Acute and chronic effects of copper and cadmium on the growth and ultrastructure of Dunaliella minuta, Dunaliella salina and Chlamydomonas bullosa

The effective copper and cadmium concentrations that limited the growth of three chlorophytes by 50%, EC(50), in 96 hour static experiments were determined. EC(50)s were 7.57 uM copper and 0.34 uM cadmium for Dunaliella minuta, 5.94 uM copper and 4.55 uM cadmium for Dunaliella salina, and 0.78 uM copper and 0.025 uM cadmium for Chlamydomonas bullosa. The relationship of the two cations was antagonistic towards the growth of the first species but synergistic for the latter two. At the ultrastructural level the relationship varied depending on the cellular component examined.; Exposure to 4.9 {dollar}times{dollar} 10{dollar}sp{lcub}-4{rcub}{dollar} uM copper or 4.5 {dollar}times{dollar} 10{dollar}sp{lcub}-6{rcub}{dollar} uM cadmium for eight months increased the tolerance of D. minuta towards its established Cu and Cd EC(50)s by 34% and 19% respectively, and the co-tolerance of Cu-treated cultures by 26%. Cd-treated D. salina was 50% more tolerant towards this cation, whereas Cu-treated cultures showed extreme sensitivity towards copper and "co-sensitivity" towards cadmium. Cu and Cd-treated C. bullosa cultures were 29% and 26% more sensitive towards copper and cadmium respectively. No changes in co-tolerance were observed.; At the ultrastructural level cadmium was shown to be more toxic than copper. Exposure to copper and/or cadmium affected a variety of cellular structures including chloroplast, pyrenoid, nucleus, starch granules, polyphosphate bodies, lipids, vacuoles, cell wall and periplasmalemmal space. In light of the observed ultrastructural changes several mechanisms of toxicity, as well as possible detoxifying mechanisms are discussed.; Rachlin et al. (1982c) proposed that toxicological responses could reflect phylogenetic relationships and thus can be ordered within a taxonomic framework. The validity of the phylogenetic hypothesis was tested using the growth responses of the three chlorophytes to metal stress. Analysis of covariance of the cadmium generated regression lines indicated that the responses of all three chlorophytes were significantly different. Analysis of the growth data under copper stress showed, contrary to expectations, that the two non-related species, C. bullosa and D. minuta, responded to the cation in similar fashion, whereas the responses of D. salina and D. minuta were significantly different. It is concluded that the phylogenetic hypothesis does not hold true for the lower levels of taxonomic organization.