Apoplastic

Bindschedler L.V. Dewdney J. Blee K. A. et al. Peroxidases -dependent apoplastic oxidative burst in Arabidopsis required for pathogen resistance // Plant J. 2006. V. 47. P. 851-863. 

Hartung, W., Radin, J.W. Hendrix, D.L. (1988). Abscisic acid movement into the apoplastic solution of water-stressed cotton leaves Role of apoplastic pH. Plant Physiology, 86, 908-13. 

Within the plant. Excessive concentrations of some ions occur in the tissue overall, in the cytoplasm, or in the apoplast. Effects include metabolic inhibition, interference with protein synthesis, cellular dehydration, stomatal closure and early senescence of leaves. Since both cytoplasm and apoplast are small compartments, imbalance between compartments may amplify the effects of excess salt, resulting in toxicity despite apparently moderate overall tissue concentrations. 

Apoplastic transport of sodium across the root Plant vigour (degree of dwarfing)... 

Even a moderate quantity of salt reaching the leaves has a drastic effect on photosynthesis and leaf ultrastructure, much more than could be accounted for by the average tissue concentration (Flowers etal., 1985). Salt may accumulate in the apoplast (because it is not taken up fast enough by the cells of the leaf), and this would result in severe localised water deficit (Oertli, 1968). Differences in apoplast/protoplast balance are thought to be responsible for varietal differences in tissue salt load which can be accommodated (tissue tolerance Yeo Flowers, 1986). The xylem concentration of Na" is very much lower to young leaves than to older leaves (Yeo et al., 1985). This is advantageous in salt resistance because it means that at least some leaves are protected from salt, which otherwise causes premature leaf death (Yeo Flowers, 1984 Fig. 2). 

Yeo, A.R., Yeo, M.E. Flowers, T.J. (1987). The contribution of an apoplastic pathway to sodium uptake by rice roots in saline conditions. Journal of Experimental Botany, 38, 1141-53. 

Smooth regions contain esterified and unesterified blocks but also regions with randomly distributed methyl groups. How are these generated What is the exact degree of esterification of the pectins exported into the apoplast ... 

Some divalent cations such as Cu and Pb form very stable complexes with pectate, but are unlikely to be present at sufiScient concentration in the apoplast of plants to form a major fraction of the counterions associated with the pectic fraction in vivo. The Al ion may deserve closer examination, as it is certainly able to displace Ca from cell walls and reaches substantial concentrations in plant roots under some conditions [60,61]. aluminium is not usually considered to be freely translocated, however. Basic peptides with their negative charges spaced at a similar interval to galacturonans (0.43 nm or a small multiple thereof) can in principle have a very high afiBnity for pectate [62,63], but the extensins that are associated with the most insoluble pectic fractions [M] do not appear to have this type of structure. The possibility that the non-extractable pectic polymers in most cell walls are very strongly complexed with some cation other than Ca " cannot be ruled out, but there is little evidence to support it at present. 

Uchida E, T Ouchi, Y Suzuki, T Yoshida, H Habe, I Yamaguchi, T Omori, H Nojiri (2005) Secretion of bacterial xenobiotic-degrading enzymes from transgenic plants by an apoplastic expression system applicability for phytoremediation. Environ Sci Technol 39 7671-7677. 

In soil, the chances that any enzyme will retain its activity are very slim indeed, because inactivation can occur by denaturation, microbial degradation, and sorption (61,62), although it is possible that sorption may protect an enzyme from microbial degradation or chemical hydrolysis and retain its activity. The nature of most enzymes, particularly size and charge characteristics, is such that they would have very low mobility in soils, so that if a secreted enzyme is to have any effect, it must operate close to the point of secretion and its substrate must be able to diffuse to the enzyme. Secretory acid phosphatase was found to be produced in response to P-deficiency stress by epidermal cells of the main tap roots of white lupin and in the cell walls and intercellular spaces of lateral roots (63). Such apoplastic phosphatase is safe from soil but can be effective only when presented with soluble organophosphates, which are often present in the soil. solution (64). However, because the phosphatase activity in the rhizo-sphere originates from a number of sources (65), mostly microbial, and is much higher in the rhizosphere than in bulk soil (66), it seems curious that plants would have a need to secrete phosphatase at all. 

