This communication reports the role of polygalacturonate network on the Fe(III) reduction by caffeic acid. The effect of phosphate ions on the redox reaction is also considered

Deiana, Salvatore Andrea

Gessa, Carlo Emanuele

Lauro, Giampaolo

Marchetti, Mauro

Usai, Marianna

English

UnissResearch

Gessa, Carlo Emanuele; Deiana, Salvatore Andrea; Lauro, Giampaolo; 
Marchetti, Mauro; Usai, Marianna (1993) Role of the polygalacturonate 
network on the iron (III) reduction by caffeic acid. Giornale botanico 
italiano, Vol. 127 (1), p. 185-186. ISSN 0017-0070. 
http://eprints.uniss.it/7832/
Documento digitalizzato dallo Staff di UnissResearch
GIORNALE 
BOTANICO 
ITALIANO 
FONDATO NEL 1844 
ISSN-OO l 7-0070 
PUBBLICATO DALLA SOCIETÀ BOTANICA ITALIANA 
CON IL CO TRIBUTO DEL CONSIGLIO NAZIONALE DELLE RICERCHE 
Vol. 127, n. 1,1993 
Società Italiana di Fisiologia Vegetale 
32° Congresso Sociale 
Udine 
5-9 Ottobre 1992 
RELAZIONI, COMUNICAZIONI 
DIMOSTRAZIONI - RIASSUNTI 
ROLE OF THE POL YGALACTURONATE NETWORK ON THE IRON (III) 
REDUCTION BY CAFFEIC ACID. 
C.Gessa*, S.Deiana**, G.P.Lauro**, M.Marchetti*** and M.Usai** 
*Istituto Chimica Agraria, Universtà di Bologna; **DI.S.A.A.B.A., Università di Sassari; 
***I.A.T.C.A.P.A. del C.N.R., via Vienna 2 Sassari. 
The complexing capacity ofthe "mucigel" is ascribed to polysaccaride acids organized in 
a fibrillar structure. Gessa C. and Deiana S. (140: 1-13, 1992a; 1992b) using a network ofCa-
polygalacturonate with a fibrillar structure similar to that found in the reaI systems, have sho\\1l 
that the mobility of meta! ions depends on their affinity for the functional groups of the 
polysaccaride. 
The availability ofthe immobilized ions for the absorbing cells is mediated principally by 
organic molecules with low molecular weight having complexing or reducing capacity. Among 
these substances caffeic acid (CAF) play an important role in the transport of the iron from soil 
to plasmalemma. Deiana S. et al., (1992) Gessa C. et al., (1992) studied the iron(III)-CAF 
system in aqueous solution defining the stoichiometry and suggesting the probable mechanism of 
the redox reaction. 
This communication reports the role of polygalacturonate network on the Fe(III) 
reduction by caffeic acido The effect of phosphate ions on the redox reaction is also considered. 
EXPERIMENTAL 
Systems containing CAF, phosphate ions and iron (III)-polygalacturonate network were 
prepared by mixing the solutions and suspension previously brought up to the working pH. The 
reaction volume was 100 mL. Iron(II) was determined as 1-10-phenantroline complex in a small 
volume of solution buffered by acetate at pH 4,5. The HPLC tests were perfonned according to 
Deiana et al (1992). The Fe(III)-networks were prepared treating Ca(II)-networks with a 
soIution of Fe(III) and D-galacturonic acid in a molar ratio of 5 at pH 3.5. The Fe(III)-networks 
were dyalized several times with distilled water. 
RESUL TS AND DISCUSSION 
To determine the role of the polygalacturonate network in presence and in absence of 
phosphate ions on the redox reaction, two systems were studied at pH 4 and 5. The system l 
was composed ofa network reticulated with 58 ~oles ofFe(III) and 16.726 ~oles ofCAF; the 
system 2 of 70.13 ~oles of Fe(In), 24.129 mmoles of CAF and 73.13 ~oles of phosphate. 
Table reports, the percentage of the Fe(II) and Fe(III) released in the external solution after 48 
hours of reaction, of exchangeable (e) and immobilized (R) by the organic matrix; the yield of 
