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AbstractBackground: There is a large demand for Family Medicine specialists, yet not enough medical students specialise in this field. This study investigated the interest of undergraduate medical students at the University of the Free State in pursuing a career in Family Medicine, factors associated with this interest, and their opinion of Family Medicine as a specialty.Methods: In this prospective cross-sectional study, anonymous, self-reporting questionnaires, available in English and Afrikaans, were distributed to first- to fifth-year undergraduates. Data were collected on demographic variables and interest in Family Medicine and other disciplines. The students had to rate the likelihood of them selecting 15 different specialties as a future career according to a five-point Likert scale. Opinions concerning Family Medicine were tested with a yes/no response as to the agreement to five statements.Results: Fifth-year students were excluded due to poor response rate (13.6%). The response rate for the first- to fourth-year groups was 86.4%. Interest in Family Medicine decreased from first to third year (22.4, 21.2 and 14.0%, respectively), but increased again in the fourth year (23.3%). Females and speakers of African languages showed the most interest in this field. Medical students, especially first years, generally had poor knowledge regarding Family Medicine.Conclusion: Family Medicine is not a preferred specialty in any of the four year groups, and students had insufficient knowledge of the field. Family Medicine should be introduced earlier into the medical curriculum.

Summary.:  Cultured suspension cells of Arabidopsis thaliana that stably express a green-fluorescent protein–α-tubulin 6 fusion protein were used to follow the development and disintegration of phragmoplasts. The development and disintegration of phragmoplasts in the living cultured cells could be successively observed by detecting the green-fluorescent protein fluorescence of the microtubules. In the early telophase spindle, where two kinetochore groups and two daughter chromosome groups had completely separated from one another, fluorescence appeared in the interzone between the two chromosome groups. The fluorescent region was gradually condensed at the previous equator and increased in fluorescence intensity, and finally it formed the initial phragmoplast. The initial phragmoplast moved from the cell center towards the cell periphery, and it lost fluorescence at its center and became double rings in shape. The expansion orientation of the phragmoplast was not always the same as that of the future new cell wall before it came in contact with the cell wall. The phragmoplast did not usually come in contact with the cell wall simultaneously with its entire length. A portion of the phragmoplast which was earlier in contact with the cell wall disappeared earlier than other portions of the phragmoplast. The duration of contact between any portions of the phragmoplast and the plasma membrane of the cell wall was 15–30 min. The fluorescence intensity of the cytoplasm did not seem to be elevated by the disintegration of the strongly fluorescent phragmoplast.

In the ovary of Aptenia cordifolia and Platythyra haeckeliana placentary papillae produce a slime containing polysaccharides and proteins. These papillae show two types of conspicuous vacuoles enclosed by rough ER cisternae and complexes of concentrically arranged rough ER. The enclosed vacuoles probably play an important role in the accumulation of the polysaccharide-protein slime. In the case of storage vesicles (first vacuole type) derivates of the Golgi apparatus are enclosed by ER. In other instances (second vacuole type) ER cisternae which have lost their membrane-bound ribosomes seem to delimit protoplasmic regions free of organelles.

Summary Tobacco (Nicotiana tabacum L.) pollen, germinated 4 hours in suspension culture, was labeled with radioactive leucine and fractionated into constituent membranes by the technique of preparative free-flow electrophoresis. Tubes were ruptured by sonication directly into the electrophoresis buffer. Unfortunately, the Golgi apparatus of the rapidly elongating pollen tubes did not survive the sonication step. However, it was possible to obtain useful fractions of endoplasmic reticulum and mitochondria. To obtain Golgi apparatus, glutaraldehyde was added to the homogenization buffer during sonication. Plasma membrane, which accounted for only about 3% of the total membrane of the homogenates as determined by staining with phosphotungstate at low pH, was obtained in insufficient quantity and fraction purity to permit analysis. Results show rapid incorporation of [3H]leucine into endoplasmic reticulum followed by rapid chase out. The half-time for loss of radioactivity from the pollen tube endoplasmic reticulum was about 10 minutes. Concomitant with the loss of radioactivity from endoplasmic reticulum, the Golgi apparatus fraction was labeled reaching a maximum 20 minutes post chase. The findings suggest flow of membranes from endoplasmic reticulum to the Golgi apparatus during pollen tube growth.

