Primitivity and convergence to stability

An exact expression for the index of primitivity g of a Leslie matrix is obtained, which applies also to time-varying matrices which share an incidence matrix. Elapsed time (not time intervals) to primitivity is shown to depend only weakly on the discretization scheme used. A lower bound for speed of convergence to the stable (fixed or time-dependent as appropriate) state is given which depends sensitively on g.     

黄腐酸增强小麦抗旱能力的生理生化机制初探

叶面喷施黄腐酸可显著提高小麦幼苗的保水能力,表现为降低叶面蒸腾强度,增加气孔扩散阻力,提高幼苗的生物量,在干旱条件下尤为明显。喷施黄腐酸可使干旱条件下叶片内脯氨酸含量提高近一倍,并在水分充足时,也能使叶片脯氨酸含量增加78%。     

用细胞融合的方法选育耐高酒精度的酿酒酵母

选择耐高渗透压、耐高酒精度和发酵终了产酒精量较高的黄酒酵母H—1和目前酒精工业生产用菌K号酒精酵母K—1,运用细胞融合技术选育发酵速度快、产酒精量高的工业用酒精酵母.双倍体黄酒酵母H—1和双倍酒精酵母K—1经过产孢前预培养和产孢培养后,蜗牛酶水解子囊孢子壁,离心收集单倍体子囊孢子,培养后得到单倍体黄酒酵母H—2和单倍体酒精酵母K—2.用硫酸二乙醇诱变处理单倍体细胞,得到单倍体黄酒酵母的维生素缺陷型H—3和单倍体酒精酵母的氨塞骏营养缺陷型K—3通过正交试验找出了H—3和K—3原生质体形成及再生的较优条件是:对数生长后期的细胞33℃、0.2%的β—巯基乙醇预处理15分钟,然后4%蜗牛酶作用2小时.用35%聚乙二醇和10mMCaC1_2诱导融合40分钟,于再生基本夹层培养基上培养获得营养互补融合子,并且考查了融合子的遗传稳定性.通过耐酒精度、一发酵速度和最终产酒精量的测定,筛选出融合子HK—6.HK—6与生产用K号酒精酵母相比,发酵速度相接近,而最终产酒精量提高了11%.可耐受16%的酒精度.     

Possible role of cell cycle-dependent morphology,geometry, and mechanical properties in tumor cell metastasis

Studies that examine the shear- and abrasion-sensitivity of proliferating cells are important in order to understand the behavior of hybridoma cells in bioreactor culture and metastasizing cancer cells in the bloodstream. Little is known about the link between morphology, structure, and mechanical properties of a given cell line, especially with respect to variations throughout the cell cycle. In our experiments with GAP A3 hybridoma cells, distinct cell morphologies were identified and correlated with phases of the cell cycle by video microscopic observation of synchronized cells, and of individual cells that were followed throughout their cell cycle. Micropipet manipulation was used to measure the geometrical (cell volume) and mechanical (apparent cell viscosity) properties of single cells. As the cell cycle progressed at 37°C, an increase in cell volume from 1400 μm³ to 5700 μm³ was accompanied by an increase in apparent cell viscosity from 430 poise to 12,000 poise, consistent with an accumulation of more cytoplasmic material in the “older” cells. Hybridomas are representative of the various leukemias derived from hemopoietic cells, and even though as a whole, they appeared to be rather shear-insensitive, the wide range of property values demonstrates that a given cell line cannot be characterized by a single value for any one property, and that properties must be related to the cell cycle when considering proliferating cells. It is interesting to see if distinct stages in the metastatic sequence of events might correlate with any of these physical features of the cell cycle, irrespective of cell type or cell line. For example, the cytokinetic doublet could represent a fragile structure that may fail and produce cell death under fluid-shear conditions that would not affect the cells at any other stage in the cell cycle. Identifying such cell cycle-dependent features in metastasizing cancer cells could lead to a better understanding of the metastatic process and to possible clinical treatments directed at making cells more shear- and abrasion-sensitive, and therefore, more likely to be killed by the natural hydrodynamic forces of the circulatory system.     

Modification of an index of biotic integrity based on fish assemblages to characterize rivers of the Seine Basin,France

The Index of Biotic Integrity (IBI) is a measure of fish assemblage health that has been used to assess catchment and stream quality throughout North America. It reflects human perturbations on natural environmental structures and processes. While preserving the ecological foundation of the original North American metrics, we have modified and adapted the IBI to the mainstem Seine River and its major tributaries in France. This successful modification of the IBI to a considerably different fish fauna on a different continent further supports its wider use outside the midwestern United States. Using data collected in 1967, 1981, and 1988–1989 from a total of 46 sites, we show spatial and temporal variation in the Seine as indicated by IBI scores. Statistically significant relationships were found between IBI and catchment area but insignificant relationships existed between IBI and an independent Water Quality Index (WQI) based on water chemistry. Comparisons between the IBI and the WQI indicate that the former is a more sensitive and robust measure of water body quality. Our results demonstrate that the IBI, combined with a statistically designed national monitoring program, would offer a reliable means of assessing spatial patterns and temporal trends in water body improvement or degradation in France. The more primitive fish families in the Basin were affected first by perturbations. These families include all the diadromous species found in the Seine and suggest serious disruption of their life histories.     

