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[SANET-MG] crops om steroids
January 31, 2005
Prof. Joe Cummins
“Crops on steroids”
For many years it was presumed that the regulators of growth and
development in plants was separate and different from the hormones
regulating animal growth and development. However, many of the
pesticides used to control insects and fungi were found to disrupt the
endocrine systems of animals. In 1979 steroid compounds called
brassinosteroids (BRs) were discoveres in the pollen of Brassica napus (
rapeseed). Later studies showed that BRs were ubiquitous among plant
species(1). BRs have structure similar to the animal hormones including
ecdysone, progesterone and testosterone. Steroid hormone signaling
includes two aspects, regulation of transcription by nuclear receptors
and by membrane bound cell surface receptors. Trans-membrane BRs
recetors have been recognized in plants (1). Recently nuclear
transcription factors acting on genes regulated by BRS were recognized
(2). Like the animal steroids, BRs acts on a number of aspects of growth
and development, as well Brs functions in a broad range of disease
resistance, functioning as an innate immunity system (3).
A number of BRs inhibitors and analogues have been produced as,
for example , in a recent study (4).BRs analogs with high growth
promoting activity have been pateneted , for example US patent
BRs analogues proved to be active in the control of mosquitoes
through their resemblance to the insect molting hormone (6). Synthetic
BRs analogues selectively inhibited multiplication of herpes simplex
virus by interfering with late viral protein synthesis (7,8). BRs
derivatives were also effective in inhibiting replication of the
measles virus (9). These finding suggest that BRs are active in both
invertebrate and vertebrate animals including human.
As in the synthesis of animal steroids , synthesis of BRs 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 (10.11).
Another cytochrome p450 gene was isolated from dwarf plants and that
gene and protein has been patented (12,13). Cotton plants with improved
fiber characteristics has been achieved using BRs treatment of cotton
seeds prior to planting or by producing cotton fiber in liquid cell
culture . Transgenic cotton plants that produce quantities of fibers
with improved characteristic when those transgenic plant were sprayed
with BRs analogues (14,15).
Brs are versatile and allow production of greater cell mass if
that is desirable , as for example in forage. BRs may also provide
dwarfism for grain crops to avoid lodging of the crops. The benefits
associated with multiple disease resistance seem to be an asset of BRs.
However, manipulation of BRs may create unexpected toxins as byproducts
of the modified p450 genes. BRs analogues may provide a happy prospect
of making crop grow larger, while warding off insect pests and curing
genital herpes. However, the seductive prospect may launch a modern
“snake oil” that “cures” the common ills. It is imperative that the BRs
transgenic crops should be tested thoroughly for untoward toxicity and
they must not be deemed “substantially equivalent” to unmodified crops.
The numerous BRs analogues destined for use as crop growth regulators
or pesticides also require careful study.
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