A new nematode trapping species of Dactylaria

Summary The paper deals with the isolation of a new predacious fungusDactylaria dasguptaii Shome &Shome from Indian soil. The fungus has been studied both in culture and soil. The predatory, morphological and reproductive characters of the new species accompanied by latin diagnosis has been described with illustrative diagrams.     

The trapping fungus Dactylaria Brochopaga: induction of trap formation,attraction, trapping and the development in some phytonematodes

All the six species of the phytonematodes induced traps directly on the spores of all the five isolates of Dactylaria brochopaga. The maximum rings induction was observed in the presence of second-stage juveniles of Meloidogyne incognita followed by Meloidogyne graminicola (J₂), Xiphinema basiri, Helicotylenchus dihystera, Tylenchorynchus brassicae and Hoplolaimus indicus. Maximum number of induced traps was recorded at temperature 28°C (98.3%) and pH 7 (96.7%) in the presence of H. indicus. In attraction assay, irrespective of the isolates of the fungus, all the six phytonematodes were attracted towards the fungal discs of the different isolates of D. brochopaga. Among all the five isolates, Isolate D attracted maximum (34.7%) number of nematodes closely followed by Isolate C (31.0%), whereas, Isolate A, B and E did not differ significantly. Maximum in vitro trapping was recorded in the case of M. incognita (J₂) followed by M. graminicola (J₂), H. dihystera and T. brassicae. The maximum ringing (pre-capturing), trapping and killing was recorded for the second-stage juveniles of M. incognita followed by M. graminicola, T. brassicae and H. dihystera. The inflation of ring cells did not occur immediately after ringing; however, the time between ringing and inflation varied with different nematodes species. Clear hyphae were observed in the invaded nematodes body after the content of nematode body was consumed. External growth of hyphae occurred only from the inflated cells of the constricting rings, which further developed several rings. Higher number of rings was observed in mycelia developed from bigger nematodes.     

Combination of the entomopathogenic nematode Heterorhabditis bacteriophora and the nematode-trapping fungi Dactylaria brochopaga and Arthrobotrys conoides for controlling Meloidogyne incognita in tomato fields

Abstract

Effects of combining an entomopathogenic nematode (EPNs) and nematode-trapping fungi to control root-knot nematode were studied in the laboratory and in a tomato field. Bioassay effects of EPNs (Heterorhabditis bacteriophora) on growth of the two nematode-trapping fungi (Dactylaria brochopaga and Arthrobotrys conoides) attacking J2 of Meloidogyne incognita were studied in the laboratory. A field experiment was conducted in a tomato field. The mortality percentages were higher in combining EPNs and trapping fungi than either by trapping fungi or EPNs alone. Combining EPNs with A. comcaides fungi caused mortality higher than application by EPNs and trapping fungi D. brochopaga. The highest mortality percentage of combined EPNs and trapping fungi on larvae, root galls and egg-masses of M. incognita in tomato field were in the treatment of combined EPNs and D. brochopaga several times and the treatment of combined EPNs and A. comcaides several times, followed by the treatment of combined EPNs and D. brochopaga one time, and treatment of combined EPNs and A. comcaides one time. In the third stage came the treatment of D. brochopaga alone, and the treatment of A. comcaides alone, finally came effects of the treatment of EPNs alone. The highest tomato yield was recorded in treatments of combined EPNs and D. brochopaga or A. comcaides compared to the separate treatments and control. Thus, we recommend farmers to use combination of EPNs and trapping fungi for increasing the mortality of M. incognita in tomato fields.     

