Phenol acidity and

Key words xylose-rich pectic polysaccharide, pectin, wheat straw, extraction, sugars, lignin, FT-IR, phenolic acids and aldehydes. 

Phenolic acids and polyphenols are natural plant constituents which impart flavor and textural components to beverages made from these plants. In order to better understand the role of these easily oxidized compounds in the flavor and stability of beverages, it is necessary to determine them at the low concentrations they occur. LCEC has been shown to be quite effective at these trace determinations... 

Allelopathic inhibition of mineral uptake results from alteration of cellular membrane functions in plant roots. Evidence that allelochemicals alter mineral absorption comes from studies showing changes in mineral concentration in plants that were grown in association with other plants, with debris from other plants, with leachates from other plants, or with specific allelochemicals. More conclusive experiments have shown that specific allelochemicals (phenolic acids and flavonoids) inhibit mineral absorption by excised plant roots. The physiological mechanism of action of these allelochemicals involves the disruption of normal membrane functions in plant cells. These allelochemicals can depolarize the electrical potential difference across membranes, a primary driving force for active absorption of mineral ions. Allelochemicals can also decrease the ATP content of cells by inhibiting electron transport and oxidative phosphorylation, which are two functions of mitochondrial membranes. In addition, allelochemicals can alter the permeability of membranes to mineral ions. Thus, lipophilic allelochemicals can alter mineral absorption by several mechanisms as the chemicals partition into or move through cellular membranes. Which mechanism predominates may depend upon the particular allelochemical, its concentration, and environmental conditions (especially pH). 

Although several allelochemicals (primarily phenolic acids and flavonoids) have been shown to inhibit mineral absorption, only the phenolic acids have been studied at the physiological and biochemical levels to attempt to determine if mineral transport across cellular membranes can be affected directly rather than indirectly. Similar and even more definitive experiments need to be conducted with other allelochemicals that are suspected of inhibiting mineral absorption. Membrane vesicles isolated from plant cells are now being used to elucidate the mechanism of mineral transport across the plasma membrane and tonoplast (67, 68). Such vesicle systems actively transport mineral ions and thus can serve as simplified systems to directly test the ability of allelochemicals to inhibit mineral absorption by plant cells. 

The results of these experiments support the hypothesis that inhibitory allelochemicals may interfere with the water balance of seedlings. Alterations in the water status of grain sorghum seedlings were caused both by known phenolic acids and by allelopathic weeds. 

Phenolic acids and aliphatic acids are both involved in the biosynthesis of suberin, and phenolic acids are not synthesized in tissue slices that do not undergo suberization. 

P. Mejanelle, J. Bleton, S. Goursaud, A. Tchapla, Identification of phenolic acids and inositols in balms and tissues from an Egyptian mummy, J. Chromatogr. A, 767, 177 186 (1997). 

Mane C, Souquet JM, Olle D, Verries C, Veran F, Mazerolles G, Cheynier V and Fulcrand H. 2007. Optimization of simultaneous flavanol, phenolic acid, and anthocyanin extraction from grapes using an experimental design application to the characterization of champagne grape varieties. J Agric Food Chem 55(18) 7224—7233. 

Michalkiewicz A, Biesaga M and Pyrzynska K. 2008. Solid-phase extraction procedure for determination of phenolic acids and some flavonols in honey. J Chromatogr A 1187( 1-2) 18-24. 

Stalikas C. 2007. Extraction, separation, and detection methods for phenolic acids and flavonoids. J Sep Sci 30(18) 3268-3295. 

NprbaskR, Aaboer DB, Bleeg IS, Christensen BT, Kondo T, Brandt K (2003) Flavone C-glycoside, phenolic acid, and nitrogen contents in leaves of barley subject to organic fertilization treatments. J Agric Food Chem 51 809-13... 

The urinary amino acids reflect both their high concentration in the blood, due to poor functioning of the liver, and failure of renal tubular reabsorption. The phenolic acids and tyrosine in the urine are evidence... 

L. Yao, N. Datta, F. A. Tomas-Barberan, F. Ferreres, I. Martos and R. Singanusong, Flavonoid, phenolic acids and abscisic acid in Australian and New Zealand Leptospermum honeys. Food Chem. 81 (2003) 159-168. 

Buchsbaum, R., Valiela, I., and Swan, A. (1984). The role of phenolic acids and other plant constituents in feeding of Canada geese in a coastal marsh. Oecologia 63,343-349. 

Phenolic Acids and Derivatives Studies on the Relationship Structure,... 

Silva, E. A. M. Borges, E Gulmaraes, C. Lima,]. L. F. C. Matos, C. Reis, S. Phenolic Acids and Derivatives Studies on the Relationship among Structure, Radical Scavenging Activity, and Physicochemical Parameters.]. Agric. Food Chem. 2000, 48, 2122-2126. 

Many nonvolatile and thermally labile allelochemicals can be well separated by liquid chromatography (LC). Identification of the separated components on-line by mass spectrometry (MS) is of great value. Fused-silica LC columns of 0.22 mm ID packed with small-particle material are used in the described LC/MS system. The shape of the column end allows direct connection to a electron impact ion source of a magnetic sector mass spectrometer. Separations by LC are reported and LC/MS mass spectra are shown for monoterpenes, diterpene acids, phenolic acids and cardiac glycosides. The LC/MS system provides identification capability and high-efficiency chromatography with a universal detector. 

Phenolic acids are often found in plant tissue, and have been implicated in many cases of allelopathy (4). Figure 6 shows a separation of three free phenolic acids and Figure 7 shows mass spectra obtained from these compounds. These spectra give both molecular weight and structural information. Phenolic acids can easily be thermally decarboxylated. The height of the molecular ion peak varies owing to ion source temperature. The variation depends also to some extent on the composition of the LC eluent, and this will be further examined. 

Several phenolic acids and many nonspecific allelopathic conditions have been shown to alter the mineral content of plants, and certainly phenolic allelochemicals may perturb cellular functions in a number of ways that are of importance to plant nutrition (34,35). However, raising fertility does not always suppress allelopathic inhibition, and the interrelationships between these two factors are still not clear. Bhowmik and Doll (36) showed that allelopathic inhibition of corn and soybeans by residues of five annual weeds was not alleviated by supplemental nitrogen or phosphorus. Similarly, an increase in fertilizer did not overcome inhibition of corn by quackgrass or circumvent the autotoxicity of berseem clover Trifolivm alexandrium L.) (37,38). Even when raising nutrient levels releases Inhibition, it does not mean that allelopathy was inoperative under the original conditions. These instances simply illustrate the importance of the Interaction of the two stress conditions. 

Two cases will be presented to illustrate the difficulty in establishing allelopathy and in linking the agent to poor crop growth. Specifically, the role of phenolic acids and the role of toxin-producing pseudomonads colonizing wheat roots will be examined. 

---