Search

Key message: Culturing axillary shoot explants of willow in liquid medium in plantform™ and RITA®vessels increased the multiplication coefficient relative to that obtained by culturing the explants in semisolid medium in jars.Abstract: A protocol for micropropagating willow by multiplying axillary shoots in liquid medium was developed, and the effects of the type of explant, medium composition, bioreactor type and frequency of immersion were investigated. The type of explant influenced shoot quality and the multiplication coefficient, with basal segments showing a higher capacity for proliferation than apical and mid-shoot segments. Hyperhydricity was not observed in shoots cultured with Murashige and Skoog medium with half-strength nitrates and supplemented with 0.22 µM BA and 3% sucrose. The willow shoots cultured in plantform™ and RITA® vessels yielded higher multiplication coefficients than shoots grown in semisolid medium. High proliferation rates were obtained by immersion of shoots for 1 min three or six times a day, with additional aeration of 1 min per hour in the plantform™ bioreactors. Transfer to medium with 1% sucrose after 4 weeks of culture in medium with 3% sucrose increased the multiplication coefficient of basal segments cultured in RITA® vessels, suggesting that the species could be micropropagated under photoautotrophic conditions. The willow shoots rooted spontaneously and were successfully acclimatized to greenhouse conditions. This is the first report of the use of a temporary immersion system to culture Salix viminalis. The study findings indicate the feasibility of the system as a method for the large-scale propagation of this species. [ABSTRACT FROM AUTHOR]

Key message : The CsGH3 - 1 gene was isolated from chestnut microshoots. Expression analysis during induction of adventitious roots indicates an alteration in shoot auxin homeostasis during maturation that negatively affects adventitious rooting. Abstract: A new auxin inducible gene isolated from chestnut microshoots was found to encode a protein belonging to group II of the Gretchen Hagen 3 (GH3) family. The gene was, therefore, named CsGH3- 1. Predicted protein sequence analysis revealed the presence of conserved domains involved in the conjugation of amino acids to indole-3-acetic acid (IAA). Modelling of the protein and molecular docking of IAA, indole-3-butyric-acid (IBA), 1-naphthaleneacetic acid (NAA), and benzothiazole-2-oxyacetic acid (BTOA) into the active site of CsGH3-1 indicated a high and similar binding affinity for the four substrates. Expression analysis by qPCR indicated that CsGH3- 1 is regulated by wounding, darkness, and auxin in chestnut microshoots, in an ontogenetic-dependent manner. Under IBA treatment, upregulation of CsGH3- 1 was higher in mature than in juvenile shoots and was negatively correlated with the ability of microshoots to form roots. High levels of auxin-induced expression of CsGH3- 1 were detected in mature shoots 24 h after the IBA treatment, whereas transcript levels decreased in rooting-competent shoots with cell-type-specific expression. CsGH3- 1 transcripts were specifically localized in cells involved in the initiation of adventitious roots only in rooting-competent shoots at the time when cells switch their fate to root initial cells. Thus, these data show a correlation between the specific localization of transcripts and rooting competence, and they also suggest a role for CsGH3- 1 in regulating auxin homeostasis during the onset of adventitious root formation. [ABSTRACT FROM AUTHOR]

Somatic embryogenesis is a powerful tool for plant regeneration and also provides a suitable material for investigating the molecular events that control the induction and development of somatic embryos. This study focuses on expression analysis of the QrCPE gene (which encodes a glycine-rich protein) during the initiation of oak somatic embryos from leaf explants and also during the histodifferentiation of somatic embryos. Northern blot and in situ hybridization were used to determine the specific localisation of QrCPE mRNA. The results showed that the QrCPE gene is developmentally regulated during the histodifferentiation of somatic embryos and that its expression is tissue- and genotype-dependent. QrCPE was strongly expressed in embryogenic cell aggregates and in embryogenic nodular structures originated in leaf explants as well as in the protodermis of somatic embryos from which new embryos are generated by secondary embryogenesis. This suggests a role for the gene during the induction of somatic embryos and in the maintenance of embryogenic competence. The QrCPE gene was highly expressed in actively dividing cells during embryo development, suggesting that it participates in embryo histodifferentiation. The localised expression in the root cap initial cells of cotyledonary somatic embryos and in the root cap of somatic seedlings also suggests that the gene may be involved in the fate of root cap cells. [ABSTRACT FROM AUTHOR]

The genus Quercus, which belongs to the family Fagaceae, is native to the northern hemisphere and includes deciduous and evergreen species. The trees of the different species are very important from both economic and ecological perspectives. Application of new technological approaches (which span the fields of plant developmental biology, genetic transformation, conservation of elite germplasm and discovery of genes associated with complex multigenic traits) to these long-rotation hardwoods may be of interest for accelerating tree improvement programs. This review provides a summary of the advances made in the application of biotechnological tools to specific oak species. Significant progress has been made in the area of clonal propagation via organogenesis and somatic embryogenesis (SE). Standardized procedures have been developed for micropropagating the most important European ( Q. robur, Q. petarea, Q. suber) and American ( Q. alba, Q. bicolor, Q. rubra) oaks by axillary shoot growth. Although regenerated plantlets are grown in experimental trials, large-scale propagation of oak species has not been carried out. The induction of SE in oaks from juvenile explants is generally not problematic, although the use of explants other than zygotic embryos is much less efficient. During the last decade, enormous advances have been made in inducing SE from selected adult trees, mainly specimens of pedunculate oak ( Q. robur) and cork oak ( Q. suber). Advances in the understanding of the maturation and germination steps are required for better use of embryogenic process in clonal forestry. Quercus species are late-maturing and late-flowering, exhibit irregular seed set, and produce seeds that are recalcitrant to storage by conventional procedures. Vitrification-based cryopreservation techniques were used successfully in somatic embryos of pedunculate oak and cork oak, and an applied genbank of cork oak selected genotypes is now under development. The feasibility of genetic transformation of pedunculate oak and cork oak somatic embryos by means of co-culture techniques with several strains of Agrobacterium tumefaciens has also been demonstrated. To date, most research on the genomics of Quercus species has concerned population genetics. Approaches using functional genomics to examine the molecular and cellular mechanisms that control organogenesis and or somatic embryogenesis are still scarce, and efforts on the isolation and characterization of genes related to other specific traits should be intensified in the near future, as this would help improve the practical application of clonal forestry in recalcitrant species such as oaks. [ABSTRACT FROM AUTHOR]