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Anthocyanin content of Apocynum cannabinum in variable light environments

Lauren Guggina and Dana Dudle

Biology Department and Science Research Fellows Program, DePauw University

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Lauren Guggina 's report (9.6 MB)

Abstract

Apocynum cannabinum growing in the Quarry Bottom.
This plant species is ideal to study because it grows in a variety
of habitats and varies in a number of phenotypic traits in
response to environmental conditions.

Apocynum cannabinum is an herbaceous perennial native to the midwest that grows in variable environments. A cannabinum contains defensive cardiac glycosides, found in the milky substance stored in its stem and leaves. A unique feature of Apocynum cannabinum is that its stem and leaf color varies from green to deep red due to varying levels of anthocyanins in these parts. Anthocyanins are the pigments in plants that give them their red, purple, and blue coloring. Anthocyanins have a variety of purposes for different plants, including photoprotection, osmotic balance, and protection of photolabile defensive compounds. We studied A. cannabinum in two distinct areas at the nature park: the abandoned quarry where stress factors included drought, poor substrate and a limited water supply, and the forested edge of the parking lot where conditions were less stressful.

We examined the relative anthocyanin content of the plant's stems and leaves in relation to light intensity. We designated plants as "sunny" or "shady" according to visual observation of their surroundings. Irradiance was then measured with a light meter at three hour intervals for three different days. After light readings were taken for each plant, we collected stem and leaf samples. Anthocyanins were extracted using acetated methanol, using a standard procedure. The anthocyanin content was assessed using a uv spectrophotometer. The readings for the samples were standardized by dividing the absorbance by the mass of each sample.

Apocynum cannibinum contains defensive cardiac
glycosides.  These are found in the milky substance
stored in its stem and leaves.  This substance protects
Apocynum from many herbivores.

There was a significant positive relationship between light intensity and stem anthocyanin content. Anthocyanin content varied significantly between sunny and shady stems but not between sunny and shady leaves. Anthocyanin content was also significantly higher in the stems than in the leaves. Although we did not find a relationship between light and anthocyanin content, there were varying amounts of pigment amongst the leaves of individual plants. Interestingly, in A. cannabinum the anthocyanins in the leaves seemed to be concentrated in the vascular tissue. A. cannabinum may protect its defensive cardiac glycosides or some other vital photolabile compound with anthocyanins. Additionally, anthocyanins could help the plant deal with osmotic stress.

Investigating the presence of anthocyanins in A. cannabinum gives insight into what makes this plant fit for primary succession. Although we found significant results relating stem anthocyanins to light intensity, in order to get more definite results, more extensive research should be done. There are many environmental variables and stresses that A. cannabinum experiences in the quarry. Anthocyanins may be helping to alleviate the stress drought, poor substrate, and limited water availability. In the future, these variables should also be measured in comparison to anthocyanin levels.

Lauren Guggina collecting data on light intensity.