Browsing by Author "Nicolas Niemenak"

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    Characterization of leafy cotyledon1-like during embryogenesis in Theobroma cacao L.
    (2008) Nicolas Niemenak; Christine Sanier; Martine Devic; Laurence Alemanno; Mariannick Rio; Jocelyne Guilleminot; Jean Luc Verdeil; Pascal Montoro
    Theobroma cacao L., an economically important crop for developing countries, can be experimentally propagated by somatic embryogenesis. Because of their potential roles in embryogenesis, a gene candidate strategy was initiated to Wnd gene homologues of the members of the leafy cotyledon family of transcription factors. A homologue of the leafy cotyledon1-like gene, that encodes the HAP 3 subunit of the CCAAT box-binding factor, was found in the cocoa genome (TcL1L). The translated peptide shared a high amino acid sequence identity with the homologous genes of Arabidopsis thaliana, Phaseolus coccineus and Helianthus annuus. TcL1L transcripts mainly accumulated in young and immature zygotic embryos, and, to a lesser extent, in young and immature somatic embryos. In situ hybridization speciWed the localization of the transcripts as being mainly in embryonic cells of young embryos, the meristematic cells of the shoot and root apex of immature embryos, and in the protoderm and epidermis of young and immature embryos, either zygotic or somatic. Non-embryogenic explants did not show TcL1L expression. Ectopic expression of the TcL1L gene could partially rescue the Arabidopsis lec1 mutant phenotype, suggesting a similarity of function in zygotic embryogenesis.
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    Effect of MgSO4 and K2SO4 on somatic embryo differentiation in Theobroma cacao L
    (2008) Emile Minyaka; Nicolas Niemenak; Fotso; Abdourahamane Sangare; Denis Ndoumou Omokolo
    Somatic embryogenesis in cacao is difficult and this species is considered as recalcitrant. Therefore, reformulation of culture media might be a breakthrough to improve its somatic embryogenesis. In cacao, acquisition of somatic embryogenesis competence involves three main stages: induction of primary callus, induction of secondary callus and embryo development. Screening for MgSO4 and K2SO4 concentrations for somatic embryo differentiation was conducted on three genotypes (Sca6, IMC67 and C151- 61) at the three stages. The effect of these two salts in culture media appears to be most efficient at the embryo development stage. At this stage, high MgSO4 (24 mM) and K2SO4 (71.568 mM) in the culture media induced direct somatic embryos on staminodes and petals of the Sca6 and IMC67 genotypes. Media supplemented with 6.0 mM and 12.0 mM MgSO4 enabled high responsive of explants and produced high proportion of embryos. The positive effect of MgSO4 and K2SO4 on the acquisition of embryogenesis competence was further tested on seven cacao genotypes reputed as non embryogenic: SNK12, ICS40, POR, IMC67, PA121, SNK64 and SNK10. All these genotypes were able to produce somatic embryos depending on the MgSO4 concentration. Thus, our results showed that the recalcitrance of cacao to somatic embryo differentiation can be overcome by screening for the suitable MgSO4 or K2SO4 concentration. Studies of the influence of different K+/Mg2+ ratios (at normal sulphate concentration) on somatic embryo differentiation revealed that sulphate supply was the main factor promoting responsive explants and the proportion of embryos. Cysteine synthase isoforms showed patterns related to morphogenetic structures sustaining that sulphur supply and its assimilation improve somatic embryogenesis in cacao.
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    Regeneration of somatic embryos in Theobroma cacao L. in temporary immersion bioreactor and analyses of free amino acids in different tissues
    (2008) Katja Saare-Surminski; Nicolas Niemenak; Denis Omokolo Ndoumou; Christina Rohsius; Reinhard Lieberei
    The present study aimed at developing temporary immersion bioreactor techniques for multiplication of cacao somatic embryos. Temporary Immersion System (TIS), i.e. flooding of plant tissue at regular time intervals provides an efficient way to propagate plants. Somatic embryos were regenerated in twin flask bioreactors. The TIS proved to be suitable for mass regeneration of somatic embryos and for their subsequent direct sowing. The number of embryos after 3 months of culture was significantly higher in TIS cultures than in the solid medium variant. TIS also improved embryo development regarding the conversion to torpedo shaped forms. Matured embryos derived from TIS and pre-treated with 6% sucrose were converted into plants after direct sowing. Additionally to the influence of culture conditions on the development of somatic embryogenesis the content and composition of free amino acids were analysed. The content of free amino acids in somatic embryos rose as immersion frequency increased. The endogenous free GABA content in embryogenic callus was significantly higher than in non-embryogenic callus.