This note reports the role of VO(IV) on Fe(III) mobilization from a Fe(III)-polygalacturonate network. The effect of the reaction on the physical properties of the system is also considered

Deiana, Salvatore Andrea

Gessa, Carlo Emanuele

Manunza, Bruno Mario Luigi

Usai, Marianna

English

UnissResearch

Gessa, Carlo Emanuele; Deiana, Salvatore Andrea; Manunza, Bruno Mario 
Luigi; Usai, Marianna (1991) Transfer of metal ions at the soil-root  
interface: role of VO2+ on Fe3+ mobilization from a Fe(III)-network. 
Giornale botanico italiano, Vol. 125 (4), p. 476-478. ISSN 0017-0070. 
http://eprints.uniss.it/7867/
Documento digitalizzato dallo Staff di UnissResearch
GIORNALE 
BOTANICO 
ITALIANO 
FONDATO NEL 1844 
ISSN-0017-0070 
PUBBLlCATO DALLA SOCIETA BOTANICA ITALlANA 
CON IL CONTRIBUTO DEL CONSIGLlO NAZIONALE DELLE RICERCHE 
Vol. 125, n. 4 , 1991 
Societa Italiana di Fisiologia Vegetale 
31 0 Congresso Sociale 
Perugia 
15-18 Ottobre 1991 
RELAZIONI , COMUNICAZIONI 
DIMOSTRAZIONI - RIASSUNTI 
TRANSFER OF METAL IONS AT THE SOIL-ROOT INTERFACE: ROLE OF V02+ 
ON Fe3+ MOBILIZATION FROM A Fe(III)-NElWORK. 
C. Gessa, S. Deiana, B. Manunza and M. Usai. 
Istituto di Chimica Agraria dell'Universita di Sassari. 
The transfer of micronutrientes from soiJ to plasmalemma is 
mediated by a mucilaginous interface composed predominantly of 
polisaccharides organized in a fibrillar structure. The flow of metal ions is 
regulated by their affinity for the functional groups of the fibrils: ions that 
interact electrostatically [e.g .. Ca(IJ), Mn(lJ) , Fe(II)] are more easily removed 
from the reticulation sites than covalently bound [e.g. Cu(lI) , Fe (11\) , 
VO(IV»). The availability of the immobilized ions for the absorbing cells is 
mediated principally by the complexation, reduction and exchange 
processes. 
As a part of our research in understanding the mechanisms involved 
in the ionic mobilization at the mucilaginous interface we synthesized a 
network of Ca-polygalacturonate with a fibrillar structure similar to that of 
the real systems (Gessa C. and Deiana 5., 129: 211-217, 1990; Gessa C. 
and Deiana S., 00: 000-000, 1991). 
The arrangement of the fibrils is altered following the substitution of 
Ca(II) with Fe(llI) ions. We have shown that biomolecules as caffeic acid 
are able to reduce the reticulated iron and that the redox process re-
establishes the porous system which characterizes the Ca-network (Gessa 
C. et al.: 136-141, 1990). This has important implications in plant nutrition 
as the porous structure of the interface makes easier the transfer of 
Ilutrients towards the plasmalemma. 
This note reports the role of VO(IV) on Fe(lII) mobilization from a 
Fe(III)-polygalacturonate network. The effect of the reaction on the 
physical properties of the system is also considered. 
EXPERIMENTAL 
Kinetic tests were carried out at room temperature in 10-2 M NaCI04 
aqueous solutions. The extent of occurrence of the reaction was monitored 
on the basis of the iron (11) content, in the form of the 1,1 O-phenantroline 
complex (absorption measurements in the visible region, at 510 nm). 
The calcium and oxovanadium ions present in the external liquid 
phase and complexed by the organic matrix were determined by using a 
plasma emission spectrometer. Electron-micrographs were made by 
scanning electron microscopy (SEM) (Gessa C. and Deiana S.,OO:OOO-
