PARENT SESSION

(07-04) Physiological and cytological responses of the marine diatom Skeletonema costatum to 2, 4-dichlorophenol.

Yang, Shao¹, Wu, Rudolf^*,1, Kong, Richard¹, ¹ Centre for coastal Pollution and Conservation, City University of Hong Kong, Hong Kong, China, Kowloon, Hong Kong SAR China

ABSTRACT- Physiological and cytological responses of the marine diatom, Skeletonema costatum, to 2,4-dichlorophenol (2,4-DCP) were investigated after exposing algal cultures to 1 to 6 mg l-1 of 2,4-DCP for 96 h. Growth rate of the diatom was significantly reduced by 2,4-DCP at and above 3.0 mg l-1 while other biological parameters such as photosynthetic and respiration rates, carotenoid and protein content, ATP level and adenylate energy charge were unaffected. Exposure to 6.0 mg l-1 2,4-DCP for 96 h. resulted in the total lipid content being increased to 304 %, while the RNA/DNA ratio was reduced to 31 % of the control values. A parallel study by transmission electron microscopy further confirmed the increase in cellular lipid content, as evidenced by the accumulation of lipid droplets within diatom cells. A slight increase in carbohydrate (+37.8 %) and decrease in Chlorophyll a (-20.4 %) and total Chlorophyll c (-14.4 %) were also found at 6.0 mg l-1 2,4-DCP. Although 2,4-DCP is known to uncouple oxidative phosphorylation, our results show that energy production was not significantly inhibited at sublethal concentrations of 2,4-DCP. The observed growth inhibition in S. costatum caused by 2,4-DCP was associated with an increase in energy storage and inhibition of protein synthesis, as indicated by a reduction in RNA/DNA ratio.

Key words: Diatoms, adenylate energy charge , cytology, chemical composition