Brassinolides is a plant steroid discovered in pollen of members of the mustard lousily, and studied in Arabadopsis. Chemically the brassinosteroids are similar to animal steroid hormones, and have similar genes that code for the steroid synthesis pathways. The functions of brassinosteorids overlap those of other plant hormones, and may be additive. Brassinosteoroids activate signal transduction pathways that promote cell elongation and cell division. Brassinosteroids also promote differentiation of xylem tissue, and perhaps other tissues, too. Brassinosteroids can also retard leaf abscis.sion. Absence of brassinolides results in dwarf plant, It is difficult to study the brassinosteroids because their effects overlap those of auxin and gibberellins.
Salicylic acid is known to activate defense genes for resistance against pathogen invaders, known as the hypersensitive response. Salicylic acid, a phenolic extract Irons willow bark, was long used as an analgesic. It is now prepared commercially and is the active ingredient of aspirin.
011gosaccharins (Clligasaccharldes) Oligosaccharins are short chain sugars in cell walls that may have a role in defense against pathogens. When a pathogen "chomps" on the oligosaccharide, the oligosaccharide activates a signal transduction pathway leading to plant defense responses. They may also help regulate growth, differentiation and flower development all by activating signal transduction pathways.
Systemin is a small peptide found in wound tissue, it may stimulate defense activities as the signal molecule (ligand) that activates the signal transduction pathways that include the jasmonates.
Jasmonates are a group of fatty acid derivatives. They appear to have a role in seed germination, root growth, and the storage of protein (especially in seeds). Jasrnonates synthesised in response to signal molecules produced in wound areas are involved in the signal transduction pathways that result in secondary metabolites (protease inhibitors) that poison the predator, or synthesis of volatile molecules that attract the predator's predators.
Plant Growth Regulators and Genetic Engineering
The new technologies of genetic engineering can result in more environmentally friendly plant pest-protection, foods with enhanced nutrition, more accurate and sensitive diagnostics, foods with improved processing and marketing characteristics, better and more efficient medical delivery, new methods for removing contaminants from soils and waters, and creation of products that are presently being made trans nonrenewable resources. Many of these changes might be considered under the broad definition of a "plant growth regulator".
While products of this technology once were confined to the research laboratory, this is no longer the case. These and other new crops represent a substantial percentage of actual production acreage in the US. Its 1998 50% of the cotton acreage, 30%, of the soybean and 20% of the maize acreage in the U.S. were genetically engineered. In the US some 60 million acres of G.E. crops were planted in 1998 and the projections for 1999 are that this number will increase, with a wider variety of products available to farmers and present in the marketplace.
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