Comparing the Nucellar Growth Index in Megagametogenesis of two ecotypes of
Arabidopsis thaliana Heynh in Holl & Heynh
Emily Novak, Department of Biology, York College
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).
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).
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.
Figure 1. Nucellar Growth Profile and Nucellar Growth Index original
concept as presented by Dr. J. M. Herr (Personal Communication).
Methods
Whole inflorescences
collected and fixed in
FPA50
Seeds of Arabidopsis
thaliana Landsberg erecta
and Columbia planted
Results
Table 1. Mean Nucellar Growth Indexes of megagametophytic stages in two
ecotypes of Arabidopsis thaliana.
24 hours
Dehydrated to 100% ethyl
alcohol
70% ethyl alcohol
10 minutes in 75%, 80%,
85%, 90%, 95%
Herr clearing fluid
Dissected using Nikon SMZ
1500 dissecting
microscope
Photographed with a
Nikon DS-Ri1 camera
Observed under oil
immersion using a Nikon
Eclipse 80i phase contrast
microscope
Functional v 2-nucleate
2-nucleate v 4-nucleate
8-nucleate v 4-nucleate
1mean
Nucellar Growth Index1
Columbia
Landsberg erecta
1.877
1.320
1.168
1.972
0.909
1.347
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 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.
Conclusions
• The tissue making up the epinucellar region is completely
consumed by the nucellar region in both ecotypes by the 8nucleate 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.
Literature Cited
Measurements were taken of epinucellus, nucellus, and
hyponucellus and applied to the Nucellar Growth Index
calculation:
eM + L′ − L + hM
(eI + hI)
Statistical analysis
Smyth, David R., John L. Bowman, and Elliot M. Meyerowitz. 1990.
Early Flower Development in Arabidopsis. The Plant Cell 2:
755-767
Future Studies
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 oneway ANOVA test.
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.
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.