Mullen, William A. (1980)
The effects of transition group metal ions and their compounds on various plant species.
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Plants from metal rich sites were analysed and Armeria maritima from Dolfrwynog bog was selected for further study. Tolerance indices were established for tolerant and non-tolerant ecotypes. Copper was found accumulated mainly in the root. Anatomical, histochemical and electron microscopical studies indicated that the major accumulating area within the tolerant plant was the hypodermis. Phloem, endodermis, medullary sheath and tannin bearing cells also showed high concentrations.
Chemical extraction schemes were carried out on root material. 29.0% Of the metal was removed with low molecular weight water soluble materials, 11.8% was solubilized by the proteolytic enzyme pronase and 49.0% was associated with pec tic and similar polysaccharidic material. Differential ultracentrifugation indicated that copper was mainly linked to cell wall material. Dialysis with tartaric acid resulted in the removal of 44.8% of the copper present in root material, suggesting only weak bonding to cell wall pectates.
Water extractable copper from roots was in the form of bis-prolinato copper(Il). A high proportion of the free amino acid pool in tolerant Armeria maritima consists of proline, even when the plant is not. under copper stress. Non-tolerant plants have much lower levels of proline. Copper is removed from sensitive sites by guttation from leaf salt glands. A multistage mechanism of tolerance is suggested.
The small fraction of the total copper in the bog available to plants is probably complexed to humic and fulvic acids. A complex(es) present in the bog extract had a mole ratio of complexing agents to copper of 1.15 and a log stability constant of 6.0.
For comparison the effects of platinum group metals on crop species were studied and plant metal levels presented. The relative order of toxicity was found to be: Pd(II) > Pt((IV) > Rh(III). Platinum was also applied in various complexed forms to corn, but no significant differences in their effects was observed.
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Institution: University of London, Bedford College (United Kingdom).