Biological Relationship of Rotyleinchulus borealis on Several Plant Cultivars

The embryogenic development of Rolylenchulus borealis, at 24-26 C, was completed on corn, in 12-15 days, and the life-cycle of the nematode from egg to egg required 35-40 days at 20-25 C. Juveniles remained in the soil as preinfective stages for 17-19 days before becoming adults. Only immature vermiform and swollen egg-laying females were found attached to corn roots. Eggs were laid in a gelatinous matrix on the root surface; the number of eggs per egg mass was 45 ± 28 on corn roots. Bean, green pea, potato, sorghum, and sweet potato were also found to be hosts of R. borealis. The nematode established a permanent feeding site on corn root in an endodermal cell that became hypertrophied. Pericyclic cells close to the feeding site showed granular cytoplasm and nuclei with hypertrophied nucleoli. A cell wall ingrowth was also noted around the area of stylet penetration into the endodermal cell.     

Host-Parasite Relationships of Atalodera spp. (Heteroderidae)

Atalodera ucri, Wouts and Sher, 1971, and A. lonicerae, (Wouts, 1973) Luc et al., 1978, induce similar multinucleate syncytia in roots of golden bush and honeysuckle, respectively. The syncytium is initiated in the cortex; as it expands, it includes several partially delimited syncytial units and distorts vascular tissue. Outer walls of the syncytium are relatively smooth and thickest near the feeding site of the nematode; inner walls are interrupted by perforations which enlarge as syncytial units increase in size. The cytoplasm of the syncytium is granular and includes numerous plastids, mitochondria, vacuoles, Golgi, and a complex network of membranes. Nuclei are greatly enlarged and amoeboid in shape. Although more than one nucleus sometimes occur in a given syncytial unit, no mitotic activity was observed. Syncytia induced by species of Atalodera chiefly differ from those of Heterodera sensu lato by the absence of cell wall ingrowths; wall ingrowths increase solute transport and characterize transfer cells. In syncytia of Atalodera spp., a high incidence of pits and pit fields in walls adjacent to vasctdar elements suggests that in this case plasmodesmata provide the pathway for increased entry of sohttes. The formation of a syncytium by species of Atalodera and Heterodera sensu lato, but a single uninucleate giant cell by Sarisodera and Hylonema, indicates a pattern of host responses that may be useful, with other characters, for phylogenetic inference for Heteroderidae.     

Pathogenicity and Histopathology of Rotylenchulus reniformis Infecting Cantaloup

Rotylenchulus reniformis was pathogenic to cantaloup (Cucumis melo ''Perlita'') under greenhouse conditions. These findings confirm field symptoms of cantaloup infected with R. reniformis. Histopathological studies show that the nematode penetrates the cortex perpendicular to the vascular system and comes to rest with the head against the endodermis in young roots. Feeding stimulated the pericycle to either side of the endodermal feeding cell and caused cell hypertrophy with enlargement of the nucleoli and granular thickening of the cytoplasm. In older roots where the endodermis had collapsed, the nematode fed directly into the pericycle and caused similar symptoms. Nematode development was more rapid at 27 C than at 21 C.     

Host Response to Sarisodera hydrophila Wouts and Sher, 1971

The histopathology of two populations of Sarisodera hydrophila Wouts and Sher, 1971 was examined on Salix lasiolepis Benth. (willow), Populus fremontii Wats. (cottonwood), and Lyonothamnus floribundus Gray (ironwood) using light microscopy as well as scanning and transmission electron microscopy. Sarisodera hydrophila induces formation of a single uninucleate hypertrophied cell (giant cell) which varies only slightly among the three hosts. The giant cell is enclosed by the root stele and contacts phloem, vascular cambium, and xylem. The single hypertrophied nucleus of the giant cell is ameboid or lobulate in shape, generally with a single nucleolus. The cell is characterized by a wall which is separated into two distinct regions about 2 μm and 13 μm thick; the thicker region occurs adjacent to the nematode head. Cell wall ingrowths, such as those associated with host responses to certain other plant-parasitic nematodes, were not observed in giant cells induced by S. hydrophila. However, a high frequency of pit fields with plasmodesmata occurred in the thinner portion of the cell wall which is adjacent to vascular elements. Roots of the three hosts simultaneously infected with S. hydrophila and Meloidogyne sp. resulted in adjacent responses characteristic of each nematode, supporting the view that the specific type of host response is a function of the nematode rather than the host. The varying expressions of host responses among Heteroderoidea may be useful in testing congruency with existing interpretations of phylogeny.     

