Absorption through plant roots

Hydroxypyrimidines do not accumulate in large concentrations in the plant tissues, but are immediately metabolised after absorption through the roots. Therefore, to ensure long-term protection the active substances must be continuously absorbed from the soil. The metabolism of the active substances in the plant has been studied with radioactive dimethirimol-2- K in cuciunbers and in barley treated with radioactive ethirimol-2- HZ (Slade et al., 1972 Calderbank,... 

Cd is readily translocated to the plant tops after absorption through the roots (Chaney and Giordano, 1977). MacLean (1976) showed that Cd was present in higher concentrations in the roots than in other parts of crops such as oats. 

Allelopathic inhibition of mineral uptake results from alteration of cellular membrane functions in plant roots. Evidence that allelochemicals alter mineral absorption comes from studies showing changes in mineral concentration in plants that were grown in association with other plants, with debris from other plants, with leachates from other plants, or with specific allelochemicals. More conclusive experiments have shown that specific allelochemicals (phenolic acids and flavonoids) inhibit mineral absorption by excised plant roots. The physiological mechanism of action of these allelochemicals involves the disruption of normal membrane functions in plant cells. These allelochemicals can depolarize the electrical potential difference across membranes, a primary driving force for active absorption of mineral ions. Allelochemicals can also decrease the ATP content of cells by inhibiting electron transport and oxidative phosphorylation, which are two functions of mitochondrial membranes. In addition, allelochemicals can alter the permeability of membranes to mineral ions. Thus, lipophilic allelochemicals can alter mineral absorption by several mechanisms as the chemicals partition into or move through cellular membranes. Which mechanism predominates may depend upon the particular allelochemical, its concentration, and environmental conditions (especially pH). 

Grainger, M. M., Absorption of Parathion through the Root System of Plants and Its Effect... 

EDTA has also been used therapeutically in agriculture to treat iron deficiency in plants, particularly fruit trees, on basic soils. Spraying with iron-EDTA solution facilitates absorption of iron into the plant through its roots, followed by breakdown of the iron chelate so that the iron becomes available to the plant76. ... 

ATPase activity was also studied by Friebe et al. in 1997.17 They correlated the BOA and DIBOA effects on radicle elongation of Avena sativa seedlings with their effects on the activity of plasma membrane H+-ATPase from roots of Avena sativa cv. Jumbo and from Vida faba cv. Alfred. They hypothesized that an alteration in the plasma membrane ATPase activity could be the reason for an abnormal nutrient absorption in plants exposed to hydroxamic acids, because of the role that this enzyme plays in the ion gradient and, therefore, in the ionic transport through plasma membrane. The results of this experiment showed a strong inhibition in the activity of this enzyme in the plasma membrane of chloroplast and mitochondria when it was exposed to BOA and DIMBOA. This alteration implies early interactions with the assayed hydroxamic acids. 

Chemicals may also be taken up by plants and animals from the environment. Plants can take up pollutants through roots or leaves, while animals can take in pollutants by ingestion of contaminated food or water, absorption through skin or gills, or inhalation into the lungs. Chemicals can be absorbed from the lungs by inhaled vapors or gases, particulate matter (e.g., dust), or aerosols (tiny droplets suspended in the... 

Thallium ions are easily taken up by plants through the roots (Ewers 1988). In animals, a rapid and almost complete absorption of thallium from soluble T1 salts was reported in rats, hamsters, sheep, and cows (Aoyama 1989, Crossmann 1984). 

The texture and structure of a soil also affect plant response to nitrogen additions through effects on root development and depth of penetration. A restricted root system limits the ability of the plant to assimilate nutrients and also limits its uptake of water. Since the movement of water through soils by capillarity is slow and limited, the plant roots must literally go after it. A deep root system, therefore, assures that a much greater proportion of the supply in the soil is available to the plant. In addition, soil compaction limits the absorption of the rainfall. Such unfavorable conditions do of course lower the efficiency of applied nitrogen. 

This is also reflected by the octanol-water partition coefficient, indicating a favorable absorption to soil (log Pqw = 0.7 at 25 °C). Plant uptake of 3 occurs via the cotyledons and roots of emerging seedlings and through the roots of established plants (see Chapter 26). 

Water is taken into the plant from the soil. This occurs mainly through the root hairs near the root tip. As the root grows the hairs are corrstarrtly replaced. A few centimetres back from the root tip the hairs disappear. Their firrtction is to increase the siuface area available for absorption of water. There are thousands of root tips on a single healthy crop plarrt (Fig. 1.4). 

The absorption of water irrto the plant in this way is due to suction ptrll, which starts in the leaves. As water transpires (evaporates) from the cells in the leaf, more water is drawn from the xylem tubes which extend from the leaves to the root tips. In these tubes the water is stretched like a taut wire. This is possible because the molectrles of water are held together very firmly when in narrow tubes by the bonds between the hydrogen and oxygen atoms (cohesion-tension). The pull of this water in the xylem tubes of the root is transferred through the root cells to the root hairs and so water is absorbed into the roots arrd rrp to the leaves. In general, the greater the rate of transpiration, the greater the amount of water taken into the plant. 

The absorption and translocation properties of clacyfos were evaluated in the greenhouse at the National Pesticide Discovery South Center in (Zhejiang) in China. Common amaranth (Amaranthus retroflexus) was used as the target plant. The data in Table 8.7 showed that clacyfos would be absorbed through buds, roots, stems, and leaves and demonstrated its inhibitory effect against plant growth. 

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