Somatic embryogenesis

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The somatic embryogenesis is a biotechnological method in which the formation of a plant embryo , starting is carried out on asexual way of a somatic cell. This is in contrast to normal zygotic embryogenesis, which is initiated by the fertilization of an egg. A similar process that takes place in nature is the apomixis , a so-called virgin generation in which an embryo is formed without the gametes having previously merged .

The somatic cells can for example be obtained from the hypocotyl , leaf sheaths or the roots . A hereditary tissue can develop from these cells vegetatively, which is why the resulting plants are also referred to as clones. Although no zygote is the starting point for embryonic development in somatic embryogenesis , strong morphological parallels can be observed in development and the product obtained in both cases is an intact, fertile plant. In addition to the term somatic embryo, the terms embryoid , adventivembryo or simply embryo-like structure are also used .

For successful somatic embryogenesis, a number of requirements must be met. On the one hand, the starting cell must have an embryogenic competence so that a conversion from a somatic into an embryogenic cell can take place, and a suitable stimulus must also be present that triggers embryonic development. The whole thing must take place in an environment (nutrient medium) that enables this development.

Stages of development

In somatic embryogenesis, different stages of development are distinguished:

  • Globular stage - a somatic cell develops into a spherical structure after successful stimulation.
  • Heart stage - cotyledons begin to emerge from the globular structure . These bulges on both sides give the embryo a heart-shaped structure.
  • Torpedo stage - by stretching the hypocotyl, the embryo takes on an elongated shape.
  • Cotyledon stage - the cotyledons are more pronounced and clearly protrude from the shape.

After reaching the fourth stage, the embryo is said to be mature. The embryonic development is complete and the embryo is now able to develop an intact plant.

Forms of somatic embryogenesis

Basically, two different forms are distinguished from each other in somatic embryogenesis.

Indirect embryogenesis

In indirect embryogenesis, callus formation occurs first . The induction of a callus can be initiated through the use of (synthetic) plant growth hormones such as 2,4-dichlorophenoxyacetic acid . These auxins are added to the medium which is used to cultivate the cells. Embryogenesis only takes place afterwards. Before the regeneration into a plant, the calli can be used as a transformation target. Various methods can be used here. For example the biolistic transformation , the transformation with agrobacteria or the transformation with the help of silicon carbide crystal needles.

Because of the high division activity of the callus tissue, somaclonal variations often occur in indirect embryogenesis.

Direct embryogenesis

In direct embryogenesis, the embryo is formed directly. This usually happens from parenchymal cells. In direct embryogenesis, somaclonal variations are much less common. However, direct somatic embryogenesis has so far only been described in very few species.

Benefits of somatic embryogenesis

In research, greenhouse or climatic chamber capacities are often a limiting factor. This is why somatic embryogenesis is of interest, since with its help a large number of plants can be produced in a small space and with little starting material.

Importance and application

Somatic embryos could enable automated clonal mass reproduction with the aid of bioreactors. This would be of particular interest for the development of artificial seeds. Here, somatic embryos are encapsulated in the torpedo stage. Polyethylene oxide or a liquid gel can be used as the material for the encapsulation. These initially used materials have been replaced by calcium alginate balls due to their better properties. Further optimizations were made by adding various additives for regulating the osmotic activity (e.g. sucrose) or the vitality of the embryos (e.g. abscisic acid).

Seed development

In contrast to a seed that has emerged from zygotic embryogenesis, seeds that have emerged from somatic embryogenesis do not have an endosperm , which is used to supply nutrients during germination . In addition, there is no firm seed coat, which primarily serves to protect against mechanical stress.