Fe(II)relative to the binary (Fe(III)-CAF) and ternary (Fe(III)-CAF-Phosphate) systems are also 
reported. The results show that the redox reaction is much more active in system l and 2 in 
respect to the aqueous binary and ternary systems, in fact only 9% and 2% of the reticulating iron 
is reduced in these last two. The presence of phosphate ions inhibits the reduction reaction inside 
the network. 
These aspects can be explained as following: 
a) high stability of the Fe(III)-polygalacturonate complex where the Fe(III) is preserved to the 
hydrolysis reactions; 
b) the stability ofthe Fe(III)-network was increased when phosphate occupies the active site of 
the redox reaction 
185 
Fe{III}-Network-CAF {Srstem I} Fe{III}-CAF 
Liguid Ehase Solid Ehase 
pH CAFa n.e- Fe(II) Fe(III) Fe(Il)e Fe(lII)e Fe(IIl)R Fe(II) 
4.0 8.40 4.70 20.90 5.45 51.35 22.30 0.00 9.30 
5.0 6.64 4.30 5.10 4.03 43.90 30.00 16.97 8.90 
Fe{III}-Network-CAF-P {Srstem 2} Fe{III}-CAF-P 
Liguid Ehase Solid Ehase 
pH Fe(II) Fe(III) Fe(Il}e Fe(IU)e Fe(ID)R Fe(II) 
4.0 5.01 4.94 5.25 0.81 30.10 0.00 58.74 2.50 
5.0 5.56 3.30 2.70 1.40 23.40 0.00 72.50 2.40 
The amo unI of Ihe iron and cajJeic acid inside Ihe network was delermined by Ireating Ihe solid phase 
with 0.1 M NaC/04 solulions. P: Phosphale; CAFa: mmoles ofreacled caffeic acid; n.e-: Fe(1J)/CApG· 
Some notes are to lay stress on: 
i) The intermediate product I present in aqueous systems (Deiana S. et al., 1992) is not detected 
eitber in tbe external liquid phase and in tbe network "free space", probably due to its instability 
inside tbe matrix; ii) tbe intermediates A and B are present in "free form" eitber in tbe external 
solution or in tbe network "free space". 
These data indicate that, in tbe redox process, is active only tbe first step of tbe 
mechanism previously reported (Deiana S. et al., 1992). 
The reduction of tbe iron restore tbe fibrillar structure of tbe system l which appears 
collapsed in tbe Fe(III)-Ca(II)-polygalacturonate. This arises from two distinct mechanisms of 
interaction of Fe(II) and Fe(III) witb tbe functional groups of tbe fibrils: electrostatically witb 
Fe(II) and covalent1y witb Fe(III). 
The regenerate fibrillar structure appears shrunk respect to tbe Fe(ll}-network prepared 
treating Ca(II)-network witb Fe(II) solutions. The mechanism of this phenomenon which appears 
to be related to tbe accumulation of CAF inside tbe fibrils as well as tbe effect of tbe phosphate 
ions on tbe physical properties of network is under study. 
REFERENCES 
1) Gessa C. and Deiana S ; (1992a), Fibrillar structure ofCa-polygalacturonate as a model for a 
soil-root interface.II: A comparison witb natural root mucilage. Plant and Soil, 140,1-13. 
2) Gessa C. and Deiana S.; (1992b), Role of soil root interface in mobilization of nutrients and 
tbeir absorption by plants. In "Trends in Soi! Science"., pp. 000-000, Elservier Amserdam. 
3) Deiana S., Gessa C., Manunza B., Marchetti M. and Usai M.;.1992, Mechanism and 
stoichiometry of tbe redox reaction between iron(ID) and caffeic acido PlanI and Soil, 
00,000-000. 
4) Gessa C., Deiana S., Usai M. and Marchetti M.; 1992, Influence of pH OD tbe reduction of 
iron(III) by caffeic acid Proceeding oj XVlth Inter. Conjerence oj JJEP,Lisboa (Portugal), 
000-000 (in corso di stampa). 
186 


Role of the polygalacturonate network on the iron (III) reduction by caffeic acid

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