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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
6,239,073.(5).
    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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