Are the carboxyl groups of pectin polymers the only metal-binding sites in plant cell walls?статья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 18 марта 2016 г.
Аннотация:Background and Aims. Are the carboxyl groups of pectin
polymers the only metal-binding sites in plant cell
walls? To answer this question we investigated Cu2+ and
Ni2+ -exchange capacities of isolated root cell walls of
seven plant species. As the ionization degree of carboxyl
groups and consequently their ability to bind metal
ions is dependent upon the solution pH it is possible to
reveal the predominant sites of metal binding at a
certain pH.
Methods. Amounts of different ionogenic groups in the
isolated cell walls was determined by potentiometric
titration, Cu2+ and Ni2+ binding capacities – by measuring
the amount of adsorbed metal ions after incubation
in 1mM CuCl2 or NiCl2 at different pHs.
Results. Carboxyl groups of polygalacturonic acid
(PGA) are the only Cu2+ and Ni2+ binding sites at pH
<5. At рН≥5 the ratio between the amount of the metal
bound and the amount of PGA carboxyl groups is >1 in
some plant species, indicating the involvement of carboxyl
groups of hydroxycinnamic acids (HCA) in Cu2+
and Ni2+ binding. HCA carboxyl groups in cell walls of
grasses bind 40–85 % of total cell wall Cu2+ and Ni2+ at
рН≥5, but in dicotyledons their contribution does not
exceed 45 % and varies widely between species.
Conclusion. Carboxyl groups of both polygalacturonic
and hydroxycinnamic acids provide Cu2+ and Ni2+ adsorption
sites in root cell walls. Their relative content
depends on plant species, and ability to bind Cu2+ and
Ni2+ – on the solution pH.