Soil amino acids

Animals, including humans, cannot synthesise all the different amino adds they need and thus require them in their diet. These amino adds are called the essential amino acids. Proteins in food are hydrolysed in the digestive tract and the resulting amino acids are reassembled into proteins within the animal s cells. All animals are ultimately dependent on plants for protein, as it is plants that create protein by combining inorganic nitrogen from the soil (as nitrate) with organic molecules derived from carbon from the atmosphere (as CO2). 

Amino Acids. Early observations on the liberation of amino acids by plant roots were reviewed by Loehwing (94), Rademacher (121), and Borner (12). Free amino acids have been isolated from soil fractions (119), and the excretion of a variety of ninhydrin-positive compounds by plant roots has been demonstrated under controlled conditions by Katznelson et al. (18), Rovira (121), and Pearson and Parkinson (115). 

In the soil, an imbalance of amino acids, the presence of D-amino acids derived from microbial metabolism, or analogs and homologs of constituent protein amino acids could produce a deviation in the... 

The uptake and biotransformation of benzene from soil and the atmosphere has been studied in a nnmber of plants. It was shown that in leaves of spinach Spinacia oleraced) the label in -benzene was fonnd in mnconic, fnmaric, snccinic, malic, and oxalic acids, as well as in specific amino acids, and that an enzyme preparation in the presence of NADH or NADPH prodnced phenol (Ugrekhelidze et al. 1997). 

Reabsorption of the ligand plus its metal partner is a necessary requirement of processes like Fe acquisition by phytosiderophores (32). However, whether or not reabsorption of diffusates, which undoubtedly occurs in solution cultures (45), has a significant role to play is uncertain, largely because in soil most diffusates (sugars, amino acids, and other organic acids) are readily utilized by microorganisms or adsorbed by soil colloids. 

W. A. Ayers and R. H. Thornton, Exudation of amino acid.s by intact and damaged roots of wheat and peas. Plant Soil 2S I93 (1968). 

A new approach to study root exudation of distinct compounds in soil-grown plants uses inoculation of roots with genetically engineered reporter bacteria, which are able to indicate the presence of particular compounds by indicator reactions, such as production of ice-nucleation proteins. This technique has been employed to detect the release of amino acids from roots of soil-grown A vena harbata (56). 

Despite increased citrate accumulation in roots of Zn-deficient rice plants, root exudation of citrate was not enhanced. However, in distinct adapted rice cultivars, enhanced release of citrate could be observed in the presence of high bicarbonate concentrations in the rooting medium, a stress factor, which is frequently associated with Fe and Zn deficiency in calcareous soils (235) (Hajibo-huid, unpublished). This bicarbonate-induced citrate exudation has been related to improved Zn acquisition in bicarbonate-tolerant and Zn-efficient rice genotypes (Fig. 9) (23S). Increased exudation of sugars, amino acids, and phenolic compounds in response to Zn deficiency has been reported for various dicotyledonous and monocotyledonous plant species and seems to be related to increased... 

T. Shepherd and H. V. Davies, Effect of exogenous amino acids, glucose and citric-acid on the patterns of short-term amino acid accumulation and loss of amino acids in the root-zone of sand-cultured forage rape (Bras.sica napiis L.). Plant Soil 158 111 (1994). 

C. B. Sulochana, Amino acids in root exudates of cotton. Plant Soil (6 312 (1962). 

D. L. Jones, A. C. Edwards, K. Donachie, and P. R. Darrah, Role of proteinaceous amino acids relea.sed in root exudates in nutrient acquisition from the rhizosphere. Plant Soil /5S 183 (1994). 

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