Pattern of dry-matter accumulation,and nitrogen concentration and uptake as influenced by levels and methods of nitrogen application in rainfed-upland rice

Summary Dry-matter accumulation, and concentration and uptake of nitrogen increased with increasing level of nitrogen at all the stages of crop growth. The differences in nitrogen concentration due to nitrogen levels were greatest at panicle initiation stage and started becoming narrower with the advancement in crop age. Split application of nitrogen with its heavier fractions at tillering and panicle initiation stages either through soil alone or soil+foliage (1/3+1/3+1/3) resulted in higher dry-matter accumulation, and higher nitrogen concentration and uptake than other methods. The crop, on an average, removed 61 kg N/ha. Plants accumulated nearly 15% of the total absorbed nitrogen, up to tillering, 50% up to panicle initiation and 85–90% up to heading. Proportionately lesser nitrogen uptake and dry-matter accumulation at post-heading stage is an indicative of a major constraint for production efficiency of rainfed-upland rice culture.     

Wall morphogenesis in diatoms: Deposition of silica by cytoplasmic vesicles

Summary Several TEM and SEM techniques were applied to examine developing structures in valves of the centric diatomThalassiosira eccentrica (Ehrenb.) Cleve after cytokinesis. It was possible to confirm that in each stage of the silicification process there is a distinction between a growing zone with a loose assemblage of silica spheres and a compacting zone in an older phase of development. The spherical structure of the silica in the growing zone results from the addition of silica by small cytoplasmic vesicles of about 300 to 400 Å in diameter. The vesicle membrane fuses with the silicalemma and the vesicle content is released into the silica-deposition vesicle. The origin of these vesicles, named STV, is still unknown.     

Relationship of actin organization to growth in the two forms of the dimorphic yeastCandida tropicalis

Summary Candida tropicalis is a dimorphic yeast capable of growing both as a budding yeast and as filamentous hyphae depending upon the source of the carbon used in the culture medium. The organization of F-actin during growth of the yeast form (Y-form) and the hyphal form (H-form) was visualized by rhodamine-conjugated phalloidin by using a conventional fluorescence microscope as well as a laser scanning confocal fluorescence microscope. In single cells without a bud or non-growing hyphae, actin dots were evenly distributed throughout the cytoplasm. Before the growth of the bud or hypha, the actin dots were concentrated at one site. During bud growth, actin dots were located solely in the bud. They filled the small bud and then filled the apical two-thirds of the cytoplasm of the middlesized bud. During growth of the large bud, actin dots which had filled the apical half of the cytoplasm gradually moved to the tip of the bud. In the formation of the septum, actin dots were arranged in two lines at the conjunction of the bud and the mother cell. During hyphal growth, the majority of actin dots were concentrated at the hyphal apex. A line of clustered spots or a band of actin was observed only at the site where the formation of a new septum was imminent. This spatial and temporal organization of actin in both categories of cells was demonstrated to be closely related to the growth and local deposition of new cell wall material by monitoring the mode of growth with Calcofluor staining. Treatment of both forms of cells with cytochalasin A (CA) confirmed the close relationship between actin and new cell wall deposition. CA treatment revealed lightly stained unlocalized actin which was associated with abnormal cell wall deposition as well as changes in morphology. These results suggest that actin is required for proper growth and proper deposition of cell wall material and also for maintaining the morphology of both forms of cells.Abbrevations FM fluorescence microscopy - EM electron microscopy - rh rhodamine - CA cytochalasin A - CD cytochalasin D - PBS phosphate-buffered saline - DMSO dimethylsulfoxide - GA glutaraldehyde     

Fibroblast heterogeneity in glucocorticoid regulation of collagen metabolism: Genetic or epigenetic?

Summary Cultured fibroblasts derived from normal human dermis show a consistent 62% inhibition of collagen synthesis by hydrocortisone, whereas cultures derived from keloids average only 30% inhibition and show a much larger strain to strain variation ranging from 75% inhibition to 49% stimulation. Examination of fibroblast clones indicates that this high variation among keloid strains is not due to differences in the proportion of normal and keloid cells in the mass culture populations. Small but significant differences in the effect of hydrocortisone on collagen deposition are also seen among these clonal populations, but are not related to the type of tissue from which cultures were derived. Two to three-fold differences among clones derived from a single individual were observed, possibly suggesting functional heterogeneity of dermal fibroblasts with regard to collagen metabolism under control conditions and in response to hydrocortisone. However, this variation among clones may simply reflect differences in clonal growth, inasmuch as both collagen synthesis and deposition, and the effect of hydrocortisone on these processes, are strongly affected by population density. This work was supported in part by PHS grants, CA-17229 from the National Cancer Institute and AG-02046 from the National Institute on Aging, DHHS; and by Grant RIM 78-17313 from the National Science Foundation.     

