Cytogenetic investigations in a family with ataxia telangiectasia

Summary Cytogenetic findings on a family with ataxia telangiectasia (A-T) in which three of four sibs were affected are described. The affected individuals had approximately twice the level of spontaneous chromosome breakage of a normla control, while the parents and the normal sib had no significant increase. Lymphocytes from all three A-T homozygotes showed specific stable chromosomal rearrangements involving chromosomes 7 and 14. All of these abnormalities involved breakage at the usual four sites associated with A-T (7p14, 7q35, 14q12, and 14q32). Two rearrangements detected in the eldest and most severely affected patient were clones, one of which [t(14;14)(p11;q12)] is not commonly found in A-T cells. No chromosomal rearrangements were encountered in lymphocytes from the control, the parents, or the normal sib. Lymphocytes from the A-T patients also were found to be 7–11 times more sensitive to the induction of chromatid aberrations by X-irradiation than control cells. Lymphocytes from the parents and normal sib showed a moderately increased frequency of X-ray induced aberrations compared with that of the control.     

Aspects of floral structure and phenology in the genusConophytum (Mesembryanthemaceae)

The complex floral structure in the southern African genusConophytum (Mesembryanthemaceae; 77 spp.) is described in detail and assigned to three basic floral types, two of which can be divided into two subtypes. Correlations between structural features and phenological patterns are demonstrated and discussed in the family context as well as in relation to the systematic subdivision of the genus.     

Crassulacean acid metabolism in Lithops insularis; a non-halophytic member of the Mesembryanthemaceae

Summary Lithops insularis, a non-halophytic member of the Mesembryanthemaceae, is shown to exhibit major features if crassulacean acid metabolism. Data are presented which demonstrate the accumulation, by this plant, of malic acid synthesised in darkness from carbon dioxide.     

CAM variations in the leaf-succulent Delosperma tradescantioides (Mesembryanthemaceae), native to southern Africa

Drought responses of diurnal gas exchange, malic acid accumulation and water status were examined in Delosperma tradescantioides , a succulent that grows in drought-prone microenvironments in summer rainfall and all-year rainfall regions of southern Africa. When well-watered, this species exhibited Crassulacean acid metabolism (CAM)-cycling, but its carbon fixation pattern changed during the development of drought, shifting to either low-level CAM or to CAM-idling. The rate and pattern of this change depended on environmental conditions, duration of water stress and leaf age. At the onset of drought, diurnal malate fluctuation increased, but was strongly depressed (by ca 70%) as drought continued, and when leaf water content and water potential were low (ca 35 and 50% of the initial levels, respectively). When rewatered, rates of growth and photosynthesis, gas exchange and water status recovered fully to pre-stressed values within two days. Whole-shoot carbon uptake rates suggested that leaf growth had continued unabated during a short-term (≅ one week) drought. This emphasises that CAM-idling allows the maintenance of active metabolism with negligible gas exchange when soil water is limiting. It is possible that old or senescent leaves may provide water for the expansion of developing leaves during initial periods of drought. Regardless of the water regime and environmental conditions, leaf nocturnal malate accumulation and water content were positively correlated and increased with leaf age. Thus the gradual loss of water from older mature leaves may induce CAM-idling, which reduces water loss. An important ecological consequence of this combination of CAM modes is the potential to switch rapidly between fast growth via C₃ gas exchanges when well-watered to water-conserving CAM-idling during drought.     

Further investigations of educational and occupational attainment in the Hawaii family study of cognition

Abstract

Associations of measures of grandparental status, parental status, cognitive abilities, and personality, and own cognitive abilities and personality with educational and occupational attainment are reported for 249 offspring, now 25 years or older, from the Hawaii Family Study of Cognition (HFSC). In general, across two ethnic groups (Americans of European ancestry (AEA) and Americans of Japanese ancestry (AJA)), the data suggest that family background had a relatively trivial influence, own cognitive abilities (particularly verbal ability and general intelligence) substantial influence, and own personality some influence on the educational and occupational attainment of males, while family background had a far more substantial influence than own ability on the attainment of females. Educational attainment was generally found to be substantially predictive of occupational attainment. Hierarchal multiple regression analyses were conducted to assess the influence of parents’ abilities over and above grandparental status and the influence of offsprings’ abilities over and above parental status and abilities on their respective educational and occupational attainments. These analyses also indicated that family background was a much greater influence than own ability on the attainment of AEA female parents and both AEA and AJA female offspring. These findings for female offspring were further confirmed by analyses of parent‐offspring and within‐sibship differences in attainment.     

