Presentation is loading. Please wait.

Presentation is loading. Please wait.

Results Comparison Among Selected Megagametophytic Stages of Arabidopsis thaliana (L.) Heynh Landsberg Erecta and Colombia Ecotypes Jaime Stum Department.

Similar presentations


Presentation on theme: "Results Comparison Among Selected Megagametophytic Stages of Arabidopsis thaliana (L.) Heynh Landsberg Erecta and Colombia Ecotypes Jaime Stum Department."— Presentation transcript:

1 Results Comparison Among Selected Megagametophytic Stages of Arabidopsis thaliana (L.) Heynh Landsberg Erecta and Colombia Ecotypes Jaime Stum Department of Biological Sciences, York College of Pennsylvania Introduction Arabidopsis thaliana, a member of the mustards (Brassicaceae family), is a small flowering plant that is important for basic research in genetics and molecular biology. Advantages such as having a rapid life cycle and a small genome that has been sequenced also make Arabidopsis a model organism in plant biology. Ovules are structures contained within the carpels of flowering plants. In A. thaliana, they are attached to the placenta on both sides of the septum and are the site of megasporogenesis and megagametogenesis (Maheshwari 1950). After fertilization, the ovules develop into seeds. An essential component of an ovule is a nucellus which develops the megasporangium. The megasporangium consists of both vegetative and sporogenous cells; two integuments that surround the nucellus, and the funiculus, that attaches the ovule to the placenta. Within the nucellus, a sporogenous cell(s) undergoes meiosis, megasporogenesis, and produces four spores. These four haploid cells, a tetrad, result in only one surviving. The surviving cell or functional spore usually undergoes three mitotic divisions thus producing a mature embryo sac of eight nuclei (Smith 1975). The objectives of this study were to 1) re-measure a previous student’s data set of A. thaliana Lansberg ecotype, and (2) to do a comparison of the re-measured data set with that of another student’s data set of A. thaliana Colombia Ecotype for statistical significance. The hypothesis for this study is there is no difference between the stages of the two ecotypes. Seeds were planted, floral buds were collected approx. 2 weeks after planting and fixed in FPA 50 * for a minimun of 24 hours. Collections continued for 6 weeks and were stored in 70% ETOH. Floral buds were serially dehydrated to 100% ETOH (80, 85, 90, 95, 100%) for a minimum of 10 minutes per concentration. Floral buds were placed in the Herr Clearing Fluid* where they remained for at least 24 hours before dissection. Floral buds were placed in a glass planchet, immersed in HCF to gain access to the ovary. The Nikon SMZ-1000 stereo zoom dissecting microscope was used for placement of ovaries on Raj slides and all dissections. Methods *Formalin, Proprionic acid and 50% ETOH *lactic acid, chloral hydrate, phenol, clove oil, xylene, 2:2:2:2:1 by weight Ovules were viewed under oil immersion using the Nikon E600 phase contrast microscope. Images were captured with the Nikon DXM-1200F digital camera and measurements were taken using the Nikon ECLIPSENET software. Results (con’t.) Megagametogenesis for A. thaliana Landsberg Ecotype Lengths and widths: The values for the size, mean, and 95% confidence interval decrease from the Tetrad through the 2-Nucleate stage, then increases with the largest values in the 4-Nucleate stage. Megagametogenesis for A. thaliana Colombia Ecotype Lengths and widths: The Colombia ecotype’s values are similar to the Landsberg Ecotype except for the decreased from the Tetrad to the FM but then increased for each of the following stages. Discussion Analysis of the results indicates variation in measured values of length and width between the successive stages of the two ecotypes that were compared. The amount of increase or decrease between successive stages is detected within the mean values of those stages (Smith 1975). The means would be expected to increase with each advancing stage as seen with the Colombia ecotype. Of all the stages in megasporogenesis, the tetrad stage has the largest values. And, this would be expected since the tetrad complex is made up of 4-linear cells each of which approximates the size of the sporogenous MMC from which it was derived. The decrease in mean growth from the tetrad to the FM is due to the three micropylar cells of the tetrad degenerating and the chalazal cell enlarging to become the functional megaspore. At this point growth should begin to increase as megagametogenesis undergoes three mitotic divisions. P values of each of the three megasporogenesis stages and the three megagametogenesis stages of both Landsberg and Colombia Ecotypes were compared for both width and length. Only the 2-Nucleate and 4- Nucleate width measurements were not significant. These results suggest that the hypothesis is not supported due to the differences between the other stages. Morphological differences of the diploid sporophyte have been noted among the many Ecotypes of A. thaliana. A difference between megagametophyte stages within and among species has not been recorded until this study. Detected differences in width and lengths of this reduced megagametophyte can now be added to those previously noted recorded differences in the morphology of the sporophytic component of these two Ecotypes. Further measurements are suggested for both ecotypes to see if the patterns of growth within the gametophytic stages are consistent with those recorded here. Literature Cited Maheshwari, P. 1950. An Introduction to the Embryology of Angiosperms. Tata Mcgraw-Hill, New Delhi. Smith, B.B. 1975. A Quantitative Analysis of the Megagametophyte of Five Species of Cornus L. American Journal of Botany. 62(4):387-394. Acknowledgements: I would like to thank Dr. Smith for his help and guidance throughout my research. I would also like to thank Dr. Rehnberg for his help with the statistical analysis. Megasporogenesis for A. thaliana Landsberg Ecotype Lengths and widths: The values for the size, mean and the 95% confidence intervals of the Landsberg ecotype of A. thaliana show great variation in the growth between the stages. The values for the Dyad are smaller compared to the MMC stage and Tetrad stage, which shows the largest values of the three stages. Megasporogenesis for A. thaliana Colombia Ecotype Lengths and widths: The values for the size, mean and the 95% confidence interval of the Colombia ecotype increase from the MMC through the Tetrad. A. Example of length and width measurements using ECLISPENET software, B. Megaspore mother cell (MMC), C. Dyad stage, D. Tetrad stage, E. Functional megaspore (FM), F. 2-Nucleate stage, G. 4-Nucleate stage. B CD FG A E Figures 1-4. The ovules were measured at each stage. The boxes represent the means and the whiskers show the range. Figures 1 and 2 show the selected stages in the A. thaliana Landsberg ecotype. Figures 3 and 4 represent the Colombia ecotype.


Download ppt "Results Comparison Among Selected Megagametophytic Stages of Arabidopsis thaliana (L.) Heynh Landsberg Erecta and Colombia Ecotypes Jaime Stum Department."

Similar presentations


Ads by Google