Sieve-plate pores in tobacco and bean

Summary Tobacco and bean plants were wilted and then fixed as whole plants with formaldehyde-glutaraldehyde for electron microscopy. In some tobacco plants the sieve-plate pores were large, with little callose. Light slime plugs were present, but there was no compaction of P-protein in the pores. Some pores in wilted bean plants were also unplugged. In other plants of both tobacco and bean the sieve-plate pores were plugged. The pores in unwilted control plants of both tobacco and bean were invariably plugged. Tobacco plants were also cut into thin slices and then immediately fixed. In specimens prepared in this way there was little callose in the pores, and many of the pores were not plugged with P-protein. These observations provide additional evidence that sieve-plate pores may be unplugged in vivo.     

P protein in the phloem of Cucurbita. I. The development of P-protein bodies

Light and electron microscopical observations of the cells of the phloem of Cucurbita maxima have shown that two distinct types of P-protein bodies are formed: a larger type which arises as fine fibrils and a smaller type which apparently arises as groups of tubules. The tubules of the smaller type of body measure 242 ± 3.6 (SE) A (n = 48) and appear morphologically identical with the P1-protein tubules of Nicotiana tabacum L. In some of these P1-protein bodies the tubules are arranged in a regular manner with a center-to-center distance of 295 A. The P protein of the larger type of P-protein body is first apparent in the cytoplasm as small aggregates of fine fibrils. This P-protein component has been designated P3 protein. As the P3 protein accumulates it is organized into large bodies. Some of these bodies contain only P3 protein, others a tubular form of protein, and still others a combination of P3 protein and a tubular form. This variability indicates that there is a developmental sequence of the formation of tubules from the P3-protein fibrils. These tubules measure 179 ± 8.2 (SE) A (n = 31) and have been designated P4 protein.     

Ultrastructure of the plasmodial slime moldPerichaena vermicularis

Summary Mature plasmodia ofPerichaena vermicularis require a light period to induce sporulation. In this paper the ultrastructure and acid phosphatase localization of the mature plasmodium ofPerichaena vermicularis are investigated. Acid phosphatase is localized in vacuoles containing remnants of bacteria and cell organelles. Morphological and histochemical evidence support the interpretation that these vacuoles constitute two types of lysosomes called respectively heterophagic and autophagic vacuoles.Coated vesicles which apparently originate from smooth endoplasmic reticulum are dispersed throughout the plasmodium and frequently associated with lysosomes. Several dumbbellshaped mitochondria are observed in the plasmodium at the onset of fruiting but not during later stages of plasmodiocarp development. Cytoplasmic microtubules are identified inPerichaena vermicularis. Some of these are closely associated with microfilaments.This work was supported by National Science Foundation grants (GB-5884 and GB-8537) to Dr.Ian K.Ross, NSF grant (GB 12371) to Dr.James Cronshaw, and an NSF Traineeship (GZ 445 and 796) to I.Charvat.This constitutes a portion of a thesis presented to the Regents of the University of California by the first author in partial fulfillment of the requirements for the Ph. D. degree.     

On the structure and operation of type I DNA restriction enzymes.

Type I DNA restriction enzymes are large, molecular machines possessing DNA methyltransferase, ATPase, DNA translocase and endonuclease activities. The ATPase, DNA translocase and endonuclease activities are specified by the restriction (R) subunit of the enzyme. We demonstrate that the R subunit of the Eco KI type I restriction enzyme comprises several different functional domains. An N-terminal domain contains an amino acid motif identical with that forming the catalytic site in simple restriction endonucleases, and changes within this motif lead to a loss of nuclease activity and abolish the restriction reaction. The central part of the R subunit contains amino acid sequences characteristic of DNA helicases. We demonstrate, using limited proteolysis of this subunit, that the helicase motifs are contained in two domains. Secondary structure prediction of these domains suggests a structure that is the same as the catalytic domains of DNA helicases of known structure. The C-terminal region of the R subunit can be removed by elastase treatment leaving a large fragment, stable in the presence of ATP, which can no longer bind to the other subunits of Eco KI suggesting that this domain is required for protein assembly. Considering these results and previous models of the methyltransferase part of these enzymes, a structural and operational model of a type I DNA restriction enzyme is presented.     

A randomised, blinded, placebo-controlled trial in dementia patients continuing or stopping neuroleptics (the DART-AD trial)

Background

There have been increasing concerns regarding the safety and efficacy of neuroleptics in people with dementia, but there are very few long-term trials to inform clinical practice. The aim of this study was to determine the impact of long-term treatment with neuroleptic agents upon global cognitive decline and neuropsychiatric symptoms in patients with Alzheimer disease.

Methods and Findings

Design: Randomised, blinded, placebo-controlled parallel two-group treatment discontinuation trial.Setting: Oxfordshire, Newcastle and Gateshead, London and Edinburgh, United Kingdom.Participants: Patients currently prescribed the neuroleptics thioridazine, chlorpromazine, haloperidol trifluoperazine or risperidone for behavioural or psychiatric disturbance in dementia for at least 3 mo.Interventions: Continue neuroleptic treatment for 12 mo or switch to an identical placebo.Outcome measures: Primary outcome was total Severe Impairment Battery (SIB) score. Neuropsychiatric symptoms were evaluated with the Neuropsychiatric Inventory (NPI).Results: 165 patients were randomised (83 to continue treatment and 82 to placebo, i.e., discontinue treatment), of whom 128 (78%) commenced treatment (64 continue/64 placebo). Of those, 26 were lost to follow-up (13 per arm), resulting in 51 patients per arm analysed for the primary outcome. There was no significant difference between the continue treatment and placebo groups in the estimated mean change in SIB scores between baseline and 6 mo; estimated mean difference in deterioration (favouring placebo) −0.4 (95% confidence interval [CI] −6.4 to 5.5), adjusted for baseline value (p = 0.9). For neuropsychiatric symptoms, there was no significant difference between the continue treatment and placebo groups (n = 56 and 53, respectively) in the estimated mean change in NPI scores between baseline and 6 mo; estimated mean difference in deterioration (favouring continue treatment) −2.4 (95% CI −8.2 to 3.5), adjusted for baseline value (p = 0.4). Both results became more pronounced at 12 mo. There was some evidence to suggest that those patients with initial NPI ≥ 15 benefited on neuropsychiatric symptoms from continuing treatment.

Conclusions

For most patients with AD, withdrawal of neuroleptics had no overall detrimental effect on functional and cognitive status. Neuroleptics may have some value in the maintenance treatment of more severe neuropsychiatric symptoms, but this benefit must be weighed against the side effects of therapy.Trial registration: Cochrane Central Registry of Controlled Trials/National Research Register (#ISRCTN33368770).     

Changes in the adrenal steroidogenic responsiveness of the mallard duck (Anas platyrhynchos) during early post-natal development

1. Plasma concentrations of corticosterone (B), aldosterone (Aldo) and deoxycorticosterone (DOC) were measured in mallard ducklings immediately before and after exposure to acute immobilization stress. 2. Except for transient declines in B and DOC between the 4th and 14th days after hatching, the resting concentration of each hormone did not change significantly during post-natal development. 3. The stress-induced in Aldo was maximal at hatching while maximal increases in B and DOC did not occur until one day later. 4. Thereafter the magnitude of the stress-induced increases in the concentrations of all of the hormones decreased steadily and on the 21st and 28th days after hatching only B increased significantly in response to stress.