Effects of UV‐C and UV‐B on cytomorphology and water permeability of inner epidermal cells of Allium cepa

Changes of cytomorphology and water permeability of inner epidermal cells of Allium cepa L. cvs Spartan and Keep Well were investigated with the light microscope after irradiation with UV‐C (254 nm) and UV‐B (280 and 310 nm). The sequence of the investigated changes of viscosity, protoplasmic streaming, organelle shape and water permeability was the same with 254 as with 280 nm. although a higher dose of 280 nm was needed to produce the same biologically equivalent effect. However, when calculated as a percentage of the lethal dose, the initial doses that produced the effects were the same for 254 and 280 nm. No changes could he observed at the cellular level after the cells were irradiated with 310 nm. The lethal dose depended upon the time between irradiation and observation. At 254 nm it was 1.1 kJ m −2 up to 1 h after irradiation and dropped to 860 J m −2 when measured 24 and 48 h later. At 280 nm a dose of 2.8 kJ m −2 killed the cells within I h while the dose needed after 24 and 48S h was 1.99 kJ m −2 . The minimum doses which caused the different cytomorphological effects did not depend upon the observation time. Normal cell structure and functions that were altered immediately alter irradiation did not recover. Doses that were not immediately effective alter irradiation caused no later damage. Doses which increased water permeability were much higher than doses which influenced cytomorphological parameters of the cell.