Changes in the ultrastructure of Capsicum annuum L. seedlings roots under aluminum stress conditions

The effect of aluminum was investigated on the cell ultrastructure of roots of fourteen-day-old 'Trapez' red pepper seedlings grown in water culture. Disorders in the cell structure were observed using transmission electron microscopy (TEM). An analysis of longitudinal sections of the apical region of the control plants' roots showed that cells of the cap and cells of the meristematic region had an arrangement and shape typical for these root regions, and cell organelles were properly developed. Changes in the cell structure under the influence of aluminum involved a reduction in the number of starch grains in the leucoplasts of the cap, the formation of lobate nuclei and a reduction in the number of cisternae in the dictyosomes as well as the damage of the cell membranes. Moreover, the swelling of mitochondria was observed with a simultaneous reduction in the number of mitochondrial cristae or the bursting of the membrane of these structures. In the vacuoles of the investigated root section, the presence of numerous electron-opaque large-sized formations was found, being most probably aluminum deposits. The cell wall, often thickened, was wavy or the formation of two walls in close distance was observed. The obtained results prove the high sensitivity of the studied red pepper cultivar to aluminum stress