1. Comparing the Nucellar Growth Index in Megagametogenesis of two ecotypes of Arabidopsis thaliana Heynh in Holl & Heynh Emily Novak, Department of Biology, York College Results Introduction Arabidopsis thaliana (L.) Heynh is an essential model in the study of plant sciences, valued for its rapid life cycle and its easy cultivation (Smyth 1990). Throughout both megasporogenesis and megagametogenesis, the nucellus of the ovule expands with each mitotic division, consuming the surrounding tissue of the hyponucellus and the epinucellus. The nucellar growth index was proposed in order to observe and determine just how much of the tissue surrounding the nucellus is consumed during these stages of ovule growth (Personal communication, J. M. Herr). Methods Statistical analysis Seeds of Arabidopsis thaliana Landsberg erecta and Columbia planted Whole inflorescences collected and fixed in FPA 50 70% ethyl alcohol 24 hours Dissected using Nikon SMZ 1500 dissecting microscope Herr clearing fluid Dehydrated to 100% ethyl alcohol 10 minutes in 75%, 80%, 85%, 90%, 95% Observed under oil immersion using a Nikon Eclipse 80i phase contrast microscope Photographed with a Nikon DS-Ri1 camera Objective The objective of this study is to apply an innovative calculation, termed the Nucellar Growth Index, in order to compare two ecotypes, Landsberg erecta and Columbia, of A. thaliana. Conclusions The tissue making up the epinucellar region is completely consumed by the nucellar region in both ecotypes by the 8- nucleate stage. In both ecotypes of A. thaliana, Landsberg erecta and Columbia appear to have similar overall net growth patterns in regards to the nucellus. When comparing the intermediate stages of nucellar growth, the ecotypes are in fact significantly different. - Landsberg erecta expresses its greatest net growth of the nucellus during the 2-nucleate to 4-nucleate interval. - Columbia exhibited the greatest net growth of the nucellus during the functional to 2-nucleate interval. Future Studies Since this study was the first documented of its kind, the possibilities for future studies are virtually endless and can provide morphologists with yet another feature in which plants can be observed, measured, and possibly even differentiated from one another. Acknowledgements I would like to thank Dr. Smith for his unyielding patience. I would also like to thank Dr. John Herr for his passion of plant morphology which lead to the contribution of the Nucellar Growth Index as well as his insight throughout my research project. Figure 1. Nucellar Growth Profile and Nucellar Growth Index original concept as presented by Dr. J. M. Herr (Personal Communication). Sample sizes were n = 10 for each group and two groups were used to calculate nucellar growth index for each column giving a total sample size of n = 20 for each column (Figures 2-5). Figure 4. Nucellar growth indexes of both A. thaliana ecotypes, Landsberg erecta and Columbia, comparing the functional stage to the 8-nucleate stage of megagametogenesis. Groups are not significantly different as indicated by a paired t-test (two-tailed p = 0.1554). Figure 5. Nucellar growth indexes of intermediate stages of megagametogenesis of the Columbia ecotype of A. thaliana. Sample sizes were n = 10 for each group and two groups were used to calculate nucellar growth index for each column giving a total sample size of n = 20 for each column. Groups are significantly different (p = 0.0030) as indicated by a one-way ANOVA test. Nucellar Growth Index 1 ColumbiaLandsberg erecta Functional v 2-nucleate1.8771.320 2-nucleate v 4-nucleate1.1681.972 8-nucleate v 4-nucleate0.9091.347 1 mean Table 1. Mean Nucellar Growth Indexes of megagametophytic stages in two ecotypes of Arabidopsis thaliana. Figure 3. Comparison of the nucellar growth indexes of intermediate stages of Landsberg erecta ecotype of A. thaliana. Groups were found to be significantly different (p = <0.0001) as indicated by a one-way ANOVA test. Figure 2. Nucellar growth indexes of intermediate stages of megagametogenesis of the Columbia ecotype of A. thaliana. Groups are significantly different (p = 0.0030) as indicated by a one- way ANOVA test. Literature Cited Smyth, David R., John L. Bowman, and Elliot M. Meyerowitz. 1990. Early Flower Development in Arabidopsis. The Plant Cell 2: 755-767