Embryo Rescue
Encyclopedia
Embryo Rescue is one of the earliest and successful forms of in-vitro culture techniques that is used to assist in the development of plant embryos that might not survive to become viable plants. Embryo rescue plays an important role in modern plant breeding
, allowing the development of many interspecific
and intergeneric food and ornamental plant crop hybrids. This technique nurtures the immature or weak embryo, thus allowing it the chance to survive. Plant embryos are multicellular structures that have the potential to develop into a new plant. The most widely used embryo rescue procedure is referred to as embryo culture, and involves excising plant embryos and placing them onto media culture. Embryo rescue is most often used to create interspecific and intergeneric crosses that would normally produce seeds which are aborted. Interspecific incompatibility in plants can occur for many reasons, but most often embryo abortion occurs In plant breeding, wide hybridization crosses can result in small shrunken seeds
which indicate that fertilization has occurred, however the seed fails to develop. Many times, remote hybridizations will fail to undergo normal sexual reproduction, thus embryo rescue can assist in circumventing this problem.
. The first successful in vitro embryo culture was performed by Hanning in 1904, he however described problems with precocious embryos that resulted in small, weak, and often inviable plantlets.
, ovule
, or ovary
culture. Ovule culture or in ovolo embryo culture is a modified technique of embryo rescue whereby embryos are cultured while still inside their ovules to prevent damaging them during the excision process. Ovary or pod culture, on the other hand employs the use of an entire ovary into culture. It becomes necessary to excise the entire small embryo to prevent early embryo abortion. However, it is technically difficult to isolate the tiny intact embryos, so often ovaries with young embryos, or entire fertilized ovules will be used.
(MS) and Gamborg’s B-5 media (Bridgen, 1994), the composition of the media will vary in terms of the concentrations of media supplements required. This will generally depend on the stage of development of the embryo. For instance, young embryos would require a complex medium with high sucrose concentrations, while more mature embryos can usually develop on a simple medium with low levels of sucrose. The temperature and light requirement is generally species specific and thus its usually regulated to be the within the same temperature requirement as that of its parent with embryos of cool-season crops requiring lower temperatures than those of warm-season crops.
Plant breeding
Plant breeding is the art and science of changing the genetics of plants in order to produce desired characteristics. Plant breeding can be accomplished through many different techniques ranging from simply selecting plants with desirable characteristics for propagation, to more complex molecular...
, allowing the development of many interspecific
Interspecific
Interspecific is a term used in biology to describe behaviors, biochemical variations and other issues between individuals of separate species, thereby contrasting with intraspecific...
and intergeneric food and ornamental plant crop hybrids. This technique nurtures the immature or weak embryo, thus allowing it the chance to survive. Plant embryos are multicellular structures that have the potential to develop into a new plant. The most widely used embryo rescue procedure is referred to as embryo culture, and involves excising plant embryos and placing them onto media culture. Embryo rescue is most often used to create interspecific and intergeneric crosses that would normally produce seeds which are aborted. Interspecific incompatibility in plants can occur for many reasons, but most often embryo abortion occurs In plant breeding, wide hybridization crosses can result in small shrunken seeds
SEEDS
SEEDS is a voluntary organisation registered under the Societies Act of India....
which indicate that fertilization has occurred, however the seed fails to develop. Many times, remote hybridizations will fail to undergo normal sexual reproduction, thus embryo rescue can assist in circumventing this problem.
History
Embryo rescue was first documented in the 18th century when Charles Bonnet excised Phaseolus and Fagopyrum embryos, planted them in soil and the cross resulted in dwarf plants. Soon after this, scientists began placing the embryos in various nutrient media. During the period of 1890 to 1904, systems for embryo rescue became systematic by applying nutrient solutions that contained salts and sugars and applying aseptic techniqueAseptic technique
Aseptic technique refers to a procedure that is performed under sterile conditions. This includes medical and laboratory techniques, such as with microbiological cultures. It includes techniques like flame sterilization...
. The first successful in vitro embryo culture was performed by Hanning in 1904, he however described problems with precocious embryos that resulted in small, weak, and often inviable plantlets.
Applications
- Breeding of incompatible interspecific and intergeneric species
- Overcoming seed dormancySeed dormancySeed dormancy is a condition of plant seeds that prevents germination when the seeds are under optimal environmental conditions for germination. Living, non dormant seeds germinate when soil temperatures and moisture conditions are suited for cellular processes and division; dormant seeds do...
