Roots symplasm

An enhanced uptake of metals into the root symplasm was found in T. caerulescens compared to the related non-accumulator, T. arvense [68,69], and a reduced sequestration into the root vacuoles was associated with the higher root to shoot translocation efficiency of T. caerulescens [49,69,70]. Xylem loading and xylem transport are key steps in Cd hyperaccumulation, as it will be discussed in detail in the section about transport proteins below, and as it was commented by White et al. already 10 years ago [71]. Also in non-hyperaccumulators, the degree of Cd accumulation in above-ground tissues mainly depends on xylem transport [72]. 

An ion entering a root may immediately enter the symplast by crossing the plasma membrane of an epidermal cell, or it may remain in the apoplasm and diffnse throngh cell walls. It may snbseqnently enter the symplasm by crossing... 

Figure 1-4 presents longitudinal and cross-sectional views near the tip of a root, indicating the types of cells that can act as barriers to flow. Water may fairly easily traverse the single cell layer of the root epidermis to reach the cortex (see Chapter 1, Section 1.1D). The root cortex often consists of 5 to 10 cell layers, with the cytoplasm of adjacent cells being continuous because of plasmodesmata (Fig. 1-14). The collective protoplasm of interconnected cells is referred to as the symplasm (see Chapter 1, Section 1.5B). In the...

Plant iron uptake can be divided into two distinct families, with quite distinct strategies. Strategy I plants reduce Fe + to Fe + outside of the roots, and then take up the Fe +. In contrast. Strategy II plants solubilise Fe + by excreting Fe +phytosiderophores, which are taken up by specihc transporters and the iron is then reduced to Fe " " in the symplasm of the root cell (Fig. 7.14). In Strategy I plants, (dicotyledons such as Arabidopsis pea. 

The Al concentration in the inner cell layers and root cell cytoplasm (symplasm) of plants was lower than in the surrounding medium (Kochian and Jones). Between 30% and 90% of absorbed Al was localized in the apoplast (Mossor-Piettraszewska 2001). Al and silicon appear to be co-localized in root cell walls, perhaps reflecting the primary internal sites of aluminosilicate formation and Al detoxification (Hodson and Sangster 1999). 

The internal pH (- 7) of cells, compared to the much lower pH around the plant root, changes Al species. During uptake, Al has been calculated to be associated with charged organic compounds present in symplasm, predominantly citrate, but also ATP and GTP, thereby reducing free cytoplasmic Al to picomolar concentrations (Kochian and Jones 1997). These do not appear to be toxic Al species, but may permit intracellular Al redistribution. 

Two ways of water transport in a plant have been recognized apoplasmic and symplasmic (Figure 32.4). It is generally agreed that the cell walls provide the major pathway of water movement in plant material. The ratio of volume flows in the apoplasmic and symplasmic (vacuole-to-vacuole) pathways is of the order of 50 1 in leaf tissue [1]. For the root cortex, the ratio is lower. 

Fig. 13. The distribution of the symplasmic tracer (CMNB - caged fluorescein (fluorescein bis-(5-carboxymethoxy-2-nitrobenzyl ether, dipotassium salt) within the Ambidopsis somatic embryo, showing a border in symplasmic communication between the root meristem and other parts of the somatic embryo, which indicates that the symplasmic subdomains correspond with the main morphological parts of the embryo (fluorescence microscope h - hypocotyl, c - cotyledon, r - root bar = 150 pm author - Wrobel, PhD thesis).

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