Population density effects on longevity

Population density, or the number of adults in an environment relative to the limiting resources, may have important long and short term consequences for the longevity of organisms. In this paper we summarize the way in which crowding may have an immediate impact on longevity, either through the phenomenon known as dietary restriction or through alterations in the quality of the environment brought on by the presence of large numbers of individuals. We also consider the possible long term consequences of population density on longevity by the process of natural selection. There has been much theoretical speculation about the possible impact of population density on the evolution of longevity but little experimental evidence has been gathered to test these ideas. We discuss some of the theory and empirical evidence that exists and show that population density is an important factor in determining both the immediate chances of survival and the course of natural selection.     

Population density of North American elk: effects on plant diversity

Large, herbivorous mammals have profound effects on ecosystem structure and function and often act as keystone species in ecosystems they inhabit. Density-dependent processes associated with population structure of large mammals may interact with ecosystem functioning to increase or decrease biodiversity, depending on the relationship of herbivore populations relative to the carrying capacity (K) of the ecosystem. We tested for indirect effects of population density of large herbivores on plant species richness and diversity in a montane ecosystem, where increased net aboveground primary productivity (NAPP) in response to low levels of herbivory has been reported. We documented a positive, linear relationship between plant-species diversity and richness with NAPP. Structural equation modeling revealed significant indirect relationships between population density of herbivores, NAPP, and species diversity. We observed an indirect effect of density-dependent processes in large, herbivorous mammals and species diversity of plants through changes in NAPP in this montane ecosystem. Changes in species diversity of plants in response to herbivory may be more indirect in ecosystems with long histories of herbivory. Those subtle or indirect effects of herbivory may have strong effects on ecosystem functioning, but may be overlooked in plant communities that are relatively resilient to herbivory.     

Somatic embryogenesis in cell cultures of Thapsia garganica

Cell cultures from different species of the genus Thapsia (Apiaceae) have been investigated. In one 4-yearold line of T. garganica L. spontaneous somatic embryogenesis up to the globular stage occurred in a suspension culture containing 1 mg l^–12,4-dichlorophenoxyacetic acid (2,4-D). Also callus cultures of this line, previously maintained on a medium containing 1 mg l^–1 2,4-D, when transferred to various media deprived of 2,4-D, produced somatic embryos that developed into plantlets. Cell culture, embryos and regenerated organs were analysed for their content of thapsigargins. The undifferentiated cell culture did not synthezise thapsigargins, but was found to produce a yet unidentified compound not present in planta. White embryos in the pre-cotyledonary stage did not synthezise thapsigargins either, but when the embryos developed to the cotyledonary stage and became green, the synthesis started. Regenerated roots and shoots also contained thapsigargins.Abbreviations BAP Benzylaminopurine - 2,4-D 2,4-Dichlorophenoxyacetic acid - EtOAc ethyl acetate - FDA fluorescein diacetate - IAA Indole-3-acetic acid - IBA indole-3-butyric acid - 2-iP 2-isopentenyladenine - NAA 1-Napthaleneacetic acid     

Somatic embryogenesis in cell cultures of Glycine species

This report describes the development of procedures for the production of somatic embryos in cell cultures of Glycine species including soybean. The conditions for callus induction and initiation of rapidly growing cell suspension cultures were defined. Methods for inducing embryogenesis were tested on 16 lines of several Glycine species and cultivars of soybean. The SB-26 Culture of a G. soja gave the best results and was used in the experiments. Embryogenesis required the presence of picloram or 2,4-D. AMO 1618, CCC, PP-333 and Ancymidol enhanced the embryogenesis frequency. Plants of the G. soja (SB-26) were grown to maturity from seed-derived shoot tips. Characteristics of the plants are discussed.     

