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Insect predation of E. Sandwicensis vs. E. Variegata
Erythrina sandwicensis, also known as Wiliwili, is a member of the legume family (Fabaceae), and is one of several native trees that can be found in Hawaii. As a dicot, its leaves contain many traits that are typical of dicot plants. The Wiliwili produces beautiful flowers that are used to make leis, as well as seeds that are also sometimes used for lei making.
Erythrina sandwicensis grows to about 35 to 45 feet tall, with a diameter of about the same length. The trunk and branches have a few short spines growing on them, becoming less noticeable as the plant gets older. "Erythrina sandwicensis is one of Hawaii's few deciduous native trees. It loses its leaves during the summer in order to conserve water and puts out new leaves in the fall. Each leaf has three round to triangular shaped leaflets. Each leaflet is up to 3 inches long" (http://www2.hawaii.edu/~eherring/hawnprop/ery-sand.htm).
The properties in its leaves that are typical of most dicots include the organization of the tissue layers within the lamina and midrib. From top to bottom, notable tissues found in both the lamina of typical dicots and in that of Erythrina sandwicensis is the adaxial epidermis, palisade mesophyll, spongy mesophyll, and abaxial epidermis.
"Palisade mesophyll is composed of columnar cells that can be one to several layers thick. It is most common on the adaxial side of the leaf where sunlight is usually most abundant. Palisade parenchyma are more efficient for photosynthesis and water retention because of their large surface areas but small intercellular air spaces" (Webb 2002).
"Spongy mesophyll is usually found on the abaxial side of the leaf. It may consist of stellate parenchyma or chains of elongate cells which have large, lateral intercellular spaces. This allows rapid diffusion of gases like CO2" (Webb 2002).
The Midrib provides the principal Vascular Connection to the Stem, with Vascular Organization varying from the Simple (one vascular bundle) to the Complex. The Midrib also provides Structural Support for the Leaf, due to the presence of Collenchyma, Sclerenchyma & Xylem (Webb 2002).
Erythrina sandwicensis is an example of a xerophyte, "a plant of arid regions having xeromorphic characteristics such as hard leaves, spines, and succulence" (Mauseth, 1988). "The term xeromorphic is used to indicate plants that have an anatomy and growth form that are especially adapted to desert conditions, particularly conditions in which water is frequently scarce" (Mauseth, 1988). With the humidity and environment of Hawaii, plants with xeromorphic traits have a much better chance to thrive. Among the characteristics of a xeromorphic plant are "a thick-walled epidermis and hypodermis, covered by a dense, waxy cuticle. Trichomes are typically abundant. These features are selectively advantageous for many reasons. All are effective in blocking excess sunlight. They are also good deterrents against insect feeding and egg laying. Salt glands may be present in many, and the coating of salt may also protect against feeding and sunlight, as well as keeping salts from accumulating in the protoplasm" (Mauseth 1988).
Leaf samples of Erythrina sandwicensis were collected from the campus of the University of Hawaii at Manoa. All samples of Erythrina sandwicensis leaves were taken from the three Wiliwili trees on Maile Way, directly behind Hamilton Library. From right to left, the trees were labeled as Trees A, B, and C.
Sectioning
Sections of the leaf were placed into a fixative antifreeze solution that contained 10% Dimethylsulfoxide, 4% Formaldehyde (w/v), 1% Tween 20 and 0.05 M Sodium Cacodylate. The pH was set at 7.5. The leaf sections were first placed in a vacuum, and then stored at 5 degrees C for approximately 3 weeks. The leaf sections were then mounted on a Reichert-Jung Cryotome machine, and sectioned at 50 microns. These were stained with Toluidine Blue (0.05%). The freezing support medium (Tissue Freezing Medium, Triangle Biomedical Sciences) was diluted with water and removed by blotting prior to staining because it formed a precipitate with the stain. Unstained specimens were mounted in the freezing support medium and viewed without further treatments.
Shown below is the Reichert-Jung Cryotome machine used for cutting the leaf sections for the slides. This image was borrowed from the website of Dr. David Webb.
All microscope images of the leaf sections were taken with a Nikon Coolpix 990 Digital Camera. The leaf sections observed were of the midrib and lamina of Erythrina sandwicensis, and were viewed and photographed at various magnifications as unstained or stained with Toluidine Blue, and viewed in both bright-field and polarized optics. All images were saved on a memory card and later downloaded onto a computer. All image editing was performed using Imaging For Windows and Microsoft Paint.
