Phytosiderophore

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. 

N. von Wiren, S. Mori, H. Marschner, and V. Romheld, Iron inefficiency in maize mutant ysl Zea mays L. cv. Yellow-stripe) is caused by a defect in uptake of iron phytosiderophores. Plant Physiol. 106 1 (1994). 

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)... 

Table 3 Effect of Various Antibiotics on Phytosiderophore (PS) Concentrations in Root Exudates and PS Uptake in Fe-deficient Barley and Sorghum...

Treatment/Plant species Phytosiderophore concentration in root exudates [relative values] Fe-PS uptake rate... 

Vesicles have also been implicated in storage and release of LMW compounds such as phenolics (91,92) and phytosiderophores (93) in plant roots, but the characterization of mechanisms remains to be established (see Sect. 4.3.2). 

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...

Formation of stable chelates with phytosiderophores occurs with Fe but also with Zn, Cu, Co, and Mn (Fig. 8) (39,207,208) and can mediate the extraction of considerable amounts of Zn, Mn, Cu, and even Cd in calcareous soils (204,209). There is increasing evidence that PS release in graminaceous plants is also stimulated in response to Zn deficiency (210-212), but possibly also under Mn and Cu deficiency (213). Similar to Fe deficiency, the tolerance of different graminaceous plant species to Zn deficiency was found to be related to the amount of released PS (211,212), but correlation within cultivars of the same species seems to be low (214). It is, however, still a matter of debate as to what extent PS release is a specific response to deficiencies of the various inicronutrients. Cries et al. (213) reported that exudation of PS in Fe-deficient barley was about 15-30 times greater than PS release in response to Zn, Mn, and Cu deficiency. In contrast, PS exudation in Zn-deficient bread wheat was in a similar range as PS... 

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). 

V. Rdmheld, The role of phytosiderophores in acquisition of iron and other micronutrients in graminaceous species an ecological approach. Plant Soil 730 127 (1991). 

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

H. Marschner, V. Romheld, and M. Kissel, Localization of phytosiderophore re-lea.se and iron uptake along intact barley roots. Physiol. Plant. 71 51 (1987). 

F. Awad, V. Romheld, and H. Marschner, Mobilization of ferric iron from a calcareous soil by plant-borne chelators (phytosiderophores). J. Plant Niitr. // 70l (1988). 

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). 

V. Romheld and H. Marschner, Evidence for a specific uptake system for iron phytosiderophores in roots of grasses. Plant Physiol. 80 15 (1986). 

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). 

J. C. Brown, V. D. Jolley, and C. M. Lytle, Comparative evaluation of iron solubilizing substances (phytosiderophores) released by oats and com iron-efficient and iron-inefficient plants. Plant Soil 130 151 (1991). 

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). 

A. Walter, A. Pich, G. Scholz, H. Marschner, and V. Romheld, Effects of iron nutritional status and time of day on concentrations of phytosiderophores and nico-tianamine in different root and shoot zones of barley. J. Plant Nutr. 18 1511 (1995). 

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). 

S. Mori and N. Nishizawa, Methionine as a dominant precursor of phytosiderophores in graminaceae plants. Plant Cell Physiol. 2S 1081 (1987). 

I. Cakmak, B. Erenoglu, K. Y. Giiliit, R. Derici, and V. Romheld, Light-mediated release of phytosiderophores in wheat and barley under iron or zinc deficiency. Plant Soil 202 309 (1998). 

Cakmak, K. Y. Giiliit, H. Marschner, and R. D. Graham, Effect of zinc and iron dehciency on phytosiderophore release in wheat genotypes differing in zinc efhciency. J. Plant Nutr. I7 (1994). 

B. G. Hopkins, D. A. Whitney, R. E. Laniond, and V, D. Jolley, Phytosiderophore release by sorghum wheat, and corn under zinc dehciency. J. Plant Nutr. 21 2623 (1998). 

D. Gries, S. Briinn, D. E. Crowley, and D. R. Parker, Phytosiderophore release in relation to micronutrient metal dehciencies in barley. Plant Soil / 72 299 (1995). 

B. Erenoglu. 1. Cakmak, H. Marschner, V. Rdmheld, S. Eker, H. Daghan. M. Ka-layci, and H. Ekiz, Phytosiderophore release does not relate well with Zn efhcieney in different bread wheat genotypes. J. Plant Nutr. / 9 1569 (1996). 

N. V. Wiren, H. Marschner, and V. Rdmheld, Roots of iron-efficient maize also absorb phytosiderophore-chelated zinc. Plant Physiol. 11 l l 9 (1996). 

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. 

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