Somatic embryogenesis in liquid cultures of a tetraploidAlstroemeria

A simple and efficient procedure was developed for regeneration of a tetraploid cultivar ofAlstroemeria (A. pelegrina x A. psittacina) via somatic embryogenesis in liquid cultures. Embryogenic callus induced from mature zygotic embryos, cultured on MS medium supplemented with 40 μM NAA and 20 μM kinetin, was used as inoculum for liquid cultures. Pre-culture of the callus on MS medium supplemented with 80 μM NAA for two days was essential for cell proliferation in the liquid medium. Embryogenic cell aggregates, obtained by sieving through a 750 μm nylon mesh, continued to proliferate in media containing 10 or 20 μM NAA and 10 or 20 μM kinetin. When transferred to a semi-solid half strength MS medium supplemented with casein hydrolysate, cell aggregates successfully differentiated into plantlets which later grew to maturity under greenhouse conditions.     

Population density and group size effects on reproductive behavior in a simultaneous hermaphrodite

Background  

Despite growing evidence that population dynamic processes can have substantial effects on mating system evolution, little is known about their effect on mating rates in simultaneous hermaphrodites. According to theory, mating rate is expected to increase with mate availability because mating activity is primarily controlled by the male sexual function. A different scenario appears plausible in the hermaphroditic opisthobranch Chelidonura sandrana. Here, field mating rates are close to the female fitness optimum, suggesting that mating activity remains unresponsive to variation in mate availability.     

Effects of culture density,conditioned medium and feeder cultures on microspore embryogenesis in Brassica napus L. cv. Topas

Summary In microspore cultures of Brassica napus L. cv. Topas, embryo yield increases with culture density up to about 40,000 microspores per ml. A much higher density (100,000 per ml) appears inhibitory to embryogenesis. A relatively high culture density (30,000 or 40,000 per ml) for the first 2–4 days of culture is crucial for embryogenesis, after which cultures may be diluted to allow better embryo growth.Medium conditioned by culturing microspores at 30,000 or 40,000 per ml for 1 day improved microspore-embryo yield in low density cultures (3,000 or 4,000 per ml) more than 3-fold. In contrast, media conditioned with microspores from 1–4 days or 0–4 days of culture were inhibitory.Use of feeder cultures resulted in up to 10-fold increase of embryo yield in low density microspore cultures, depending on the method used. Filter papers and other membranes placed on top of feeders greatly inhibited embryogenesis in the feeder layer as well as microspores cultured on the feeder, possibly due to poorer gaseous exchange.     

Somatic embryogenesis from leaf cultures of potato

An efficient procedure has been developed for inducing somatic embryogenesis from leaf cultures of potato cv. Jyothi. Leaf sections were initially cultured on 2,4-dichlorophenoxyacetic acid (2,4-D) + benzyladenine (BA) and -naphthaleneacetic acid (NAA) + BA supplemented Murashige and Skoog (MS) media. Nodular embryogenic callus developed from the cut ends of explants on media containing 2,4-D and BA, whereas compact callus developed on media containing NAA and BA. The explants with primary callus were subsequently moved onto MS media containing zeatin and/or gibberellic acid (GA₃) and BA. Treatment with zeatin (22.8 M) and BA (10.0 M) resulted in the induction of the highest number of somatic embryos directly from meristematic centres produced on the nodular tissue. Embryo induction and maturation took place on this medium. The cotyledonary stage embryos developed into complete plantlets on hormone-free MS medium. A distinct feature of this study is the induction of somatic embryogenesis in leaf cultures of potato which has not been reported previously.     

Somatic embryogenesis from callus cultures ofNardostachys jatamansi

Callus cultures ofNardostachys jatamansi DC, an endangered medicinal and aromatic plant, were established using petiole explants on MS medium supplemented with 16.1 µM -naphthaleneacetic acid and 1.16 µM kinetin. Embryogenesis in these callus cultures took place only upon sequential subculture of the callus on media having gradually decreasing auxin (16.1 to 1.34 µM NAA) and simultaneously increasing cytokinin (1.16 to 9.30 µM kinetin) concentrations over a period of 7 months. Somatic embryo to plantlet conversion took place on a medium containing 9.30 µM kinetin and 1.34 µM NAA.     