Adaptive phenology of desert and Mediterranean populations of annual plants grown with and without water stress

Summary The dynamics of vegetative and reproductive growth were compared in matched pairs of Mediteranean and desert populations of three unrelated annual species, Erucaria hispanica (L.) Druce, Brachypodium distachyon (L.) Beauv. and Bromus fasciculatus C. Presl., under high and low levels of water availability in a common-environment experiment. Plants of all desert populations showed earlier switches to reproductive development and to subsequent phenophases, and the transition to flowering occurred at smaller plant sizes. Water stress had no effect (E. hispanica) or slightly accelerated the transition to flowering in B. fasciculatus (by 1–2 days) and in B. distachyon (by 4–6 days). Plant senescence was strongly enhanced by water stress, and this enhancement was greater in desert populations than in corresponding Mediterranean ones. Duration of life cycle was greatly shortened by water stress in all three species. Desert and Mediterranean populations of the three species exhibited small differences in their relative response, i.e. phenotypic plasticity, to water stress for phenological and plant size parameters. In E. hispanica and B. fasciculatus the population x water regime interaction amounted to less than 3% of total variance. By contrast, the Mediterranean population of B. distachyon was much more plastic in its response to water stress than the desert population in its transition to plant senescence. Plants from the desert populations appeared to be adapted to shorter, more compact growth cycles, culminating in earlier dates of seed maturation and plant senescence. In addition, they showed larger phenotypic plasticity in the transition to plant senescence, which trait was enhanced or magnified by sustained or repeated lack of water. By contrast, plants from Mediterranean populations delayed switchover from one phenophase to the next, seeming thus to bet on more water being forthcoming.     

Roles of iron in neoplasia

Research and clinical observations during the past six decades have shown that: 1. Iron promotes cancer cell growth; 2. Hosts attempt to withhold or withdraw iron from cancer cells; and 3. Iron is a factor in prevention and in therapy of neoplastic disease. Although normal and neoplastic cells have similar qualitative requirements for iron, the neoplastic cells have more flexibility in acquisition of the metal. Excessive iron levels in animals and humans are associated with enhanced neoplastic cell growth. In invaded hosts, cytokine-activated macrophages increase intracellular ferritin retention of the metal, scavenge iron in areas of tumor growth, and secrete reactive nitrogen intermediates to effect efflux of nonheme iron from tumor cells. Procedures associated with lowering host intake of excess iron can assist in prevention and in management of neoplastic disease. Chemical methods for prevention of iron assimilation by neoplastic cells are being developed in experimental and clinical protocols. The antineoplastic activity of a considerable variety of chemicals, as well as of radiation, is modulated by iron. The present article focuses on recent findings and suggests directions for further cancer-iron research.     

Metabolism of p-fluorophenylalanine in p-fluorophenylalanine sensitive and resistant tobacco cell cultures

The metabolism of D- and L-p-fluorophenylalanine (PFP) in DL-PFP resistant and sensitive tobacco cell cultures (Nicotiana tabacum), cell lines TX4 and TX1, respectively, has been compared. The amino acid analogue was taken up at a lower rate by the resistant cell line TX4. Incorporation of PFP into protein was also considerably reduced in TX4 cells, compared to TX1 cells. This, however, resulted mainly from a diminished availability of PFP due to a more rapid conversion of PFP by TX4 cells. TX1 cells and TX4 cells converted PFP qualitatively in the same way. The only detectable metabolite of D-PFP was N-malonyl-D-PFP, while all metabolites of L-PFP were identified as sequent products of the initial deamination of L-PFP by the enzyme phenylalanine ammonia-lyase (PAL). As TX4 cells were endowed with higher PAL-activity than TX1 cells, the resistant cells were able to metabolize L-PFP more rapidly to give, e.g., p-fluorocinnamoyl glucose ester and p-fluorocinnamoyl putrescine. In the presence of the specific PAL-inhibitor -aminooxy--phenylpropionic acid TX4 cells were slightly more sensitive to PFP. This suggests that the better detoxification contributes to the acquired resistance. The use of PFP as specific indicator for cell lines with increased PAL-activity, and hence increased levels of phenolic compounds, is discussed.Abbreviations AOPP -aminooxy--phenylpropionic acid - MCW methanol:chloroform:water - PAL phenylalanine ammonia-lyase - PFP p-fluorophenylalanine - Phe phenylalanine     

Drought susceptibility of two tomato (Lycopersicum esculentum) varieties

The effects of three levels of moisture under greenhouse conditions and also identical moisture levels under field conditions, on the growth yield and water relations of two tomato cultivars, Fireball and Ife I, were investigated. The objective was to ascertain the drought susceptibility of these two tomato cultivars. The cultivar, Ife I, was more drought susceptible than Fireball and the drought susceptibility increased with the level of soil water stress. The drought tolerance, of Fireball is attributed to a lower leaf area, better root system development in terms of average root length and rooting depth, and a higher leaf water potential. The higher leaf stomatal resistances of Fireball variety suggest an inbuilt mechanism to regulate water vapour flow in times of stress.     

Effects of Visible and Ultraviolet Light on Carotene-deficient Mutants of Crypthecodinium cohnii

Synopsis.
The ability of carotenoids to protect a heterotrophic dinoflagellate, Crypthecodinium cohnii , from photodynamic damage by sunlight in the presence of an exogenous dye was demonstrated. Wild-type C. cohnii and 2 carotcnoid-deficient mutants were plated on agar-solidified media and exposed to natural sunlight. The wild-type strain, which synthesizes γ–carotene and β–carotene, had the lowest mortality. Mutant car 17 which accumulates mainly §–carotene had an intermediate mortality rate while the albino mutant, car 3, which contains only phytoene, lost viability most rapidly. Wild-type cells treated with diphenylaminc, a carotenogenic inhibitor, were killed at the same rate as mutant car 3. The survival rate of mutants on exposure to sunlight was dependent upon the chromophore length of the accumulated carotenoids. The 3 strains showed no difference in rate of mortality when exposed to ultraviolet light. Protection from sunlight by accumulation of carotenes may be an important ecological factor for this species whose natural habitat is tidepools.