THE PRIMARY ROOT EPIDERMIS OF PANICUM VIRGATUM L. I. ONTOGENY AND FINE STRUCTURE OF THE EPIDERMAL CYTOPLASMIC INCLUSIONS

The ontogeny of large, globular, epidermal cytoplasmic inclusions (ECI) in P. virgatum roots was studied at the ultrastructural level. These ECI were seen to originate in meristematic cells as small electron translucent vesicles. Subsequently, the ECI, which appeared to be temporary storage sites, were seen to enlarge and increase in density by accumulating masses of a granular matrix as well as some small vesicular inclusions. In the zone of elongation, as the epidermal cells matured, the ECI within each cell gradually fused and the contents were lost. The pattern of the ontogeny of the ECI in the growing epidermal cells was consistent with the presence of cells of different physiologies in the zone of cell elongation of these roots.     

Why Doesn't the Creed Read "Always Be Critical"? An Examination of a Liberal Curriculum

Using ethnographic data collected in a second grade classroom over the course of a school year, this paper describes the ways in which one school's discourse of liberalism is deleteriously deployed. We view the school's discipline creed as emblematic of the school's liberal curriculum, and interrogate the effects on four African American boys in the classroom when the school enacts this creed. Despite the agency that these boys obviously had, they were unable to control the ways in which they were placed at a structural disadvantage and manipulated by a system far more powerful than they were. The results were that these four boys suffered. Not only did the intended liberal curriculum fail to be translated fully into the enacted curriculum, the liberal underpinnings of this curriculum precluded teachers and students from taking any critical stance.     

Parasitoid behaviour: predicting field from laboratory

Abstract.  1. Most of what is known about parasitoid behaviour comes from laboratory observations: field quantitative observations on searching parasitoids are extremely difficult to do and are rare. The basic components of Aphytis melinus 's response to California red scale ( Aonidiella aurantii ) were studied in the laboratory: encounter, rejection, drumming, probing, oviposition, and host-feeding. It was then asked whether these observations provided a reliable guide to behaviour in the field in a situation that was very different from the laboratory.
2. Field observations were carried out on bark on the trunk and interior branches of trees where live scale density is extremely high in patches, dead scale make up 90% of all scale, and could be expected to interfere with Aphytis search.
3. The laboratory observations predicted well the time taken in the field for each basic event (drumming or probing) and average times spent on a scale. Also well predicted were the distributions of times spent on drumming, probing, and total time on a scale. Rejection rates were much higher in the field. Thus, the laboratory studies predicted foraging behaviour in the field with variable success; potential explanations for observed mismatch between laboratory and field and its possible larger implications are discussed.     

Formation of Metallogenium-like structures by a manganese-oxiding fungus

Structures resembling Metallogenium spp. were observed in agar and in liquid cultures of a Mn-oxidizing basidiomycetous fungus only when Mn²⁺ was oxidized. Fungal viability was necessary for formation of the structures; Mn²⁺ concentration and the presence or absence of agar in the medium were important factors determining their morphology. Slide cultures revealed no identifiable cells in any stage of development. Fluorescent dyes that stained nucleic acids and polysaccharides in the fungal hyphae did not stain the Metallogenium-like structures. Likewise, Rhodamine 123, a fluorescent probe for membrane potential, stained fungal mitochondria, but did not stain the structures. Thin sections through the structures showed no biological membranes or other cellular features. Only the characteristic ultrastructure of biological Mn oxides were observed in serial thin sections. In agar, unfixed structures disappeared permanently during reduction of Mn oxides with hydroxylamine. Glutaraldehyde fixation stabilized these structures. Fixed structures lost most of their original phase density during reduction with hydroxylamine, but continuous microscopic observations showed that their phase density could be restored by staining with Coomassie blue. Structures that formed in liquid medium did not require stabilization with glutaraldehyde during reduction of Mn oxides. They, too, lost their original phase density during reduction with hydroxylamine; phase density could be restored by staining with cationic colloidal iron or Coomassie blue. The results suggest that the Metallogenium-like structures were formed as a result of Mn oxidation associated with exopolymers produced by the fungus.Non-standard abbreviations HEPES (N-hydroxyethylpiperazine-N-2-ethane sulfonic acid) - DAPI (4,6-diamidino-2-phenylindole) - PIPES (piperazine-N,N-bis[2-ethane sulfonic acid])     

