M.J. Hutchinson

Two distinct regions of FC gamma RI initiate separate signalling pathways involved in endocytosis and phagocytosis.

Cross‐linking of the high affinity receptor for IgG, Fc gamma RI, can result in both endocytosis of immune complexes and phagocytosis of opsonized particles in myeloid cells, although the cytoplasmic domain of the receptor lacks the tyrosine activation motif which has been implicated in signal transduction triggered by cross‐linking of other Fc receptors. To identify the structural determinants of Fc gamma RI‐mediated ligand internalization, we have expressed Fc gamma RI or truncated versions of Fc gamma RI in COS cells, either alone or in the presence of the Fc epsilon RI gamma subunit (which contains a classical tyrosine activation motif and associates with Fc gamma RI in myeloid cells), and assessed their ability to mediate endocytosis and phagocytosis. We have found that Fc gamma RI alone (in the absence of the gamma subunit) is capable of mediating endocytosis in COS cells and that the process occurs via a novel, tyrosine kinase‐independent signalling pathway. Activation of this pathway following cross‐linking appears to require only the receptor extracellular domain. In contrast, Fc gamma RI phagocytic function in COS cells is dependent on an interaction between the receptor transmembrane domain and the gamma subunit and is mediated by recruitment of tyrosine kinase activity. Our data therefore indicate that distinct domains of the receptor regulate ligand internalization following receptor cross‐linking by either immune complexes (endocytosis) or opsonized particles (phagocytosis) and that these functions are mediated by different intracellular signalling pathways.

Morphoregulatory role of thidiazuron: Evidence of the involvement of endogenous auxin in thidiazuron-induced somatic embryogenesis of geranium (Pelargonium × hortorum Bailey)

Summary Thidiazuron-induced somatic embryogenesis in hypocotyl cultures of geranium ( Pelargonium × hortorum Bailey cv. Scarlet Orbit Improved) consists of an induction phase on 10 or 20 (µmol·L −1 thidiazuron (TDZ) followed by an expression phase on a basal medium lacking growth regulators. The induction and development of somatic embryos were found to be closely related to levels of endogenous and exogenous auxin. Inclusion of the auxin-action inhibitor, PCIB, and the auxin-transport inhibitor, TIBA, in a TDZ-induction medium decreased embryogenic response of the cultures by different mechanisms. The decrease of the embryogenic response in the presence of PCIB was accompanied by a corresponding decrease in endogenous levels of auxins, cytokinins, and ABA. These changes in the profiles of endogenous plant growth regulators were not evident when TIBA was used. High concentrations of exogenous LAA in the expression medium suppressed the development of somatic embryos. Although the precise mode of action of TDZ is unknown, the results of this study provide evidence that TDZ modulates endogenous auxin metabolism during somatic embryo development in geranium hypocotyl cultures.

Acetylsalicylic acid enhances and synchronizes thidiazuron-induced somatic embryogenesis in geranium (Pelargonium x hortorum Bailey) tissue cultures

SummaryThidiazuron (TDZ) effectively induced somatic embryogenesis in cultured hypocotyl explants of geranium (Pelargonium x hortorum Bailey) during only a 3-day period of induction. The presence of acetylsalicylic acid (ASA) during this period caused a two-fold increase in the number of somatic embryos and enhanced synchronization of embryo development compared to the TDZ treatment alone. Salicylic acid was ineffective in modulating similar embryogenic responses as ASA. The ASA-induced enhancement and synchronization of somatic embryogenesis could possibly be used as an experimental system to study the interplay of growth regulators in somatic embryogenesis.

Inhibitory effect of GA3 on the development of thidiazuron-induced somatic embryogenesis in geranium (Pelargonium xhortorum Bailey) hypocotyl cultures

Somatic embryogenesis in geranium (Pelargonium xhortorum Bailey cv ‘Scarlet Orbit Improved’) can be achieved by incubating hypocotyl explants on MS medium supplemented with thidiazuron (TDZ; 10 μM for 3 days followed by subculture on medium devoid of any plant growth regulators. The presence of gibberellins (GAs) during both the induction and expression phases of embryogenesis was significantly detrimental to somatic embryo formation on the hypocotyl explants. The addition of the GA-synthesis inhibitors paclobutrazol, uniconazole or ancymidol during the period of growth and differentiation of somatic embryos increased the number of somatic embryos formed on each explant. However, paclobutrazol added during the period of induction had no significant influence on somatic embryo formation. Results suggest that both exogenously supplied as well as endogenous GAs play a role, albeit a negative one, on somatic embryogenesis of geranium.

