Aryltetralin Lignans Inhibit Plant Growth by Affecting the Formation of Mitotic Microtubular Organizing Centers

Abstract

The aryltetralin lignans podophyllotoxin, α-peltatin, and β-peltatin, their respective O-β-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.