32 research outputs found
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Cryopreservation of winter-dormant apple: III Bud water status and survival after cooling to -30°c and during recovery from cryopreservation
Abstract
In a continuing study to improve the efficiency of dormant bud cryopreservation for
tissues hardened in maritime climates, the water status of dormant buds was monitored
between -4°C and recovery from liquid nitrogen (LN). Measurement of water content, simple
thermal analysis and differential scanning calorimetry were employed. Buds did not lose
water during cooling to, or holding at -30°C indicating that cryodehydration and/or other
adaptive responses contributed during this essential step. A bud exotherm that was an artefact
of warming was detected due to necessary handling at -4°C before cooling to -30°C. There
were no significant differences between cultivars with respect to water status at -30°C or
immediately upon rewarming from LN despite significant differences in post-LN survival.
Buds rehydrated in 5 days, but up to 14 days may be needed for recovery for some cultivars.
In some instances buds could be grafted without rehydration, taking up water across the early
graft union
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Cryopreservation of winter-dormant apple buds: II - tissue water status after desiccation at -4°c and before further cooling
Abstract
The established protocol for the cryopreservation of winter-dormant Malus buds requires
that stem explants, containing a single, dormant bud are desiccated at -4°C, for up to 14 days,
to reduce their water content to 25-30% of fresh weight. Using three apple cultivars, with
known differences in response to cryopreservation, the pattern of evaporative water loss has
been characterised, including early freezing events in the bud and cortical tissues that allow
further desiccation by water migration to extracellular ice. There were no significant
differences between cultivars in this respect or in the proportions of tissue water lost during
the desiccation process. Differential Scanning Calorimetry (to -90°C) of intact buds indicated
that bud tissues of the cultivar with the poorest response to cryopreservation had the highest
residual water content at the end of the desiccation process and froze at the highest
temperature
Keywords: Malus, cryopreservation, dormant bud, dehydratio
Increase of the mean inner Coulomb potential in Au clusters induced by surface tension and its implication for electron scattering
Electron holography in a transmission electron microscope was applied to
measure the phase shift induced by Au clusters as a function of the cluster
size. Large phase shifts Df observed for small Au clusters cannot be described
by the well-known equation Df=C_E V_0 t (C_E: interaction constant, V_0: mean
inner Coulomb potential (MIP) of bulk gold, t: cluster thickness). The rapid
increase of the Au MIP with decreasing cluster size derived from Df, can be
explained by the compressive strain of surface atoms in the cluster
Density-Dependent Mortality of the Human Host in Onchocerciasis: Relationships between Microfilarial Load and Excess Mortality
Human onchocerciasis (River Blindness) is a parasitic disease leading to visual impairment including blindness. Blindness may lead to premature death, but infection with the parasite itself (Onchocerca volvulus) may also cause excess mortality in sighted individuals. The excess risk of mortality may not be directly (linearly) proportional to the intensity of infection (a measure of how many parasites an individual harbours). We analyze cohort data from the Onchocerciasis Control Programme in West Africa, collected between 1974 and 2001, by fitting a suite of quantitative models (including a ‘null’ model of no relationship between infection intensity and mortality, a (log-) linear function, and two plateauing curves), and choosing the one that is the most statistically adequate. The risk of human mortality initially increases with parasite density but saturates at high densities (following an S-shape curve), and such risk is greater in younger individuals for a given infection intensity. Our results have important repercussions for programmes aiming to control onchocerciasis (in terms of how the benefits of the programme are calculated), for measuring the burden of disease and mortality caused by the infection, and for a better understanding of the processes that govern the density of parasite populations among human hosts
Genomics and disease resistance studies in livestock
