Frequency and Timing of Leaf Removal Affect Growth and Podophyllotoxin Content of Podophyllum peltatum in Full Sun

Abstract

Podophyllotoxin is a pharmaceutical compound found in leaves and rhizomes of American mayapple (P. peltatum L.), a species being investigated as an alternative to that of the Indian mayapple (P. emodi). Leaves alone can serve as a renewable source of podophyllotoxin (and other lignans) leaving rhizomes undisturbed to produce leaf biomass in subsequent years. It is not known, however, how frequently or severely plants can be defoliated without adversely affecting future plant growth, lignan content, or podophyllotoxin yield (g·m^-2). This study compared harvest strategies that were mild to severe in frequency and timing of leaf removal. A wild population in full sun was subjected to leaf removal treatments of varying frequency (every year, every 2^nd or 3^rd year) and timing (early or late). Control plots not previously harvested were included every year. Plots were 1.0 m² and established during spring of 2001. Duration of the study was four years. P. peltatum plants did not tolerate the most severe harvest treatment: annual harvest frequency in combination with early harvest time. Early annual harvests reduced total leaf dry mass and total leaf area in a consistent and linear manner. In contrast, plants tolerated annual harvests when conducted late in the growing season and tolerated early harvests when conducted every 2^nd or 3^rd year. The number of sexual shoots was reduced to zero by early annual harvests. Podophyllotoxin content was 2.7 to 6.5 times greater in leaves harvested early compared to those harvested late, though content was significantly greater in only two out of four years. In conclusion, we can recommend leaf removal every year from well-established P. peltatum populations grown in full sun if harvests are conducted late in the growing season. This harvest strategy ensures maximum podophyllotoxin yield without jeopardizing future leaf biomass yield. Leaves harvested early appear to have greater podophyllotoxin content, but we discourage early harvest every year. Instead, our results indicate that leaves can be harvested early every other year without reducing long-term performance of P. peltatum populations.

American mayapple - lignans - α-peltatin - β-peltatin - defoliation

References

• 1 Bedows E, Hatfield G M. An investigation of the antiviral activity of Podophyllum peltatum .  J Nat Prod. 1982;  45 725-9
• 2 Jackson D E, Dewick P M. Tumor-inhibitory aryltetralin lignans from Podophyllum pleianthum .  Phytochemistry. 1985;  24 2407-9
• 3 Lerndal T, Svensson B. A clinical study of CPH 82 vs. methotrexate in early rheumatoid arthritis.  Rheumatology (Oxford). 2000;  39 316
• 4 Foster S. Medicinal plant conservation and genetic resources: Examples from the temperate Northern hemisphere.  Acta Hortic. 1993;  330 67-73
• 5 Rai L K, Prasad P, Sharma E. Conservation threats to some important medicinal plants of the Sikkim Himalaya.  Biol Conserv. 2000;  93 27-33
• 6 Cushman K E, Maqbool M. Propagule type and planting time affect subsequent mayapple growth.  Hort Science. 2005;  40 640-4
• 7 Cushman K E, Maqbool M, Gerard P D. Mulch type, mulch depth, and rhizome planting depth for field-grown American mayapple.  Hort Science. 2005;  40 635-9
• 8 Cushman K E, Maqbool M, Lata H, Bedir E, Khan I A, Moraes R M. Podophyllotoxin content and yield of American mayapple leaves in sun and shade.  Hort Science. 2005;  40 60-3
• 9 Meijer W. Podophyllum peltatum - Mayapple a potential new cash-crop plant of Eastern North America.  Econ Bot. 1974;  28 68-72
• 10 Moraes R M, Burandt Jr C, Ganzera M, Li X, Khan I, Canel C. The American Mayapple revisited - Podophyllum peltatum - still a potential cash crop?.  Econ Bot. 2000;  54 471-6
• 11 Moraes R M, Momm H G, Silva B, Maddox V, Easson G L, Lata H. et al . Geographic information system method for assessing chemo-diversity in medicinal plants.  Planta Med. 2005;  71 1157-64
• 12 Moraes R M, Bedir E, Barret H, Burandt C, Canel C, Khan I. Evaluation of Podophyllum peltatum L accessions for podophyllotoxin production.  Planta Med. 2002;  68 341-4
• 13 Lubbers A E, Lechowicz M J. Effects of leaf removal on reproduction vs. belowground storage in Trillium grandiflorum .  Ecology. 1989;  70 85-96
• 14 Rockwood L L, Lobstein M B. The effects of experimental defoliation on reproduction in four species of herbaceous perennials from northern Virginia.  Castanea. 1994;  59 41-50
• 15 Canel C, Dayan F E, Moraes R M, Burandt C. Enhanced yield of podophyllotoxin from natural products through in situ conversion methods. US Patent 6,143,304; 2000. 
• 16 Canel C, Dayan F E, Ganzera M, Khan I A, Rimando A, Burandt C L. et al . High yield of podophyllotoxin from leaves of Podophyllum peltatum by in situ conversion of podophyllotoxin 4-O-β-D-glucopyranoside.  Planta Med. 2001;  67 97-9