Nematophagous Fungi Associated with Root Galls of Rice Caused by Meloidogyne graminicola and its Control by Arthrobotrys dactyloides and Dactylaria brochopaga

Root galls of rice caused by Meloidogyne graminicola were examined for natural colonization by nematophagous fungi from four fields with different nematode infestations. Old galls from severely infested fields had a higher frequency of Monacrosporium eudermatum and Stylopaga hadra than young galls. The frequency of Arthrobotrys oligospora, Arthrobotrys dactyloides, Dactylaria brochopaga and Monacrosporium gephyropagum was lower. A greater proportion (%) of root galls were colonized by nematophagous fungi in those fields in which rice roots had a greater root gall index. This indicated that disease severity supported the colonization of galls by nematophagous fungi. In vitro predacity tests of four fungi showed that A. dactyloides was most effective in capturing and killing J₂ of Mel. graminicola followed by D. brochopaga and Mon. eudermatum. Application of inocula of A. dactyloides and D. brochopaga in soil infested with Mel. graminicola, respectively, reduced the number of root galls by 86% and of females by 94%, and eggs and juveniles by 94%. The application of these fungi to soil increased plant growth: shoot length by 42.7% and 39.8%, root length by 45.5% and 48.9%, fresh weight of shoot by 59.9% and 56.7% and fresh weight of root by 20.3% and 25.1%, respectively, compared to these parameters for plants grown in nematode‐infested soil.     

The mechanism of the ring trap of the predacious hyphomyceteDactylella brochopaga Drechsler

Summary A mutant ofDactylella brochopaga which produces giant functional ring traps, was isolated and studied. From experiments in which such traps were compressed, punctured and caused to inflate and deflate in environments of varying humidity levels it was concluded that trap cells are inflated by absorbing water or water vapour directly through their cell walls from their surroundings. Water entry occurs by osmosis, is initiated by a sudden increase in plasma membrane permeability and the increased pressure causes the inner of the two cell wall layers either to expand elastically or to unfold from a prepackaged state. In the fully inflated cell this wall layer becomes plastic finally.     

Chemical induction of trap closure inDactylella brochopaga

Summary Constricting ring traps can be sprung by exposure to dilute alcohol solutions and even by the vapours of higher alcohols. The greater the lipid solubility of the alcohol, the lower the concentration required to spring 100% of treated traps. This implies first that their primary action is at the plasma membrane, and second that some traps in a population are more reactive than others. Over 80% of traps could be activated between pH 5.5 and 8.2 suggesting an adaptation to permit prey capture even in unfavourable micro-environments.     

Some ring-trap mutants of the fungusDactylella brochopaga drechsler

Mutagenesis with nitrosoguanidine yielded two classes of ring trap mutants in the predacious HyphomyceteDactylella brochopaga: strains which could make no traps and those with a proportion of giant, functional traps. A third strain, derived from a trapless strain made abnormally small functional traps. The giant traps are described, together with developmental abnormalities they sometimes display. The characteristics of the chief mutant strains are discussed.This research was supported by a grant from the National Research Council of Canada which is gratefully acknowledged     

The induction of giant ring traps and regulation of conidiogenesis in the predacious fungus Dactylella brochopaga

The nematophagous fungus Dactylella brochopaga was grown and supplied with prey under different conditions of light and atmospheric stagnation. Poor ventilation induced the formation of functional giant traps, hitherto unreported. Darkness inhibited sporulation. The adaptive significance of these changes is discussed.     

The neck constriction in plasmodesmata

Simple plasmodesmata between mesophyll and bundle sheath cells in actively expanding leaves of Salsola kali L. and roots of Epilobium hirsutum L. are shown to possess specialized structures, called sphincters, around their neck regions. The sphineters are made visible by the combined effects of tannic acid and heavy metal staining; they are localized just outside that area of the plasmalemma, which forms the collar around the entrance to each plasmodesmos. This localization corresponds to a very active area of the plasmodesmos/olasmalemma complex (i.e. enzyme activity and/or presence of strongly reducing substances).Evidence is presented that these ring structures are structural equivalents to hypothetical sphincters performing some valve function; i.e. participating in the control of rates and directions of symplastic transport of solutes through plasmodesmata. The middle layer of the plasmalemma in the neck region is composed of closely-packed, globular subunits appearing in negative contrast. Apparently, these subunits correspond to particle clusters observed at the plasmodesmatal entrance in freeze-fracture preparations. They appear similar to particle clusters in animal tight junctions, and their possible function in providing electrical coupling via low resistance junctions between plant cells is discussed.     

