Article

Barrier function of the cell wall during uptake of nickel ions

Russian Journal of Plant Physiology (Impact Factor: 0.62). 01/2011; 58(3):409-414. DOI: 10.1134/S1021443711030137

ABSTRACT Cell walls were isolated from roots of six plant species to study their ion-exchange capacity for nickel ions (S
Ni) at Ni2+ concentration of 10−3 M. The S
Ni values varied depending on the plant species from 50 to 150 μmol Ni2+ per gram dry wt; the sorption capacity increased in a row: Poaceae < Chenopodiaceae < Fabaceae. At pH 5 the sorption capacity
of cell walls for nickel ions was determined by the presence of carboxyl groups of polygalacturonic acid in the polymeric
cell-wall matrix. In all cases the ion-exchange capacity of cell walls was higher at pH 8 than at pH 5, indicating that Ni2+ binds also to a carboxyl group different from that of polygalacturonic acid. Irrespective of plant species, the presence
of EDTA in the solution diminished drastically the absorption capacity of cell walls for Ni2+. It is concluded that the presence of 10−3 M EDTA weakens the defense properties of cell walls. The sequestration of Ni2+ in the cell wall can be considered as an effective means of plant cell defense against elevated concentrations of nickel
ions in the external medium.

Keywordshigher plants–cell walls–nickel ions–carboxyl groups–EDTA

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    ABSTRACT: To investigate the mechanisms of Ni(2+) effects on initiation and maintenance of polar cell growth, we used a well-studied model system-germination of angiosperm pollen grains. In liquid medium tobacco pollen grain forms a long tube, where the growth is restricted to the very tip. Ni(2+) did not prevent the formation of pollen tube initials, but inhibited their subsequent growth with IC(50) = 550 μM. 1 mM Ni(2+) completely blocked the polar growth, but all pollen grains remained viable, their respiration was slightly affected and ROS production did not increase. Addition of Ni(2+) after the onset of germination had a bidirectional effect on the tubes development: there was a considerable amount of extra-long tubes, which appeared to be rapidly growing, but the growth of many tubes was impaired. Studying the localization of possible targets of Ni(2+) influence, we found that they may occur both in the wall and in the cytoplasm, as confirmed by specific staining. Ni(2+) disturbed the segregation of transport vesicles in the tips of these tubes and significantly reduced the relative content of calcium in the aperture area of pollen grains, as measured by X-ray microanalysis. These factors are considered being critical for normal polar cell growth. Ni(2+) also causes the deposition of callose in the tips of the tube initials and the pollen tubes that had stopped their growth. We can assume that Ni(2+)-induced disruption of calcium homeostasis can lead to vesicle traffic impairment and abnormal callose deposition and, consequently, block the polar growth.
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