eM; L’; hM eI L hI

Megasporogenesis and Megagametogenesis of Thlaspi arvense L. and Measurement of the Nucellar Growth Index (NGI) and Nucellar Growth Profile (NGP)

Ryan King Department of Biological Sciences, York College of Pennsylvania

Introduction•Megasporogenesis and megagametogenesis were studied for Thlaspi arvense L. . This data will be added to other morphological data already in the literature for future phylogenetic interpretations within the Brassicaceae family.

•Megasporogenesis is the study of the cells that undergo meiosis in the nucellar tissue of the ovule. Megagametogenesis is the study of the surviving spores from megasporogenesis and the subsequent mitotic divisions leading up to the embryo-sac.

•A plant tissue clearing technique, developed by John Herr, with some modifications since its publication in 1971 in the American Journal of Botany was used to prepare the flowers for dissection. All of the images found for this study were obtained using this clearing technique.

•The Nucellar Growth Index and Nucellar Growth Profile are recently developed techniques to measure the nucellar tissue as the ovule progresses through the megasporogenesis and megagametogenesis stages. This is yet another quantitative value that can be used to note differences between and among species being compared phylogenetically.

•This common weed, T. arvense, is being studied for the first time, recording the features mentioned above.

•This study adds data, not available at this time, to contrast ovule developmental stages along with the new NGI and NGP against similar data of other closely related genera within the Brassicaceae family.

Discussion•The Herr fluid clearing technique worked well so that I could see and capture the stages of megasporogenesis and megagametogenesis. I was able to clearly see the nucellus which allowed for the measuring of the Nucellar Growth Profile (NGP) and Nucellar Growth Index (NGI). The NGI and NGP are both unpublished methods of measuring the nucellus as it is used up during the development into the embryo-sac and eventually the seed.

Acknowledgements I would like to thank Dr. Bruce Smith for his help and support throughout this process

as well as Team Ahhsome for their support throughout these years.

Objectives•Use the Herr clearing fluid (1971) to photograph the stages of Megasporogenesis and megagametogenesis in T. arvense

•Use Dr. Herr’s new method of measuring (Nucellar Growth Index and Nucellar Growth Profile) to obtain quantitative data

MMC Dyad

Tetrad 2-Nucleate

4-Nucleate 8-Nucleate

NGI= 6.09 (n=5)

NGP= 7.74; 4.06; 2.66 (n=5)

ResultsObtain buds from T.

arvense and place into fixative 50FPA

Transfer buds from 50FPA to 70% ETOH after 24 hours

After 24 hours transfer to dehydrations series, 80%-

100% ETOH

After 24 hours transfer to Herr Fluid

Dissect ovaries to remove ovules on Raj

slide

Use Phase Contrast Microscopy to take pictures

and measure the NGI and NGP

Measure NGP and NGI of MMC and 8-nucleate stages

NGP:

eM + (L’+L) + hM (eI + hI)

NGI:

Future Studies•There are other species of Thlaspi in the area and a study similar to this one would provide more data as to the phylogenetic connection between the species.

Methods

Literature CitedHerr, John 1971. A New Clearing-squash Technique for the Study of Ovule Development in Angiosperms. American Journal of Botany 58: 785-790

MMC with measurements

8-Nucleate with measurements