Submitted to: Pesticide Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2001
Publication Date: 1/1/2002
Interpretive Summary: Plant lignans such as podophyllotoxin, alpha-peltatin, beta-peltatin and their glucosides can act as herbicides by inhibiting root growth. We tested a series of these lignan natural products and their glucoside derivatives to determine how potent they were. We also attempted to establish the mechanism by which they inhibit root growth using labeling and fluorescence microscopy of the proteins involved in mitosis. We found that these compounds affect the formation and organization of the microtubule protein involved in the separation of chromosomes during cell division.
Technical Abstract: The aryltetralin lignans podophyllotoxin, alpha-peltatin, beta-peltatin, their respective O-beta-d-glucosides, and the semisynthetic derivative etoposide were tested for phytotoxicity. The aglycones were more potent inhibitors than their respective glucosides, and podophyllotoxin was the most active natural lignan tested. These compounds were more active against rye (Lolium multiflorum L.) and onion (Allium cepa L.) than lettuce (Lactuca sativa L.). The semisynthetic lignan etoposide was more active than any of the natural analogues and was phytotoxic to both monocotyledonous and dicotyledonous species. Inhibition of root growth was the main developmental response observed on plants tested with the lignans. At the cellular level, podophyllotoxin and etoposide caused similar symptoms in actively dividing meristematic cells of onion root tips. All phases of mitosis were inhibited by nearly 50%, relative to the controls. Both compounds also induced abnormal star anaphase chromosomal configurations. While the precise molecular mechanism of action of these compounds remains to be identified in plants, a primary effect is the alteration of the formation of the spindle microtubular organization centers, resulting in the formation of multiple spindle poles and an asymmetrical convergence of the chromosomes.