The characteristics of soybean root tip cell ultrastructure
showed that Al toxicity harmed Z.3 more severely than Z.2. Without
Al stress, the configuration of the root tip cells was well structured
and the ultrastructural characteristics were normal: the nuclei
were found in random locations within the cell space, the nuclei
and karyotheca structures were clearly seen, the mitochondria’s
rounded kidney-shaped was well defined, the mitochondria were
widely distributed in the cellular space, and the vacuoles contained
large aggregates of electron-dense deposits and sedimentation
(Fig. 5).
The root tip cells of Z.2 and Z.3 grown in the 10 mg L1 Al
solutions had a mixture of normal and abnormal characteristics
(Fig. 6): the cell wall had irregular thickness, the mitochondria and
vacuole inclusions were more than those observed in the check,
and the external membrane of the nuclei were swollen and its
borders had less clarity than those of the check. The mitochondria,
however, showed normal configurations and an abundant and
well-organized inner membrane system. Except for a large proliferation
of endoplasmic reticulum in Z.2, there was no other
observable difference between the two cultivars.
The following characteristics were observed in the 30 mg L1 Al
treatments: the cellular configurations remained intact but the size
of the cells appeared to swell; the nucleolus disaggregated, but the
karyotheca maintained its structure; vacuole inclusions were fewer
than those in the check; the mitochondria was irregular in shape
and swollen; the cristae system was a little bit distorted. Fig. 7
showed the breakdown of the inner membrane of the mitochondria
as well as its erupted membrane. In addition, plasmolysis was
observed in the cells of both Z.2 and Z.3 in the 30 mg L1 Al
treatment, but the damages were not severe.
As showed in Fig. 8, plasmolysis was clearly detected in the root
tip cells in the 60 mg L1 and 90 mg L1 Al treatments. In these
cells, the cytoplasm was disorganized, the nucleolus had broken
down, and the mitochondria and other organelle had disappeared.
After the high Al treatment (90 mg L1), both Z.2 and Z.3 had lost all
their cellular configurations, their cell walls had ruptured, and the
cellular contents had disappeared. The cells were dead.