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18 Agricultural Research/April 199

HarvestingDrugs

FromMedicinalPlants

Annual wormwood,

Artemisia annua L.,yields the important

antimalarial drug

artemisinin. Photo by

Scott Bauer (K8027-2)

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would play a role in increasing thesupply of this beneficial compound.

It was already known that worm-

wood has little balloonlike glands onits leaf surface, Duke says. Wefound that as the plant matures, theseballoons fill with artemisinin. Pestprotection is natures goal. As the

plant matures, the glands swell biggerand finally burst, covering the plantwith self-made pesticide.

It is the natural pesticide aspect ofannual wormwood that brings it evenmore within Dukes expertise. Hisresearch groups primary mission is

to find natural products to controlagriculture pestsespecially inAmericas secondary crops.

Theres money to be made infighting pests, but its mainly inprotecting the nations agronomicsuperstarscorn, wheat, and soy-beans. That can mean that important,but less prominent, crops such as

avocados and orchids are ripe for newprotective treatments.

The scientists in Dukes researchunit search the plant and microbialkingdoms for pest-fighters that workin harmony with the environment.Artemisinin, forexample, may alsoyield its protective

powers to otherwisevulnerable crops.

We found thatwithout the geneticcoding for the gland,Artemisia wontproduce artemisinin,

says Duke. For theplant, its essential tohave the geneticinstructions for boththe toxin and thestorage mechanism.

Knowing how aplants DNA programsit for pest protectionmay lead researchers

to ways to provide the

same pest resistance to currentlyvulnerable plants.

Products for People TooBesides the crop protection

aspects of their research, Duke andhis team of scientists are also lookingat the pharmaceutical value of theseplants. In fact,Artemisia is just oneof the plants theyre exploring.

Another plant thats intriguedDuke is St. Johns-wort, whichbelongs to the genusHypericum.

Greek texts dating back to 2000 B.C.have noted uses and harvesting

techniques for this plant. Currently,its claim to fame is as an alternativetreatment for depression.

St. Johns-wort is the preferredtreatment for mild depression inEurope, says Duke. Physicians

there choose it four to five timesmore often than synthetic drugsbecause they believe it has fewer sideeffects. Europeans get their supplyfrom Albania, but it grows wild inthe United States.

Much to the chagrin of rancherswho know St. Johns-wort as a pest,horses and cattle that eat the plant

ncient medical texts, somedating back to the earlyGreeks, talk about medici-

nal plants. Now modern scienceincluding some done by USDAsAgricultural Research Serviceistaking this ancient art to new levels.

Plant physiologist Stephen O.Duke heads ARS Natural ProductsUtilization Research Unit at Oxford,Mississippi. Part of his research

involves discovering how plantsmake their beneficial compounds andhow to better extract them.

One example of his work is

understanding the plant known asannual wormwood,Artemisia annua.This gray-green aromatic plant andits relatives in the genusArtemisia

have been used to make absinthe andflavored wines since earliest times.Now this plant family could bring anew gift: Its natural pest-fightingdefense may protect humans frommalaria.

Its no secret that malaria-fightingdrugs have done a lot for civiliza-tionthe Panama canal is one

testimony of their success. But whathappens when the organisms thatcause the disease develop resistanceto current treatments?

Right now, scientists are preparingto solve this problem before it everoccurs by having alternative treat-ments ready. One of these under-

study cures could be artemisinin, anatural compound produced byArtemisia plants.

Medical researchers, especially in

the military, want to know moreabout wormwoods malaria-fightingproperties. Thats because when dutycalls U.S. troops to a tropical area,the disease is always a potential

problem.The question Duke wants to

answer is exactly how the plantproduces this potentially life-savingcompound. Knowing the physiology

Chemist Agnes Rimando and plant physiologist StephenDuke use steam distillation to determine the essential oilcontent of wormwood leaves.

SCOTT BAUER (K8025-11)

A

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20 Agricultural Research/April 199

develop a sensitivity to light, result-ing in a rash, Duke says. Understand-ing the biochemistry involved might

help reduce the effects.But now, however, Dukes main

concern is extracting a red pigmentfrom the plant to benefit people.

St. Johns-wort tablets are stan-dardized by the amount of the redpigment, called hypericin, whichsome researchers suspect is the activeingredient. Hypericin is being studiedas both an anti-viral and anti-cancer

drug.St. Johns-wort has yet to receive

FDA approval for use as a treatmentfor depression in the United States.But several companies are doingphase I and II clinical trials, a steptoward gaining approval. Currently,Americans can buy St. Johns-wort asa diet supplement.

Getting the Good Stuff Out

Finding an economical extractionmethod for hypericin would be

and leaves of St. Johns-wort and thatit was effective in pest control. Buthypericin, if given in a high enough

concentration, is toxic to all livingthings, including St. Johns-wort. Theplant protects itself by sealing thehypericin dots off with a thin cell

layer.Normally, hypericin is extracted

by chopping the plant up and extract-ing it with ethanol. But Duke mayhave a better way.

The plant has other enzymes thatcan destroy hypericin when the cellscontaining the toxin are breached, he

says. Crushing the plant releasesthese hypericin-destroying proteins,defeating your purpose. We are look-ing at chemical extraction methodsthat may work betterlike soakingthe leaves in a solution that gently re-moves the hypericin without havingto cut them.

While breeders and pharmaceutical

companies are waiting to see whatthis plant can do, they can also staytuned to Dukes research team.Already these scientists are hot on thetrail of new helpful plants and betterextraction techniques. Last fall, Dukehad just finished completing hisstaffing, and the scientists were busy

ordering equipment to start newresearch projects.

All I can say is we are excitedabout the new research projectsweve begun, and were alwayslooking for new ideas, says Duke.We hope to excel in this newandyet ancientfield of natural pesti-

cides and pharmaceuticals.By JillLee, ARS.

Stephen O. Duke is in the USDA-

ARS Natural Products Utilization

Research Unit, National Center for

the Development of Natural Products,

Room 1011, University of Missis-

sippi, Oxford, MS 38677; phone

(601) 232-1036, fax (601) 232-7062,

e-mail sduke@ag.govx

helpful in developing St. Johns-wort both for medicinal purposesand as an anti-viral agent. Sinceplant extraction and physiology areaspects of Dukes work, he began

with research on the plant.It was already known that hyperi-

cin was concentrated in small blackand red dots found on the flowers

Microscopic view of a hypericin-containing gland of St. Johns-wort, Hypericumpunctatum.

A highly effective chloroform dipprocedure enables plant biotechnologistCamilo Canel to extract over 90 percent ofartemisinin from the glandular hairs ofwormwood leaves.

MARY DUKE (K8027-20)

SCOTT

BAUER

(K8026-8)