A (Sub)field Guide to Quality Control in Hippocampal Subfield Segmentation on Highresolution T2-weighted MRI.

Inquiries into properties of brain structure and function have progressed due to developments in magnetic resonance imaging (MRI). To sustain progress in investigating and quantifying neuroanatomical details in vivo, the reliability and validity of brain measurements are paramount. Quality control (QC) is a set of procedures for mitigating errors and ensuring the validity and reliability of brain measurements. Despite its importance, there is little guidance on best QC practices and reporting procedures. The study of hippocampal subfields in vivo is a critical case for QC because of their small size, inter-dependent boundary definitions, and common artifacts in the MRI data used for subfield measurements. We addressed this gap by surveying the broader scientific community studying hippocampal subfields on their views and approaches to QC. We received responses from 37 investigators spanning 10 countries, covering different career stages, and studying both healthy and pathological development and aging. In this sample, 81% of researchers considered QC to be very important or important, and 19% viewed it as fairly important. Despite this, only 46% of researchers reported on their QC processes in prior publications. In many instances, lack of reporting appeared due to ambiguous guidance on relevant details and guidance for reporting, rather than absence of QC. Here, we provide recommendations for correcting errors to maximize reliability and minimize bias. We also summarize threats to segmentation accuracy, review common QC methods, and make recommendations for best practices and reporting in publications. Implementing the recommended QC practices will collectively improve inferences to the larger population, as well as have implications for clinical practice and public health.

False recognitions in short-term memory - Age-differences in neural activity.

While the knowledge on age-related differences in susceptibility to episodic false memories is extensive, little is known about this phenomenon in visual short-term memory (STM). Our previous behavioural research indicated that older adults are more confident of their erroneous STM recognitions than young adults. However, unlike in episodic memory, we did not find support for older adults' higher rate of false alarms. To further understand this specific age-difference, here we investigated its neural correlates. First, the pattern of behavioural results replicated the one from our previous experiment. Second, younger adults, when compared to older adults, exhibited higher false recognition-related activity of the visual cortex, the anterior cingulate cortex, the frontal operculum/insular cortex as well as regions within the anterior and dorsolateral prefrontal cortex. No age-differences were observed in hippocampal activity. Third, younger but not older adults presented higher activity in the anterior cingulate cortex and the frontal operculum/insular cortex for false recognitions when compared to highly confident correct rejections. Finally, frontal activity was influenced by both the individuals' performance and their metacognitive abilities. The results suggest that age-related differences in confidence of STM false recognitions may arise from age-differences in performance monitoring and uncertainty processing rather than in hippocampal-mediated binding.

Alterations in the sugar metabolism and in the vacuolar system of mesophyll cells contribute to the desiccation tolerance of Haberlea rhodopensis ecotypes.

Haberlea rhodopensis belongs to the small group of resurrection plants having the unique ability to survive desiccation to air dry state retaining most of its chlorophyll content and then resume normal function upon rehydration. It prefers the shady valleys and northward facing slopes of limestone ridges in mountain zones with high average humidity. Nevertheless, it can be found rarely on rocks directly exposed to the sunlight, without the coverage of the canopy. In the present study, we follow the alterations in the subcellular organization of mesophyll cells and sugar metabolism upon desiccation of shade and sun H. rhodopensis plants. Composition and content of soluble carbohydrates during desiccation and rehydration were different in plants grown below the trees or on the sunny rocks. Sucrose, however, was dominating in both ecotypes. The amount of starch grains in chloroplasts was inversely related to that of sugars. Concomitantly with these changes, the number of vacuoles was multiplied in the cells. This can be explained by the development of small (secondary) vacuoles peripherally in the cytoplasm, rather than by the fragmentation of the single vacuole, proposed earlier in the literature. Accordingly, the centripetal movement of chloroplasts and other organelles may be a result of the dynamic changes in the vacuolar system. Upon rehydration, the inner vacuoles enlarged and the organelles returned to their normal position.

A novel mechanism of abscission in fronds of Lemna minor L. and the effect of silver ions.