The two types of glandular trichomes occurring on the leaves of Nicotiana tabacum, N. sylvestrisand N. rusticawere investigated using light, fluorescence and electron microscopy. The long trichomes, which secrete a clear resinous material, contain electron dense inclusions in chloroplasts and in small vacuoles of their head cells, whereas the short ones exhibit such substances in a different type of plastid, in large vacuoles and in the apoplast of their heads. The long type of trichome is numerous in N. tabacumand N. sylvestrisbut scarce in N. rustica. This latter difference is probably reflected by the composition of the leaf surface gum, which has been shown to contain cembratrienediol in N. tabacumand N. sylvestrisbut not in N. rustica(Heemannet al. 1983). It is suggested that this diterpene is produced and secreted by the long trichomes since the short ones do not exhibit resinous material on their surfaces. Instead, the short trichomes probably extrude water containing nicotine since this drug can be detected in aqueous droplets forming around the short trichomes under conditions of high atmospheric humidity.

Ultrastructural studies of the pollen tubes of Nicotiana sylvestris grown in the pistil revealed an extensive development of plasmatubules formed by evaginations of the plasma membrane. The plasmatubules occurred as twisted tubular structures in the periplasmic space along the tube wall and, in cross section, exhibited circular profiles with an outer diameter of 28±4 nm. They were also seen in deep, pocket-like invaginations of the plasma membrane and in this case the profiles had an outer diameter of 34±8 nm. In the pocket-like invaginations they were partially branched and often closely packed to form groups with obvious patterns. The enlargement of the plasma-membrane area resulting from plasmatubules formed along the tube wall was about six-to tenfold. Pollen tubes grown in vitro exhibited poorly developed plasmatubules. It is suggested that the large extension of the plasma membrane could enhance the uptake of nutrients, and thus might be responsible for the comparatively fast growth of pollen tubes in the pistil. Moreover, it is also assumed that the turnover rate of the Golgi apparatus must be higher in pollen tubes growing in vivo than in vitro, in order to provide a sufficient amount of membrane for the formation of the plasma membrane with its tubular modifications.

The slime-producing dictyosomes in the placentary papillae of Aptenia cordifolia (L.f.) Schwant. show some structural peculiarities: (1) the number of their cisternae is conspicuously large in comparison with those of other cormophyta; (2) the spaces between the extremely flat vesicle-producing cisternae of the maturing face are considerably higher than those between the other cisternae; (3) the intercisternal elements show a pearl-string form rather than a fibrillar form-especially on tangential sections. Based on personal and on cited findings, the following hypothesis is developed: The intercisternal elements effect the compression of the central region of the secretory cisternae. This causes the production of vesicles to remain restricted to the marginal region of the cisternae, even if these cisternae contain hypertonic or soaking substances.

Summary Recently, we found that the anti-microtubule drugs colchicine and propham caused the absence of microtubules and thus loss of cytoplasmic zonation in in vitro growing pollen tubes ofNicotiana sylvestris, but did not seriously affect growth. In the present study we used the herbicide carbetamide as an anti-microtubule drug. It had the same effect as colchicine and propham: the cytoplasm, including the generative cell, was no longer concentrated in the tip but was distributed randomly. In addition, ultrastructural investigations have shown that even the vesicle zone, usually found at the very tip of pollen tubes, had disappeared in some tubes. Nonetheless, in vitro growth was not inhibited by more than 20% over a period of 22 h.

