Embryo rescue is one of the earliest and successful forms of

in-vitro culture Tissue culture is the growth of tissues or cells in an artificial medium separate from the parent organism. This technique is also called micropropagation. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, such ...

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 Plant breeding is the science of changing the traits of plants in order to produce desired characteristics. It has been used to improve the quality of nutrition in products for humans and animals. The goals of plant breeding are to produce cr ...

, allowing the development of many

interspecific Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organi ...

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

seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosper ...

s 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 ''Phaseolus'' (bean, wild bean) is a genus of herbaceous to woody annual and perennial vines in the family Fabaceae containing about 70 plant species, all native to the Americas, primarily Mesoamerica. It is one of the most economically importan ...

'' and '' Fagopyrum'' embryos and was successful in it , 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 technique Asepsis is the state of being free from disease-causing micro-organisms (such as pathogenic bacteria, viruses, pathogenic fungi, and parasites). There are two categories of asepsis: medical and surgical. The modern day notion of asepsis is deri ...

. 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 dormancy Seed dormancy is an evolutionary adaptation that prevents seeds from germinating during unsuitable ecological conditions that would typically lead to a low probability of seedling survival. Dormant seeds do not germinate in a specified period of ...

* Determination of seed viability * Recovery of maternal haploids that develop as a result of

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins ar ...

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

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

ovule 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'' (or remnant of the megasporangium), and the ...

, or

ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...

culture. Ovule culture or in vitro 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

Embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

s are manually excised and placed immediately onto a

culture medium A growth medium or culture medium is a solid, liquid, or semi-solid designed to support the growth of a population of microorganisms or cells via the process of cell proliferation or small plants like the moss ''Physcomitrella patens''. Differ ...

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 medium Murashige and Skoog medium (or ''MSO ''or '' MS0'' ''(MS-zero)'') is a plant growth medium used in the laboratories for cultivation of plant cell culture. MS0 was invented by plant scientists Toshio Murashige and Folke K. Skoog in 1962 during Mu ...

(MS) and Gamborg’s B-5 media (Bridgen, 1994), the composition of the medium 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. Both plant and animal cells, tissues and organ culture is possible in artificial nutrient medium in controlled laboratory conditions. Many desired products can be obtained through tissue culture like pharmaceutical drugs, vaccines, and monoclonal antibodies.

References

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External links