Fine structure of sheet-webs of Linyphia triangularis (Clerck) and Microlinyphia pusilla (Sundevall), with remarks on the presence of viscid silk

We examined the webs of Linyphia triangularis (Clerck) and Microlinyphia pusilla (Sundevall) using light and scanning electronic microscopic techniques and compared them with the better known orb‐webs. The linyphiid sheet‐web consists of an unordered meshwork of fibres of different thicknesses. The sheet is connected to the scaffolding by means of attachment discs. Thin threads with globules, which appear similar to the viscid silk droplets of orb‐webs, are present in most webs examined. Webs of M. pusilla had a higher density of these globules than did webs of L. triangularis. Webs of both species possess five types of thread connections and contain no aqueous glue for prey capture. Instead, unlike orb‐webs, the sticky substances produced by the linyphiid aggregate glands cement the different layers and threads of the sheet by drying up after being produced. Due to their function, sheet webs may not require viscid silk, thereby leading to a more economic web. The assumption made in most previous studies, that the globules in linyphiid webs have the same properties and function as viscid silk in orb‐webs, is unfounded.     

Studies on the Characterization of Root Morphology of White Clover Infected by Transconjugant of Rhizobium leguminosarum

White clover plants were inoculated with transconjugant strain' 290 which was obtained from introduction of host specific nodulation genes of wild-type Rhizobium trifolii strain ANU 843 to Rhizobium leguminosarum strain 300. The characterization of root morphology of white clover induced by the transconjugant was observed and compared to the plants induced by the parent strains. White clover started tO form a typical root hair curling inoculated with transconjugant strain 290 24h after inoculation, at 48h a part of cell wall of root hair was degradated, infection thread was observed in the infected root hair cell, cortical cell divisions occurred extensively. All these characterizations were similar to that infected by strain ANU 843. Plant inoculation test indicated that no nodule was formed when inoculated by R. leguminosarum strain 300, while plants nodulated when inoculated with transconjugant strain 290 as well as R. trifolii ANU 843. This suggests that introduction of host specific nodulation genes of R. trifolii results in conferring the nodulation ability of R. leguminosarum on white clover.     

Capture thread extensibility of orb-weaving spiders: testing punctuated and associative explanations of character evolution

Spider orb-webs contain sticky prey capture threads and non-sticky support threads. Primitive orb-weavers of the Deinopoidea produce dry cribellar threads made of thousands of silk fibrils that surround supporting axial fibres, whereas the viscous threads of modern Araneoidea orb-weavers produce adhesive threads with an aqueous solution that coalesces as droplets around the axial fibres. We have previously shown that the greater diversity of the Araneoidea is phylogenetically significant and attributed this disparity to a number of advantages, considered key innovations, that adhesive thread has over cribellar thread. An important putative advantage of adhesive thread demonstrated by Kohler and Vollrath in their 1995 study is its greater extensibility, a feature that better adapts it to absorb the kinetic energy of a prey strike. However, this conclusion is based on a two-species comparison that does not take advantage of the modern comparative method that requires hypotheses to be tested in a phylogenetic context. Using a transformational analysis to examine threads produced by nine species, our study finds no support for the punctuated explanation that adhesive thread has a greater extensibility than cribellar thread. Instead, it strongly supports the associative null hypothesis that capture thread extensibility is tuned to spider mass and to architectural features of the web, including its capture area, capture spiral spacing, and capture area per radius.     

Rhizobial purine and pyrimidine auxotrophs: nutrient supplementation,genetic analysis,and the symbiotic requirement for the novo purine biosynthesis

Previously described Rhizobium leguminosarum bv. phaseoli mutants elicit nodules on bean without infection thread formation. These mutants were shown to be purine or, in one case, pyrimidine auxotrophs. Each of the seven purine auxotrophs grew normally when supplied the penultimate precursor of inosine, 5-aminoimidazole-4-carboxamide riboside. Four seemed blocked early in the purine pathway, because they were also thiamine auxotrophs. Reversion analysis and genetic complementation using cloned wild-type DNA showed that in each mutant a single mutation was responsible for both the symbiotic defect and purine or pyrimidine auxotrophy. The mutations were mapped to five dispersed chromosomal locations. The previously reported weak Calcofluor staining of these mutants on minimal agar appeared to be caused by partial growth on contaminating nutrients in the agar, rather than deficient exopolysaccharide production. Nodulation by the mutants was not enhanced by supplying purine or pyrimidine compounds exogenously. Furthermore, with or without added purine, the purine auxotrophs grew in the root environment as well as the wild type. However, nodulation by the purine auxotrophs was enhanced greatly in the presence of 5-aminoimidazole-4-carboxamide riboside. The results suggest that undiminished metabolic flow through de novo purine biosynthesis, or a particular intermediate in the pathway, is essential in early symbiotic interactions.     

