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Processes of the cytological differentiation in the synergids of Pulmonaria angustifolia L. (2n = 14) and P. mollissima Kern. (2n = 18) were studied. In both species the process of polyploidization started soon after the formation of the mature embryo sac. The lack of mitoses, rhythmical enlargement of the synergid nuclei as well as their characteristic structures pointed to endoreduplication as the mechanism of polyploidization. Detailed analysis of nuclear volume measurements permitted to distinguish five size-classes of nuclei; they correspond to the degrees of ploidy evaluated as: n, 2n, 4n, 8n and 16n. Moreover, in P. mollissima one nucleus could be identified with 32n level. In polyploid nuclei the occurrence of aggregations of chromatin enlarging with the degree of polyploidization was stated. Their increase in thickness in high polyploid nuclei permitted to suppose that they represented the polytene chromosomes. The synergids in Pulmonaria probably are involved in the nutrition of the egg cell before fertilization. It may be supposed that the persistent synergid retains its physiological activity up to the stage of 4-8-celled embryo.
Berkheya coddii Roessler (Asteraceae), an endemic herbaceous and perennial nickel-hyperaccumulating plant growing on Ni-enriched ultramafic soils in South Africa, is perceived as a promising species for phytoremediation and phytomining due to its large biomass production and high Ni content. Total concentrations of a number of elements in mature leaves, soil and related bedrock were obtained. The average Ni concentration in leaves was 18,000 µg · g-1 dry mass, whereas in soil and bedrock the total amount of Ni was 1,300 µg · g-1 and 1,500 µg · g-1, respectively. Exceptionally high average Ni concentrations (55,000 ± 15,000 µg · g-1, n = 6) were found in B. coddii leaves from Songimvelo Game Reserve, including the highest-ever reported concentration of Ni in leaves (76,100 µg · g-1 - maximum value in a single sample). Young plants grown in pots with ultramafic soil accumulated small quantities of Cd, Pb or Zn, but the concentrations of these elements increased after the addition of metal solutions to the soil. Excised shoots immersed in concentrated solutions of Cd, Ni, Pb or Zn accumulated large amounts of these metals in the leaves.
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