Somatic embryogenesis from cell suspension cultures in Carica candamarcensis

Cell suspension cultures of Carica candamarcensis derived from hypocotyl calli were tested concerning their in vitro embryogenic capacity to improve asexual propagation rates in this species. Somatic embryos developed in culture from cells in suspension or from microcalli. Responses were affected by nutrient media and phytohormones used. Best results were obtained by growing the cells in suspension in Nitsch and Nitsch medium containing naphthaleneacetic acid and then plating them upon the same medium containing benzyladenine, or combinations of both hormones.     

Repetitive somatic embryogenesis from peanut cultures in liquid medium

Summary A regeneration system based on repetitive somatic embryogenesis was developed for peanut (Arachis hypogaea L.). Embryogenic suspension cultures were initiated using individual somatic embryos induced from immature cotyledons cultured on a modified Murashige and Skoog medium containing 40 mg/l 2,4-D for 30 days. After transfer to a modified MS liquid medium, the somatic embryos produced masses of secondary and tertiary embryos which continued to proliferate following manual separation and subculture of the embryogenic clumps. The cultures exhibited exponential growth, and have been maintained for over one year without apparent loss of embryogenic potential. Further embryo development, germination, and conversion were achieved by placing embryo clumps onto hormone-free, solid medium. The inclusion of a desiccation period during embryo development enhanced conversion four-fold. Plants have been established in soil and appear to be phenotypically normal.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - NAA 1-naphthaleneacetic acid - BA 6-benzylaminopurine - MSO Modified Murashige and Skoog basal medium - EM embryogenic masses     

Inhibitory conditioning for carrot somatic embryogenesis in high-cell-density cultures

Carrot somatic embryogenesis was strongly inhibited in high-cell-density cultures. This inhibition was not caused by depletion of nutrients or physical damage but by factor(s) released into the culture medium from cells during culture. A conditioned medium prepared by eliminating cells after high-cell-density culture inhibited somatic embryogenesis. The degree of inhibition increased with the amount of conditioned medium. A dialysis experiment revealed that the molecular weight of the inhibiting factor(s) was below 3,500. We also found that the conditioned medium contained a high-molecular-weight factor(s), which stimulated somatic embryogenesis. Received: 13 March 1998 / Revision received: 19 May 1998 / Accepted: 1 June 1998     

Totipotency and embryogenesis in plant cell and tissue cultures

Summary An important development in the field of plant cell and tissue culture has been the demonstration in the past decade of the totipotency of higher plant cells. Isolated single cells were first successfully grown on a nurse tissue separated by a filter paper and gave rise to a callus tissue. Later, completely isolated single cells of tobacco were grown in microchambers to form small clumps of cells which then could be differentiated to form adult tobacco plants. Indirect evidence of the totipotency of higher plant cells has also been provided in a number of other plants. Embryo-like structures (or embryoids) or whole plants, or both, have been obtained from such highly differentiated cells as the pollen grains (gametic and haploid), photosynthetic palisade cells in leaves, epidermal cells from the hypocytyl, and the triploid endosperm cells; all of these cell types perform very highly specialized functions in the plant. Plant protoplasts (cell wall is digested with enzymes) have also been cultured to give rise to normal adult plants. In many instances embryoids have been produced in vitro from several species of flowering plants which do not show such asexual activity in nature. These embryoids are normally indistinguishable morphologically from embryos produced by gametic fusion, often follow the same pattern of cell divisions and differentiation as the developing zygote, and are economically important as they provide clonal populations. Early work in this area emphasized the necessity of dissociating tissues into single cells and providing a nutritional environment identical to that of the zygote in the embryo sac (usually by supplementing the medium with liquid endosperm from coconuts), before the cells could be released morphogenetically to express their totipotency by forming embryoids. Much of the recent work, however, has shown that perfect development of embryoids can be obtained in completely synthetic media in callus tissues as well as in suspension cultures. This paper is dedicated to the memory of the late Professor Philip R. White, a dear friend who provided much counsel and inspiration to us both. for his pioneering work, valuable contributions and untiring efforts in developing the science of plant cell, tissue, and organ culture. Florida Agricultural Experiment Stations Journal Series No. 4699. Presented in the Symposium on Functional Differentiated Systems at the 23rd Annual Meeting of the Tissue Culture Association, Los Angeles, California, June 5–8, 1972.     