000, 1991). 
476 
RESULTS AND DISCUSSION 
In aqueous phase the VO(IV) reduces the Fe(lII) according to the 
following stoichiometry: 
In Fig. 1 A and 1 B are reported the yield in Fe(lI) as a function of pH and 
time, respectively. These plots show a high redox activity of the system in 
the pH range of 2 - 4.5: about 90% of the Fe(lIl) is reduced in few minutes. 
30 1 /;;0-=' 
:0 ::V
1 
'" 1:0: 
"1=<15 :::t.. IS 
10 
5 
o i 
2.0 
I 
~ 
pH 
I :~~~~~~-r~~-r~ 
6 0 I 12 I 16 20 '28 
TIME (min) 
Fig.1A Iron(lI) yield as a fundion of pH after 3 h. 
Fig.l B. Iron(lI) yields as a fundion of time measured at pH 3.5; 4 and 4.5. 
Initial concentrations: Fe3+. 34.2JLM; V02+. 33.8 JLM. 
The redox reaction was then studied by immerging a network, 
reticulated with 0.08 mmol of Fe(lII) and 0,03 mmol of Ca (11), in 300 mL of 
solution containing 0.0187 (system 1) and 0.187 mmol(system 2) of 
VO(IV) at pH 3.8. 
------~ 
.03 /13"""'" 
] .02 
E'OI,~~1 
o f'C I I I I 
o 24 49 72 96 120 
.04 
TIME (h) 
Fig. 2. {j Sistem 1; 0 Sistem 2 
In Figure 2 is reported the 
amount of Fe(lI) released from the 
network during the diffusion of the 
VO(IV) into the mucilaginous 
material in function of the time. The 
redox reaction inside the membrane 
appears to procede more slowly as a 
result of the strong interaction of the 
Fe(lII) with the functional groups of 
the matrix. Furthermore, the redox 
kinetics could be influenced by the 
477 
diffusion time of both VO(IV) from the external solution to the reticulation 
sites and Fe(lI) from the matrix to the external solution. 
The metal ions in the external solution and those immobilized by the 
organic matrix. determined at the equilibrium. are reported in Table 1. 
TABLE 1 
Uquid phase Solid phase 
mmol mmol 
Fe2+ Fe3+ Fe2+ Ca2+ (V02++VO~) 
SYSTEM 1 0.013 0.064 0.0030 0.03 0.010 
SYSTEM 2 0.038 0.045 0.0041 0.01 0.066 
The redox reaction is more active in the liquid phase: only 50% of 
the reticulating iron is reduced in the sistem 2. 
These data suggest that three steps could be involved. in the 
reduction process: 
1 - diffusion of the VO(IV) into the network: 
2 - exchange of iron by vanadium: 
3 - reduction of the iron by VO(IV) in the free space volume. 
The reduction of the iron does not improve the structural 
arrangement of the network which appears collapsed both in the Fe(III)-
Ca(II) and VO(IV)-Ca(IJ)-polygalacturonate. Further studies at this regard 
as well as about the distribution of the vanadium species (V02+ and 
V02 +) in the system are in progress. 
REFERENCES. 
1) Deiana S. and Gessa C.; (1991). Fibrillar structure of Ca-polygalacturonate as a 
model for a soil-root interface. 11: A comparison with natural root mucilage. Plant and 
Soil; 00.000-000. 
2) Gessa C. and Deiana S.; (1990). Fibrillar structure of Ca-polygalacturonate as a 
model for a soil-root interface. Part I. A hypotesis on the arrangement of the 
polymeric chains inside the fibrils. Plant and Soil; 129. 211-217. 
3) Gessa C .• Deiana S .. Marchetti M. e Usai M.; (1990). Reazioni di complessazione 
e redox nell'interfaccia suolo radice. Proceeding C.N.R. -Stress Ambientali nei 
Vegeta\i-; 136-141. 
478 


Transfer of metal ions at the soil-root interface: role of VO<sup>2+</sup> on Fe<sup>3+</sup> mobilization from a Fe(III)-network

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