Sinorhizobium meliloti succinylated high‐molecular‐weight succinoglycan and the Medicago truncatula LysM receptor‐like kinase MtLYK10 participate independently in symbiotic infection

The formation of nitrogen‐fixing nodules on legume hosts is a finely tuned process involving many components of both symbiotic partners. Production of the exopolysaccharide succinoglycan by the nitrogen‐fixing bacterium Sinorhizobium meliloti 1021 is needed for an effective symbiosis with Medicago spp., and the succinyl modification to this polysaccharide is critical. However, it is not known when succinoglycan intervenes in the symbiotic process, and it is not known whether the plant lysin‐motif receptor‐like kinase MtLYK10 intervenes in recognition of succinoglycan, as might be inferred from work on the Lotus japonicus MtLYK10 ortholog, LjEPR3. We studied the symbiotic infection phenotypes of S. meliloti mutants deficient in succinoglycan production or producing modified succinoglycan, in wild‐type Medicago truncatula plants and in Mtlyk10 mutant plants. On wild‐type plants, S. meliloti strains producing no succinoglycan or only unsuccinylated succinoglycan still induced nodule primordia and epidermal infections, but further progression of the symbiotic process was blocked. These S. meliloti mutants induced a more severe infection phenotype on Mtlyk10 mutant plants. Nodulation by succinoglycan‐defective strains was achieved by in trans rescue with a Nod factor‐deficient S. meliloti mutant. While the Nod factor‐deficient strain was always more abundant inside nodules, the succinoglycan‐deficient strain was more efficient than the strain producing only unsuccinylated succinoglycan. Together, these data show that succinylated succinoglycan is essential for infection thread formation in M. truncatula, and that MtLYK10 plays an important, but different role in this symbiotic process. These data also suggest that succinoglycan is more important than Nod factors for bacterial survival inside nodules.     

红豆草根瘤侵入线的超微结构研究

用透射电镜对红豆草根瘤侵入线的超微结构进行了观察研究.结果表明,(1)红豆草根瘤侵入线由胞间隙和胞间层细胞壁内陷形成,它们的体积较小,多为管状,基质丰富,含菌很少,常有分叉和1个以上的基质区,而且不同基质区的电子密度、细菌数量和侵入线壁厚度都不相同.(2)红豆草根瘤的侵入线十分丰富,它们不仅大量存在于根瘤分生细胞和幼龄侵染细胞中,也经常出现在发育成熟的侵染细胞内.(3)红豆草根瘤中有一种近似圆形的特殊结构,表面由一层膜包围,其内电子密度较低且无固定结构,且只位于侵染细胞的细胞质中,常在侵入线附近,从不出现在侵染细胞的液泡内和非侵染细胞里面.     

Congruent species delimitation of two controversial gold‐thread nanmu tree species based on morphological and restriction site‐associated DNA sequencing data

Species delimitation is fundamental to conservation and sustainable use of economically important forest tree species. However, the delimitation of two highly valued gold‐thread nanmu species (Phoebe bournei (Hemsl.) Yang and P. zhennan S. K. Lee & F. N. Wei) has been confusing and debated. To address this problem, we integrated morphology and restriction site‐associated DNA sequencing (RAD‐seq) to define their species boundaries. We obtained consistent results from the two datasets, supporting two distinct lineages corresponding to P. bournei and P. zhennan. In P. bournei, higher order leaf venation is more prominent, petioles are thicker, and leaf apex angle is narrower, compared to P. zhennan. Both datasets also revealed that the former putative P. bournei populations from northeastern Guizhou belong to P. zhennan. The two species are now distinct in distributions except in the Wuling Mountains, where they overlap. Phoebe bournei occurs mainly in central Fujian, southern Jiangxi, the Nanling Mountains, and the Wuling Mountains, whereas P. zhennan is found in the adjoining eastern regions of the Qionglai Mountains, the southern Sichuan hills, and the Wuling Mountains. The re‐delimitation of P. bournei and P. zhennan and clarification of their ranges provide a better scientific basis guiding the conservation and sustainable utilization of these tree species.     