Lemna minor L. (duckweed) forms colonies through vegetative propagation because mother fronds remain connected for some time with their daughter fronds by stipes. The colony size is controlled by abscission of stipes at a specific preformed abscission zone. Application of silver ions (Ag(+) ) enhances the rate of frond abscission, thus resulting in smaller colonies. The mechanism behind this process has not yet been identified. Silver caused an abscission response that saturated after 7 h of treatment. The half-maximal effective concentration was 0.72 µm Ag(+) for the standard clone, L. minor St. Other clones of the same species show sensitivities that differ by one order of magnitude. Transmission electron microscopy revealed: (i) large numbers of vesicles close to the plasmalemma in cells adjacent to the abscission zone, which proves a vesicular type secretory activity; and (ii) a moderately electron-dense secretion accumulated in the enlarging intercellular spaces, and seemed to flow from the adjacent cells towards the abscission zone. We assume that increasing pressure causes this material to push apart the cells, thereby causing the break in the abscission zone of the stipe. This is a novel mechanism of abscission that has not previously been described. The same mechanism occurs in stipes of both control and Ag(+) -treated samples. Silver ions only accelerate the process leading to abscission of stipes, without affecting the mechanism involved.

Effects of nickel on the chloroplasts of the duckweeds Spirodela polyrhiza and Lemna minor and their possible use in biomonitoring and phytoremediation.

Toxic effects of Ni(2+) on the chloroplasts of the two duckweed species Spirodela polyrhiza, clone SJ and Lemna minor, clone St were investigated according to the ISO 20079 protocol. Ni(2+) induced a transition from chloroplasts to chloro-amyloplasts and amylo-chloroplasts, but not to gerontoplasts, as shown by electron microscopy. The contents of the chlorophylls a and b decreased strongly, whereas that of carotenoids remained approximately constant. Most striking was, however, the accumulation of transitory starch. Bell-shaped dose-response curves showed that Spirodela and Lemna amassed maximum starch contents of approximately 10% and 7%, respectively, on a fresh weight basis. Because Ni(2+) in the concentrations applied does not stimulate photosynthesis, the Ni(2+)-induced starch accumulation indicates that the export of carbohydrates out of the plastids decreased, most probably due to the lower demand of the rest of the cells as a result of the Ni(2+)-dependent inhibition of growth. The half-maximal concentrations for inhibition of the fresh weight increase over the 7-day test period were 3.7 microM and 6.6 microM for Spirodela and Lemna, respectively: Spirodela was thus somewhat more sensitive to the heavy metal. Both species accumulated approximately 3g of Ni(2+) per kg of dry weight after application of 100 microM NiCl(2). Because of their high sensitivity to phytotoxic effects, however, Spirodela and Lemna do not appear to be particularly suitable for phytoremediation of Ni(2+)-contaminated waste water. The high sensitivity to Ni(2+) makes them instead a suitable system for ecotoxicological testing in accordance with the ISO 20079 protocol.

On the mechanism of rejuvenation of ageing detached bean leaves by low-concentration stressors.

The effect of low concentrations of some stress-inducing compounds of different toxicity and chemical nature, such as Cd and Pb salts or DCMU, was investigated on the senescence of chloroplasts in detached primary leaves of bean (Phaseolus vulgaris L.). After 1 week of senescence followed by root development from the petiole, these agents stimulated chlorophyll accumulation and photosynthetic activity ((14)CO(2) fixation) as compared to the control, thus inducing rejuvenation. Low-concentration stressors increased the level of active cytokinins in roots and leaves during the treatment, as monitored by the Amaranthus betacyanin bioassay and high-pressure liquid chromatography. The lithium ion, an inhibitor of the PIP(2)-IP(3)/DAG signal transduction pathway, abolished the stimulating effect of stressors, both in roots (retarding cytokinin synthesis) and consequently also in leaves (reducing cytokinin-dependent chlorophyll accumulation). This suggests the involvement of the PIP(2)-IP(3)/DAG signal transduction pathway in generation of these consecutive organ-specific responses.

Involvement of the phosphoinositide signaling pathway in the anti-senescence effect of low-concentration stressors on detached barley leaves.

The effect of low concentration of some stress-inducing compounds of different toxicity and chemical nature like Pb and Ti salts or DCMU on the senescence of chloroplasts was investigated in detached primary leaves of barley (Hordeum vulgare cv. Omega). These agents stimulated chlorophyll accumulation, photosynthetic activity ((14)CO (2) fixation), and decreased the number of plastoglobuli in chloroplasts compared to the control, thus delaying senescence. Low-concentration stressors did not increase the level of active cytokinins of leaves during the treatment. Lithium and stearoylcarnitine chloride inhibited the stimulating effect of stressors. This points to the involvement of the PIP (2)-IP (3)/DAG signal transduction pathway in generation of the specific responses.

Structural-functional changes in detached cucumber leaves, and modelling these by hormone-treated leaf discs.

