Elementary plant Biochemistry and Biotechnology (2+1)

Embryo culture

 
• Embryo culture is the sterile isolation of an immature or mature embryo in vitro with the goal of obtaining a viable plant.


Types

1. Culture of immature embryos originating from unripe seeds, that is mainly to avoid embryo abortion with the purpose to produce a viable plant.
2. Culture of mature embryos derived from ripe seeds.
 
Factors affecting the success of embryo culture

1. Genotypes
2. Developmental stage of the embryo at isolation
3. Growth conditions of the mother plant
4. Composition of the nutrient media
5. Light
6. Temperature
 
Practical applications

1. Elimination of inhibitors of seed germination
2. Shortening breeding cycle
3. Overcoming self sterility of seeds e.g. Musa bulbisiana and tubers crops: Colocasia esculenta & C. antiquorum.
4. Seed Testing: Rapid means of determining viability of particular lot of seeds eg. seeds of conifers, shrubs, vines and fruit trees.
5. Prevention of embryo abortion in early ripe fruits e.g. Peach, cherry, apricot, plum.
6. Prevention of embryo abortion as a result of incompatibility (embryo rescue). E.g. In interspecific (Phseolus, lily flex, cotton, tomato, rice and barely), intergenic (Hordeum x Seale and Triticum x Seale. ) crosses and crosses between diploids and tetraploids (barley and Rye).
7. Vegetative propagation. E.g. In Gramineae and Coniferae embryos are often used as a starting material.
8. Other applications. To study fundamental problems in experimental embryogenesis. Host pathogen interaction. e.g. formation of ergot by infection of rye (Phaseolus vulgaris) embryos by claviceps purpurea and fusarium wilt of seedlings. In latter case, incorporation of fungal toxin fusaric acid into culture medium interfere with water uptake by germinated embryos of rye and induce characteristics wilting of embryonic leavesCultured embryos have been used as test objects to evaluate the mutagenic ability of irradiated substrates on living tissues. For this embryos of certain cereals were planted on X-irradiated nutrient medium for evaluation.
 
Embryo rescue

• Distant crosses may fail due to one or more of several reasons such as inability of pollen to germinate, failure of pollen tubes to grow or perhaps more commonly degeneration of endosperm. When embryo fails to develop due to endosperm degeneration, embryo culture is used to recover hybrid plants. This is called as hybrid rescue through embryo culture. Some recent examples are the recovery of hybrids from Hordium vulgare X Secale cereale, Triticum aestivum X Agropyron repens, H. vulgare X Triticum aestivum etc., In case of Triticale rare combinations between Triticale and Secale develop viable seeds.
  


• But most of the tetraploid and hexaploid wheat carry two dominant genes, Kr1 and Kr2, which prevent seed development in crosses with Secale. The majority of the hybrid seeds are small, poorly developed and show very poor germination. Further, seeds are obtained from only 5-10% of the florets pollinated. The recovery of hybrid seedlings is much greater (50-70%) when embryos from 10-14 day old caryopses are removed and cultured on a suitable medium.