Untangling the Tangle-Web: Web Construction Behavior of the Comb-Footed Spider Steatoda triangulosa and Comments on Phylogenetic Implications (Araneae: Theridiidae)

Theridiidae typically construct a three-dimensional web often described as irregular. The web consists of a supporting structure and lines under tension termed gumfooted lines. We used automated methods to observe web construction in the theridiid Steatoda triangulosa under laboratory conditions. Web construction lasted several nights. After orientation, spiders built a three-dimensional structure of several threads radiating sideways and downward from the retreat. To build gumfooted lines, they started from the retreat, moved along a structural thread, then dropped down to attach the thread to the lower substrate. On returning, they coated the lowest part of the thread with viscid silk before moving up along the same thread back to the structural thread. They then continued moving along the same structural thread to drop down again to build the next gumfooted line. This behavior was continued until the spiders had built a series of gumfooted lines (a bout). There were regular intervals between the construction of two bouts. Thus, a single web included many bouts built in different stages. We show that gumfooted lines are not homologues to sticky web elements of orb-weavers and present new synapomorphic characters that support the monophyly of Theridiidae + Nesticidae and the monophyly of araneoid sheet web weavers. Further, the time allocation pattern for different behavioral stages and the fine structure of a gumfooted line are presented.     

Plasmolysis of Pteridium protoplasts: A study using light and scanning-electron microscopy

A study was undertaken using gametophytes of the fern Pteridium aquilinum to examine the effects of plasmolysis on the topography of protoplasts. Methods are described whereby the surfaces of non-isolated protoplasts can be observed in the plasmolysed condition using scanning electron microscopy. Plasmolysed gametophytes were also examined in the light microscope using differential interference contrast and ultra-violet fluorescence microscopy after staining with fluorescein diacetate. With scanning electron microscopy, plasmolysed protoplast surfaces appeared smooth with no evidence of wrinkling or infolding of excess membrane. The formation of irregular-shaped protoplasts, protoplasmic threads, subprotoplasts, and protoplasmic networks covering internal wall surfaces all provided evidence for strong wall adhesion of the protoplasm. The availability of membrane for uptake into folds or vesicles is therefore thought to be minimal. Transmission electron microscopy showed some protoplasmic threads to be plasmodesmata, the remainder being cell-wall contact points. Remnants of these threads were occasionally observed on isolated protoplasts in both the light and electron microscopes.     

Ultrastructure of infection-thread development during the infection of soybean by Rhizobium japonicum

The location and topography of infection sites in soybean (Glycine max (L.) Merr.) root hairs spot-inoculated with Rhizobium japonicum have been studied at the ultrastructural level. Infections commonly developed at sites created when the induced deformation of an emerging root hair caused a portion of the root-hair cell wall to press against an adjacent epidermal cell, entrapping rhizobia within the pocket between the two host cells. Infections were initiated by bacteria which became embedded in the mucigel in the enclosed groove. Infection-thread formation in soybean appears to involve degradation of mucigel material and localized disruption of the outer layer of the folded hair cell wall by one or more entrapped rhizobia. Rhizobia at the site of penetration are separated from the host cytoplasm by the host plasmalemma and by a layer of wall material that appears similar or identical to the normal inner layer of the hair cell wall. Proliferation of the bacteria results in an irregular, wall-bound sac near the site of penetration. Tubular infection threads, bounded by wall material of the same appearance as that surrounding the sac, emerge from the sac to carry rhizobia roughly single-file into the hair cell. Growing regions of the infection sac or thread are surrounded by host cytoplasm with high concentrations of organelles associated with synthesis and deposition of membrane and cell-wall material. The threads follow a highly irregular path toward the base of the hair cell. Threads commonly run along the base of the hair cell for some distance, and may branch and penetrate into subjacent cortical cells at several points in a manner analagous to the initial penetration of the root hair.     

Genetic and functional analysis of the nodulation region of the Rhizobium leguminosarum Sym plasmid pRL1JI

Thirty Tn5- or Tn1831-induced nodulation (nod) mutants of Rhizobium leguminosarum were examined for their genetic and symbiotic properties. Thirteen mutants contained a deletion in Sym plasmid pRL1JI. These deletions cover the whole nod region and are 50 kb in size. All remaining seventeen mutations are located in a 6.6 kb EcoRI nod fragment of the Sym plasmid. Mutations in a 3.5 kb part on the right hand side of this 6.6 kb fragment completely prevent nodulation on Vicia sativa. All mutants in this 3.5 kb area are unable to induce marked root hair curling and thick and short roots.Mutations in a 1.5 kb area on the left hand side of the 6.6 kb nod fragment generate other symbiotic defects in that nodules are only rarely formed and only so after a delay of several days. Moreover, infection thread formation is delayed and root hair curling is more excessive than that caused by the parental strain. Their ability to induce thick and short roots is unaltered.Mutations in this 1.5 kb region are not complemented by pRmSL26, which carries nod genes of R. meliloti, whereas mutations in the 3.5 kb region are all complemented by pRmSL26.Abbreviations Rps repression of production of small bacteriocin - Mep medium bacteriocin production - Nod nodulation - Fix fixation - Tsr thick and short roots - Flac root hair curling - Hsp host specificity - Flad root hair deformation - Tc tetracycline - Km kanamycin - Cm chloramphenicol - Sp spectinomycin - Sm streptomycin - R resistant     

The development and structure of root nodules on bambara groundnut [Voandzeia (Vigna)subterranea]