Summary The polarity of a growing pollen tube is clearly reflected by a distinct zonation of the cytoplasmic content. The vegetative nucleus and the generative cell (GC) are located in the tip region of the tube, and the basal cytoplasmic portion is highly vacuolated. Using pollen tubes ofNicotiana sylvestris Spegazz. & Comes grown in vitro, we examined the effects of varying concentrations of the microtubule inhibitors colchicine and propham. The depolymerization of the cortical microtubules by 25 µM colchicine led to a disorganization of the cytoplasm, i.e., vacuolization of the tip region, and to a deranged position of both the vegetative nucleus and the generative cell. The same concentration of colchicine inhibited tube growth by 10–20% of the control. Mitosis of the GC was not affected. Only from concentrations of 200 µM the configuration of the GC's microtubules was altered and an inhibition of mitosis was observed. At this concentration the disorganization of the cytoplasm was always reversible, but neither inhibition of mitosis nor derangement of the nuclear positioning was. At 1,800 µM colchicine, pollen tube growth was inhibited by 50% of the control. Using propham, the same three steps of action were observed, although propham proved to be about a hundred times more effective than colchicine. We conclude that the cortical microtubules of the pollen tube are involved in maintaining cellular polarity, probably as a part of a heterogeneous cytoskeletal network including also microfilaments and membranous elements. Nuclear positioning seems to be dependent on both, the tube's cortical and the GC's microtubules. A possible involvement of the extracellular matrix in maintaining intracytoplasmic polarity is suggested.

Summary The effect of elevated temperatures on semivivo growth and ultrastructure of tobacco pollen tubes was investigated. Tube growth was decreased by about 50% at 35 °C, independent of the duration of treatment, and at 40 °C and above there was no growth of tubes. Heat treatment caused ultrastructural changes like accumulation of membranous materials, concentric stacking of rough endoplasmic reticulum, reduction in vesicle production by dictyosomes, increase in the fenestrated regions of the Golgi cisternae, swelling of mitochondrial saccules and increase in the electron density of the mitochondrial matrix. Furthermore, the dictyosomes of the treated tubes showed significant increase in the number of cisternae from 30 to 45 °C. The temperature induced changes were persistant at least for 24 h in 35 °C grown pollen tubes. The possible reasons for the tube growth inhibition are discussed on the basis of the ultrastructural alterations caused by elevated temperatures.

Summary During anthesis the young stigma papillae ofAptenia cordifolia produce a slime containing polysaccharides and proteins. Among other details of the ultrastructure there are chloroplasts during their transformation into chromoplasts, and, as the most conspicuous item, numerous vesicles with fibrillar contents, measuring 0,5–1,5 µm in diameter, partly fused with each other. Some vesicles are directly connected with the intracisternal space of the ER, other vesicles are merged with the plasmalemma. The Golgi apparatus is developed but weakly, and shows no hypersecretory activity. Because of these observations a transport and an exocytotic extrusion of the secretion substances via ER vesicles is concluded.

This study was designed to compare the cytotoxic concentrations of chemicals, determined with three independentin vitro cytotoxicity testing protocols, with each other and with established animal LD50 values, and against human toxic concentrations for the same chemicals. Ultimately, these comparisons allow us to evaluate the potential ofin vitro cell culture methods for the ability to screen a variety of chemicals for prediction of human toxicity. Each laboratory independently tested 50 chemicals with known human lethal plasma concentrations and LD50 values. Two of the methods used monolayer cell cultures to measure the incorporation of radiolabeled amino acids into newly synthesized proteins and cellular protein content, while the third technique used the pollen tube growth test. The latter is based on the photometric quantification of pollen tube mass production in suspension culture. Experiments were performed in the absence or presence of increasing doses of the test chemical, during an 18- to 24-h incubation. Inhibitory concentrations were extrapolated from concentration-effect curves after linear regression analysis. Comparison of the cytotoxic concentrations confirms previous independent findings that the experimental IC50 values are more accurate predictors of human toxicity than equivalent toxic blood concentrations (HETC values) derived from rodent LD50s. In addition, there were no conclusive statistical differences among the methods. It is anticipated that, together, these procedures can be used as a battery of tests to supplement or replace currently used animal protocols for human risk assessment.

Computer-generated three-dimensional reconstructions of higher plant dictyosomes from electron micrographs are presented from different viewing angles in the form of shaded perspective displays. The image processing has revealed complicated structures indicating a central cisternal stack surrounded by a cloud of vesicles and vesicular and tubular protrusions. The entire dictyosome is suggested as being an approximately spherical body that is marginally penetrated by plates and tubules of the endoplasmic reticulum.