Does ethylene play a role in thidiazuron-regulated somatic embryogenesis of geranium (Pelargonium × hortorum bailey) hypocotyl cultures?

SummaryThe accumulation of ethylene in headspace of hypocotyl cultures of geranium (Pelargonium × hortorum Bailey) and its possible role in thidiazuron-mediated somatic embryogenesis was investigated. The action of ethylene as determined by various ethylene synthesis and action inhibitors was varied. Silver nitrate (AgNo3), aminoethoxyvinylglycine (AVG), and silver thiosulphate (STS) had no significant influence on the embryogenic response, while 1-methylcyclopropene (1-MCP) applied during the initial 3 d of induction or the expression phase, significantly increased the number of somatic embryos formed. Thidiazuron-treated tissues accumulated large quantities of ethylene within 6 h of culture, but the levels decreased after 12 h and reached very low levels after 3 d in culture. In the presence of acetylsalicylic acid (ASA), the levels of ethylene decreased by 20 to 50% during the first 48 h of culture. Analysis of endogenous auxin, cytokinins, and abscisic acid (ABA) indicated possible interactions of ethylene with other phytohormones during the induction of somatic embryos on geranium hypocotyl explants. Thidiazuron (10 µM) increased, while ASA decreased the levels of endogenous auxin, cytokinins, and abscisic acid during this period of induction.

Light Mediates Endogenous Plant Growth Substances in Thidiazuron-induced Somatic Embryogenesis in Geranium Hypocotyl Cultures

Thidiazuron-induced somatic embryogenesis in geranium (Pelargonium x hortorum Bailey) was readily achieved under both light and darkness. The hypocotyl explants treated with TDZ formed well differentiated embryos when incubated under conditions of continuous light, complete darkness or 16-h photoperiod. However, embryogenesis was significantly impaired by light at both 16-h and continuous light exposure. Maintaining the cultures in the dark increased the frequency of the somatic embryos formed with a corresponding moderate elevation of the endogenous plant growth substances measured. In the complete absence of TDZ, all of the hypocotyl explants cultured in the dark remained thin but formed etiolated roots. The number of explants that formed roots decreased with increasing light exposure time; in addition the roots formed were shorter in length. The levels of endogenous adenine, adenosine, DHZ, zeatin, isopentenyladenine (2iP), tryptamine, IAA and ABA remained elevated for the first 2 days of culture in explants maintained on MSO and under continuous light, while they decreased on day 3 of culture. We provide evidence that the interaction between TDZ and light treatments modulated the endogenous plant growth substances, which in turn affected the embryogenic process in geranium hypocotyl explants.

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.

Callus induction and plant regeneration from mature zygotic embryos of a tetraploid Alstroemeria (A. pelegrina × A. psittacina).

SummaryA simple procedure was developed to induce callus growth and whole plant regeneration for a tetraploid cultivar of Alstroemeria. The callus, induced from mature zygotic embryos cultured on a medium supplemented with 20 μM kinetin with 10 or 20 μM NAA, could be maintained for one year without any loss of regeneration potential. Maximum frequency of regeneration (40%) was obtained with calli maintained on the medium containing 20 μM kinetin and 20 μM NAA. Whole plant regeneration occurred via somatic embryogenesis in the absence of growth regulators and the plantlets grew to maturity and flowered in the greenhouse conditions.

Genetic Diversity of Kenyan Potato Germplasm Revealed by Simple Sequence Repeat Markers

