Analysis of the morphology and function of reproductive structures in Acanthus mollis


Members: Frank, Allison, Jessica, Madhara, Emily

Introduction
Acanthus mollis (A. mollis), commonly known as Bear's Breeches or "Oyster Plant", is a herbaceous perennial plant with an underground rhizomes. The plant is native to Mediterranean region from Portugal and northwest Africa east to Croatia and it is one of the earliest cultivated species.

Flower structure
The flowers of Acanthus mollis are white in colour and are covered by leaves on either side forming a cup shape. This makes it most suitable to be pollinated by bees and insects as the cup around the flower provide cover for pollinators, allowing them to stay there for an extended amount of time. Pollen grains that are expelled can easily be stopped by the leaves which make it easy to rub onto insects as they look for nectar inside the flower. This also reduces energy expenditure as less pollen would be lost so a lower amount of pollen would be sufficient for reproduction. The flowers are located all around the stalk to allow access from all directions. The stalk is very hard with bark to support the plant and allow it to stay upright in the dry season.

flower 2.jpg
flower 2.jpg

Figure 1: photograph of the flower of Acanthus mollis showing the flower being covered by leaves on either side. Scale bar = 20 mm.

dissect 2.jpg
dissect 2.jpg

Figure 2: photograph of the stamen and ovule from Acanthus mollis showing the white pollen hanging off the anther. The ovule was dissected along the bilateral plane. Scale bar = 5 mm.

caliper 1.jpeg
caliper 1.jpeg

Figure 3: photograph showing the use of calipers to measure the size of petals in Acanthus mollis.


Table 1: comparison of the petal width and style length measured using calipers as well as number of stamens per flower in A. mollis.
Replicate
Petal width (mm)
Style length (mm)
Number of stamens
1
13.9
23.15
5
2
12.3
18.4
4
3
7.95
24
4
4
10
23.4
4
Average
11.04
22.24
4.25
Standard deviation
2.61
2.58
0.5

The mean petal width was 22.64 mm which was not particularly large. Possible reasons for this may be the limit water loss and energy usage. This may be specifically important for A. mollis as it has leaves on both sides of the flower so having larger flowers would require it to increase leaf sizes on both sides. This may be studied further by mutating the gene responsible for petal size and analyzing the effects of this on the plant's ability to survive.

Pollen
The pollen from Acanthus mollis are white grains and the sizes are between 50 to 100 ┬Ám. Their small sizes makes it very easy for them to be dispersed as well as rubbing easily onto insects or bees which then disperse the pollen. Despite their small size, the pollen grains are unlikely to be carried by wind as the presence of leaves above the flower would trap pollen that are released but any pollen that does not get trapped by the leaf can easily drift away due to their small size.

pollen 0.jpg
pollen 0.jpg

Figure 4: light microscope image of pollen from Acanthus mollis, viewed under 40x objective.The pollen was stained onto a 2 mm by 2 mm square of fuchsin gel.

The pollen shown in the above image are likely to be in their immature stage as the different cell types such as generative cell and tube cells could not be seen.

Nectar
Acanthus mollis contain small amounts of nectar deep inside its flower which forces pollinators to reach deep inside the flowers in order reach the nectar. This maximizes the amount of pollen taken up by pollinators as well as maximizing the probability of pollen from other flowers carried by pollinators being transferred to the style during the process which results in fertilisation.

ovule 2.jpg
ovule 2.jpg

Figure 5: photograph of a dissected section of the ovule and stamens of A. mollis showing the location of nectar deep inside the flower near the ovary.

Table 2: calculation the concentration of sucrose in nectar extracted from A. mollis using a refractometer. The nectar was extracted using capillary tubes and diluted with de-ionised water before the refractometer readings were taken.
Refractometer reading (%)
X Dilution
% Brix
2.3
10
23
0.2
100
20
13.0
2
26
3.3
10
33
2.0
15
30

average
26.4

standard deviation
5.22
Nectar extracted from A. mollis had a mean of 26.4% sucrose concentration which was fairly high. The high sucrose concentration makes it especially attractive for pollinators and despite it being buried deep within the flower, the high sugar content will still attracts many pollinators.




References

School of Biological Sciences (2012) Living Systems BIOL1002 Laboratory Manual 2012. pp. 56-62, University of Sydney, Sydney.

iGarden Pty Ltd (2012) Acanthus mollis(online) iGarden Pty Ltd. [accessed 17/10/2012] at http://www.igarden.com.au/plant-type.jsp?t=Acanthus

Ryan, S (2009) Fact Sheet: Acanthus mollis (online) ABC Australia. [accessed 17/10/2012] at http://www.abc.net.au/gardening/stories/s2621456.htm