Lindsay Johnson and Dr. Eric N. Jellen, Agronomy and Horticulture
The motivation behind this project involves the desire to assign diploid oat linkage groups to specific locations on the physical diploid oat chromosome (1). In order to accomplish this, a stock of monosomic oat plants is required. Monosomic plants are defined as plants that are chromosome deficient. To achieve monosomic lines, two unrelated parent plants are crossed through artificial pollination, followed by backcrosses of the progeny with one of the parent plants.
In the case of my project, three different crosses were made using a synthetic hexaploid oat plant. This synthetic plant, derived from G. Ladizinsky at the Hebrew University of Jerusalem, served as the female while either Eastern gamma grass (tripsicum) or corn served as the male. Because these two plants are unrelated, artificial pollination could result in monosomic plants.
This procedure involved the removal of the oat anthers, followed by artificial pollination using corn or gamma grass pollen. One to two days following pollination the oat plants were treated with an injected solution containing the plant hormone 2,4-D to encourage embryo growth. Ten days following pollination, the embryos were rescued. The occurrence of an oat embryo following this procedure is incredibly rare. Of the 1260 crosses conducted approximately 25 viable embryos were been obtained. Of these viable embryos, only one of these embryos matured into an actual plant (Fig.1).
Several rescued embryos lost viability due to a fungus contamination of the petri dishes in which the embryos were housed. This problem was solved by the use of a plant preservative mixture known as PPM. By shaking embryos in a highly concentrated solution of PPM for 5 minutes prior to their placement onto petri dishes, fungus contamination was eliminated.
The development of even one mature plant is very exciting because it is such a rare occurrence. The next step is to take a root tip sample and test to see if it is indeed haploid. Needless to say, this project will require continued research. If this plant is, in fact, haploid, it will be grown until it reaches reproductive maturity. At that point, the haploid plant will be backcrossed with its synthetic hexaploid parent. The resulting offspring will be monosomic (missing one chromosome). With the development of these monosomic lines, it will then be possible to use their unique genetic make-up in order to achieve the ultimate goal of identifying the specific sites of linkage groups on the actual diploid oat chromosome.
References
- Fox, S.L., E.N. Jellen, S.F. Kianian, H.W. Rines, and R.L. Phillips. 1999. “Chromosomal organization of oat RFLP linkage groups using an F1 monosomic series”. Theoretical and Applied Genetics. (submitted)
- Special thanks for research assistance to Jeremy Beard, Agronomy and Horticulture