Monday, August 19, 2019
Plant hormones Essay -- essays research papers
Plant hormones are specialized chemical substances produced by plants. They are the main internal factors controlling growth and development. Hormones are produced in one part of a plant and transported to others, where they are effective in very small amounts. Depending on the target tissue, a given hormone may have different effects. Plant hormones play an integral role in controlling the growth and development of plants. A plant hormone is generally described as an organic compound synthesized in one part of the plant and translocated to another part, where in low concentrations elicits a physiological response. There are five generally recognized classes of plant hormones; some of the classes are represented by only one compound, others by several different compounds. They are all organic compounds, they may resemble molecules which turn up elsewhere in plant structure or function, but they are not directly involved as nutrients or metabolites. Hormone     Source     Action Auxins     apical meristem (only moves down), embryo of seed, young leaves     †¢Ã‚     Control of cell elongation †¢Ã‚     apical dominance (prevents lateral buds) †¢Ã‚     prevents abscission †¢Ã‚     continued growth of fruit †¢Ã‚     cell division in vascular and cork cambium --formation of lateral roots from pericycle --formation of adventitious roots from cuttings Gibberellins     Roots and young leaves     †¢Ã‚     Cell (stem) elongation (works in stems and leaves, but not roots) †¢Ã‚     breaking seed/bud dormancy †¢Ã‚     stimulating fruit set Cytokinins     roots, embryos, fruits actively growing     †¢Ã‚     Promote cell division --signal axillary/lateral bud growth --prevent leaf abscission †¢Ã‚     chloroplast development †¢Ã‚     breaking dormancy in some seeds †¢Ã‚     enhance flowering †¢Ã‚     promote fruit development Abscissic Acid    ... ...ascade ultimately resulting in modification of enzyme activity, altered metabolic processes, and different phenotypes. One thing plant hormones specifically control is gene expression. The exact mechanisms by which hormones regulate gene expression are poorly understood. Gene expression is part of a large amplification process. This process involves repeated transcription of DNA resulting in many copies of mRNA (1st amplification step); mRNA is processed and enters the cytoplasm where it is translated many times by ribosomes into a gene product such as an enzyme (2nd amplification step); enzymes are modified to become functional and capable of high catalytic activity even at low concentrations. They catalyze the production of many copies of an important cellular product (3rd amplification step). It is likely that gene regulation is affected by certain enzymes after initial hormone binding. Genes may be altered by secondary and tertiary messengers of a cellular cascade as well. Hormones may indirectly control gene expression through these enzymes and messengers at a number of control sites such as transcription, mRNA processing, mRNA stability, translation, and post-translation Plant hormones Essay -- essays research papers Plant hormones are specialized chemical substances produced by plants. They are the main internal factors controlling growth and development. Hormones are produced in one part of a plant and transported to others, where they are effective in very small amounts. Depending on the target tissue, a given hormone may have different effects. Plant hormones play an integral role in controlling the growth and development of plants. A plant hormone is generally described as an organic compound synthesized in one part of the plant and translocated to another part, where in low concentrations elicits a physiological response. There are five generally recognized classes of plant hormones; some of the classes are represented by only one compound, others by several different compounds. They are all organic compounds, they may resemble molecules which turn up elsewhere in plant structure or function, but they are not directly involved as nutrients or metabolites. Hormone     Source     Action Auxins     apical meristem (only moves down), embryo of seed, young leaves     †¢Ã‚     Control of cell elongation †¢Ã‚     apical dominance (prevents lateral buds) †¢Ã‚     prevents abscission †¢Ã‚     continued growth of fruit †¢Ã‚     cell division in vascular and cork cambium --formation of lateral roots from pericycle --formation of adventitious roots from cuttings Gibberellins     Roots and young leaves     †¢Ã‚     Cell (stem) elongation (works in stems and leaves, but not roots) †¢Ã‚     breaking seed/bud dormancy †¢Ã‚     stimulating fruit set Cytokinins     roots, embryos, fruits actively growing     †¢Ã‚     Promote cell division --signal axillary/lateral bud growth --prevent leaf abscission †¢Ã‚     chloroplast development †¢Ã‚     breaking dormancy in some seeds †¢Ã‚     enhance flowering †¢Ã‚     promote fruit development Abscissic Acid    ... ...ascade ultimately resulting in modification of enzyme activity, altered metabolic processes, and different phenotypes. One thing plant hormones specifically control is gene expression. The exact mechanisms by which hormones regulate gene expression are poorly understood. Gene expression is part of a large amplification process. This process involves repeated transcription of DNA resulting in many copies of mRNA (1st amplification step); mRNA is processed and enters the cytoplasm where it is translated many times by ribosomes into a gene product such as an enzyme (2nd amplification step); enzymes are modified to become functional and capable of high catalytic activity even at low concentrations. They catalyze the production of many copies of an important cellular product (3rd amplification step). It is likely that gene regulation is affected by certain enzymes after initial hormone binding. Genes may be altered by secondary and tertiary messengers of a cellular cascade as well. Hormones may indirectly control gene expression through these enzymes and messengers at a number of control sites such as transcription, mRNA processing, mRNA stability, translation, and post-translation
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