Changes in morphological and anatomical structure of cabbage (Brassica oleracea L.) outer leaves and in ultrastructure of their chloroplasts caused by an in vitro excess of nickel

Abstract

Morphological, anatomical and ultrastructural changes, the quantity and quality of stomata, and the chlorophyll (Chl) content in primary outer leaves of cabbage plants cv. Slawa from Enkhouizen were examined. The plants were grown in agar with basic MS medium containing added nickel (as NiSO4×7 H2O) in concentrations of 0, 5, 10, and 20 g m-3 (Ni0, Ni5, Ni10, Ni20). Reduction of leaf blade area, of succulence and of leaf density, and growth of specific leaf area were noticed in plants treated with all concentrations of Ni. In Ni-treated plants the total number of stomata and open stomata decreased, and the number of defective stomata in both adaxial and abaxial side of leaves was higher. In all Ni-treated samples the volume of spongy and palisade mesophyll cells was smaller in comparison to control, and it was decreasing when the Ni concentration was increasing; at the same time, the number of mesophyll cells on the same area of cross sections of leaves was increasing. In comparison to control, the intercellular spaces of mesophyll tissue decreased in Ni10 and Ni20 plants and increased in Ni5 plants. In Ni5 plants the number of chloroplasts in mesophyll cells was higher than in the Ni0 control. Reduction of grana size and increase of number of non-appressed lamellae, which often had central arrangement, were observed. In the Ni10 and Ni20 plants, the number and size of chloroplasts decreased, and their internal membranes (especially grana) were reduced and swollen. In Ni5 plants the concentration of Chl in leaves was slightly higher than in the control; in Ni10 and Ni20 plants it was lower than in the control.