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Valtcho D. Zheljazkov, Andrew M. Jones, Bharathi Avula, Victor Maddox, and Dennis E. Rowe

Podophyllotoxin is an anticancer compound found in high concentrations in Indian mayapple [ Podophyllum emodii Wall. (syn. P. hexandrum Royle.)], American mayapple ( Podophyllum peltatum L.), Eastern red cedar ( Juniperus virginiana L.), and

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Muhammad Maqbool, Kent E. Cushman, Rita M. Moraes, and Patrick D. Gerard

American mayapple (Podophyllum peltatum L.) is a rhizomatous, herbaceous perennial found in wooded areas of eastern North America and is a source of the pharmaceutical compound podophyllotoxin. This research was conducted to determine the optimum duration of low temperature exposure in overcoming dormancy of fall-harvested rhizome segments for subsequent use as propagules in greenhouse plantings. Two types of rhizome segments were harvested from the wild and used in this study: two-node rhizome segments consisting of a terminal node and its adjacent one-year-old node and one-node rhizome segments consisting of a single node, other than a terminal node, of unknown age or rhizome position. For growth cycle I, rhizome segments were exposed to low temperature (≈4 °C) for 30, 45, 60, 75, or 90 days, planted in pots, and grown in a greenhouse set at 21 °C. Shoot emergence, shoots per pot, and plant height were recorded. Leaves were removed from plants when senescence first became evident, and leaf area was recorded. For growth cycle II, rhizome segments remained undisturbed in the original pots and were exposed to low temperatures (≈4 °C) for 90 days. Pots were again placed in the greenhouse and shoot emergence, shoots per pot, plant height, and leaf area were recorded. Increasing duration of low temperature exposure of rhizome segments up to 75 days appeared to increase percent emergence and plant height and decrease days to emergence, though changes in greenhouse conditions over the study period may have also influenced shoot emergence and plant growth. Two-node rhizome segments exhibited higher percent shoot emergence, shoot longevity, leaf area, and plant height than single-node segments during each growth cycle. Two-node rhizome segments also exhibited fewer days to emergence during growth cycle I. Rhizome segments produced no more than a single shoot in growth cycle I, whereas more than one shoot was produced in growth cycle II. Most of the effects of low temperature exposure during growth cycle I persisted throughout growth cycle II. These results indicate that dormancy of mayapple rhizomes can be overcome with low temperature exposure and shoots can be induced to grow at any time of year.

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Kent Cushman and Muhammad Maqbool

American mayapple (Podophyllum peltatum) is being investigated as a domestic, renewable, and alternative source of podophyllotoxin, a precursor compound used in the manufacture of several drugs. Indian mayapple (P. emodi) is the current source of the compound. The objective of this study was to examine growth of transplanted rhizome segments of American mayapple at four transplant times during the year. Two-node rhizome segments were carefully dug with roots intact from naturally occurring wild populations near Holly Springs, Miss. Segments were dug in Oct. 2002, Dec. 2002, Feb. 2003, or June 2003. Within 1 day of each harvest, segments were transplanted into 1-gal pots containing a mixture of sandy soil and a finely ground pine bark mulch. Pots were then set in a raised bed, such that the soil surface within the pots was even with that of the plant bed. Pots and plant bed then received a 3-inch layer of pine bark mulch. Rhizome segments were harvested from pots four times during the year following the date of transplant. Rhizome and roots were separated according to new or old growth and then dried. Rhizome segments transplanted during October and December increased about 36% in dry mass during the 1-year period after transplant. This was significantly greater than an increase of 12% for segments transplanted during June. Segments transplanted during February performed intermediately, increasing by 22%. Our results show that rhizome segments of American mayapple performed better when transplanted during fall and winter compared to those transplanted during summer. Segments transplanted during spring performed intermediately.

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Kent Cushman, Muhammad Maqbool, Ebru Bedir, Hemant Lata, Ikhlas Khan, and Rita Moraes

Podophyllotoxin is a pharmaceutical compound extracted from rhizomes of Indian mayapple (Podophyllumemodi). Leaves of American mayapple (P. peltatum) also contain podophyllotoxin, and the species is being investigated as a domestic, renewable, and alternative source of the compound. The objective of this study was to explore strategies of leaf removal that would not adversely affect regrowth of American mayapple shoots in subsequent years. Plots were established in two locations among naturally occurring populations in the wild, one in full sun and one in partial shade. Plots were 1.0 m2 and leaves were removed from plants every spring, every other spring, or every third spring. In addition, leaves were removed in early spring, soon after shoots emerged and leaves had fully expanded, or in late spring, when leaves first showed evidence of yellowing and beginning to senesce. Sexual and asexual leaves were harvested separately. Leaf number, leaf area, and dry weight were recorded. Subsamples of leaf material were extracted to determine podophyllotoxin, α-peltatin, and β-peltatin contents. Results clearly showed that leaf removal every year, in combination with early harvest, was too severe and plants lost vigor over the 4-year period of this study. Plants subjected to this treatment combination produced significantly less leaf area and dry weight than any of the other treatment combinations. Results were similar for both sun and shade locations. Lignan content was not affected by treatment. Our results indicate that leaves can be removed from mayapple plants as often as every year provided harvests are not scheduled too soon after shoot emergence.