Cellular senescence involves stochastic processes causing loss of expression of differentiated function genes: visualization by in situ hybridization for steroid 17 alpha-hydroxylase in bovine adrenocortical cells

When grown for long periods in culture, bovine adrenocortical cells lose the expression of a differentiated function gene, steroid 17 alpha-hydroxylase. Previously, we documented a decline in 17 alpha-hydroxylase mRNA with increasing culture passage level after induction with cyclic AMP (P. J. Hornsby et al., 1987, Proc. Natl. Acad. Sci. USA 84, 1580). We used in situ hybridization to investigate the loss of expression of this gene during cellular senescence at an individual cell level. In primary cultures, cells were uniformly positive for hybridization with cDNA for 17 alpha-hydroxylase after cyclic AMP induction. After two passages, cultures comprised a mixture of hybridizing and nonhybridizing cells. Cells appeared either to hybridize at a level comparable to that in primary cultures or to be nonhybridizing. When in situ hybridization was combined with immunofluorescence, cells positive for immunofluorescence were also positive for hybridization. Senescing mass cultures showed decreasing numbers of positive cells, and after 30 passages cultures comprised entirely nonhybridizing cells. Thus, the previously observed decline in overall 17 alpha-hydroxylase mRNA levels results from a decline in the fraction of expressing cells in the culture, and the rate of loss of expressing cells is in agreement with the rate of loss of total 17 alpha-hydroxylase mRNA. Primary clones, even when isolated at an early stage of clonal expansion, had mixtures of subclones of hybridizing and nonhybridizing cells. On recloning, hybridizing subclones usually produced uniformly nonhybridizing sub-subclones. Some subclones within primary clones had a morphology associated with replicative senescence (flattened cells with sparse intercellular contacts), yet had high numbers of hybridizing cells. We conclude that, in both mass and clonal populations, cells initially expressing 17 alpha-hydroxylase rapidly give rise to clones of nonexpressing cells. Such cells are continually derived by a stochastic process from cells originally expressing the gene.     

Behavior of captive-raised rattlesnakes (Crotalus enyo) as a function of rearing conditions

Two litters of rattlesnakes (Crotalus enyo; n = 6 per litter) were raised in large cages and small plastic boxes, respectively. No significant differences in exploration of a novel environment were observed between the litters, or between either of them and a group of wild-caught C. enyo, suggesting that the common practice of rearing baby snakes in small cages has no debilitating consequences on these measures. In the absence of differences between the litters, the two samples were pooled and additional analyses revealed the existence of reliable individual variation. Experiment 2 compared the two litters and the wild-caught snakes on measures of prey-directed behavior. The two captive-reared litters did not differ, but both exhibited lower levels of strike-induced chemosensory searching than did wild-caught snakes.     

Tired,weak, or in need of rest: fatigue among general practice attenders.

OBJECTIVES--To determine the prevalence and associations of symptoms of fatigue. DESIGN--Questionnaire survey. SETTING--London general practice. PARTICIPANTS--611 General practice attenders. MAIN OUTCOME MEASURES--Scores on a fatigue questionnaire and reasons given for fatigue. RESULTS--10.2% Of men (17/167) and 10.6% of women (47/444) had substantial fatigue for one month or more. Age, occupation, and marital status exerted minor effects. Subjects attributed fatigue equally to physical and non-physical causes. Physical ill health, including viral infection, was associated with more severe fatigue. Women rather than men blamed family responsibilities for their fatigue. The profile of persistent fatigue did not differ from that of short duration. Only one person met criteria for the chronic fatigue syndrome. CONCLUSIONS--Fatigue is a common complaint among general practice attenders and can be severe. Patients may attribute this to physical, psychological, and social stress.