Senescence and rejuvenation were investigated in detached cucumber (Cucumis sativus L.) leaves after cultivation in nutrient solution for one week or four weeks. Rooting of the petiole (visible generally from the 7th day) elicited a combination of different morphological, anatomical, and physiological changes in the lamina. Extensive growth in area and thickness, extreme regreening, changes of chloroplast structure and activity, as well as the pattern of Chl-protein complexes were observed and compared either to the corresponding parameters of young detached leaves or mature attached leaves. These responses could be provoked separately by treating excised leaf discs with kinetin, benzyladenine, or indolylacetic acid. The hormones showed mutuality in their effects, benzyladenine being responsible for the growth of cells, while indolylacetic acid and kinetin promoted an increase in chlorophyll content. However, none of the treatments resulted in the growth of the chloroplasts in the leaf discs, which was only prominent in the rooting leaves.

Rejuvenation of ageing bean leaves under the effect of low-dose stressors.

The effect of low concentrations of some stress-inducing compounds like Cd, Pb, Ni, and Ti salts and DCMU on the senescence of chloroplasts was investigated in detached primary leaves of bean. After the petioles of ageing leaves had developed roots, these low-dose stressors stimulated chlorophyll synthesis and photosynthetic activity, as compared to the control, thus causing rejuvenation in treated leaves. The amount of photosystem I (lowest in DCMU-treated leaves) and light-harvesting complex II increased, while that of photosystem II decreased or remained unchanged. Fluorescence induction parameters indicated unchanged electron transport (except for DCMU treatment). CO2 fixation and, in some cases, starch accumulation was stimulated. In parallel, the occurrence of large plastoglobuli seemed to decrease in plastids of heavy metal-treated leaves. A cytokinin bioassay of leaf extracts confirmed the cytokinin-mediated effect of low-dose stressors, as the slopes of Chl and cytokinin curves were similar during the rejuvenation process. It is assumed that these stressors generate non-specific alarm reactions, which involve changes in the hormonal balance by increasing the synthesis of cytokinins.

Effect of gamma and UV-B/C radiation on plant cells.

The biological effect of gamma-rays is based on the interaction with atoms or molecules in the cell, particularly water, to produce free radicals, which can damage different important compounds of plant cell. The UV-B/C photons have enough energy to destroy chemical bounds, causing a photochemical reaction. The biological effect is due to these processes. This paper is focused on the structural and biochemical changes of the cell wall and plastids after gamma and/or UV-B irradiation. Gamma-rays accelerate the softening of fruits, causing the breakdown of middle lamella in cell wall. They also influence the plastid development and function, such as starch-sugar interconversion. The penetration of UV-B light into the cell is limited, while gamma-rays penetrate through the cells. For this reason, UV-B light has a strong effect on surface or near-to-surface area in plant cells. UV-B radiation influences plastid structure (mostly thylakoid membranes) and photosynthesis. Some kinds of pigments, such as carotenoids, flavonoids save plant cells against UV-B and gamma irradiation. Plant cells are generally ozone sensitive. The detoxifying systems operate at the cellular level. Methods for studying structural changes in plant cells develop in direction to molecular biology, combined with immunoassays and new microscopical techniques. Nowadays, UV-B radiation is undergoing much research, being an environmental factor which causes damage to both humans and plant cells.

Nuclear Involvement in the Appearance of a Chloroplast-Encoded 32,000 Dalton Thylakoid Membrane Polypeptide Integral to the Photosystem II Complex.

The genetic locus for the high chlorophyll fluorescent photosystem II-deficient maize mutant hcf(*)-3 has been definitively located to the nuclear genome. Fluorography of lamellar polypeptides labeled with [(35)S]methionine in vivo revealed the specific loss of a heavily labeled 32,000 dalton thylakoid membrane polypeptide as well as its chloroplast encoded precursor species at 34,000 daltons. Examination of freeze-fractured mesophyll and bundle sheath thylakoids from hcf(*)-3 revealed that both plastid types lacked the large EFs particles believed to consist of the photosystem II reaction center-core complex and associated light harvesting chlorophyll-proteins. The present evidence suggests that the synthesis or turnover/integration of the chloroplast-encoded 34,000 to 32,000 dalton polypeptide is under nuclear control, and that these polyipeptides are integral components of photosystem II which may be required for the assembly or structural stabilization of newly formed photosystem II reaction centers in both mesophyll and bundle sheath chloroplasts.

Photosynthetic functions and thylakoid membrane polypeptide composition in light-sensitive mutants of Chlamydomonas reinhardii.

