exclusively by the trigeminal nerve and occurs principally at the pontomedullary level, although the potential exists for contribution of the prejunctional mechanism. The inhibition of BVB might contribute to cardiovascular regulation associated with protection from atmospheric hazards.