The effects of parasitic water mite larvae (Arrenurus spp.) on zygopteran imagoes (Odonata)

Arrenurus larvae, ectoparasitic on zygopteran imagoes, attach to the host's cuticle and tear it to obtain the host's tissue fluids. Within the host's epidermis, each larval mite produces a feeding device, the stylostome, a narrow gelatinous resilient blind sac. Heavy mite infestation brings about several wounds in close proximity, accompanied by loss of more or less extensive areas of the epidermis. Despite wound repair by congregating hemocytes, local lack of epidermis seems to enfeeble the host, presumably owing to desiccation. Heavily mite-loaded zygopterans have lost the typical agility and are easily caught. A mite-induced mortality seems to exist in zygopteran populations; the infestation contributes to reduced longevity. The study of formation and decline of the arrenurid stylostome in zygopterans renders it possible to trace cellular defence reactions under natural conditions. Most stylostomes seem to thwart the ability of the host to recognize them as foreign bodies. The host's defence appears as a two-step reaction: (1) initial hemolymph clotting and deposition of melanin associated with aggregating hemocytes at the penetration site, (2) occasional subsequent melanization and cellular encapsulation of the stylostome.     

Endocrine influence upon the development of vitellogenic competency in Oncopeltus fasciatus

Immunoelectrophoretic analysis of the blood of precocious adult females of Oncopeltus demonstrated the presence of the A form of vitellogenin but no detectable AB form, the form present in mature adult-female haemolymph. Although the appearance of the AB form could be induced by topical treatment of precocious adult females with juvenile hormone, no yolk deposition was induced in these females. Histological examination revealed that the ovaries of precocious adult females reached only a previtellogenic stage of development with or without treatment with juvenile hormone. Topical treatment of normal larvae and adults with the hormone demonstrated that vitellogenin synthesis could not be induced with juvenile hormone treatment alone until after adult emergence. Since the precocious adult females are chronologically younger than normal last-stage larval instars, we suggest that a transition period during which juvenile hormone is absent (i.e. the precocious moult in treated animals; the final moult in control animals) must occur before some tissue of the precocious or normal adult females, presumably the fat body, becomes competent to respond to further exposure to the hormone by making the AB form of vitellogenin. The ovary requires a similar transition period prior to becoming capable of depositing vitellogenin; however, the times when the fat body and the ovary become competent to respond to the transition period differ.     

Genetics of lipid deposition in the Japanese quail

Summary The research presented here was designed to investigate the mode of inheritance of fat and lean tissue deposition, and the relationship between them and body weight in Japanese quail. Heterotic effects were found for weight, size, and number of adipocytes in the abdominal fat depots, weight of the sartorial fat depot and percentage carcass fat with means for the hybrids being lower than those for the parental lines. General inferences concerning the importance of nonadditive genetic variation for lean and body weight were precluded due to inconsistencies observed among mating combinations. Thus, although heterosis and recombination effects were general for characteristics associated with fat deposition, the situation for body weight and lean was unique to the populations involved. It may be hypothesized that heterosis in the efficiency of feed utilization is reflected by the heterosis for fat deposition which explains why hybrids utilize feed better than their parental lines.     

The control of cellulose microfibril deposition in the cell wall of higher plants

In maize (Zea mays L.) and pine (Pinus taeda L.) seedlings, cellulose microfibril impressions are present on freeze-fractured plasma membranes. It has been proposed that impressions of newly synthesized microfibrils are a record of the movement of terminal synthesizing complexes through the plasma membrane (Mueller and Brown, 1980, J. Cell Biol. 84, 315–326). The association of terminal complexes with the ends of microfibril impressions or with the ends of microfibrils torn through the membrane indicates the orientation of microfibril tips. Unidirectionally-oriented microfibril tips (all pointing in the same direction) are associated with the organized deposition of parallel arrays of microfibrils. Multidirectionally-oriented microfibril tips were observed in a cell in which microfibril deposition was unusually disorganized. Microfibril patterns around pit fields are asymmetric and resemble flow patterns. Unidirectionally-oriented tears are associated with these microfibrils. Although microfibril orientations are deflected around pit fields, the main axis of microfibril orientation is maintained across the surface of the cell. The hypothesis is proposed that the interaction of a flowing plasma membrane with microfibril synthesizing complexes in the plane of the membrane may result in unidirectional deposition and asymmetric microfibril impressions around pit fields.Some of this work has been published in preliminary form (Brown 1979)     

An ultrastructural study of iron and manganese deposition associated with extracellular polymers of pedomicrobium-like budding bacteria

Morphological characteristics of two Pedomicrobium-like budding bacteria are described. A structured surface layer was regularly observed on strain 868. Ruthenium red- and Alcian blue-staining polymers were found on both strains.When either strain was grown in the presence of iron or manganese, the corresponding oxides accumulated on their surfaces. In thin sections iron oxides appeared as fine threads, arrays of particles or dense coatings, depending on the source of iron. Manganese oxides appeared as branching filaments or convoluted ribbons. Both metal oxides stained with ruthenium red. Extraction of the oxides followed by ruthenium red staining revealed that polyanionic polymers previously deposited on the cells were associated with the metals.Treatment of cultures with glutaraldehyde, HgCl₂, or heat, inhibited manganese but not iron deposition, suggesting that iron oxides accumulated by passive, non-biological processes. Manganese oxides apparently accumulated under control of a biological manganese-oxidizing factor. Incomplete inhibition of manganese deposition observed in cell suspensions suggested that, if the oxidizing factor was an enzyme, it was unusually stable.Based on these results, possible mechanisms of iron and manganese deposition in association with extracellular polymers are suggested.