Dr. Paul G. Mahlberg
American Cannabis researcher
One of only two DEA permits to grow Cannabis in the United States is held by Dr. Paul Mahlberg of the Biology Department at Indiana University, Bloomington. His research program began over 20 years ago and continues to the present, specializing in the ultra structure of the resin-producing gland and the biogenesis of its cannabinoids. With his post-doctoral fellows and graduate students, he has explored these and other topics important to the definition of Cannabis as either a drug or fiber plant.
Journal of the IHA: How and when did you first become interested in Cannabis?
Paul Mahlberg: My research interests focus on the secretion phenomenon in plants, with particular emphasis on the specialized laticifer cell, the secretory gland and secondary products in these structures. Cannabis is an excellent model for use in such studies because it possesses a great abundance of lipophilic glands as well as laticifers. Cannabinoids represent interesting secondary products in this dioecious/monoecious plant because they occur only in this one genus. Flower development, which is day-length dependent, can be induced even in a very young plant making it an excellent experimental subject. These characters, which attracted my interests in about 1970, are desirable for our particular studies.
JIHA: Your laboratory is one of only two in the United States with DEA permission to grow Cannabis. When and for what purpose were you granted your first research permit?
PM: I received my license to study Cannabis about 1970 for the purpose of cultivating the plant and studying its morphology and cannabinoid composition.
JIHA: How many graduate students and post-doctoral fellows have studied Cannabis in your laboratory?
PM: Six graduate students and 6 post doctorates or visiting faculty members have studied with me on the topic of Cannabis.
JIHA: What research topics concerning Cannabis have you explored in your laboratory?
PM: Our investigations have included several
areas, in part, reflecting topics my students have chosen for their research.
Results from some of these studies are yet to be published. One broad area
includes studies on gland development and distribution, and formation of secretory
content, including cannabinoids, at various phases of plant development. This area
includes our interests in gland evolution not only in Cannabis, among its many
strains, but in relation to glands among angiosperms. We have been developing new
concepts on gland development, and would like to examine them in relation to glands in
other families. Of course, we do wonder about cannabinoid evolution among the
strains, as well. It is curious as to why the pathway "ends" with THC
(assuming CBN may be an artifact), yet evolved laterally, in a sense, with formation of
propyl and other forms. These two facets of evolution are still very much in need of
We have studied plant growth and cannabinoid composition and distribution in Cannabis clones to learn more about the interrelationships between genetically stable plants, and the role of selected environmental factors on cannabinoid production. Included in this area have been our initial studies on the biosynthesis of these compounds.
The development of tissue-cultured materials to study cannabinoid synthesis attracted our attention, and still does, with the objective to manipulate the medium to control both cannabinoid formation and root-shoot formation. While we are having some success with the latter, we must also concentrate on learning about factors that can stimulate cannabinoid formation. Perhaps further study in this area can aid in identifying the gene controlling cannabinoid biosynthesis, with subsequent silencing of it in strains for economic utilization.
JIHA: Which line of your research has yielded the most significant results in terms of our understanding of Cannabis?
PM: Our most significant results derive from studies on the gland and the role of the gland in localization of cannabinoids. The disc cells, and particularly the secretory cavity, of the gland perform a major role in the physiology of secondary products, activities yet to be understood. This is so for glands not only in Cannabis but other plants as well. Whereas in other studies, individuals have directed attention to the secretory cells, they have ignored the secretory cavity - the very feature that characterizes the "gland". Thus, the data and concepts derived from our studies will reflect not only upon the glands of Cannabis, but perhaps will broaden our understanding of the nature of the secretory cavity in other glands.
JIHA: What are you working on now and plan to explore in the future?
PM: Several research topics or directions are
being pursued at present and very briefly are presented here. We employ several
techniques in our studies including electrophoresis, chromatography, electron microscopy,
morphology and tissue culture procedures. While our studies represent basic research
thrusts, they also have application to my interest in developing hemp as an
Karl Hillig, a graduate student, is utilizing our germplasm collection of 200 strains to study the evolution and taxonomy of the genus. He is using several techniques to accumulate data to interpret interrelationships between the strains which include, fiber, oil and drug-related forms.
Dr. Eun-Soo Kim and I are studying cannabinoid localization and secretion in glands using THC antibodies as probes to identify the organelle or membrane involved with THC synthesis, and the mechanism of secretion into the secretory cavity. This study is a facet of our ongoing study on the mechanism of plant cell secretion. Perhaps it will be possible to identify the gene(s) related to THC and other cannabinoid syntheses.
In our tissue culture studies, Dr. Tom Hammond and I are examining the role of different compounds in the synthesis of cannabinoids, and in shoot (plantlet) formation. We wish to learn the mechanism of cannabinoid formation with the objective to control formation of these compounds.
JIHA: If funded, what line of Cannabis research would you personally find the most interesting to pursue?
PM: My current and future studies will
interrelate basic research with applied aspects of the study of hemp for commercial
utilization. One aspect of the latter is the development of hemp as a sustainable
source of fiber. A particular application of the fiber is for the production of
particleboard. C&S Specialty Builder's Supply, Inc., has utilized hemp stalks,
grown in Canada, to produce particleboard equal or better than that from trees. An
important aspect of this particleboard program is that the particleboard industry need not
retool to produce it. A manufacturer can use hemp or tree fiber in any combination
for production of the board. Thus, hemp can be grown as an annual crop to provide a
sustainable source of income to farmers and provide a source of fiber to supplement wood
fiber for industrial utilization. In the United States, we are unable to grow hemp
at this time because of the law preventing cultivation of all forms of Cannabis.
