Inactivation of the (+) gamete agglutinin during the mating-type reaction in chlamydomonas

Sex cell contact in Chlamydomonas is due to complementary sex-specific glycoproteins (mating-type substances, MTSs). Their interaction causes an instantaneous but labile flagella agglutination between sexually different gametes. The dynamic nature of this contact permits partner exchange between agglutinated gametes and accounts for the transitoriness of the contact, flagella adhesion being terminated upon ensuing pairing. This paper describes molecular events that underlie the adhesion potential of differentiated (+) gametes. In the contact-establishing interaction with its receptors on the (?) flagella, the agglutinin of differentiated (+) gametes is inactivated. Compensating for this inactivation, the adhesion potential of gametes in agglutination is sustained by continuous replenishment of the inactivated MTS by newly synthesized units. If this glycoprotein neosynthesis is blocked by tunicamycin (TUM), the adhesiveness of differentiated (+) gametes ceases. It is postulated that this complex interaction with incapacitation and neosynthesis forms the basis of the dynamic nature of the flagella contact and eventually accounts for its termination at pairing.     

Preliminary results from a controlled evaluation of thermal biofeedback as a treatment for essential hypertension

In a controlled trial, thermal biofeedback (n=20) and abbreviated progressive relaxation (n=22) were compared in the treatment of mild to moderate hypertensive patients whose blood pressures (BP) were initially controlled on two medications. For the clinical end point of maintaining control of BP on a single drug after treatment, biofeedback was superior to relaxation training (at 3 months, 47% success for biofeedback versus 23% for relaxation). This same result tended to be true for patient-measured home BPs. BPs from laboratory psychophysiological testing showed no consistent advantage for one treatment over the other.This research was supported by a grant from NHLB1, HL-27622.     

Ultrastructural and histochemical studies on guard cells

Serial thick sections of guard cells from Vicia faba L., Nicotiana tabacum L., Allium cepa L., Zea mays L. and Beta vulgaris L. were obtained systematically (600–800 nm) and viewed with the transmission electron microscope in an effort to demonstrate the presence or absence of a symplastic transport pathway within the stomatal complex. Eight to ten stomata from each species were examined, and no continuous plasmodesmata were found connecting guard cells to sister guard cells or to adjacent epidermal or subsidiary cells. Continuous plasmodesmata were observed in immature guard cells, but were sealed (truncated) during the development of the mature cell wall. Histochemical stains, phosphotungstic acid and silver methenamine, were used to demonstrate differentiation within the mature guard-cell wall. The structural differentiation of the stomatal apoplastic region is discussed in relation to fanctional specialization. Plasma-membrane elaborations or plasmalemmasomes were identified in the guard cells of Zea, and it is suggested that these structures may function in ion transport.Abbreviations PTA-HCl phosphotungstic acid and hydrochloric acid - SM silver methenamine - UA-LC uranyl acetate and lead citrate     

Cell interactions during the fusionin vitro ofDrosophila eye-antennal imaginal discs

Summary The fusion of the eye-antennal discs during culturein vitro has been investigated, and the complex morphogenetic movements which occur during the formation of the head capsule of the insect are described. The initial contact between the eye anlagen is by means of cell processes spanning the gap between the two discs. Subsequently the two epithelia become firmly apposed, and then the integrity of the epithelium in the region of fusion breaks down, cells appearing to move to new positions in order to form an epithelium which unites the two discs. The epithelium eventually secretes a pattern of cuticular structures which is continuous between the derivatives of the two discs. Bristles on either side of the line of fusion are perfectly aligned, and structures such as the median ocellus, which are formed jointly by the cells of the two discs, differentiate normally. This is also found when left and right eye-antennal discs of different genotypes are placed side-by-side, indicating that processes of pattern regulation can occur in culture.     

The development and vertical distribution of populations of gas-vacuolate bacteria in a eutrophic,monomictic lake

The role of gas vacuoles in the vertical stratification of planktonic bacteria is analysed. Measurements made with certain gas-vacuolate bacteria in laboratory culture suggest that only colonial forms could sink or float fast enough to form population maxima in lakes by vertical migration from other depths. It is suggested that in the case of individual cells the importance of the buoyancy provided by gas vacuoles is to minimise sinking rates and thereby to increase residence times of the organisms at depths where conditions support their growth.Changes in the vertical distribution of a number of gas-vacuolate bacteria were followed throughout the year in a monomictic, eutrophic lake (Crose Mere, Shropshire). All were restricted to the anaerobic hypolimnion which developed in summer. The various species formed maxima at different depths and times. With some of them (e.g. species of Thiopedia, Pelonema and Brachyarcus) growth was necessary to explain their development. In others (e. g. species of Pelodictyon and two colourless bacteria) vertical migrations might also have contributed to their development.     

