Heavy Metals in Crop Plants: Transport and Redistribution Processes on the Whole Plant Level

Abstract

Abstract:Copper, zinc, manganese, iron, nickel and molybdenum are essential micronutrients for plants. However, when present in excess they may damage the plant or decrease the quality of harvested plant products. Some other heavy metals such as cadmium, lead or mercury are not needed by plants and represent pollutants. The uptake into the roots, the loading into the xylem, the acropetal transport to the shoot with the transpiration stream and the further redistribution in the phloem are crucial for the distribution in aerial plant parts. This review is focused on long-distance transport of heavy metals via xylem and phloem and on interactions between the two transport systems. Phloem transport is the basis for the redistribution within the shoot and for the accumulation in fruits and seeds. Solutes may be transferred from the xylem to the phloem (e.g., in the small bundles in stems of cereals, in minor leaf veins). Nickel is highly phloem-mobile and directed to expanding plant parts. Zinc and to a lesser degree also cadmium are also mobile in the phloem and accumulate in meristems (root tips, shoot apex, axillary buds). Iron and manganese are characterized by poor phloem mobility and are retained in older leaves.

Nano iron (Fe) complex is an effective source of Fe for tobacco plants grown under low Fe supply

“…Remobilization and re-translocation of Fe via phloem to youngest leaves can reduce the severity of the chlorosis severity. However, an extremely poor redistribution via the phloem was found for Fe (Page and Feller, 2015). solutes (Offler et al, 2003).…”

“…solutes (Offler et al, 2003). In an experiment using 59Fe it has been observed that Fe is transported with the transpiration stream to minor leaf veins, followed by an accumulation in non-vascular tissues (Page and Feller, 2015) revealing a low xylem-phloem exchange for this element. In our work, however, probably due to its lower size, nano Fe was likely able to use this pathway more effectively than bulk Fe.…”

Accumulation of some heavy metals in plants and soils adjacent to Cairo – Alexandria agricultural highway

“…Moreover, inner leaves contained relatively higher Ni concentrations than the outer leaves. Such a result probably shows that cabbage probably needs Ni as a beneficial element (Welch & Shuman, 1995& Yusuf et al, 2011 since Ni is highly phloem-mobile (Page and Feller, 2015). Nickel concentrations exceed the permissible level (i.e.…”

Nutrient Concentration in Vegetative Organs of the Orchid <i>Laelia anceps</i> subsp. <i>anceps</i> Based on Mineral Fertilization and Biofertilization

“…The roots are the main site where mineral nutrient uptake takes place, and the mobilization of such nutrients from the roots to other tissues may depend on the nature of the mineral element. For instance, only a small amount of heavy metals reach the shoots and they stay mainly in the roots, since heavy metals show a low solubility at the root surface and in the root apoplast, or to compartmen-tation in cells avoiding release to the xylem (Page and Feller, 2015).…”