Amino acids exudation

G. Costa, J. C. Michaut, and A. Guckert, Amino acids exuded from axenic roots of lettuce and white lupin seedlings exposed to different cadmium concentrations. J. Plant Nutr. 20 883 (1997). 

Some ectomycorrhizal AF utilize amino acids (glycine, asparagine) (Table 4.1). This might allow these fungi to survive in ectomycorrhizal sym-bioses in untreated soils, utilizing amino acids exudated from plant roots and other sources of nutrients in the soil. Furthermore, nonectomycorrhizal EP AF also might survive in the form of vegetative hyphae in the rhizosphere or rhizoplane, since they also utilize amino acids as mentioned already (Yamanaka 2002). 

Root exudates Diffusates Sugars, organic acids, amino acids,... 

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). 

Only limited information is available on effects of potassium (K) supply on root exudation. Increa.sed exudation of sugars, organic acids, and amino acids has... 

In contrast to strategy 1 plants, grasses are characterized by a diffeient mechani.sm for Fe acquisition, with Fe-mobilizing root exudates as main feature. In response to Fe deficiency, graminaceous plants (strategy II plants) (39) are able to release considerable amounts of non-proteinaceous amino acids (Fig. 8B), so called phytosiderophores (PS), which are highly effective chelators for Felll (Fig. 8)... 

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a stress factor, which is frequently associated with Fe and Zn deficiency in calcareous soils (235) (Hajibo-huid, unpublished).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... 

Increased root exudation of amino acids in response to Cd toxicity has been reported for lettuce and white lupin grown in a hydroponic culture system under... 

Diffusion-mediated release of root exudates is likely to be affected by root zone temperature due to temperature-dependent changes in the speed of diffusion processes and modifications of membrane permeability (259,260). This might explain the stimulation of root exudation in tomato and clover at high temperatures, reported by Rovira (261), and also the increase in exudation of. sugars and amino acids in maize, cucumber, and strawberry exposed to low-temperature treatments (5-10°C), which was mainly attributed to a disturbance in membrane permeability (259,262). A decrease of exudation rates at low temperatures may be predicted for exudation processes that depend on metabolic energy. This assumption is supported by the continuous decrease of phytosiderophore release in Fe-deficient barley by decreasing the temperature from 30 to 5°C (67). 

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). 

Materials deposited by roots into the rhizosphere can be divided roughly into two main groups first, water-soluble exudates such as sugars, amino acids, or-... 

Nutrient availability also plays a major role in exudation, with deficiencies in N, P, or K often increasing the rate of exudation (218). It is believed that nutrient deficiency may trigger the release of substances such as organic acids or nonproteinogenic amino acids (phytosiderophores), which may enhance the acquisition of the limiting nutrient (219,220). An example here might be the release of phenolic acids such as caffeic acid in response to iron deficiency, which results in an increase in uptake of the cation (221). 

More recently, it was realized that rhizosphere cartton dynamics are more complex than these early models envisaged. Jones and Darrah (51-53) showed lhal roots actively scavenge their root exudates and that the re-uptake of exudates was selective. In most situations, sugars and amino acids were. scavenged by roots, while organic acid exudates were not (54). The authors also found that exudation losses were largely passive. This active involvement of the root essen-... 

A variety of chemicals may be leached from the aerial portions of plants by rainwater or by fog-drip (16) including organic acids, sugars, amino acids, pectic substances, gibberellic acids, terpenoids, alkaloids, and phenolic compounds. Colton and Einhellig (17) suggested that leaf leachates of velvetleaf (Abutilon theophrasti) may be inhibitory to soybean (Glycine maxT We have recently discovered specialized hairs on the stems of velvetleaf plants which exude toxic chemicals. 

Root exudates A wide variety of chemicals, such as sugars, amino acids, and aromatics, is excreted by roots of plants. Very little information is available on the allelopathic interaction of root exudates with the higher plants, except for the identification of a few products in isolated cases (46). 

The alkali-soluble protein of the peel of lemons treated with hydrogen sulfide, sulfur dioxide, and sulfuric acid contained radioactive sulfur, but the fruit treated with hydrogen sulfide had a significantly lower per cent specific activity in the alkali-soluble protein fraction than did the sulfur dioxide or sulfuric acid treated fruits (Table VII). These results suggest that sulfur dioxide and sulfuric acid react with protein more directly, while hydrogen sulfide perhaps must be oxidized first, as indicated in Table III. It also appears (from Table VII) that the alkali-soluble protein may have been dismuted as the amounts isolated were less in both the hydrogen sulfide and sulfur dioxide treated fruit than in the incubated or nonincubated controls. Other evidence of dismutation has been obtained in experiments where incubation at 60° C. was accompanied by the production of free ammonia (18), and the recovery of free ammonia and six amino acids in the exudates of incubated and sulfur-dusted fruits (18). 

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