Resistance and Resistant Reaction of Gossypium arboreum to the Reniform, Nematode,Rotylenchulus reniformis

Gossypium arboreum ''Nanking CB 1402'' possessed a high level of resistance to Rotylenchulus reniformis. Within 16 h, the nematode penetrated roots of resistant and susceptible cottons equally. After 36 h, significantly fewer nematodes were found in resistant roots. Larvae fed in either an endodermal or pericyclic cell and had no specificity for root tissue of a particular age. In roots of resistant G. arboreum ''1402,'' wall breakdown of pericyclic cells was evident after 3 d, endodermal and cortical cells collapsed, and the hypertrophied pericyclic cells disintegrated within 12 d. Cell walls immediately adjacent to the nematode''s head were thickened and more safranin positive in resistant than in susceptible cotton cultivars. Several other cultivars of G. arboreum were also resistant to R. reniformis, based on nematode fecundity and percent egg reduction.     

Studies on the pathogenicity of three host races of Rotylenchulus reniformis on castor

Three races (race 2, 3 and 4) of Rotylenchulus reniformis were identified using host differential from 20 populations collected from Aligarh, India. Pathogenicity tests were conducted using 250, 500, 1000, 2000, 4000 and 8000 immature females/kg soil of three races of R. reniformis on castor. The threshold inoculum levels of Race-2, Race-3 and Race-4 on castor were 500, 1000 and 2000 immature females/kg soil, respectively. Out of these three races present in Aligarh district, Race-2 was found more pathogenic followed by Race-3 and Race-4. Infected plants with all the three races of reniform nematode showed stunting, necrosis, leaf shedding and growth reduction at and above the inoculum threshold level of each race. Reduction in castor growth was directly proportional to the inoculum level of R.reniformis. The rate of nematode multiplication was density dependent.     

Observations on the Mode of Parasitism and Histopathology of Meloidodera floridensis and Verutus volvingentis (Heteroderidae)

Some aspects of the host-parasite relationships of two heteroderid nematodes are described. Meloidodera floridensis induced formation of single uninucleate giant cells in the stelar parenchyma tissue of sand pine (Pinus clausa) roots. Wrinkling and yellowing of the cuticle were associated with maturation of the adult female (cystoid stage). The mode of parasitism of different life stages of Verutus volvingentis on buttonweed (Diodia virginiana) is described. The nematode caused extensive necrosis during penetration and the formation of a large feeding site consisting of nonhypertrophied parenchyma cells with enlarged nuclei and thickened cell walls in the cortex. Walls between cells within the feeding site degenerated, resulting in the formation of a syncytium. Two citrus rootstocks, rough lemon (Citrus lirnon) and trifoliate orange (Poncirus trifoliata), were not hosts of V. volvingentis.     

Host Response to Meloidodera spp. (Heteroderidae)

Host responses to Meloidodera floridensis Chitwood et al., 1956, M. charis Hooper, 1960, and M. belli Wouts, 1973 were examined on loblolly pine, peony, and sage, respectively, with light, scanning, and transmission electron microscopy. In each case the nematodes induce a single uninucleate giant cell. The giant cell is initiated in the pericycle and expands as it matures. The mature giant cell induced by M. floridensis is surrounded by vascular parenchyma, whereas that caused by M. charts and M. belli coutacts xylem and phloem. The cell wall of giant cells induced by all three Meloidodera spp. is generally thicker than that of surrounding cells, with the thickest part adjacent to the lip region of the nematode. The thinner portion of the wall includes numerous pit fields with plasmodesmata, but wall ingrowths were not detected in a thorough examination of the entire wall. The nucleus of a giant cell induced by M. goridensis is highly irregular in shape with deep invaginations, whereas those caused by M. charis and M. belli include a cluster of apparently interconnected nuclear units. Organelles, including mitochondria, endoplasmic reticulum, and plastids of giant cells caused by Meloidodera, are typical of those reported in host responses of other Heteroderidae. The formation of a single uninucleate giant cell by Meloidodera, Cryphodera, Hylonerna, and Sarisodera, but a syncytium by Atalodera and Heterodera sensu lato, might be considered in conjunction with additional characters to determine the most parsimonious pattern of phylogeny of Heteroderidae.     

