Oxygen root transport

The acquisition of iron in plant roots has been described in Chapter 7. Once in the apoplast of the root, the iron must be transported through the roots to the xylem and thence to the leaves. In order to ensure that the iron does not precipitate or generate oxygen radicals during its transport, the iron is bound to an intracellular transporter of iron (both Fe2+and Fe3+),... 

The carbon dioxide comes from the air, and the water comes from the soil in which the plant grows. When a plant is watered or when it rains, water enters the root and is transported to the leaves by plant cells called xylem. To protect themselves against drying out, leaves have structures called stomata that allow gas to enter and leave. Stoma is from the Greek and means hole. Both carbon dioxide and the oxygen produced during photosynthesis pass in and out of the leaf through the opened stomata. 

Cohner, T.D. 2003. Long-distance transport of gases in plants a perspective on internal aeration and radial oxygen loss from roots. Plant Cell Environ. 26 17-36. 

The presence of iron oxyhydroxide coatings (i.e., Fe plaque, often dominated by ferrihydrite) on the surface of wetland plant roots is visual evidence that subsurface iron oxidation is occurring in otherwise anoxic wetland soils and sediments. Oxygen delivered via radial O2 loss may react with reduced iron in soil pore spaces to form oxidized iron that can be deposited on the plant roots as Fe plaque. Despite a long history of observing Fe plaque on wetland plant roots and understanding the basics of plaque formation [i.e., reaction of plant-transported O2 with Fe(II) in soils and sediments], it was largely assumed that plaque formation is predominately an abiotic (i.e., chemical) process because the kinetics of chemical oxidation can be extremely rapid (Mendelssohn et al., 1995). However, recent evidence has demonstrated that populations of lithotrophic FeOB are associated with Fe plaque and may play a role in plaque deposition. 

Aluminum ions (Al3+) have toxic effect on plants, and number of studies documented the toxic impact of Al3+ on roots,1 hypocotyls,2 and germinating pollen.3,4 It has been proposed that early effects of Al3+ toxicity at the root apex, such as those on cell division, cell extension or nutrient transport, involve the direct intervention of A1 on cell function.5 Model mechanisms of Al3+ toxicity has been proposed that A1 stimulates the NADPH oxidase and induces the generation of superoxide (02j that triggers the influx of calcium ion (Ca2+). The resultant reactive oxygen species (ROS) and cytosolic free Ca2+ concentration elevation may lead to development of phytotoxicity.6... 

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