The nucleolar chromatin and the secondary constriction

We have traced the nucleolar chromatin from early prophase to the metaphase stage. In prophase this chromatin begins to condense and in metaphase it is fully condensed. In mitotic chromosomes, this chromatin remains surrounded by achromatic materials resembling the fibrillar centre. As such this region of the chromosomes appears as a gap or constriction at the light microscope level. The possible role of this achromatic material in relation to nucleologenesis and satellite association has been discussed.     

Development of Dactylaria eudermata Drechsler a predaceous fungi in Meloidogyne incognita

Dactylaria eudermata Drechsler is one of the important predaceous fungi occurring widely in different soils. The fungus produces hyphal bails and network compound in which nematodes are entangled. This hyphal nets as trapping structure which may be single dimensional to two or three dimensional and are formed through repeated hyphal anastomosis, which capture nematodes either through the adhesive material present on the surface of hyphal nets or due to physical entanglement. In the experiment it was observed that inflation of hyphal bails takes 30 to 50 minutes and capturing and killing the nematode by a single conidia in water takes 35–55 hours, were as time required for inflation of hyphal bails and real trapping and killing of a nematode in maize meal (MMA: water (1:10) medium) takes one minute and 30–50 hours respectively.     

Formation of the zebrafish midbrain-hindbrain boundary constriction requires laminin-dependent basal constriction

The midbrain-hindbrain boundary (MHB) is a highly conserved fold in the vertebrate embryonic brain. We have termed the deepest point of this fold the MHB constriction (MHBC) and have begun to define the mechanisms by which it develops. In the zebrafish, the MHBC is formed soon after neural tube closure, concomitant with inflation of the brain ventricles. The MHBC is unusual, as it forms by bending the basal side of the neuroepithelium. At single cell resolution, we show that zebrafish MHBC formation involves two steps. The first is a shortening of MHB cells to approximately 75% of the length of surrounding cells. The second is basal constriction, and apical expansion, of a small group of cells that contribute to the MHBC. In the absence of inflated brain ventricles, basal constriction still occurs, indicating that the MHBC is not formed as a passive consequence of ventricle inflation. In laminin mutants, basal constriction does not occur, indicating an active role for the basement membrane in this process. Apical expansion also fails to occur in laminin mutants, suggesting that apical expansion may be dependent on basal constriction. This study demonstrates laminin-dependent basal constriction as a previously undescribed molecular mechanism for brain morphogenesis.     

The dynamics of cell constriction during division

The approximate equation is derived for the rate of constriction of a dividing cell, describing the phenomenon from its early stages. The equation previously derived by G. Young for the case when the constriction has already considerably progressed is obtained as a limiting case.     

Mutations of DMYPT cause over constriction of contractile rings and ring canals during Drosophila germline cyst formation

Ring canals, also known as stable intercellular bridges, are derived from the contractile rings of incomplete cytokinesis (IC) in most organisms. Formation of ring canals is necessary to generate functional eggs and sperm in multiple organisms including insects, birds, mammals and various plants. How the constriction of a contractile ring is arrested and how an arrested contractile ring is transformed into a ring canal is unknown. We describe here the function of the Drosophila melanogaster myosin binding subunit of myosin phosphatase (DMYPT) in both processes. We have found that DMYPT is highly enriched in the cytoplasm of cells undergoing IC during oogenesis. DMYPT mutations in germ cells, but not in somatic follicle cells, resulted in over-constriction of contractile rings and ring canals. This leads to formation of small ring canals and mis-regulation of centriole migration during female germline cyst formation. Our results suggest that there may be two parallel mechanisms to prevent the contractile rings from being completely closed, physical resistance and inhibition of myosin II activity via DMYPT.     

Widening the scope of constriction

JGP modeling study suggests that selectivity filter constriction is a plausible mechanism for C-type inactivation of the Shaker voltage-gated potassium channel.