Histological Observations of Rotylenchulus reniformis on Gossypium longicalyx and Interspecific Cotton Hybrids

Observations on the development of reniform nematode (Rotylenchulus reniformis) on roots of Gossypium longicalyx, G. hirsutum, and two interspecific hybrids derived from them were made by light microscopy. Gossypium longicalyx is reported to be immune to reniform nematode, but the mechanism(s) for resistance are unknown. Penetration of G. longicalyx roots by female nematodes was confirmed, and incipient swelling of the females, indicating initiation of maturation of the reproductive system, was observed. Female maturation occurred up to the formation of a single embryo inside the female body but not beyond this point. In both hybrids, development was inhibited but progressed further than in the immune parent. Reactions ranged from highly compatible, with the formation of active syncytia and full development of females, to incompatible with little or no development of the female. Compatible plants showed characteristic hypertrophied cells, enlarged nuclei, dense cytoplasm, and partial dissolution of cell walls, whereas incompatible plant reactions included lignification of the cells adjacent to the nematode head, or the complete collapse and necrosis of the cells involved. The need to characterize reactions and to carefully select among the plants descended from the hybrids during the introgression process, as well as the importance of combining the results of reproduction tests with histological observation of the plant-nematode interactions, is discussed.     

An ultrastructural study of the response of Blatella germanica (Orthoptera: Blattidae) to the nematode Abbreviata caucasica (Spirurida: Physalopteridae)

An ultrastructural study of the response of Blatella germanica (Orthoptera: Blattidae) to the nematode Abbreviata caucasica (Spirurida: Physalopteridea). International Journal for Parasitology4: 133–138. This study investigates the response of the roach, Blatella germanica L. to the invading spirurid nematode, Abbreviata caucasica v. Linstow. Soon after the first stage nematodes entered the epithelial cells of the colon wall, the surrounding host cells broke down into syncytial giant cells. Large polychromatic epithelial cell nuclei occurred throughout the giant cells and the nematodes moved freely within the cytoplasmic matrix. These giant cells were in turn surrounded by blood cells responding to the disruption. The nematodes developed to the infective third stage juveniles within the giant cells and ingested the syncytial cytoplasm. After reaching the third stage, the parasites remained in a quiescent state within the vacuolated cell which was surrounded by a double tissue layer.Evidence indicated that successful development of the parasite was dependent on the disrupted epithelial cells forming a giant syncytial cell which protected and supplied nourishment to the parasite.     

Gall Formation on Cirsium arvense by Ditylenchus dipsaci

Ditylenchus dipsaci was found to cause gall formation on the stems of Cirsium arvense. The galls were characterized by extensive hypertrophy and hyperplasia, differentiation of nutritive tissue, nuclear modification, and a central cavity containing nematodes. These findings emphasize the importance of host response in investigations of host-parasite interactions and suggest that D. dipsaci may be evolving a host race by reproductive isolation within the confines of a plant gall.     

Histopathology of Root-knot Nematode (Meloidogyne incognita) Infection on White Yam (Dioscorea rotundata) Tubers

White yam tissues naturally and artificially infected with root-knot nematodes were fixed, sectioned, and examined with a microscope. Infective second-stage juveniles of Meloidogyne incognita penetrated and moved intercellularly within the tuber. Feeding sites were always in the ground tissue layer where the vascular tissues are distributed in the tubers. Giant cells were always associated with xylem tissue. They were thin walled with dense cytoplasm and multinucleated. The nuclei of the giant cells were only half the size of those found in roots of infected tomato plants. Normal nematode growth and development followed giant cell formation. Females deposited eggs into a gelatinous egg mass within the tuber, and a necrotic ring formed around the female after eggs had been produced. Second-stage juveniles hatched, migrated, and re-infected other areas of the tuber. No males were observed from the tuber.     

N.K. Kol'tsov's Theory of Synthetic Biology

The state of theoretical biology in the twentieth century is characterized, as well as the appearance and development of N.K. Kol'tsov's scientific program, his original methodology of interdisciplinary synthesis, and, based on it, the concept of theoretical biology.     