AbstractThis paper considers the application of genetic and genomic techniques to disease resistance, the interpretation of data arising from such studies and the utilisation of the research outcomes to breed animals for enhanced resistance. Resistance and tolerance are defined and contrasted, factors affecting the analysis and interpretation of field data presented, and appropriate experimental designs discussed. These general principles are then applied to two detailed case studies, infectious pancreatic necrosis in Atlantic salmon and bovine tuberculosis in dairy cattle, and the lessons learnt are considered in detail. It is concluded that the rate limiting step in disease genetic studies will generally be provision of adequate phenotypic data, and its interpretation, rather than the genomic resources. Lastly, the importance of cross-disciplinary dialogue between the animal health and animal genetics communities is stressed
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Transmission of cocoa swollen shoot virus by seeds
A study was undertaken to determine whether cocoa swollen shoot virus is transmitted by seeds, to improve the robustness of quarantine procedures for international exchange and long term conservation of cocoa germplasm. PCR/capillary electrophoresis, using cocoa swollen shoot virus primers designed from the most conserved regions of the six published cocoa genome sequences, allowed the detection of cocoa swollen shoot virus in all the component parts of cocoa seeds from cocoa swollen shoot virus-infected trees. PCR/capillary electrophoresis revealed the presence of cocoa swollen shoot virus in seedlings raised from seeds obtained from cocoa swollen shoot virus-infected trees. The high frequency with which the virus was transmitted through the seedlings suggested that cocoa swollen shoot virus is transmitted by seeds. This has serious implications for cocoa germplasm conservation and distribution. (C) 2008 Elsevier B.V. All rights reserved
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The effectiveness of somatic embryogenesis in eliminating the cocoa swollen shoot virus from infected cocoa trees
Investigations were undertaken on the use of somatic embryogenesis to generate cocoa swollen shoot virus (CSSV) disease free clonal propagules, from infected trees. Polymerase chain reaction (PCR) capillary electrophoresis revealed the presence of CSSV in all the callus tissues induced from the CSSV-infected Amelonado cocoa trees (T1, T2 and T4). The virus was transmitted to primary somatic embryos induced from the infected callus tissues at the rate of 10 (19%), 18 (14%) and 16 (15%) for T1, T2 and T4, respectively. Virus free primary somatic embryos from the infected callus tissues converted into plantlets tested CSSV negative by PCR/capillary electrophoresis 2 years after weaning. Secondary somatic embryos induced from the CSSV-infected primary somatic embryos revealed the presence of viral fragments at the rate of 4 (4%) and 9 (9%) for T2 and T4, respectively. Real-time PCR revealed 23 of the 24 secondary somatic embryos contained no detectable virus. Based on these findings, it is proposed that progressive elimination of the CSSV in infected cocoa trees occurred from primary embryogenesis to secondary embryogenesis. (C) 2008 Elsevier B.V. All rights reserved
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Suitability of cryopreservation for the long-term storage of rare and endangered plant species: a case history for Cosmos atrosanguineus
The suitability of cryopreservation for the secure, long-term storage of the rare and endangered species Cosmos atrosanguineus was investigated. Using encapsulation/dehydration of shoot tips in alginate strips, survival rates of up to 100 % and shoot regeneration of up to 35 % were achieved. Light and electron microscopy studies indicated that cellular damage to some regions of the shoot tip during the freeze/thaw procedure was high, although cell survival in and around the meristematic region allowed shoot tip regeneration. The genetic fingerprinting technique, amplified fragment length polymorphisms (AFLPs), showed that no detectable genetic variation was present between material of C. atrosanguineus at the time of initiation into tissue culture and that which had been cryopreserved, stored in liquid nitrogen for 12 months and regenerated. Wearied plantlets that were grown under glasshouse conditions exhibited no morphological variation from non-frozen controls. (C) 2003 Annals of Botany Company
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Cell and nuclear degradation in sweetpotato [Ipomoea batatas (L.) Lam.] root meristems following exposure to salinity
Sodium chloride-induced cell and nuclear degradation in the root meristems of sweetpotato [Ipomoea batatas (L.) Lam.] were determined using fluorescent microscopy and flow cytometry analysis. Two sweetpotato cultivars were grown in liquid Murashige and Skoog medium and subjected to 0 mM and 500 mM NaCl, with or without 15 mM CaCl2, for periods up to 24 h. Changes to the nuclei of root meristematic cells showed a similar pattern of damage to the nuclei using both fluorescent microscopy and flow cytometry analysis. Damage occurring after only a few hours was followed by nuclear degradation at 24 h. Flow cytometry histograms showed a reduction in G1 and G2 nuclei and an increase in degraded nuclei in NaCl-stressed roots. Salinity-induced nuclear degradation was alleviated by the addition of CaCl2