Regulation by the H-2 gene complex of delayed type hypersensitivity

Identity at the major histocompatibility complex (MHC) was essential for successful transfer of delayed type hypersensitivity (DTH) in mice. The regions of the MHC involved differed according to the antigen used for sensitization. In the case of fowl gamma globulin (FGG), identity atI-A was necessary, whereas with dinitrofluorobenzene (DNFB), identity at theK, I, orD region was sufficient. These different genetic constraints probably reflect differences in the mechanisms by which antigens are presented to T lymphocytes. Cells from sensitized (CBA×C57BL)F₁ mice transferred DTH to FGG into parental-strain mice, but transfer was more effective in C57BL than in CBA with the same cell dose. This phenomenon is governed by the MHC, since there was better transfer intoH-2 ^b than intoH-2 ^k mice, regardless of their backgrounds. It may reflect the activity of an Ir gene-dependent process. Cells of one genotype (e.g., CBA), sensitized in chimeric mice derived from two MHC-incompatible strains (CBAC57BL), transferred DTH to both strains. These results do not support the notion that the genetic constraint observed in DTH transfer may be a result of the necessity for sensitized T and stimulator cells to match an identical MHC-coded cell interaction molecule. Rather, they favor the hypothesis that T cells recognize antigen, not as a naked determinant, but in close association with products of genes of the MHC.     

Defect in macrophage effector function confers Salmonella typhimurium susceptibility on C3H/HeJ mice

The defective allele of the endotoxin response locus (Lps^d) renders mice (e.g., C3H/HeJ strain) both endotoxin hyporesponsive and susceptible to Salmonella typhimurium. In this study, the mechanism of Lps^d-regulated susceptibility to murine typhoid was examined. C3H/ HeJ mice became significantly more resistant to S. typhimurium by reconstitution with bone marrow from syngeneic C3H/HeN mice (Lpsⁿ, salmonella resistant). Thus, the Lps^d resistance defect appeared to reside in a radiosensitive bone marrow-derived cell(s). At least one of the abnormal cell types appeared to be a macrophage because C3H/HeJ mice preinfected with Mycobacterium bovis (BCG) were, in contrast to controls, able to restrict early salmonella replication in their spleens and displayed a signficant increase in mean time to death. In contrast, no deficiency in uptake of salmonellae by C3H/HeJ macrophages was observed. These results indicate that the early deaths of C3H/HeJ mice following S. typhimurium challenge reflect a failure of their macrophages to limit the growth of these gram-negative bacteria.     

Cerebral Metabolic Effects of Monoamine Oxidase Inhibition in Normal and 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Acutely Treated Monkeys

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces dopaminergic cell death in the substantia nigra pars compacta (SNpc) and clinical parkinsonism in humans and experimental animals. Pretreatment with monoamine oxidase inhibitors prevents this cell death and associated parkinsonism by blocking the oxidation of MPTP to a toxic intermediate. The 2-deoxyglucose method was used to study the acute effects of MPTP in the monkey brain and the effects of monoamine oxidase inhibition on local cerebral glucose utilization in both normal and MPTP-treated monkeys. MPTP administration alone caused a major increase in glucose utilization in the SNpc and smaller increases in some subnuclei within the ventral tegmental area in which eventual dopaminergic cell loss also occurs. Pretreatment with pargyline abolished these metabolic increases, a finding suggesting both that the oxidized product of MPTP generates the metabolic increases and that the increased glucose consumption may contribute to cell toxicity. On the other hand, in most cortical, thalamic, striatal, brainstem, and cerebellar areas MPTP alone caused reductions in glucose utilization, and pargyline failed to prevent these effects. Pargyline alone depressed metabolism in the locus coeruleus and a few other monoaminergic structures.     

Cell Damage Associated with Changing the Medium of Mesencephalic Cultures in Serum-Free Medium Is Mediated via N-Methyl-D-Aspartate Receptors

Dopaminergic neurons from embryonic rat mesencephalon were grown in simple serum-free media. The cells develop over a period of several weeks in vitro, particularly between day 14 and day 23. Removing the culture medium and replacing it with fresh medium during this interval caused severe damage to the cultures; this damage is mediated by excitatory amino acids acting through glutamate receptors. Damage could be completely prevented by antagonists of the N-methyl-D-aspartate subtype of glutamate receptor. As expected, medium that contains glutamate (i.e., Ham's F-12 medium) caused damage; however, medium that contains no glutamate or aspartate (i.e., Dulbecco's modified Eagle medium) also caused severe damage, and most of the damage was dependent on the presence of glutamine in the medium. The presence of the antibiotics penicillin and streptomycin greatly enhanced damage caused by medium change.     

The purification and characterisation of the two forms of soluble starch synthase from developing pea embryos

Soluble starch synthase was purified 10000-fold from developing embryos of pea (Pisum sativum L.). The activity was resolved into two forms which together account for most if not all of the soluble starchsynthase activity in the embryo. The two isoforms differ in their molecular weights but are similar in many other respects. Their kinetic properties are similar, neither isoform is active in the absence of primer, and both are unstable at high temperatures, the activity being abolished by a 20-min incubation at 45° C. Both isoforms are recognised by antibodies raised to the granule-bound starch synthase of pea. Isoform II, which has the same molecular weight (77 kDa) as the granulebound enzyme, is recognised more strongly than Isoform I.