In contrast, many western countries, including our neighbor Canada, permit
cultivation of hemp. There are other components obtainable from the plant - such as
oil from seeds or pharmaceuticals, but the possibility of gaining legal approval to
cultivate non-hemp Cannabis in the United States in the near future is less
probable than for hemp fiber strains.
Our present and future research will include a number of thrusts with the aim of enabling us to distinguish hemp from marijuana. These goals include: a) to alter hemp morphologically so that it appears unlike marijuana, b) to further reduce the already low THC content in hemp strains with the objective to reduce it to zero, c) to evaluate the taxonomic relationships of accessions in our germplasm collection using molecular procedures to review speciation in this genus, d) to identify the gene controlling THC synthesis with the objective to block or alter its activity, and e) to utilize tissue culture procedures to alter the THC gene or introduce genetic markers to distinguish hemp from marijuana. These research directions have the objective to develop superior fiber strains free of THC so that they can become an acceptable agricultural crop to law enforcement authorities.
JIHA: How is your laboratory funded?
PM: Our support is very minimal. The strictures against all forms of Cannabis does adversely influence funding from national agencies. We are fortunate to have some research support from private sources, including HortaPharm B. V., Amsterdam, and C &S Specialty Builder's Supply, Inc., Oregon, as well as from the Indiana University Faculty Research Support Office. These sources do not provide money for salaries. Fortunately, students and visiting faculty have provided their own salary support in conjunction with their dedication to research interests. Thus, our studies are very much underfunded, which makes it very difficult to progress at a desirable research pace. Yet even at this slow pace we have made progress in several.directions as indicated above.
JIHA: How many different accessions of Cannabis have you grown, which general gene pools do they represent and what is the purpose of investigating such diversity?
PM: We have accumulated approximately 200 accessions in our germplasm collection with the aid of import permits. These accessions include historically important strains from Europe, Asia and other world-wide sources. Mr. Hillig is utilizing all of these strains in his studies.
JIHA: Various theoretical pathways for the biosynthesis of cannabinoids have been proposed by you and other researchers. Do you have any new theories on the biosynthesis of cannabinoids?
PM: The cannabinoid pathway is most interesting
in that it is known to occur only in the genus, Cannabis. This phenomenon
suggests that the pathway, and this genus, are evolutionarily recent in origin, or that
the precursor(s) are unique to this genus, or that yet another factor may relate to the
origin of this pathway in Cannabis. The general interpretation that a
terpene and a phenol condense to form cannabinoids (purportedly CBG being the first
cannabinoid) contrasts with an earlier one describing cannabinoid derivation from fatty
acids. Chemical synthesis supports the first interpretation and, while both terpenes
and phenols are individually common in plants, this condensation appears unique to Cannabis.
Since the terpenoid (or geranyl) component represents a precursor in various
pathways in different plants, we have become particularly interested in the role of the
phenol component. In chemical synthesis of cannabinoids, olivetol
(1,5-dihydroxypentylbenzene) is interpreted to serve as the phenolic precursor, yet
olivetol is not detected in plant extracts. While olivetol is detectable in GLC of
samples, it is also known that certain cannabinoids decompose during GLC to yield small
quantities of olivetol.
Recently, we have reported an abundance of glycosidic or free phloroglucinol (1,3,5-trihydroxybenzene) in the laticifer and gland, whereas no olivetol was detectable. These and other data raise the question as to which phenol(s) is involved in the biological synthesis of cannabinoids.
JIHA: The inability of police to readily distinguish between Cannabis grown for marijuana and industrial fiber hemp has interfered with efforts to establish the latter crop in many areas. A 1991 FAO publication suggests that morphological markers could be introduced into hemp to aid in their easy identification. Do you have any interest in developing these easily recognized, low THC varieties?
PM: Because of my interest in the agro-industrial
development of hemp, I am most interested in developing markers in fibers strains to
enable law enforcement officials to distinguish between hemp and marijuana. We have
begun a pilot study in this direction to develop a morphological marker. In addition
to studies on the normal plant, tissue cultures (including somatic hybridization) could be
utilized to modify or introduce traits into cells, stimulate callus formation and induce
plantlets to subsequently develop a flowering clone for character analysis. I
consider the development of such morphological variants to be important both for short and
long term success of the hemp industry, given the present social climate concerning 'drug
Hemp is a non-drug form of Cannabis, as we know. It is necessary for us to assist law enforcement officials to recognize that hemp does differ from drug forms.
JIHA: What do you feel will be Cannabis' greatest benefit to humanity?
PM: We must view Cannabis as we do any
other crop plant. If it can be cultivated profitably by growers to provide products
such as fiber, oil, seed or pharmaceuticals, we must scientifically, socially and
economically consider its potential value for utilization. We know that hemp, as a
fiber source, can contribute industrial products for development of a major industry.
Unfortunately, restrictive laws in the United States at present prohibit the cultivation of hemp as a fiber crop, thereby making it impossible to evaluate the potential of hemp as an agro-industrial crop in this country. A revision of the statutes in the United States is necessary, and timely, to permit the cultivation of hemp for its industrial development.