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[SANET-MG] plant steroids
ISIS Press Release 30/03/06
Plant Steroids in Transgenic Plants Safe for Humans?
There are too many similarities between plant and animal steroids for
them to be presumed safe. Prof. Joe Cummins
A fully referenced version of this article is posted on ISIS members’
website. Details here.
For many years, it was presumed that the regulators of growth and
development in plants are distinct from the hormones that regulate
growth and development in animals. Yet, many of the pesticides used to
control insects and fungi were found to disrupt the endocrine systems of
In 1979, steroid compounds called brassinosteroids (BRs) were discovered
in the pollen of Brassica napus (rapeseed). Later studies showed that
BRs are ubiquitous among plant species. BRs are similar in structure to
animal steroid hormones, including ecdysone, progesterone and
testosterone. Steroid hormones regulate transcription through nuclear
receptors and by membrane bound cell surface receptors. Trans-membrane
BRs receptors have been recognized in plants. Recently, nuclear
transcription factors regulated by BRS were recognized. Like animal
steroids, BRs act on a number of aspects of growth and development, and
function in a broad range of disease resistance as part of an innate
A number of BR inhibitors and analogues have been produced, and BR
analogs with high growth promoting activity have been patented.
BR analogues proved active in the control of mosquitoes through their
resemblance to the insect molting hormone. Synthetic BR analogues
selectively inhibited multiplication of herpes simplex virus by
interfering with late viral protein synthesis. BR derivatives were also
effective in inhibiting replication of the measles virus. These finding
suggest that BRs are active in both invertebrate and vertebrate animal
viruses including those infecting humans. Might they not interfere with
the synthesis or action of human steroid hormones?
As in the synthesis of animal steroids, synthesis of BR is achieved
using certain cytochrome p450 molecules. Researchers from the Salk
Institute patented transgenic plants altered to either impair or
over-express a gene for cytochrome p450 activity. The resulting
transgenic plants could be manipulated to produce insect resistance,
dwarfism and darker green foliage compared to wild type plants. Another
cytochrome p450 gene was isolated from dwarf plants and that gene and
protein patented. Cotton plants with improved fibre characteristics
resulted from treatment of cottonseeds with BRs prior to planting, or by
producing cotton fibre in liquid cell culture. Transgenic cotton plants
also produced fibres with improved characteristics when sprayed with BR
BRs are versatile and allow the production of greater cell mass if
desired, as for example in forage. BRs may also provide dwarfism for
grain crops to avoid lodging of the crops. BRs appear to be associated
with multiple disease resistance. However, manipulation of BRs may
create unexpected toxins as byproducts of the modified p450 genes.
BR analogues may provide the happy prospect of making crops grow larger,
while warding off insect pests and curing genital herpes. But it is
imperative that BRs and transgenic crops producing them should be tested
thoroughly for untoward toxicity for human beings and other
non-targpplant sterois in
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