Physiological and Structural Aspects of In Vitro Somatic Embryogenesis in Abies alba Mill

Effects of plant growth regulators and sucrose on proliferation and quality of embryogenic tissue in Picea pungens

Embryogenic tissue (ET) is important for genetic modification and plant re-generation. The proliferation ability and vigor of ET are crucial for plant propagation via somatic embryogenesis. In this study, ET was induced from mature zygotic embryos in blue spruce (Picea pungens Engelm.). There were significant differences in ET induction between two provenances, i.e. 78.8 ± 12.5% and 62.50 ± 12.8% respectively. Effects of 2,4-Dichlorophenoxy acetic acid (2,4-D), 6-Benzyl amino-purine (6-BA) and/or sucrose on ET proliferation and somatic embryo (SE) maturation were further investigated with four cell lines. The highest ET proliferation rate reached 1473.7 ± 556.0% biweekly. Concentrations of 2,4-D or 6-BA applied at tissue proliferation stage impacted SE maturation among the cell lines, whereas sucrose showed less effects. The highest rate, 408 ± 230 mature SEs/g FW, was achieved in SE maturation cultures. This research demonstrated that the culture conditions, i.e. the specific concentrations of 2,4-D and BA, at ET proliferation stage affected not only ET growth, but also the quality of ET for SE maturation. This study revealed the necessity and benefit in developing both the general and the genotype-specific protocols for efficient production of mature SEs, or somatic plants in blue spruce.

Phenotypically abnormal cotyledonary Vitis vinifera embryos differ in anatomy, endogenous hormone levels and transcriptome profiles

In many perennial fruit species, including grapevine (Vitis vinifera L.), the highly complex process of somatic embryogenesis (SE) can result in the formation of a deformed embryo, although the underlying reasons are still poorly understood. Here, V. vinifera cv. 'Chardonnay' cotyledonary embryos with distinct morphologies were used to address this issue. Normal cotyledonary embryos (NCEs) and elongated cotyledonary embryos (ECEs) were observed to have better-developed vasculature and shoot meristems than the vitrified cotyledonary embryos (VCEs) and fused cotyledonary embryos (FCEs), but ECEs were less developed. We determined that the morphological differences in these phenotypically abnormal embryos were likely associated with endogenous hormone levels, since concentrations of the phytohormones indoleacetic acid (IAA) and abscisic acid (ABA) in NCEs were higher than in the other three types. Comparative transcriptome analysis revealed large differences in gene expression of the hormone signaling pathways in normal and abnormal cotyledonary embryos. Weighted gene co-expression network analysis of the different cotyledonary types allowed the identification of co-regulated gene modules associated with SE, suggesting a role for ERF family genes and other transcription factors (TFs) in regulating morphology. Moreover, an analysis of morphology-specific gene expression indicated that the activation of a specific protein kinase, small heat shock proteins (sHSPs) and certain TFs was closely associated with the formation of normal cotyledonary embryos. Our comparative analyses provide insights into the gene networks regulating somatic cotyledon development and open new avenues for research into plant regeneration and functional genomic studies of malformed embryos.

Accumulated effects of factors determining plant development from somatic embryos of Abies nordmanniana and Abies bornmuelleriana

Despite a much later inception of somatic embryogenesis (SE) propagation protocols for gymnosperms than for angiosperm species, SE is becoming increasingly important due to its applications for commercial forestry. For many conifers, there are however still major bottlenecks in the SE plant production process limiting the use of SE for forestry operations, Christmas tree production and research projects. In the present case study, the effects on plant growth from different cultural factors applied during the SE developmental process were studied in two conifer species of high value for Christmas tree production. Seven clones of Abies nordmanniana and two clones of Abies bornmuelleriana were included in the study. Accumulated effects from cultural treatments were recorded from the start of germination of mature embryos of different quality scores through development into plants in the third growing period. Experimental factors of the cultural treatments included were: germination temperature, germination time, light conditions, survival ex vitro and traits for plant growth and vitality. The results reveal that most of the studied experimental factors influenced plant growth during the first three years however their relative importance was different. Plant survival rate at end of the nursery stage was strongly impacted by germination temperature (p<0.001), initial embryo score (p=0.007), clone (p<0.001) and to a lesser extend week of germination (p=0.017). This case-study highlights and quantifies the strong interrelation between the developmental steps of somatic embryogenesis and show the importance of considering all cultural steps when optimizing SE plant production protocols.

Application of Tissue Culture in Plant Reproduction

The increasing degradation of forests, together with a higher demand for wood and fruit, has led to the need for more efficient trees adapted to the current climatic conditions and, thus, to the need for genetic improvement programs [...]