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.MODE AND MECHANISM OF ACTION OF MICROTUBULE ASSEMBLY, MITOSIS AND LIPID SYNTHESIS INHIBITORS
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- 3. Based on their action at cellular site, have been categorized into: 1. Photosynthesis Inhibitors 2. Respiration Inhibitors 3. Lipid Biosynthesis Inhibitors 4. Nucleic acid, amino acid and protein synthesis Inhibitors 5. Cell Division Inhibitors 6. Membrane Function Inhibitors
- 4. In cell biology, mitosis is a part of the cell cycle when replicated chromosomes are separated into two new nuclei. Mitosis is the division of nucleus and cytokinesis is the division of cytoplasm.
- 6. Microtubules are one of the cyto- skeletal filament systems in eukaryotic cells which involved in the transport of material within cells, carried out by motor proteins that move on the surface of the microtubule.
- 7. Microtubules play a role in the migration of chromosomes to opposite ends of a mitosis cell during the anaphase. Microtubules are hollow tubes 24 to 25 nano-meters in diameter composed of 13 parallel rows.
- 8. Lipids are molecules that contain hydrocarbons and make up the building blocks of the structure and function of living cells. Lipids include fats, waxes and most of the non-protein membrane of cells.
- 9. The phase of growth inhibited are: 1.Early germination i.e. enlargement of radicle 2. seedling establishment at the expense of endosperm or cotyledonary reserves.cotyledonary reserves. 3. growth of seedling after the seed reserves are exhausted inhibitory affects on the early germination phase are generally accompanied by a failure of the mobilization of the seed reserves.
- 10. Mitosis inhibitors include asulam, barban, propham, chlorepropham (carbamates) EPTC (Thiocarbamates) cinmethylin (Benzyle ethers) maleic hydrawzide (MH) “Mitotic poison,, is a class of herbicides, which block mitosis in primary meristem.in primary meristem. A few dicotyledonous species e.g. cucumber are said to be susceptible to carbamates. Cucumber root tip when treated with chlorpropham, showed the inhibition of mitosis and precocious enlargement and maturation of cells near apex.
- 11. Microtubule Inhibitors are generally applied pre-emergence to control annual grasses and some broadleaf weeds in many crops and turf grass. These herbicides are absorbed by both roots and shoots of emerging seedlings but are not readily translocated. The emerging shoot is the primary absorption and action site in grass species. These herbicides are mitotic poisons that inhibit cell division. Thus, the meristematic regions, such as the growing points of stems and roots, are most affected.
- 12. Spindles structures, which attach one of the two chromatids of a chromosome and draw them to either of the poles are formed during metaphase. Spindles are composed of filamentous protein called microtubules. Microtubules are hollow cylindrical structures primarily composed of dimeric protein tubulin (polymerized tubulin protein, a – and b – tubulins) which in turn is composed of similar but distinct subunits of 55 kilo Daltons each (Dodge,1990,Rodosevich et.al., 1997).kilo Daltons each (Dodge,1990,Rodosevich et.al., 1997). Dinitroaniline herbicide when present in sensitive plants bind to the heterodimer in the cytoplasm. As the herbicide tubuline complex is added to the + ve end, of growing microtubules further growth of microtubule ceases. With depolymerisation of microtubule continuing from the – ve end, the tubules become shorter and shorter, eventually resulting in the complete loss of microtubules. This result is uneven thickening of cell wall and incomplete cytokinesis and abnormally oriented cell wall.
- 14. Benzamide, benzoic acid (DCPA), dinitroaniline, phosphoramidate, and pyridine herbicides are examples of herbicides that bind to tubulin, the major protein needed to polymerize microtubules that are essential for cell division. Herbicide-induced microtubule loss may cause the observedHerbicide-induced microtubule loss may cause the observed swelling of root tips as cells in this region neither divide nor elongate. Symptoms on weed species include short, swollen coleoptiles, callus formation, brittle stems near the soil surface, short, stubby secondary roots and club-shaped roots and crinkle leaves etc. are observed.
- 15. Chemistry Common Name Benzamide Propyzamide (= pronamide) Benzoic acid DCPA Dinitroaniline Pendimethalin Benefin Chemistry Group and Common Names of Microtubule Assembly Inhibitors Ethalfluralin Oryzalin Trifluralin Prodiamine Pyridine Dithiopyr Thiazopyr
- 16. Herbicides in this mode of action are most effective on annual grasses and some broadleaf weeds. In general, these herbicides are applied pre-planting or pre- emergence and incorporated into the soil. Most herbicides in this mode of action are volatile and need toMost herbicides in this mode of action are volatile and need to be incorporated immediately after application to avoid excessive vapour loss. These herbicides are absorbed through both roots and emerging shoots but are translocated only in the xylem. The primary site of absorption and action is the emerging shoot and growing point.
- 17. Herbicides in this mode of action belong to four chemistries including benzofuranes, chlorocarbonic acids, phosphorodithioates, and thiocarbamates. The specific mode of action of these herbicides is not well elucidated, but there is strong evidence that they interfere with biosynthesis of fatty acids and lipids in the newly developing shoot, which may account for reported reductions in cuticular wax deposition. In addition, these herbicides cause abnormal cell development or prevent cell division in germinating seedlings. They stop the plant from growing by inhibitingdivision in germinating seedlings. They stop the plant from growing by inhibiting cell division in the shoot and root tips while permitting other cell duplication processes to continue. Injury Symptoms: Symptoms on grass plants include failure of the shoot to emerge from the coleoptile or whorl of the plant, giving the plant a buggy-whip appearance. Susceptible grass seedlings often fail to emerge from the soil. Injury symptoms on broadleaf plants include enlarged cotyledons, restricted growth of the true leaves, and a dark green color, a symptom sometimes referred to as bud seal. The roots become short, thick, brittle, and club-shaped.
- 18. Chemistry Common Name Benzofurane Ethofumesate Phosphorodithioate BensulidePhosphorodithioate Bensulide Thiocarbamate Cycloate EPTC Triallate
- 19. Dr. Narendra PandeyDr. Narendra Pandey Dr. M.C.BhambriDr. M.C.Bhambri