In response to prolonged activation, many K⁺ channels spontaneously reduce the membrane conductance by undergoing C-type inactivation, a kinetic process crucial for the pacing of cardiac action potentials and the modulation of neuronal firing patterns. In the pH-activated bacterial channel KcsA, C-type inactivation appears to involve constriction of the channel’s selectivity filer that prohibits ion conduction, but whether voltage-gated channels like Drosophila Shaker use a similar mechanism is controversial (1). In this issue of JGP, a computational study by Li et al. suggests that filter constriction is indeed a plausible mechanism for the C-type inactivation of Shaker (2).(Left to right) Jing Li, Benoît Roux, and colleagues use computational modeling to show that selectivity filter constriction, allosterically promoted by opening of the intracellular activation gate, is a plausible mechanism for the C-type inactivation of voltage-gated K⁺ channels such as Drosophila Shaker. The selectivity filter is conductive (left) when the intracellular gate is partially open, but adopts a constricted conformation (right) when the gate is open wide.Various structural approaches have shown that C-type inactivation of KcsA channels is associated with the symmetrical constriction of all four channel subunits at the level of the central glycine residue in the selectivity filter. Benoît Roux and colleagues at The University of Chicago used MD simulations to show that the KcsA pore can transition from the conductive to the constricted conformation on an appropriate timescale, and that this transition is allosterically promoted by the wide opening of the pore’s intracellular gate (3). Modeling by Roux and colleagues suggests that C-type inactivation of cardiac hERG channels could also involve selectivity filter constriction, though in this case it appears to be an asymmetric process in which only two of the channel’s subunits move closer together (4).“In view of the high similarity between the pore domains of Shaker and KcsA (almost 40% sequence identity), we wanted to examine if it’s possible for the Shaker selectivity filter to constrict and, if so, how similar it is to KcsA,” Roux explains. Led by first author Jing Li—now an assistant professor at the University of Mississippi—Roux and colleagues developed several homology models of the Shaker pore domain with the intracellular gate open to various degrees (2).MD simulations and free energy calculations revealed that the Shaker selectivity filter can dynamically transition from a conductive to a constricted conformation, and that this transition is allosterically coupled to the intracellular gate; the constricted conformation is stable when the gate is wide open. “Our computations strongly suggest that constriction is a plausible mechanism for the C-type inactivation of Shaker,” Roux says. “There’s no reason based on the currently available information to reject the existence of a constricted state in Shaker channels.”As with KcsA, Shaker channels appear to constrict symmetrically at the level of the selectivity filter’s central glycine. But Li et al.’s simulations revealed some small variations between the two channels, including differences in the number of water molecules bound to each channel subunit and the arrangement of the hydrogen-bond network they form to stabilize the constricted state.Li et al. also modeled the pore domain of the Shaker W434F mutant, which is widely assumed to be trapped in a C-type inactivated state. The simulation suggests that the mutant channel’s filter adopts a stable constricted conformation even when the intracellular gate is only partially open, although the constriction is asymmetric and occurs at the level of a different filter residue (2).Constriction may therefore be a universal mechanism of C-type inactivation, even if the exact conformation varies from channel to channel. But, says Roux, confirming this will require more experimental work using the right conditions and mutations to capture the structure of inactivated channels.     

The stalk region of dynamin drives the constriction of dynamin tubes

The GTPase dynamin is essential for numerous vesiculation events including clathrin-mediated endocytosis. Upon GTP hydrolysis, dynamin constricts a lipid bilayer. Previously, a three-dimensional structure of mutant dynamin in the constricted state was determined by helical reconstruction methods. We solved the nonconstricted state by a single-particle approach and show that the stalk region of dynamin undergoes a large conformational change that drives tube constriction.     

The nuclei of the giant traps of a mutant of Monacrosporium bembicodes (Drechsler) Subram (Dactylella brochopaga Drechsler)

A mutant strain, MG-20, of the predacious hyphomycete Monacrosporium bembicodes (Drechsler) Subram (Dactylella brochopaga Drechsler) develops gaint ring traps, as well as normal ones when supplied with prey. Both types are functional. Giant traps contain more nuclei per cell than normal ones, and as they age, all their nuclei break into fragments which persist in the cell. These findings are briefly discussed.This research was supported by a grant from the National Research Council of Canada which is gratefully acknowledged.