The infection of Vigna subterranea (formerly Voandzeia subterranea) by Bradyrhizobium strain MAO 113 (isolated from V. subterranea) was examined by light and transmission electron microscopy. Bacteria accumulated on the epidermis close to root hairs, and subsequently entered the latter via infection threads. Most of the steps involved in nodule formation were generally characteristic of determinate nodules, such as those which form on the closely related V. radiata. For example, nodule meristems were induced beneath the root epidermis adjacent to infected root hairs, but prior to infection of the meristem by rhizobia. Moreover, after the infection of some of the meristematic cells by the infection threads, and the release of the rhizobia into membrane-bound vesicles, the infection process ceased and dissemination of the rhizobia was by division of already-infected host cells. However, there were some aspects of this process in V. subterranea which have been more commonly described in indeterminate nodules. These include long infection threads entering a number of cells within the meristems simultaneously and a matrix within infection threads which was strongly labelled with immunogold monoclonal antibodies, MAC236 and MAC265, which recognize epitopes on an intercellular glycoprotein. The MAC236 and MAC265 antibodies also recognized material in the unwalled infection droplets surrounding bacteria which were newly-released from the infection threads. The amount of labelling shown was more characteristic of the long infection threads seen in indeterminate nodules such as pea (Pisum sativum) and Neptunia plena. The structure of mature V. subterranea nodules was similar to that described for other determinate nodules such as Glycine max, Vigna unguiculata and V.radiata, i.e. they were spherical and the infected zone consisted of both infected and uninfected cells. Surrounding the infected tissue was an inner cortex of uninfected cell layers containing the putative components of an oxygen diffusion barrier (including glycoprotein-occluded intercellular spaces), and an outer cortex with cells containing calcium oxalate crystals.     

Effects of artificial epibionts on byssogenesis,attachment strength,and movement in two size classes of the blue mussel,Mytilus edulis

Blue mussels (Mytilus edulis) can alter the strength of byssal attachment and move between and within mussel aggregations on wave‐swept shores, but this movement ability may be limited by epibiont fouling. We quantified the effects of artificial epibiont fouling on the production of byssal threads, attachment strength, and movement in two size classes of blue mussels. In a factorial experiment, large epibiont‐covered mussels produced more functional byssal threads (i.e., those continuous from animal to substrate) after 24 h than large unfouled and small fouled mussels, but not more than small unfouled mussels. Small unfouled mussels formed and released more byssus bundles compared to any other treatment group, which indicates increased movement. Conversely, epibiont fouling resulted in decreased numbers of byssus bundles shed, and therefore reduced movement in small mussels. Epibiont‐covered mussels started producing byssal threads sooner than unfouled mussels, while small mussels began producing byssal threads earlier compared to large mussels. Mean attachment strength from both size classes increased by 9.5% when mussels were artificially fouled, and large mussels had a 34% stronger attachment compared to small mussels. On the other hand, a 2.3% decrease in attachment strength was found with increasing byssus bundles shed. Our results suggest that fouling by artificial epibionts influences byssal thread production and attachment strength in large mussels, whereas epibionts on small mussels impact their ability to move. Mussels are able to respond rapidly to fouling, which carries implications for the dynamics of mussel beds in their intertidal and subtidal habitats, especially in relation to movement of mussels within and among aggregations.     

基于illumina测序的厚壳贻贝足组织转录组研究

贻贝足丝是贻贝足组织分泌的足丝蛋白形成的非细胞组织,具有在水环境下的极强粘附性能,是当前生物粘附剂及抗腐蚀材料的研发热点．为进一步了解贻贝足丝蛋白的分子多样性特征,采用新一代Illumina高通量测序平台对厚壳贻贝(Mytilus coruscus)足组织进行转录组测序,首次构建了厚壳贻贝足组织的转录组数据库．共计获得7 199 799 840 nt的碱基数据经过序列拼接和组装,获得88 825条unigene．对上述unigene开展了序列注释,共计37 007条unigene获得注释．在此基础上,经序列检索和比对,从中筛选出与目前已知的11种足丝蛋白同源的56条unigene序列并进行分析．结果表明,厚壳贻贝足丝蛋白具有明显的氨基酸偏好性,部分足丝蛋白具有重复序列,且厚壳贻贝足丝蛋白与其他种类的贻贝足丝蛋白具有较高的序列相似性．上述结果为后续贻贝足丝蛋白的批量鉴定以及在此基础上的贻贝足丝形成、固化以及粘附机制相关研究奠定了基础．     

Byssus production ability and degree of byssal-gland development in the infaunal clam Ruditapes philippinarum

Byssus production of Ruditapes philippinarum clams becomes reduced with growth. This tendency is well recognized but has not been analysed in detail. Additionally, it remains uninvestigated whether the lack of competence to produce byssus threads in the adult stage is caused by atrophy of the byssal glands or not. The objective of this study was to evaluate the byssus production ability of clams through the juvenile to adult stages and to examine the importance of two endogenous factors (i.e. shell size, somatic condition) in determining the byssus production probability (proportion of clams with byssus production in a population). This study also histologically confirmed the presence of byssal glands in juvenile to adult clams. For these purposes, field surveys to investigate the relationship among byssus production, shell size and somatic condition of clams collected from four intertidal sites and a histological study for byssal glands of the clams was conducted. This study revealed that byssus production probability decreases with increasing shell size and declining somatic condition and that the lack of byssus production is not caused by the loss of the byssal glands.     

Rhizobium induces marked root hair curling by redirection of tip growth: a computer simulation

Computer simulation shows that Rhizobium can induce marked curling in legume root hairs by growth induction. Essential elements are: a) the attachment of one inducing principle (e.g. one bacterium or a group of bacteria), preferably within the growth area of the root hair; b) translocation of the inductor along the growing root hari tip; and c) redirection of the original plant-driven tip growth. Also other root hair deformations, for example root hair branching and infection thread growth, can be explained with the proposed model.