CAM variations in the leaf-succulent Delosperma tradescantioides (Mesembryanthemaceae), native to southern Africa

Drought responses of diurnal gas exchange, malic acid accumulation and water status were examined in Delosperma tradescantioides , a succulent that grows in drought-prone microenvironments in summer rainfall and all-year rainfall regions of southern Africa. When well-watered, this species exhibited Crassulacean acid metabolism (CAM)-cycling, but its carbon fixation pattern changed during the development of drought, shifting to either low-level CAM or to CAM-idling. The rate and pattern of this change depended on environmental conditions, duration of water stress and leaf age. At the onset of drought, diurnal malate fluctuation increased, but was strongly depressed (by ca 70%) as drought continued, and when leaf water content and water potential were low (ca 35 and 50% of the initial levels, respectively). When rewatered, rates of growth and photosynthesis, gas exchange and water status recovered fully to pre-stressed values within two days. Whole-shoot carbon uptake rates suggested that leaf growth had continued unabated during a short-term (∼ one week) drought. This emphasises that CAM-idling allows the maintenance of active metabolism with negligible gas exchange when soil water is limiting. It is possible that old or senescent leaves may provide water for the expansion of developing leaves during initial periods of drought. Regardless of the water regime and environmental conditions, leaf nocturnal malate accumulation and water content were positively correlated and increased with leaf age. Thus the gradual loss of water from older mature leaves may induce CAM-idling, which reduces water loss. An important ecological consequence of this combination of CAM modes is the potential to switch rapidly between fast growth via C₃ gas exchanges when well-watered to water-conserving CAM-idling during drought.     

Cellular Structure and Light Absorbtion in Leaves of Frithia pulchra (Mesembryanthemaceae)

In order to quantify the structural differences between celltypes of leaves from a ‘ window’ plant, an ultrastructuralmorphometric analysis was made of the epidermal, window andchlorenchyma tissues of Frithia pulchra. Epidermal cells arethe largest cells found in Frithia leaves and are characterizedby the presence of a thick outer tangential cell wall and numerousvacuolar inclusions. Epidermal tissue has an optical densityof 0.30. The transparent window tissue (i.e. optical density= 0.08) has a uniform ultrastructure throughout the length ofthe leaf. The vacuome comprises aproximately 97 per cent ofthe protoplasmic volume of window cells. Chlorenchyma cellspossess thin cell walls and are surrounded by numerous intercellularspaces. Cells of the apical chlorenchyma tissue possess approximately30 plastids per cell. These chloroplasts have an average individualvolume of 220 µm². Cells of the basal chlorenchyma tissuecontain chloroplasts that are five to six times smaller andmore numerous than those in cells of the apical chlorenchyma.The increased volume of chloroplasts in the apical comparedwith basal chlorenchyma cells (i.e. 31.4 and 20.2 per cent ofthe protoplasm, respectively) is positively correlated withtheir optical densities of 1.46 and 0.97, respectively. Frithia pulchra, stereology, leaf, light absorption, window plant     

Zur Morphologie und Taxonomie der Mitrophyllinae Schwantes (Mesembryanthemaceae)

Die bemerkenswerte Heterophyllie der Mitrophyllinae wird — ausgehend von der isophyllen Gattung Jacobsenia, deren Keimpflanzen jedoch eine charakteristische Blattfolge aufweisen — als Ergebnis von in der Phylogenie fixierten ontogenetischen Abbreviationen und periodischen Zeitkorrelationsänderungen gedeutet. Für diese Phänomene werden aus dem Verwandtschaftsbereich der Mitrophyllinae weitere Beispiele angeführt. Die sich hieraus ergebenden taxonomischen Konsequenzen werden kurz diskutiert.     

