Apoplastic phenolics

Some apoplastic phenolics play constitutive chemical defense as it has been demonstrated in bark tissues of woody plants (Franceschi et al, 2005). In leaf mesophyll of Quercus robur L., immunohistological studies revealed that cell wall is the main site of common accumulation of pentagalloylglucose, the precursor of the esterification enzyme (galloyltransferase)... 

In summary the rate of depletion (i.e., root uptake and microbial utilization) varies with type phenolic acid present, concentration, pH, time of day, time of day of treatment, number of treatments, composition of phenolic acid mixtures, whether uptake is apoplastic or symplastic, phenolic acid-utilizing microbial populations present on roots and in the nutrient solution, and aeration. Phenolic acid treatments of seedlings in nutrient culture modify microbial populations on root surfaces (rhi-zoplane) and in the nutrient solutions. Once taken up by roots, phenolic acids were distributed throughout seedlings. Highest concentrations, however, were retained in the roots. 

Takahama, U., 1993b, Regulation of peroxidase-dependent oxidation of phenolics by ascorbic acid Different effects of ascorbic acid on the oxidation of conyferyl alcohol by the apoplastic soluble and cell wall-bound peroxidases from epicotyls of Vigna angularis, Plant Cell Physiol. 34 809-817. 

Phenolics as major components of apoplastic chemical protection... 

Fig. 6.9 Phenolics in apoplast and vacuoles play an equivalent role as AsA in chloroplast and cytosol. Ascorbate peroxidases (APX) scavenge H2O2 at the expense of ascorbic acid (AsA) within both chloroplasts and cytosol. Similarly, apoplastic peroxidase (POX) apoplastic peroxidases (POX) scavenge H2O2 within apoplast and vacuoles at the expense of phenolics. Phenoxyl radicals can be reduced in apoplast and vacuoles via monodeshydrogenoascorbate (MDHA) reductase (MDHAR) or AsA. Enzymes are represented in boxes. Modified from Sakihama et al. (2000, 2002).

Traces of L-rhamnose and L-fucose were found in the xylem of Pinus sylvestris (27). These sugars, along with L-arabinose and D-galactose with which they were found, could have arisen from the breakdown of pectic substances (Sect. 4.10.2) or phenolic glycosides (Sect. 4.8). Traces of the D-ribose have been found in both the symplast and apoplast of Betula pendula (50). 

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)... 

Ethofumesate and fluridone are slightly more lipophilic little information is available about ethofumesate whereas fluridone is transported in the apoplast. Dinoseb and related phenols show limited movement in the apoplast, probably because they act primarily as contact herbicides causing... 

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