|Jeyaretnam, Ben - DEPT. OF HORT. UNIV. GA|
|Phatak, Sharad - COASTAL PLAIN EXP. STN.|
|Wetzstein, Hazel - DEPT. OF HORT. UNIV. GA.|
Submitted to: Journal of Horticultural Science and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 19, 1999
Publication Date: September 16, 1999
Citation: Jeyaretnam, B., Levi, A., Phatak, S.C., Wetzstein, H.Y. 1999. Changes in growth, water content and protein reflect embry0 development in pecan (carya illinoinensis). Journal of Horticultural Science and Biotechnology. 74:315-320. Interpretive Summary: Pecan is an important nut crop grown mainly in the southeastern United States. In recent years elite pecan trees with superior performance and yield have been developed. However, the propagation of genetically identical sister trees from an elite tree is slow and requires several years. Thus, experiments were conducted to develop a rapid propagation procedure that would save significant time and money in nursery production of pecan trees. We conducted experiments to produce pecan plants on a medium in a test tube using a procedure called somatic embryogenesis. This procedure involves a piece of tissue that is taken from the plant and placed on a medium that contains a hormone. The hormone causes the cells in the plant tissue to divide and form new embryos. These embryos are called somatic embryos because they are formed from non-reproductive (non-sex) cells. In contrast, seed embryos are formed from reproductive (sex) cells following pollination of the flower. In our experiments we found that it is possible to treat a tissue of pecan with hormones and induce it to form a somatic embryo on a medium inside a tube (in vitro). However, it is very difficult to convert these embryos to plants because they do not follow normal development like the seed embryo. Thus, in order to be able to convert the somatic embryos to plants, we first must have a through understanding of the events that take place during the development of the pecan seed embryo. The present study thoroughly describes the events that take place during the development of the pecan seed embryo. This information will enable us to simulate these events during the development of somatic embryos and readily convert them to plants.
Technical Abstract: The morphology, fresh and dry weights, and water content of pecan [Carya illinoinesis (Wangenh.) K. Koch] embryos were studied for three years, and soluble and insoluble protein profiles characterized in trees grown in the southeastern United States (Watkinsville, GA). Embryo development was divided into histodifferentiation, cotyledon (Cot), maturation (Mat), and post-abscission (PA) phases. Embryos became macroscopically visible at 97 days post pollination (DPP), and developed through Cot and Mat stages for 20 and 32 days, respectively. Embryo fresh and dry weights increased rapidly during Cot and Mat stages, and ceased upon ovule abscission. Water content declined during the same developmental period, with sharp declines during Mat and PA. The Cot stage was associated with expression of soluble proteins and in later stages with insoluble proteins. Seasonal variations in embryo development were documented over a three-year period. Percent water content and protein profiles were useful parameters for characterizing and defining the relative age of embryos during pecan fruit development and were more reliable than chronological staging.