Weathers, Pamela J.
Artemisinin, a sesquiterpene lactone, produced in hairy roots of Artemisia annua contains a rare endoperoxide bridge that is sensitive to peroxidase (POD). Peroxidases are involved in the growth, development, and defense responses of plants and exist in many isoforms. Not all isoforms necessarily degrade artemisinin. There are two main types of peroxidases found in A. annua: ascorbate peroxidase (APX), a Class I peroxidase, and guaiacol peroxidase (GPX), a Class III peroxidase. Using histological assays of the root surface in the matric region, APX was the dominant POD whereas GPX was dominant in the root tip. In cross sections, APX was dominant in the cortex whereas GPX was more prevalent in the stele. Where lateral roots emerge, there is mainly GPX activity but little APX activity. Border cells, released from the root tip, showed APX and GPX activity. Peroxidases were also assayed in root extracts and culture media from late lag phase, mid log phase, and early stationary phase. Root extracts had an 80 fold higher APX activity than GPX activity; culture media showed a three times higher APX than GPX activity. Both APX and GPX activity increased in [sic] during the culture period. APX had a 6.5 times increase between inoculation compared to the rest of the culture period. GPX activity increased linearly as culture aged. Artemisinin content (mg/g DW) is known to be higher in the lag phase of roots, declining with culture age. These and other data suggest that some peroxidases may degrade artemisinin whereas other peroxidase isoforms may assist in the production of artemisinin.
Worcester Polytechnic Institute
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Biology and Biotechnology