Centerpiece微型钛板固定与传统丝线悬吊在颈椎后路单开门椎管扩大成形术中的应用效果比较研究

目的:比较Centerpiece微型钛板固定与传统丝线悬吊在颈椎后路单开门椎管扩大成形术中的应用效果。方法:选取于2015年2月～2017年9月期间北京大学第一医院收治的拟行颈椎后路单开门椎管扩大成形术的脊髓型颈椎病患者169例,根据治疗方式的不同将患者分为悬吊组(n=87,给予传统丝线悬吊治疗)和钛板组(n=82,给予Centerpiece微型钛板固定治疗),比较两组手术时间、术中出血量、术后颈椎疼痛时间、术后再关门发生率、轴性症状评分、日本骨科协会量表(JOA)评分、颈椎活动度、颈椎管矢状径、颈椎管横截面积、颈椎曲度、开门角度。结果:两组患者手术时间、术中出血量比较差异无统计学意义(P0.05),钛板组术后颈椎疼痛时间明显短于悬吊组,术后再关门发生率低于悬吊组(P0.05)。两组患者术后2个月、末次随访JOA评分均高于术前,且钛板组高于悬吊组(P0.05),两组患者末次随访轴性症状评分高于术后2个月,且钛板组术后2个月、末次随访轴性症状评分均高于悬吊组(P0.05)。与悬吊组相比,钛板组术后2个月、末次随访颈椎活动度、颈椎管矢状径升高(P0.05);而钛板组术后2个月颈椎管横截面积小于悬吊组,末次随访颈椎管横截面积大于悬吊组(P0.05)。悬吊组末次随访颈椎曲度小于术前、术后2个月(P0.05),钛板组手术前后颈椎曲度比较差异无统计学意义(P0.05);钛板组术后2个月、末次随访颈椎曲度、开门角度均大于悬吊组(P0.05)。结论:颈椎后路单开门椎管扩大成形术中应用Centerpiece微型钛板固定比传统丝线悬吊治疗的临床效果更好,可有效维持患者颈椎功能及活动度,并能改善神经功能。     

Localization of acid phosphatase activity in the apoplast of pea (Pisum sativum L.) root nodules grown under phosphorus deficiency

ACPase activity was localized in the apoplast of pea root nodules under phosphorus deficiency. Pea plants (Pisum sativum L. cv. Sze ciotygodniowy) where inoculated with Rhizobium leguminosarum bv. viciae 248 and were cultured on nitrogen-free medium with phosphate (−N/+P) or phosphate-deficient (−N/−P) one. In comparison with control nodules, P-deficient nodules showed the increase of ACPase activity in plant cell walls and the infection threads. The increase in bacterial ACPase activity under P-deficiency may reflect higher demand for inorganic phosphorus that is necessary for bacteria multiplication within the infection threads. The increase of ACPase activity in nodule apoplast under P stress may enlarge the availability of phosphate for plant and bacteria.     

黄连-姜黄水煎剂治疗豚鼠皮肤真菌感染

目的 建立石膏样毛癣菌感染皮损豚鼠动物模型并观察黄连-姜黄复方水煎剂的疗效.方法 于32只豚鼠背部建立石膏样毛癣菌感染皮损128处,分四组:(A)100%浓度复方水煎剂治疗组;(B)200%浓度复方水煎剂治疗组;(C)2%硝酸咪康唑软膏治疗组;(D)空白对照组.于感染第4天开始用药,分别于用药第0、3、7、10天做真菌镜检、培养并测量皮损直径.结果 A、B、C组治疗效果均明显好于D组(P<0.01),2%硝酸咪康唑软膏及复方水煎剂均对皮肤石膏样毛癣菌有治疗作用;B、C组治疗效果明显好于A组(P<0.01);B组治疗效果好于C组(P<0.05),治疗过程中无一例出现皮肤刺激症状.结论 黄连一姜黄复方水煎剂对皮肤石膏样毛癣菌有明显治疗作用,无刺激性,具有临床应用前景.