- Determination of seed viability
- Recovery of maternal haploids that develop as a result of chromosomeChromosomeA chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
elimination following interspecific hybridization - Used in studies on the physiology of seed germination and development
Techniques
Depending on the organ cultured, it may be referred to as either embryoEmbryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
, ovule
Ovule
Ovule means "small egg". In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: The integument forming its outer layer, the nucellus , and the megaspore-derived female gametophyte in its center...
, or ovary
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
culture. Ovule culture or in ovolo embryo culture is a modified technique of embryo rescue whereby embryos are cultured while still inside their ovules to prevent damaging them during the excision process. Ovary or pod culture, on the other hand employs the use of an entire ovary into culture. It becomes necessary to excise the entire small embryo to prevent early embryo abortion. However, it is technically difficult to isolate the tiny intact embryos, so often ovaries with young embryos, or entire fertilized ovules will be used.
Factors to consider
Embryos are manually excised and placed immediately onto a culture media that provides the proper nutrients to support survival and growth (Miyajima 2006). While the disinfestation and explant excision processes differ for these three techniques, many of the factors that contribute to the successful recovery of viable plants are similar. The main factors that influence success are; the time of culture, the composition of the medium, and temperature and light. Timing mainly refers to the maturation stage of the embryo before excision. The optimal time especially for the rescue of embryos involving incompatible crosses would be just prior to embryo abortion. Nevertheless, due to difficulties involved with the rearing of young embryos compared to those that have reached the autotrophic phase of development, embryos are normally allowed to develop in vivo as long as possible. While in general, two main types of basal media are the most commonly used for embryo rescue studies, i.e Murashige and Skoog mediumMurashige and Skoog medium
Murashige and Skoog medium or is a plant growth medium used in the laboratories for cultivation of plant cell culture. MSO was invented by plant scientists Toshio Murashige and Folke K. Skoog in 1962 during Murashige's search for a new plant growth regulator...
(MS) and Gamborg’s B-5 media (Bridgen, 1994), the composition of the media will vary in terms of the concentrations of media supplements required. This will generally depend on the stage of development of the embryo. For instance, young embryos would require a complex medium with high sucrose concentrations, while more mature embryos can usually develop on a simple medium with low levels of sucrose. The temperature and light requirement is generally species specific and thus its usually regulated to be the within the same temperature requirement as that of its parent with embryos of cool-season crops requiring lower temperatures than those of warm-season crops.
See also
- Plant embryogenesisPlant embryogenesisPlant embryogenesis is the process that produces a plant embryo from a fertilised ovule by asymmetric cell division and the differentiation of undifferentiated cells into tissues and organs. It occurs during seed development, when the single-celled zygote undergoes a programmed pattern of cell...
- Callus (cell biology)Callus (cell biology)Plant callus is a mass of undifferentiated cells derived from plant tissue for use in biological research and biotechnology. In plant biology, callus cells are those cells that cover a plant wound. To induce callus formation, plant tissues are surface sterilized and then plated onto in vitro...
- Plant tissue culturePlant tissue culturePlant tissue culture is a collection of techniques used to maintain or grow plant cells, tissues or organs under sterile conditions on a nutrient culture medium of known composition. Plant tissue culture is widely used to produce clones of a plant in a method known as micropropagation...
- Plant hormonePlant hormonePlant hormones are chemicals that regulate plant growth, which, in the UK, are termed 'plant growth substances'. Plant hormones are signal molecules produced within the plant, and occur in extremely low concentrations. Hormones regulate cellular processes in targeted cells locally and, when moved...
- HyperhydricityHyperhydricityHyperhydricity is a physiological malformation that results in excessive hydration, low lignification, impaired stomatal function and reduced mechanical strength of tissue culture-generated plants. The consequence is poor regeneration of such plants without intensive greenhouse acclimation for...
- Somatic EmbryogenesisSomatic EmbryogenesisSomatic embryos are mainly produced in vitro and for laboratory purposes, using either solid or liquid nutrient media which contain plant growth regulators . The main PGRs used are auxins but can contain cytokinin in a smaller amount. Somatic embryogenesis is a process where a plant or embryo is...