Ultrastructural response of cabbage outer leaf mesophyll cells (Brassica oleracea L.) to excess of nickel

Abstract

Changes in the structure and in the ultrastructure of cabbage outer leaf mesophyll cells [Brassica oleracea L.] cv. Sława from Enkhouizen were examined by means of light and electron microscopy. The examined plants were grown on the basic Murashige and Skoog medium with addition of excesive concentrations of nickel (added as NiSO₄ x 7H₂O),i.e. Ni 5, Ni 10 and Ni 20 mg/dm³. In Ni 5 mg samples mainly adaptation changes to the conditions of stress were observed. These changes were manifested by the increase of cytoplasm content and by cytoplasm vacuolization, by the increase of nucleus and nucleous volume, nucleolus vacuolization, the increase of plasmalemma invaginations and of the amount of rough ER, by the central arrangement of smooth ER and of the thylakoids of chloroplasts; it was also shown by the growth of the number of mitochondria and of peroxisomes in the cell. In Ni 10 mg samples, apart from adaptation changes, such as the increase of the nucleus volume, increase of plasmalemma invaginations, cytoplasm and nucleolus vacuolization, degeneration changes were also observed. They concerned mainly the nucleus (the increasing amount of condensed chromatin), ER (swelling and fragmentation of rER and sER), mitochondrium (swelling and reduction of cristae), Golgi apparatus (disintegration and decay) and chloroplasts (changes of shape, swelling and reduction of thylakoids, disappearance of starch and presence of big plastoglobuli). In Ni 20 mg samples cell protoplasts were in different stages of degeneration and the cell organelles that were identifiable, were usually damaged.