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Nikon Coolpix 990 Digital Camera
(image from Dr. David Webb) |
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This picture shows the flowers of Erythrina sandwicensis. |
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To the right is a diagram of a typical dicot leaf. Notable structures that are visible and labeled include both the adaxial and abaxial epidermis of the leaf, the midrib, midvein, palisade mesophyll, and spongy mesophyll. From this, we can see its similarities to the leaves of Erythrina sandwicensis. This slide was borrowed from Dr. David Webb's website. |
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Shown here is a picture of a healthy, mature, whole leaf specimen of Erythrina sandwicensis. Sections were taken from this leaf and used for observation. Of the three trees located outside of Hamilton Library, this tree was located on the far right. |
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A heavy layer of pubescence can be seen on the abaxial surface of the juvenile leaves. This may be one xeromorphic trait that this plant exhibits. |
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This is a labeled cross-section of the lamina of Erythrina sandwicensis. We can see how similar it is to that of a typical dicot. |
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Similar to the last slide, this image emphasizes the dense layer of palisade mesophyll, the thick adaxial epidermis, and the branched trichomes present. The latter two traits show the xeromorphic adaptations of Erythrina sandwicensis. |
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Close-up view of the abaxial surface of Erythrina sandwicensis. This image shows the compartmentalization features of the leaf, as well as the branched trichomes present. |
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This slide shows again a clear picture of the different tissue layers in the lamina of Erythrina sandwicensis. Also clearly shown in this image is the degree of compartmentalization in the leaves. Image borrowed from Dr. David Webb's website. |
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An image of the lamina stained with Toluidine Blue. The cells that stained red indicate the presence of lignin. |
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An image of the lamina using polarized optics. This image helps to show the detail of tissues like the epidermis and compartmentalization. |
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Cross-sectional view of a branched trichome on the abaxial surface. Image borrowed from Dr. David Webb's website |
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Secretory trichome, were found on the abaxial surface of Erythrina sandwicensis. |
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An image of the unstained midrib, showing the vascular bundles. |
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An image of the midrib, viewed with cross-polarizers. The cells showing high bi-refringence indicate that they are highly organized. |
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An image of the lower midrib, stained with Toluidine Blue. This helps to easily distinguish tissues like xylem and phloem. The waxy cuticle is another xeromorphic trait. |
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From the observations and results found, it was determined that the leaves of Erythrina sandwicensis are very typical to that of a normal dicot. The lamina and midrib showed all of the typical tissues one would expect to find in a dicot leaf, including a thick adaxial and abaxial epidermis, a palisade mesophyll, spongy mesophyll, and vascular bundles.
Endemic to Hawaii, the leaves of Erythrina sandwicensis also showed several xeromorphic traits. The first of these xeromorphic traits was the presence of heavy pubescence on the abaxial surface of the immature leaves, and the presence of branched trichomes on the abaxial surface of mature leaves. These can serve purposes of helping the leaves to retain its water and moisture, allowing the leaf to be more resilient in the excessively dry conditions of the external environment. Another xeromorphic trait of Erythrina sandwicensis was the presence of a thick epidermis and waxy cuticle. These xeromorphic traits mentioned serve to protect the leaf from excess sunlight, and from insect feeding and egg laying.
Compartmentalization was also found to be very prominent on the abaxial surface of these leaves. Compartmentalization is a very useful feature to protect the leaf from excess damage. The presence of these compartments allow the leaf to survive, even if substantial damage has been done to an adjacent part of the leaf. With the vital tissues of the leaves separated into its "own" region, the leaves become more resilient to damage and death.
Among other interesting things found in the leaves was the presence of secretory trichomes. It was previously assumed that the leaves of Erythrina sandwicensis did not contain secretory trichomes. However, after careful observations, pictures were taken of these structures and sent to an authority on secretory trichomes, Dr. Fahn, from Israel. In his reply, he confirmed the fact that these structures that we had found in the leaves of Erythrina sandwicensis were, in fact, secretory trichomes!
Mauseth, J. D. (2002). Plant Anatomy. University of Texas, Austin: The Benjamin/Cummings Publishing Company, Inc.
HNPPD website. www2.hawaii.edu/~eherring/hawnprop/ery-sand.htm. College of Tropical Agriculture and Human Resources - University of Hawaii at Manoa. "Hawaiian Native Plant Propagation Database: Erythrina sandwicensis."
Webb, D. T. (2002). http://www.botany.hawaii.edu/faculty/webb/BOT410/Leaves/wiliwili.htm. Dr. David Webb's Botany 410 lecture website - University of Hawaii at Manoa. "Wiliwili - Erythrina sandwicensis".
