Apoplastic space

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... 

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. 

In transgenic plants, the expression of heterologous proteins can be targeted in different organs, whereas in animals the biological liquids where antibodies can be expressed and then separated are blood and milk. Accumulation in different cellular compartments such as the cytosol, the apoplastic space, and the endoplasmic reticulum are well-described locations where antibodies are expressed.48 A high accumulation of active antibodies was found when targeting the apoplastic space. This has been demonstrated in tobacco seeds and potato tubers.48 The amount of expressed protein compared to the total extractable proteins is also an important information for the purification of antibodies. In corn seeds, for instance, the expressed proteins represent up to about 5% of total extractable proteins.49... 

Trifolium repens Linamarin Apoplastic space Butler et al. (1965), Kakes (1985)... 

Hevea brasiliensis Linamarin Apoplastic space Selmar et at. (1987), Kurzhals et at. (1990)... 

Lotus comiculatus Linamarin 7 Apoplastic space Rissler and Millar (1977)... 

Phaseolus lunatus Linamarin 7 Apoplastic space Frehner and Conn (1987)... 

The plasma membranes of growing plant cells select to incorporate sugars, amino adds, ions and other low molecular weight compounds from the apoplastic space, and then, the cells have a certain level of osmotic pressure. The difference between their osmotic pressure and their wall pressure (=turgor pressure) is due to motive power (suction force) to suck water from the apoplastic space (Figure 1). The plant hormone auxin, which decreases the wall pressure in a growing plant cell, therefore induces cell elongation or expansion. 

Flg.1 Three models explaining aspects of subceUular transport of phenolic compounds, (a) Transporter model. Following biosynthesis at multienzyme complexes localized at the cytosolic face of ER membranes (yellow stars), flavonoids (red cicrcles) diffuse in the cytosol and are transported into the vacuole or into the apoplastic space by directly energized pumps (blue) or H+-driven antiporters (violet)... 

Given that the cuticle is the result of a relatively slow accumulation of compounds excreted by the epidermis cells through exocytosis, and that the final steps of their biosynthesis occur in the apoplastic space, it seems likely that decreasing clearly the external accumulation of waxes or cutin requires a long time during which biosynthesis of these compounds has to be severely inhibited. The inhibitors selected for this experimentation had therefore to be stable for days inside the plant. 

The leaching of cations, in particular of K, Ca and Mg, plays a crucial role in leaf ionic relations. As a regular part of the biogeo-chemical nutrient cycling, the flux of leached cations needs to be balanced by an equivalent uptake and translocation. The plant s ability to adjust an increased flux due to acidic deposition determines the extent and duration of leaching-induced, altered ionic relations, first of all within the apoplastic space. - Basic principles and implications of cation leaching will be presented in order to elucidate this kind of an indirect effect of acid rain. 

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