In this paper we compared the pigment composition, photochemical activity, chloroplast ultrastructure, thylakoid membrane polypeptide composition and ribosomal content of wild-type and seven light-sensitive mutants of Chlamydomonas reinhardii.All the mutants had low chlorophyll and carotenoid content compared to wild-type. Mutants lts-30 and lts-135 were also characterized by a complete absence of visible carotenoids, while mutant lts-19 was fully deficient in chlorophylls.In most mutants, the chloroplast fragment could not carry out any DCIP photoreduction and O2 evolution was also blocked. The PSI/P700/activity was decreased in most cases.The mutant strains contained mostly single lamellae in their plastids, that is the stacking capacity of the thylakoid membranes was very decreased or fully absent. In most cases the number of lamellae was also very low.The relative amounts of 70 S ribosomes were decreased in all of the mutants. The thylakoid membranes showed anomalies in the region of 24 000-30 000 dalton polypeptides. The common characteristic for them was the relatively higher amount of the 30 000 dalton polypeptide and considerably decreased level of the 27 000 and 24 000 dalton polypeptides relative to the wild-type. These polypeptides were probably constituents of the chlorophyll-protein complex II which has been suggested to be the light harvesting pigment complex for PSII. The polypeptide of 30 000 daltons is the precursor for the LHCP apoprotein (24 000 dalton protein). It may be that the lighstimulated conversion of this precursor into LHCP apoprotein was blocked in our pigment-deficient mutants.

Evidence for a close spatial location of the binding sites for CO2 and for photosystem II inhibitors.

1. CO2-depletion of thylakoid membranes results in a decrease of binding affinity of the Photosystem II (PS II) inhibitor atrazine. The inhibitory efficiency of atrazine, expressed as I50-concentration (50% inhibition) of 2,6-dichlorophenolindophenol reduction, is the same in CO2-depleted as well as in control thylakoids. This shows that CO2-depletion results in a complete inactivation of a part of the total number of electron transport chains. 2. A major site of action of CO2, which had previously been located between the two electron acceptor quinone molecule B (or R) and Photosystem II inhibitor atrazine as suggested by the following observations: (a) CO2-depletion results in a shift of the binding constant (kappa b) of [14C]atrazine to thylakoid membranes indicating a decreased affinity of atrazine to membrane; (b) trypsin treatment, which is known to modify the Photosystem II complex at the level of B, strongly diminishes CO2 stimulation of electron transport reactions in CO2-depleted membranes; and (c) thylakoids from atrazine-resistant plants, which contain a Photosystem II complex modified at the inhibitor binding site, show an altered CO2-stimulation of electron flow. 3. CO2-depletion does not produce structural changes in enzyme complexes involved in Photosystem II function of thylakoid membranes, as shown by freeze-fracture studies using electron microscopy.

[Study of the texture of furosemid tablets. Part 2 (author's transl)]. / Untersuchung der Textur von Furosemid-Tabletten. Teil 2.

The authors studied the alterations of the texture and of the physical properties of Furosemid tablets, which are prepared with the aid of hydroxypropylcellulose mucilage, that occur during storage. Klucel MF mucilage proved to be a very good binding agent. Though the film bursted on drying during storage, by which the pore volume of the tablets increased, the mechanical strength remained almost unchanged. The cause of this is the formation of solid bridges.

Light and electron microscopic investigation of in vitro starch synthesis in chromoplasts.

Chromoplasts having a globular inner structure in the petals of Forsythia suspensa can form starch grains in their stroma when incubated with glucose solution. The same result was obtained with chromoplasts, similar in structure, from Laburnum anagyroides and Ranunculus acer. Fibrillar chromoplasts in tepals of Lilium croceum are able to synthesize starch in vitro, not, however, from glucose but from glucose-1-phosphate. This starch differs from the above mentioned both in respect of electron microscopic structure and digestibility with alpha-amylase, a feature presumably caused by the relatively high activity of the branching (Q) enzyme. The substrate specificity of Lilium-starch synthesis can be explained by blocking of the phosphorylation of glucose in the cytoplasm, rather than by the selective permeability of the plasmalemma.

Studies on the biological effect of fast neutrons. II. Variation of total nucleic acid content and ultrastructure in barley leaves vs. dose.

The effect of fast neutrons on the ultrastructure and nucleic acid content of leaves of barley seedlings was studied. Irradiation led to chloroplast degeneration. The walls of the cells containing degenerated plastides were abnormally thickened. Irradiation reduced the water content of the leaves. Variations in the RNA and DNA content of the leaves, expressed on a dry weight basis, could not be written as a simple function of the dose. Their content have a minimum at the semi-lethal dose.