W. J. Horst, The role of the apoplast in aluminium toxicity and resistance of higher plants a review. Z. Pjianz.enerndhr. Bodenk. I5S A 9 (1995). 

Further progress may derive from a more accurate definition of the chemical and physical properties of the humic substances present at the rhizosphere and how they interact with the root-cell apoplast and the plasma membrane. An interaction with the plasma membrane H -ATPase has already been observed however this master enzyme may not be the sole molecular target of humic compounds. Both lipids and proteins (e.g., carriers) could be involved in the regulation of ion uptake. It therefore seems necessary to investigate the action of humic compounds with molecular approaches in order to understand the regulatory aspects of the process and therefore estimate the importance of these molecules as modulators of the root-soil interaction. 

Bonfante et al. (73) used monoclonal antibodies and enzyme-gold complexes to reveal pectins and cellulose at the interface between the fungal wall and the host plasma membrane in AM roots (Fig. 6), and additional wall components have been investigated with other molecular probes (74-76). These studies indicate that the interface is an apoplastic space of high molecular complexity where the boundaries of the partners are defined. The examination of other endomycorrhizal systems has demonstrated that their interface is morphologically similar but different in composition. Cellulose and pectins are present at the interface... 

Takahama, U. Oniki T. Shimokawa H. A possible mechanism for the oxidation of sinapyl alcohol hy peroxidase-dependent reactions in the apoplast enhancement of the oxidation hy hydroxycinnamic acids and components of the apoplast. Plant Cell Physiol. 1996, 37, 499-504. 

IV. Superoxide dismutase (EC 1.15.1.1) Within a cell the superoxide dismutases (SODs) constitute the first line of defense against ROS. Superoxide radical (02) is produced where an electron transport chain is present, as in mitochondria and chloroplasts, but 02 activation may occur in other subcellular locations such as glyoxysomes, peroxisomes, apoplast and the cytosol. Thus SODs are present in all these cellular locations, converting superoxide into hydrogen peroxide and water (i.e. copper/zinc SODs are typically found in the nuclei and cytosol of eukaryotic cells). 

Alterations to the proteins and pre-proteins expressed by cultured plant cells have been used to facilitate product recovery. A leader sequence is required for foreign protein secretion from plant cells into the apoplast and then into the culture medium. As indicated in Table 2.1, plant, mammalian and viral sequences have been employed to achieve the entry of transgenic proteins into the bulk-flow pathway in plant cultures. 

Proteins produced in plant cells can remain within the cell or are secreted into the apoplast via the bulk transport (secretory) pathway. In whole plants, because levels of protein accumulated intracellularly, e. g. using the KDEL sequence to ensure retention in the endoplasmic reticulum, are often higher than when the product is secreted [58], foreign proteins are generally not directed for secretion. However, as protein purification from plant biomass is potentially much more difficult and expensive than protein recovery from culture medium, protein secretion is considered an advantage in tissue culture systems. For economic harvesting from the medium, the protein should be stable once secreted and should accumulate to high levels in the extracellular environment. 

Transcriptional inhibitors could be used simultaneously. Rifampicin blocks chloroplast and mitocondrian RNA synthesis [23, 24], while tagetitoxin is a very specific inhibitor of chloroplast RNA polymerase [25]. Treatment with these antibiotics does not inhibit Rubisco SSU synthesis since the promoter is part of the nuclear genome, while the cytosolic ribosomes are not affected by streptomycin. Therefore SSU promoters can be used to drive transgene expression and facilitate the accumulation of recombinant proteins. Expressed proteins are targeted to a suitable cellular compartment, such as the cytoplasm, apoplastic space or chloroplast, depending on the nature of the protein. 

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