OCCURRENCE AND DEGENERATION OF AL-STRUCTURES IN ROOT CAP CELLS OF ALLIUM-CEPA L AFTER AL-TREATMENT

A13+ ions, in concentrations similar to those found in acidificated soil solutions, cause severe damage to growing roots of Allium cepa. A structure or organelle, the ‘Al‐structure’, was discovered earlier (fiskesjö 1983). and was observed regularly in the cytoplasm of root cap cells after 2 days of treatment with Al (10‐3M AIC13). In the present investigation, with observations at 4 h intervals, it was revealed in 4 experiments that the inner meristem cells and the root cap cells were affected in different ways. In the meristem cells, material leached out from the nucleus into the cytoplasm, forming hyaline bubbles, unstained by oceans. In the root cap cells., on the other hand, similar material formed cavities or characteristic oblong ‘Al‐structures’. It was implied that the ‘Al‐structures’ eventually divided into two, one on each side of the nucleus and both oriented lengthwise in the cell. Treatment with 10‐3M Al for 48–56 h, started at 9.00 or 13.00 hours, gave the highest incidence of ‘Al‐structures’ compared to treatments started later during the day. After treatments longer than 48 h, the nuclei degenerated at the same time as the ‘Al‐structures’ increased in size, and after 3–4 days of treatment the nucleic degeneration was accompanied by decomposition of the ‘Al‐structures’ in the cytoplasm. Whether Al constitutes a part of the ‘Al‐structures’, and whether this structural manifestation is common among plants remain to be seen. Copyright © 1990, Wiley Blackwell. All rights reserved