The toxic effect of nickel on lipid content and cell membrane structure in leaves of sunflower seedlings (Helianthus annuus) was studied. Addition of 2-5 mg 1“1 nickel sulphate to the nutrient medium resulted in a decrease in the total lipid and phospholipid contents of the seedlings. The ultrastructural study of mesophyll cells showed nickel to cause destruction to the tonoplast membranes, as well as other changes to the cell ultrastructure. The response of plants to harsh environmental factors is discussed.