Effect of arsenic on cell growth of the cellular slime mould, Dictyostelium discoideum.

The growing D. discoideum cells were killed in a dose-dependent manner when exposed to 100 and 140 ppm of arsenic (As2O3) at mid-log phase for 20 min. Reduced plaque sizes and changed cell and colony morphologies were observed in the treated cells. Endocytotic functions (both phagocytosis and pinocytosis) were also inhibited in the treated cells. Arsenic treated cell showed a lower DNA and protein synthetic activities. These findings are discussed in relation to known mechanism of action of the heavy metal on growth-related cellular functions.

Sodium chloride stress induced morphological and ultrastructural changes in Aspergillus repens.

Halotolerant fungus, A. repens, showed a considerable difference in its growth rate, morphology, ultrastructural and molecular composition under NaCl stress as compared to control i.e. non-stressed condition. Light microscopic observations revealed significant differences in their mycelial thickness, their branching and septa. Transmission electron microscopic observations of both the conditions depicted significant differences in the qualitative and quantitative changes in mitochondria. Frequent pinocytotic vesiculation (vacuoles) of plasma membrane was observed in fungus under stress but no such vesiculation in control. The multivesiculate structures observed under stress with their origin from the cell membranes and subsequent release into vacuoles have not been reported in fungi under normal physiological conditions. The observations on pinocytosis are discussed in relation to ion compartmentation and salt tolerance in A. repens.