144 • Impacts of Applied Genetics— Micro-Organisms, Plants, and Animals 
plant products or byproducts. In recent years, 
economic benefits have been achieved from the 
production of plant constituents through cell 
culture. Among those currently produced com- 
mercially are camptothecin (an alkaloid with 
antitumor and antileukemic activity), proteinase 
inhibitors (such as heparin), and antiviral sub- 
stances. Flavorings, oils, other medicinals, and 
insecticides will also probably be extracted from 
the cells. 
The vinca alkaloids— vincristine and vin- 
blastine, for instance— are major chemothera- 
peutic agents in the treatment of leukemias and 
lymphomas. They are derived from the leaves 
of the Madagascar periwinkle [Catharanthus 
roseus). Over 2,000 kilograms (kg) of leaves are 
required for the production of every gram of 
vinca alkaloid at a cost of about $250/g. Plant 
cells have recently been isolated from the peri- 
winkle, immobilized, and placed in culture. This 
culture of cells not only continues to synthesize 
alkaloids at high rates, but even secretes the ma- 
terial directly into the culture medium instead 
of accumulating it within the cell, thus remov- 
ing the need for extensive extraction pro- 
cedures. 
Similarly, cells from the Cowage velvetbean 
are currently being cultured in Japan as a 
source of L-Dopa, an important drug in the 
treatment of Parkinson’s disease. Cells from the 
opium poppy synthesize both the plant’s normal 
alkaloids in culture and, apparently, some alka- 
loids that have not as yet been found in extracts 
from the whole plant. 
Another pharmaceutical, diosgenein, is the 
major raw material for the production of corti- 
costeroids and sex steroids like the estrogens 
and progestins used in birth control pill. The 
large tuberous roots of its plant source, 
Dioscorea, are still collected for this purpose in 
the jungles of Central America, but its cells have 
been cultured in the laboratory. 
Other plant products, from flavorings and 
oils to insecticides, industrial organic chemicals, 
and sweeteners, are also beginning to be de- 
rived from plants in cell-cultures. Glycyrrhiza, 
the nonnutritive sweetener of licorice, has been 
produced in cultures of Glycyrrhiza glabra, and 
anthraquinones, which are used as dye bases, 
accumulate in copious amounts over several 
weeks in cultures of the mulberry, Morinda citri- 
folia. 
PHASE II: ENGINEERING CHANGES TO ALTER 
GENETIC MAKECP; SELECTING DESIRED TRAITS 
The second phase of the cycle inxoKes the 
genetic manipulation of cells in tissue culture, 
followed by the selection of desired traits. 
Tissue culturing, in combination with the new 
genetic tools, could allow the insertion of new 
genetic information directly into plant cells. 
Several approaches to exchanging genetic infoi’- 
mation through new engineering technologies 
exist: 
• culturing plant sex cells and embryos; 
• protoplast fusion; and 
• transfer by DNA clones and foreign \ec- 
tors. 
These are then followed by: 
• screening for desired traits. 
Culturing^ Plant Cells and Embryos.— 
Culturing the plant’s sex cells— the ogg from the 
ovary and the pollen from the anther (pollen- 
secreting organ)— can inci’ease the (d'ficitMicy of 
creating pure plant lines for breeding. Since sex 
cells contain only a single set of unpaiiH'd 
chromosomes per cell, plantlets derived from 
them also contain only a single set. I'hus, any 
genetic change will heconu; ap[)arent in the re- 
generated plant, because a second paired gene 
cannot mask its effect. I,ai’g(> numheis of hap- 
loid plants (cells contain half the normal num- 
ber of chromosomes) haw. been |)i {)duc«‘d lor 
more than 20 sp(!cies. Sim|)l(? treatment with 
the chemical, colchicine, can usually induc»' 
them to du{)licate their genomes lhaploid .set of 
chromosomes)— resulting in fully normal, dip- 
loid plants. The only major crop that has been 
bred by this technitiue is the aspai agus " 
If the remaining technical harrieis can he 
overcome, the techni(|ue can he used to en- 
hance the selection of ('lite trees and to create 
hybrids of important crops. Although still 
"J. C. I'orrev, "Cvtiulidci ciiliiilion in ( iiltni rd ( i-IU .mil I 
HortSciencp 12(2): 1 3«. 1!)77 
