2. Results
2.1. Effect of potato glycoalkaloids onF. solaniultrastructure
The controls without potato glycoalkaloid treatment presented thin and
uniform cell walls, complete structure, hyphae surrounded by a
continuous outer layer, intact internal tissue structure, no
extravasation of cell contents, normal development, and clearly visible
vacuoles, mitochondria, and other organelles (Fig. 1A). However, after
treatment with EC50 potato glycoalkaloids, the fungal
cell walls became thinner and irregular, cell internal structure was
disrupted, and some membrane structures were incomplete (Fig. 1B).
Furthermore, after treatment with 2 g·mL−1 potato
glycoalkaloids, cell walls of mycelia had a bubble shape, outer layer
components were altered, cell wall structure was incomplete, the outer
cell membrane was discontinuous, structure of mitochondria and other
organelles was not obvious, and extracellular inclusions were exuded
(Fig. 1C). In contrast, following treatment with methanol, the cell wall
structure was clear, mitochondria and ribosomes were clearly visible,
and the vacuolar structure was intact, indicating that methanol did not
affect antibacterial activity of potato glycoalkaloids (Fig. 1D). These
findings indicated that potato glycoalkaloids destroyed the cell surface
morphology of F. solani , severely damaging the cytoplasm,
mitochondria, and other organelles, as well as increasing the cell
membrane permeability and so causing leakage of cell contents.
2.2. Effect of potato glycoalkaloids onF. solani cell membrane
permeability
Figure 2 shows the effects of potato glycoalkaloids on the cell membrane
permeability of F. solani . The relative cell membrane
permeability increased with time in both the control and treatment
groups. However, the relative cell membrane permeability was
significantly higher for the treatment compared with the control group.
In both the control and treatment groups, the relative cell membrane
permeability rapidly increased during 1–4 h, with a greater increase
for the treatment than the control group. After 4 h, the difference in
relative cell membrane permeability quickly broadened between the two
groups, indicating that the F. solani cell membrane damage caused
by potato glycoalkaloids at EC50 concentration
intensified at 4 h. Subsequently, the relative cell membrane
permeability of the control group gradually decreased during 4–9 h,
whereas that of the treatment group increased by 25.2% at 9 h, and
remained stable at 8 and 9 h.
2.3. Effect of potato glycoalkaloids on
soluble protein in F.
solani
The soluble protein leakage in the treatment group exhibited an upward
trend with time, which significantly differed from that in the control
group (Fig. 3). During 0–6 h, soluble protein leakage in the treatment
group increased from 66.50 to 169.51 μg∙mL−1, which
was much higher than that in the control group. However, during 6–24 h,
the soluble protein leakage in the treatment group gradually decreased
with time, possibly due to consumption of soluble proteins by newly
formed F. solani cells for growth. After 24 h, the soluble
protein leakage in the treatment and control groups gradually increased
and stabilized.
2.4. Effect of potato glycoalkaloids on
soluble sugar in F.
solani
Soluble sugar leakage in the treatment group significantly differed from
that in the control with time (Fig. 4). During 0–24 h, soluble sugar
leakage in the treatment group increased from 117.4 to 132.5
μg∙mL−1, which was much higher than that in the
control group. However, after 24 h, leakage in the treatment group
decreased with time owing to consumption of soluble sugar in the
extracellular fluid by newly formed F. solani cells for
growth.
2.5. Effect of potato glycoalkaloids on
reducing sugar content in F.
solani
The reducing sugar content in the extracellular fluid significantly
differed between the treatment and control group with time (Fig. 5). In
both groups, the reducing sugar content in the extracellular fluid
sharply decreased during 0–2 h, but gradually reduced during 2–72 h,
indicating that potato glycoalkaloids significantly decreased the
absorption and utilization of reducing sugar by F. solani.
2.6. Effect of potato glycoalkaloids on fat
content in F.
solani
The fat content in the extracellular fluid of both the treatment and
control groups increased during 0–48 h, with significantly higher fat
leakage for the treatment compared with the control group (Fig. 6). The
fat content in the extracellular fluid of the treatment group increased
by 54.20% and 52.07%, compared with sterile water and methanol control
groups at 48 h, respectively, indicating that potato glycoalkaloids
damaged the cell structure and caused fat content leakage from F.
solani plasma membrane. However, after 48 h, fat content in the
extracellular fluid of both treatment and control groups showed a
downward trend, possibly resulting from a weakening effect of potato
glycoalkaloids or a self-remediation mechanism of F. solani .