Somatic embryogenesis and polyembryogenesis in Douglas-fir cell suspension cultures

A proliferating embryonal-suspensor mass (ESM) was initiated from immature embryos of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), 4–5 weeks after fertilization, on modified MS medium with 2,4-dichlorophenoxyacetic acid (2,4-D), kinetin, and N⁶-benzylaminopurine (BAP). ESMs were maintained for over 6 months as cell suspension cultures on modified DCR media with low 2,4-D and with kinetin and BAP. The development of individual somatic embryos was initiated in suspension culture by the gradual reduction of plant growth regulators and by addition of abscisic acid. The early stages of zygotic embryogenesis in Douglas-fir are unique among conifers and cleavage polyembroyogenesis is unknown. In somatic embryogenesis, characteristic stages of zygotic embryonic development were recapitulated and complete embryos were recovered by inhibiting cleavage polyembryony with abscisic acid and culturing individual embryos without growth regulators. Histological examination confirmed bipolar organization of somatic embryos. While conversion is low, plantlets with multiple cotyledons have been transferred to soil and continue to grow with production of a new shoot.     

Juvenoid effects on Rhodnius prolixus embryogenesis

Protein electrophoretic techniques demonstrate that the normal patterns of protein synthesis accompanying embryogenesis of Rhodnius prolixus are altered by the juvenoid compound Ro 13.5223 (fenoxycarb). Electrophoretic analysis reveals that embryonic perturbation by fenoxycarb is due in part to alterations in the normal molecular events accompanying development. Using high-resolution 2-D gel electrophoresis, major differences in protein patterns were observed. Three proteins normally absent, were expressed in fenoxycarb perturbed embryos (two on day 3 and one on day 7).     

Somatic embryogenesis in suspension cultures of Gossypium klotzschianum anderss

Somatic embryoids differentiated in suspension cultures of G. klotzschianum after 3–4 weeks of culture in a liquid medium containing glutamine (optimally, 10–15 mM). Embryogenesis occurred after a preculture of callus on a medium containing 10 mg/l of the cytokinin, 2iP. The embryoids had meristematic regions, a well formed epidermis, and formed roots and vestigial leaves. Asparagine was much less effective than glutamine in promoting embryoid differentiation. The presence of 2,4-D in the medium resulted in increased vigor of the suspension cultures and subsequently in the formation of many embryoids, but does not seem to be necessary for somatic embryogenesis in cotton.Technical Article 14646 from the Texas Agricultural Experiment Station     

MDCK microcarrier cultures: Seeding density effects and amino acid utilization

Summary The growth of Madin Darby canine kidney cells on microcarriers was studied at different cell seeding densities. Maximum growth was attained when a cell-to-bead ratio of 7∶1 was used. Under these conditions an initial concentration of above 3×10⁵ cells/ml resulted in a yield of over 2×10⁶ cells/ml in 2 d. The amino acid utilization of cells from Dulbecco's modified Eagle medium was studied under the above conditions. Eight amino acids (arg, cys, gln, ile, leu, met, ser, and val) showed rapid and near complete depletion from the medium. Five amino acids (his, lys, phe, thr, and tyr) showed limited depletion. Two amino acids (ala and gly) were released into the medium by the cells.