Introduction:• Arabidopsis Thaliana, a member of the mustard (Brassicaceae) family was first described by Johannes Thal in the Harz Mountains during the 16th century.

•It has attained the distinction of one of the most popular plants for both genetic and organismal research.

•A. thaliana was the first plant to have its full genome mapped.

•The physical differences between the now more than 800 known ecotypes have been studied since Laibach in the 1930’s (Robbelen 1965).

•There has however never been significant research conducted concerning measured size differences of the megagametophyte in the haploid generation of these different ecotypes.

Examination and Comparison of the Megagametophytic life cycle for mean length and width for two ecotypes of Arabidopsis Thaliana

Shane Lohss and Bruce Smith

Functional cell 2-nucleate

4-nucleate 8-nucleate

Mean Width

Mean Length

L + WL / W

18th division

Methods:

Results:

Objectives :To study the early developmental stages of A. Thaliana specifically the development of the megagametophyte in order to determine if the physical differences among ecotypes apparent in developed diploid plants are apparent in the haploid generation. Mean lengths and widths of the gametes were recorded and placed into a Fibonacci summation for interpretation.

Hypothesis:It is believed that there will be no significant differences between the developments of the two ecotypes which would be indicated by both ecotypes achieving a Phi value of 1.6180339 at the 18th division meaning mean width is 10-50.5% of mean length.

References:Herr Jr, John. 1967.On The Nature of Variation. Phytomorphology. Volume 17Maheshwari, Panchanan. 1950. An Introduction to the Embryology of Angiosperms. New York.Robbelon G. 1965. The Laibach standard collection of natural races of Arabidopsis. Inf. Serv. 2: 36-47Smith, Bruce. 1973. The Use of a New Clearing Technique For The Study Of Early Ovule Development, Megasporogenesis, and Megagametogenesis in five species of cornus L. American Journal of Botany 60(4) 322-338. Smyth, David. Bowman, John. Meyerowitz, Elliot. 1990. Early Flower Development in Arabidopsis. The Plant Cell V. 2, 755-767.Smith, Bruce. Johnson, L. 1980. Early Ovule Development, Megasporogenesis and Megagametogenesis in Solidago Graminifolia Var. Nuttallii and Solidago Canadensis Var. Canadensis. American Journal of Botany 67(5): 612-618.

Discussion:Based upon the results of the Fibonacci sequence all stages for both ecotypes achieved the Phi value of 1.618 by the 11th division and 1.6180339 by the 18th division. Therefore the mean width equals 10-50.5% of mean length and based upon the numerical data there is no significant difference between the haploid generations of the two ecotypes. While both of these ecotypes shared the typical mean length/width ratio for angiosperms it is possible that if the plants were grown outside a difference could occur as observed by John Herr when working with Plaseolus aureus. Despite the lack of quantitative variation between the ecotypes there was variation in the location of the nuclei between different ovules regardless of ecotype most notably in the 4-nucleate stage. Most of the gametophytes at this stage either had all four nuclei relatively linear or had the nuclei in two parallel groups of two separated with a vacuole between them. However examples like the one shown were observed for both ecotypes with one group of two being perpendicular to the other two along with a major difference in width of the ovule between the two pairs. While these two examples of A. thaliana lack a discernible difference there are still several hundred more ecotypes left to be observed and possibly some of them will yield signs of variation.

Two ecotypes of A. thaliana were acquired from the Arabidopsis Biological Resource Center at OSU and grown.

cs 1380 from Libya elevation 100M ASL cs 57924 from Tajikistan elevation 3400M ASL

Flowers were removed fixed in FPA 50 and dehydrated in

an ethanol series

The mean length and width values were used in a Fibonacci Summation

Flowers were cleared in Herr Clearing Fluid

Ovules were removed and observed in order for the lengths and widths of ten examples of each stage to be

recorded