Implications of the changing phylogenetic relationships of Acacia s.l. on the biological control of Vachellia nilotica ssp. indica in Australia

Plant relationships have implications for many fields including weed biological control. The use of DNA sequencing and new tree building algorithms since the late 1980s and early 1990s have revolutionised plant classification and has resulted in many changes to previously accepted taxonomic relationships. It is critical that biological control researchers stay abreast of changes to plant phylogenies. One of the largest plant genera, Acacia, has undergone great change over the past 20 years and these changes have ramifications for weed biological control projects in a number of countries. Vachellia nilotica (prickly acacia) is a major weed in Australia, originating from the Indian subcontinent and Asia, and it has been a target for biological control since 1980. Once a member of Acacia, a large (>1,000 spp.) and iconic group in Australia, prickly acacia is now part of the genus Vachellia. Current knowledge suggests that Vachellia is more closely related to mimosoid genera than it is to Acacia s.s. There has also been a recent reclassification of legume subfamilies with subfamily Mimosoideae now part of subfamily Caesalpinioideae, and four new subfamilies. In this paper we review the changes that have occurred to this group since the prickly acacia biological control project began and discuss the implications for the project. A new host test list for quarantine testing is proposed. Developed following the modernisation of the centrifugal‐phylogenetic method, it is shorter than past lists, containing 46 species, although still lengthy because of the expectations of regulatory bodies, which are slower to accept advances in scientific knowledge. The list includes five Vachellia species, six “Mimoseae” species and 26 Acacia species. The number species from legume subfamilies other than the new Caesalpinioideae is greatly reduced.     

Tomasello,Wittgenstein, and Vygotsky: The Problem of the Intermental

The subject of this article is the early mental development of children in the light of research by two classical scholars from the last century and several of our contemporaries. L.S. Vygotsky contended that before the higher mental functions are mastered by a child, they are in a state distributed between the child and an adult “as an intermental category.” However, he subsequently developed this productive notion in a very narrow sense, and the intermental was concretized as it was expressed in language. L. Wittgenstein persuasively showed that mastery of language is impossible without a practical “demonstration” of the meanings of words as part of “language games” within practical activities. At the same time, he argued that there could be no theory regarding this process. M. Tomasello, in works written already in this century, shows that “language games” are learned by the child long before mastering spoken language, based on gestures that in turn rely on joint intentions and joint attention—i.e. on the intermental in the sense in which one can interpret Vygotsky’s comments. The article clarifies the principal difficulties of exploring the topic of the intermental in psychology. A function distributed between an adult and a child cannot be objectified (it was an attempt to objectify that resulted in a narrowing of Vygotsky’s topic). Moreover, the interpretation of the intersubjective status of some forms of the psychic leads to the notion that any mental function remains intermental throughout one’s lifetime. In the view of the author of the article, such an interpretation is essential, but requires serious advances in the philosophical-methodological development of the subject under study.     

The ultrastructure and possible functions of nephrocytes in the trombiculid mite Hirsutiella zachvatkini (Acariformes: Trombiculidae)

The ultrastructure of nephrocytes during the post-larval development of the trombiculid mite Hirsutiella zachvatkini (Schluger) was investigated by means of transmission electron microscopy. Nephrocytes are situated either individually or in groups inside the haemocoelic space and are always ensheathed by a basal membrane. They contain numerous tubular elements, electron-dense inclusions and sometimes electron-lucent vacuoles. Invaginations of the plasma membrane, often in the form of labyrinthine channels, with coated pits of plasma membrane and characteristic slit diaphragms linking adjacent pedicels, typically occupy the peripheral parts of the cells. However, no distinct zonation of organelles in the nephrocytes of trombiculids was observed. The number of nephrocytes in the haemocoel and the intensity of development of their tubular elements and in particular of labyrinthine channels vary significantly during the ontogenesis of mites. The possible functions of nephrocytes and their structure and differentiation in comparison with other arachnids are discussed.     

The Cell Biology of Antigen Processing

Abstract

T lymphocytes recognize antigen only after a series of intracellular events known as antigen processing. The result of antigen processing is the production of short segments of the primary peptide sequence bound to a polypeptide-binding groove on major histo compatibility complex (MHC) molecules. Antigen originates from one of two sites: intracellular or extra cellular. There are two corresponding pathways for antigen processing and two corresponding classes of MHC molecule. Analysis of each pathway has demonstrated that their separation is not purely anatomical, but is maintained by molecular interactions with other molecules. Antigen processing has been shown to regulate the overall immune response, but the mechanisms involved remain obscure.