Individual evidence

  1. ↑ a b Neumann KH ( 1995 ) Plant cell and tissue cultures , Ulmer Verlag, Stuttgart.
  2. ↑ a b Heß D. ( 1992 ) Biotechnology of Plants , Ulmer Verlag, Stuttgart.
  3. ↑ Ahmadabadi, M., S. Ruf, et al. ( 2007 ). "A leaf-based regeneration and transformation system for maize (Zea mays L.)." Transgenic Research 16 (4): 437-448.
  4. ^ Huang, XQ and ZM Wei ( 2004 ). "High-frequency plant regeneration through callus initiation from mature embryos of maize (Zea Mays L.)." Plant Cell Reports 22 (11): 793-800.
  5. ↑ a b Sidorov, V., L. Gilbertson, et al. ( 2006 ). "Agrobacterium-mediated transformation of seedling-derived maize callus." Plant Cell Reports 25 (4): 320-328.
  6. ↑ a b Bhojwani SS and Razdan MK ( 1983 ) Plant tissue culture: theory and practice , Elsevier Verlag, Amsterdam.
  7. ^ Frame, BR, HY Zhang, et al. ( 2000 ). "Production of transgenic maize from bombarded type II callus: Effect of gold particle size and callus morphology on transformation efficiency." In Vitro Cellular & Developmental Biology-Plant 36 (1): 21-29.
  8. ↑ Brettschneider, R., D. Becker, et al. ( 1997 ). "Efficient transformation of scutellar tissue of immature maize embryos." Theoretical and Applied Genetics 94 (6-7): 737-748.
  9. ^ Frame, BR, HX Shou, et al. ( 2002 ). "Agrobacterium tumefaciens-mediated transformation of maize embryos using a standard binary vector system." Plant Physiology 129 (1): 13-22.
  10. ↑ Hiei, Y., S. Ohta, et al. ( 1994 ). "Efficient transformation of rice (Oryza sativa L) mediated by agrobacterium and sequence-analysis of the boundaries of the tDNA." Plant Journal 6 (2): 271-282.
  11. ↑ Ishida, Y., Y. Hiei, et al. ( 2007 ). "Agrobacterium-mediated transformation of maize." Nature Protocols 2 (7): 1614-1621.
  12. ↑ Ishida, Y., H. Saito, et al. ( 1996 ). "High efficiency transformation of maize (Zea mays L.) mediated by Agrobacterium tumefaciens." Nature Biotechnology 14 (6): 745-750.
  13. ↑ Tingay, S., D. McElroy, et al. ( 1997 ). "Agrobacterium tumefaciens-mediated barley transformation." Plant Journal 11 (6): 1369-1376.
  14. ^ Frame, BR, PR Drayton, et al. ( 1994 ). "PRODUCTION OF FERTILE TRANSGENIC MAIZE PLANTS BY SILICON-CARBIDE WHISKER-MEDIATED TRANSFORMATION." Plant Journal 6 (6): 941-948.
  15. ↑ Petolino, JF, NL Hopkins, et al. ( 2000 ). "Whisker-mediated transformation of embryogenic callus of maize." Plant Cell Reports 19 (8): 781-786.
  16. ↑ Kitto, SL and J. Janick ( 1985 ). "PRODUCTION OF SYNTHETIC SEEDS BY ENCAPSULATING ASEXUAL EMBRYOS OF CARROT." Journal of the American Society for Horticultural Science 110 (2): 227.
  17. ↑ Kitto, SL and J. Janick ( 1985 ). "PRODUCTION OF SYNTHETIC SEEDS BY ENCAPSULATING ASEXUAL EMBRYOS OF CARROT." Journal of the American Society for Horticultural Science 110 (2): 277-282.
  18. ↑ Liu, JR, JH Jeon, et al. ( 1992 ). "DRY TYPE OF CARROT (DAUCUS-CAROTA L) ARTIFICIAL SEEDS." Scientia Horticulturae 51 (1-2): 1-11.
  19. ↑ Timbert, R., JN Barbotin, et al. ( 1996 ). "Effect of sole and combined pre-treatments on reserve accumulation, survival and germination of encapsulated and dehydrated carrot somatic embryos." Plant Science 120 (2): 223-231.
  20. ↑ Timbert, R., JN Barbotin, et al. ( 1996 ). "Enhancing carrot somatic embryos survival during slow dehydration, by encapsulation and control of dehydration." Plant Science 120 (2): 215-222.