International potato germplasm (Solanum tuberosum L.) has been long introduced to and bred in Kenya and the accumulated Kenyan Solanum germplasm is unique in its geographical and climatic ranges of adaptation to tropical highlands. However, little is known about the genetic diversity of these improved Solanum accessions. A representative set of 48 potato accessions grouped as farmer varieties, local genotypes and modern varieties was selected and studied using the simple sequence repeat (SSR) technique. Twenty-two SSR primer pairs were applied and 122 polymorphic bands were scored. The frequencies of polymorphic bands ranged from 0.02 to 0.98 and averaged 0.35. The proportion of total SSR variation occurring among four origin categories (International Potato Centre (CIP), Europe, Kenya and Unknown) of accessions was 6.32%; between accessions introduced before and after 1980 4.79%; and among three germplasm classes of accessions 4.36%. Accessions from the CIP displayed more SSR variation than those from Europe. More SSR variation was detected in the accessions introduced/bred after 1980. The modern varieties displayed slightly more diversity than the farmer varieties and local genotypes. Some dominant groups of accessions largely from CIP and Europe were found, but these groups were not distantly separated. Both the genetically most distinct accessions and the possibly genetically related accessions were identified. These results not only demonstrate the considerable genetic variation harbored in the Kenyan potato germplasm, but also are significant for developing effective strategies of acquiring genetically diverse germplasm and for selecting genetically distinct potato materials to widen the Kenyan improved gene pool.ResumenDesde hace tiempo se ha introducido y mejorado germoplasma internacional de papa (Solanum tuberosum L.) en Kenia y el germoplasma acumulado de Solanum Keniano es único en sus amplitudes de adaptación geográfica y climática a altiplanos tropicales. No obstante, poco se sabe sobre la diversidad genética de estas introducciones mejoradas de Solanum. Se seleccionó y estudió, utilizando la técnica de una secuencia simple de repetición (SSR), un juego representativo de 48 introducciones agrupadas como variedades de los productores, genotipos locales y variedades modernas. Se aplicaron veintidós pares de iniciadores SSR y se registraron 122 bandas polimórficas. Las frecuencias de bandas polimórficas variaron de 0.02 a 0.98 con un promedio de 0.35. La proporción de la variación total de SSR que se presentó entre cuatro categorías por origen (Centro Internacional de la Papa CIP, Europa, Kenia y desconocido) de las introducciones, fue 6.32%; entre las introducciones hechas antes y después de 1980 fue de 4.79; y entre tres clases de accesiones de germoplasma, de 4.36%. Las introducciones del CIP mostraron más variación de SSR que las de Europa. Se detectó más variación de SSR en las accesiones introducidas o mejoradas después de 1980. Las variedades modernas mostraron ligeramente más diversidad que las de los productores y que los genotipos locales. Se encontraron algunos grupos dominantes de introducciones, mayormente del CIP y Europa, pero estos grupos no estaban distantes en separación. Se identificaron tanto a las introducciones genéticamente más diversas como a las que posiblemente estaban genéticamente relacionadas. Estos resultados no solo demuestran la considerable variación genética con la que se cuenta en el germoplasma de papa Kenyano, sino que también es significativo para el desarrollo de estrategias efectivas en la adquisición de germoplasma diverso genéticamente y para seleccionar materiales de papa genéticamente distintos para ampliar el acervo genético mejorado de Kenia.

Incidence of Jelly Seed Disorder in ‘Tommy Atkins’ and ‘Van Dyke’ Mangoes as Affected by Agro-Ecological Conditions in Kenya

Jelly seed disorder is one of the major problems in mango production in Kenya as well as other mango producing countries in the world. This problem manifests itself through breakdown of tissues around the seed of the affected fruits resulting in unmarketable fruits. Although the exact cause of jelly seed in mango is unknown, some reports indicate that the condition could be due to imbalance related to Ca, Mg, N and K supply to the fruit. To establish the extent of this problem in Kenya, a study was conducted in 2013 in three major mango producing counties located in different agroecological zones namely Embu, Murang’a and Meru. Three farms with homogenous trees of “Tommy Atkins” and “Van Dyke” mangoes were randomly selected per county. Soil and mango leaf analysis were carried out to determine the nutrient status. Rainfall and temperature data were also recorded during the study period. At harvest time, 50 tree-ripe fruits of each variety were randomly sampled from 25 trees per site and sliced along the endocarp to expose the seed then visually examined and scored for the incidence of jelly seed using Galan Sauco scale. Soil analysis showed Original Research Article Njuguna et al.; IJPSS, 11(5): 1-9, 2016; Article no.IJPSS.26447 2 that, Meru vertisol and lithosols soils had higher Ca, Mg, K content compared to Murang’a eutric Nitisol soils and Embu ferralic arenosal soils. Similarly, mango leaves and fruits sampled from Meru county had higher Ca, Mg and K contents than those from Murang’a and Embu. Fruits (both varieties) from Embu county showed higher incidents of jelly seed that those from Murang’a and Meru county. Significantly higher jelly seed incidents were reported in ‘Van Dyke’ compared to ‘Tommy Atkins’ mangoes. It can therefore be concluded that incidences of jelly seed depend on the variety as well as agro-ecological zone where the mangoes are produced.