Smoke-induced germination of succulents (Mesembryanthemaceae) from fire-prone and fire-free habitats in South Africa

Previous studies have shown germination to be stimulated by fire-related cues such as heat and charate extract and, more recently, plant-derived smoke extract. However, smoke extract has not been tested on non-fire-prone species. We hypothesized that smoke-induced germination would be restricted to fire-prone species and investigated responses of members of the family Mesembryanthemaceae which has genera confined to fire-prone and to non-fire-prone habitats as well as genera with species across both habitats. Results of germination trials of smoke effects did not support the hypothesis. Plant-derived smoke extract stimulated germination in both fire-prone and non-fire-prone species. These results cast some doubt on the ecological significance of smoke as a fire-related cue and we suggest that investigation of effects of fire-related cues on non-fire prone species may throw light on general mechanisms of germination.     

Cytogenetic investigations in three cell types of a Saudi family with ataxia telangiectasia

Summary Chromosomal analyses were performed on lymphocytes, fibroblasts and lymphoblastoid cell lines derived from a Saudi family with ataxia telangiectasia (AT). The three siblings of a consanguineous marriage were all affected. The lymphocytes of the AT homozygotes (probands) showed an increase of 2- to 6-fold and 4- to 8-fold respectively, in the frequency of spontaneous and X-ray-induced chromosomal aberrations compared with controls, while the parents (obligate heterozygotes) of the patients showed no notable difference. The unirradiated lymphocytes from the oldest AT sibling, an 11-year-old boy (AT1), showed specific rearrangements involving chromosomes 7 and 14 [t(7;14)(q35;q12)] and 12 and 14 [t(12;14)(q23;q12)] in two different clones. The most severely affected sibling was a 9-year-old girl (AT2) who presented with a clone showing a novel rearrangement involving chromosomes 14 and 17, namely: del(14) (q31q32) and dup(17)(q21–q24). The lymphocytes from the third sibling, a 2-year-old boy (AT3), showed a t(2;14)(p24;q12). In addition, an inv(14)(q12q32) was observed in all three AT patients, while inv(7)(p14q35) was found only in patients 2 and 3. The lymphocytes from the AT parents and controls showed normal karyotypes. The breakpoints involving chromosomes 2,12 and 17, observed in our studies, have rarely been reported in other series of AT patients. No non-random chromosomal rearrangements were observed either in the skin fibroblasts or in the lymphoblastoid cell lines derived from the AT patients, although all cell lines showed an increase in both spontaneous and radiation-induced chromosomal breaks per cell. The present study constitutes the first report on a cytogenetic analysis of a Saudi family with three AT siblings.     

Remarkable medium-term dynamics of leaf succulent Mesembryanthemaceae shrubs in the winter-rainfall desert of northwestern Namaqualand,South Africa

Populations of shrubs in a winter-rainfall (ca. 70 mm yr_-1 desert community (Succulent Karoo), dominated by leaf succulents, showed remarkable dynamics over a 17-yr period. After a severe drought in 1979, which caused high plant mortality, perennial species number in a permanent 10 m×10 m plot doubled between 1980 and 1996, when the maximum of 41 species was recorded. Numbers of individuals of evergreen, leaf succulent shrubs also doubled over the same period, but showed fluctuations in response to dry years during the monitoring period. Detailed observations on the four dominant leaf succulent shrubs (all members of the Mesembryanthemaceae) between 1983 and 1996, showed species-specific patterns in population turnover. Mortality of all observed individuals ranged between 60% and 85%, and the proportion of the population that was recruited over this period ranged from 62% to 89%. In only one species did individuals persist throughout the monitoring period. Mean ages of individuals, excluding seedlings with lifespans of <1 yr, and individuals observed at the beginning of the monitoring period, ranged from 4.6 yr to 5.6 yr. Patterns of mortality and recruitment showed substantial differences among species and were not all attributable to rainfall patterns. Overall, the turnover of the shrub populations over the 15-yr monitoring period was remarkably high for a system of desert perennials. These unusual population patterns may explain the unique structure of leaf succulent-dominated communities in the Succulent Karoo.     

