No abstract

The effects of hydrogen ions on the growth and ultrastructure of Chlamydomonas applanata Pringsheim were examined. This species exhibits wide tolerance growing at pH values ranging from 3.4 to 8.4, with optimum growth obtained at 7.4. Growth is noticeably depressed at pH 4.4 and 3.4. At the ultrastructural level, exposure to pH 4.4 results in a 10% decrease in cell volume of single vegetative cells, an increase in pyrenoidal volume, and reduction of starch reserves. Palmelloid colonies also appear. pH 3.4 induces excessive production of mucilage and leads to the preponderance of palmelloid colonies. Cell death of both colony and single cells is seen, as well as loss of motility and abnormal cell division. Surviving single cells are significantly larger than controls, with thicker cell walls, smaller chloroplasts, and larger vacuome. Such cells entering dormancy ensure the survival of the species in times of stress.

The effective concentrations of copper and cadmium which reduced the population growth of Dunaliella minuta by 50% after 96 h of static exposure, were determined to be 7.57 microM Cu and 0.34 microM Cd. Short-term static exposure to both metals indicated that their combined action is antagonistic with respect to growth of this chlorophyte. Additionally, long-term exposure to low levels of Cu or Cd led to the acquisition of tolerance towards Cu and Cd, respectively, and co-tolerance towards Cu.

The ultrastructural changes taking place after short-term acute exposure to copper, cadmium and a combination of the two metals were examined. Additionally, the effects of long-term (8 months) exposure to ambient concentrations of these metals were investigated. Exposure to 0.34 microM cadmium affected the photosynthetic potential of this alga, by reducing the relative volume of the chloroplast by 23.27%. It also led to 74.6% increase in the relative volume of starch granules. Cells challenged with 0.34 microM cadmium and 7.57 microM copper had 33.49% larger volumes than controls, and their relative lipid volumes increased by 170%. In contrast, the relative volume of their pyrenoids decreased by 41.46%. Similar results were obtained after chronic exposure to 4.9 x 10(-4) microM copper with the relative volume of the pyrenoid being 28% smaller than the controls.