Phytosiderophores acid

Phytosiderophores structures and properties of tnugineic acids and their metal complexes. Y. Sugiura and K. Nomoto, Struct. Bonding (Berlin), 1984,58,107 (50). 

Strohmeier W (1968) Problem und Modell der homogenen Katalyse. 5 96-117 Sugiura Y, Nomoto K (1984) Phytosiderophores - Structures and Properties of Mugineic Acids and Their Metal Complexes. 58 107-135 Sun H, Cox MC, Li H, Sadler PJ (1997) Rationalisation of Binding to Transferrin Prediction of Metal-Protein Stability Constants. 88 71-102 Swann JC, see Bray RC (1972) II 107-144... 

Sugiura, Y., Nomoto, K. Phytosiderophores - Structures and Properties of Mugineic Acids and Their Metal Complexes. Vol. 58, pp. 107-135. 

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. 

Amino acids and amides All 20 proteinogenic amino acids, aminobutyric acid, homoserine, cysrathionine, mugineic acid phytosiderophores (mugineic acid, deoxymugineic acid, hydroxymugineic acid, epi-hydroxymugineic acid, avenic acid, distichonic acid A)... 

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)... 

Table 5 Effect of Anion-Channel Antagonists (Anthracene-9-carboxylic acid, ethacrynic acid each 100 fiM) and of Brefeldin A (Exocytosis Inhibitor 45 fiM) on Release of Phytosiderophores from Roots of Fe-Deficient Barley and Mai/.e...

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). 

S. Tagaki, K. Nimito, and T. Takemoto, Physiological aspect of mugineic acid, a possible phytosiderophore of graminaceous plants. J. Plant Nuir. 7 469 (1984). 

T. Sakaguchi, N. K. Nishizawa, H. Nakanishi, E. Yoshimura, and S. Mori, The role of potassium in the secretion of mugineic acids family phytosiderophores from iron-delicient barley roots. Plant Soil 275 221 (1999). 

J. F. Ma, and K. Nomoto, Effective regulation of iron acquisition in graminaceous plants. The role of mugineic acids as phytosiderophores. Physiol. Plant. 97 609 (1996). 

S. Kawai, S. Tagaki, and Y. Sato, Mugineic acid-family phytosiderophores in root secretions of barley, corn and sorghum varieties. J. Plant Nutr. // 633 (1988). 

S. Tagaki, S. Kamei, and M. H. Yu, Efficiency of iron extraction from. soil by mugineic acid family phytosiderophores. J. Plant Nutr. 11 643 (1988). 

S. Shojima, N. Nishizawa, S. Fushiya, S. Nozoe, T. Irifune, and S. Mori, Biosynthesis of phytosiderophores in vitro biosynthesis of 2 -deoxymugineic acid from L-methionine and nicotianamine. Plant Phy.siol. 93 1491 (1990). 

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). 

In the first case the mechanisms are based on an increased reducing capacity of Fe(lll)-chelates, a necessary step in the uptake process, with a concurrent increase in acidification and release of organic acids into the rhizosphere in the latter case molecules having high affinity for Fe (phytosiderophores) are synthesized and released into the rhizosphere when Fe is lacking. 

In the rhizosphere, microorganisms utilize either organic acids or phytosiderophores to transport iron or produce their own low-molecular-weight metal chelators, called siderophores. There are a wide variety of siderophores in nature and some of them have now been identified and chemically purified (54). Pre.sently, three general mechanisms are recognized for utilization of these compounds by microorganisms. These include a shuttle mechanism in which chelators deliver iron to a reductase on the cell surface, direct uptake of metallated siderophores with destructive hydrolysis of the chelator inside the cell, and direct uptake followed by reductive removal of iron and resecretion of the chelator (for reviews, see Refs. 29 and 54). 

These data strongly suggest that siderophore production by root-colonizing microorganisms is induced only at a level neeessary to supplement that which is not provided by phytosiderophores and organic acids released during the plant iron stress response. Thus, the plant iron stress response may control iron availability to microorganisms in the rhizosphere. 

E. Jurkevitch, Y. Hadar, Y. Chen, M. Chino, and S. Mori, Indirect utilization of the phytosiderophore mugineic acid as an iron source to rhizosphere fluorescent Pseudomonas. BioMetals 6 119 (1993). 

Dissolved organic molecules have many acidic functions (hydroxol and carbonic groups) to complex trace elements and their compounds to form soluble chelates. This is one of the reasons why solubility and bioavailability of trace elements in the rhizosphere are higher than bulk soils. At the same time, many organic acids also directly dissolve trace elements and their compounds in soils. Plant-produced phytosiderophores facilitate elements, such as Fe and Zn, uptake by plants (Zhang et al., 1991 Romheld, 1991 Hopkins et al., 1998). However, Shenker et al. (2001) did not find significant uptake of the Cd-phytosiderophores complex by plant roots. 

Nicotianamine is converted to a first phytosiderophore, 2 -deoxym ugeneic acid, by amino transfer and subsequent reduction (Figure 4.3). Nicotianamine aminotransferase, which catalyzes the initial amino transfer reaction, the first step... 

The mugineic acid family of phytosiderophores comprises six compounds mugineic acid, avenic acid, 3-hydroxymugeneic acid, 3-epihydroxymugeneic acid,... 

Figure 7.8 Structure of the phytosiderophore mugeneic acid and its precursor nicotianamine.

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