Diurnal course of the temperature in a Lithops sp. (Mesembryanthemaceae Fenzl) and its surrounding soil

Abstract. The embedding of Lithops plants into the soil could be an adaptation to protect the plants from critical low or high temperatures. Thermoelectric measurements on Lithops lesliei N.E. Br and L. turbiniformis (Haw.) N.E. Br. were made to determine whether the temperatures of the plant tissues at various depths differ from those in the soil close to the plant. The environmental conditions of their habitat were simulated in a growth chamber equipped with a cold sky to simulate the net radiation loss during a cool and clear night. The effects of microclimatic conditions resulting in dew or hoar-frost formation on the plant were investigated, as well as the temperature range where freezing occurs.
The results provide no evidence that the embedding of a Lithops plant into the soil yields advantages to the plants in respect of critical low or high temperatures. Plant temperatures are always very close to the soil temperatures at the same depth, but heat fluxes from the bottom or the plant and its surrounding soil to the top of the plant can occur if the plant freezes. No positive effect on the temperature relations could be detected when dew or hoar-frost is formed on the top of the plant. Lithops is frost hard to at least –3°C.     

Mexican copalchis of the Rubiaceae family: more than a century of pharmacological and chemical investigations

Phytochemistry Reviews - The term copalchi has been used in the scientific literature to define a group of plants of the Rubiaceae and Euphorbiaceae families with extremely bitter stem-barks,...     

Tissue Partitioning During Leaf Development in Ornamentally-grown Frithia pulchra (Mesembryanthemaceae), a 'Window Plant'

Young (i.e. 5-mm long) leaves of the window-plant Frithia pulchra(Mesembryanthemaceae) allocate approx, 21 % of their volumeto epidermis, 49 % to chlorenchyma, and 29 % to window tissue.By the time leaves are 25 mm long, the relative volumes of epidermisand chlorenchyma decrease to approx, 7 and 27 % respectively.During the same period, the relative volume of window tissueincreases from 29 to 66 %. The relative volumes of epidermis,window, and chlorenchyma tissues do not change as leaf lengthincreases from 25 to 57 mm. These results indicate that earlystages of leaf development in F. pulchra involve preferentialreallocations of volume to different tissues, whereas laterstages of leaf development involve uniform expansion of allof the leaf's tissues (i.e. the relative volumes of tissuesdo not change). The relative volumes of epidermis and windoware always largest in the lower third of a leaf. The relativevolume of chlorenchyma is largest in the upper third of youngleaves but becomes constant in the upper two thirds of leavesduring later stages of development. These results, indicatingthat leaves and tissues of F. pulchra are asymmetric and developpolarly, are discussed relative to corresponding studies ofcellular size and leaf structure. Frithia pulchra, leaf development, Mesembryanthemaceae, stereology, window plant     

Interactive effects of photon fluence rates and drought on CAM‐cycling in Delosperma tradescantioides (Mesembryanthemaceae)

The ability of photosynthesis and CAM to acclimate to low (220 µmol m^?2 s^?1; LL) and relatively high (550 µmol m^?2 s^?1; HL) photosynthetic photon flux densities (PPFD) was investigated in the CAM-cycling species Delosperma tradescantioides by means of CO₂ gas exchange and chlorophyll fluorescence analysis. Furthermore, the influence of short-term drought on malic acid accumulation and the activity of photosystem II (PSII) was studied to assess the possible interactions between drought and the prevailing PPFD in this species. HL plants showed features of sun versus shade acclimation relative to LL plants. Nocturnal malic acid accumulation (Δ-malate) and leaf water content also tended to be higher in HL plants. Irrespective of the PPFD during growth, the weak Δ-malate doubled within 3 days of drought. Despite largely restricted CO₂ uptake, photosynthetic activity as estimated from fluorescence analysis declined only ca 5%. After 7 days of drought, when plants showed CAM-idling and Δ-malate had decreased again, potential carbon assimilation was still ca 84% of that in well-watered plants and remained relatively constant throughout the day. Decarboxylation of malic acid accounted for ca 23% of potential assimilation assuming total oxidation of a maximum portion of this organic acid. Drought did not affect predawn maximum photochemical efficiency (F_v/F_m). Nonphotochemical quenching (qN) increased (24%) in response to desiccation and resulted in a more or less constant reduction state of PSII. This increase in qN resulted mainly from the change in its fast-relaxing component (qNF), while the slow component (qNS) was significant only at or above saturating PPFD in both HL and LL plants. The photon response characteristics of PSII, which differed between LL and HL plants, were unaffected by short-term drought. Photon harvesting and photon use were always adjusted to guarantee a low reduction state of PSII. Results suggest that in both LL and HL plants CAM-cycling may help to stabilize photosynthesis but to a large extent by other means than simply providing internally derived CO₂.