Root Mitotic Inhibitors
Symptomology
Development Summary
Site of Action Summary
Injury Symptoms
Time-lapsed Video
Herbicide Families
Herbicides
Symptomology Development Summary
These herbicides inhibit
cell division and elongation of newly forming root cells. The most often observed
effect in plants not totally killed during emergence are poorly developed
root systems (often referred to as clubbed roots). Affected roots are incapable
of further growth or nutrient absorption. Although clubbed
roots are the most common symptom of affected plants, other symptoms
may include stunting, purpling, and other
symptoms generally associated with nutrient deficiencies typical of plants
with poorly developed root systems.
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Root growth occurs near the root tip where cells divide and elongate. Mitosis is the process by which chromosomes (the genetic material of cells) are replicated prior to cell division, which gives rise to two daughter cells. Cells in the meristematic region constantly cycle through this process. The cycle flows from mitosis to G1 to S to G2 then back to mitosis. Nuclear synthesis, including doubling of chromosomes, occurs in the S phase. The alike chromosomes (sister chromatids) are joined at a common point called a centromere. Cellular growth and protein synthesis occur in the G phases.
After the completion of G2 the cell enters mitosis. Mitosis includes the phases prophase, metaphase, anaphase, and telophase. In prophase sister chromatids align (which are still attached at their centromeres) on the equatorial plate (the center of cell). Spindle fibers form from the poles and attach to the centromeres. In metaphase spindle fibers contract to separate the sister chromatids. Identical copies of the genetic material are split and pulled toward opposing poles. In anaphase the poles retreat away form one another. In the final phase, telophase, the nuclear envelope, plasma membrane, and cell wall form between the two poles of genetic material resulting in two genetically identical daughter cells. Each of the daughter cells returns to phase G1 of the cell cycle.
Dinitroanalines inhibit
cell division and elongation within the meristematic tissue of seedling roots
by inhibiting the formation of spindle fibers. Spindle fibers are needed to
separate the sister chromatids. Spindle fibers are composed of microtubules
that are made up of tubulin. Early research has proven that the dinitroanaline
herbicides impact the formation of tubulin in dividing meristematic root cells
of susceptible species. The result is root cells with multiple sets of chromosomes
(polyploidy) and faulty cell walls incapable of further growth or nutrient
absorption.
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Effects of mitotic inhibition
are clubbed or swollen root tips, and symptomology includes the visual properties
commonly associated with nutrient deficiencies: Yellowing of leaves; Purpling
of leaves and stem; Whitening due to inability to produce chlorophyll; Weak
stems due to poor cell wall development.
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