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Apocynum cannabinum: genetic variation in anthocyanin production

Erica Ross, Allison Barnes, and Dana Dudle
Biology Department and Science Research Fellows Program, DePauw University
Summer 2006

Anthocyanin is a water-soluble pigments responsible for red, blue, and purple coloring in plants.  Anthocyanin does not undergo photosynthesis like chlorophyll but can act as an antioxidant by absorbing wavelengths of light that chlorophyll does not.  Apocynum cannabinum plants produce anthocyanin in their stems.  Apocynum plants in the DePauw Nature Park vary in anthocyanin expression, displaying stems ranging from green to dark red.  High light intensity and other environmental stresses increase the production of anthocyanin in some plant species, indicating that there may be adaptive value to this trait under stressful conditions.  Our goal was to investigate the effect of light intensity on production of anthocyanin in Apocynum and to investigate the extent of genetic variation within the population.

We manipulated light intensity using shade cloth in an outdoor experimental garden.  We planted seeds from 13 maternal families of Apocynum plants; 218 plants were exposed to a full sun environment and 100 plants were placed in 60 percent shade.  We used a spectrophotometer to measure light reflectance and pigment production of each plant.  We measured morphological characteristics of each plant, including the number of branches and nodes. 

Results and Discussion
Both light intensity and maternal family affected the growth rate and morphology of the plants. Sun plants produced more branches and more nodes on the main axis than shade plants. Anthocyanin production was higher in sun plants than shade plants.  There was significant variation among maternal families in pigment production, indicating that genetic variation exists in the population.  Maternal families also varied in the magnitude of their response to changes in light intensity.  Future work should address the mechanisms by which families vary, and whether the genetic variation for pigment production and sensitivity to light intensity is related to increased fitness in variable environments.