Effects of diazepam on photosynthesis, respiration, rubidium uptake, and finestructure of Scenedesmus obliquus in synchronous cultures

Abstract

Effects of diazepam (Valium) on photosynthesis, chlorophyll/photosynthesis ratios, respiration, uptake of rubidium ions, and ultrastructure of Scenedesmus obliquus synchronized by a light-dark regimen of 14:10 hrs were determined. 80 and 160 muM diazepam, added to the nutrient medium at the start of the light-dark change (i.e., start of the cell cycle) gradually reduced rates of photosynthesis, below the initial rates from the beginning of the experiment. Contents of chlorophyll, however, remained nearly unaffected. Consequently, the diazepam-treated cells had a higher chlorophyll/photosynthesis ratio--also with regard to respiration in order to calculate the gross photosynthesis. The occurrence of photorespiration cannot be assumed. The net influx of rubidium was slightly reduced by 100 muM diazepam 0.5 and 2.0 hrs after the start of the cell cycle and was strongly inhibited after 5 to 14 hrs. 80 and 160 muM diazepam caused separation of thylakoids, formation of giant mitochondria and enlargement of vacuoles.

Cell cycle dependent expression of toxicity by the ichthyotoxic prymnesiophyte Chrysochromulina polylepis

“…Although not always possible to apply, this method has clear advantages over the block-release method for studying periodic responses since no sudden stress is necessary to induce synchronicity. At least in the case of metabolic inhibitors, there is also less potential for introducing artefacts into the cell cycle (Edvardsen & Vaulot 1996), and has also been reported for many other microalgae including chlorophytes of the genera Chlorella, Scenedesmus, and Chlamydomonas and the euglenophyte Euglena (Wanka et al 1972, Ober 1975, Carré & Edmunds 1993, Lemaire et al 1999. In practice, the induction of synchronous (as opposed to merely phased) cell division by manipulation of the photoperiod is only possible when the length of the celldivision cycle closely approximates the length of the photoperiod (1 div.…”

“…Partial synchronisation induced by light:dark cycles has been obtained for the haptophytes Phaeocystis spp. (Vaulot et al 1994, Jacobsen 2002, Prymnesium parvum (Chisholm 1981, Larsen & Edvardsen 1998 and C. polylepis (Edvardsen & Vaulot 1996), and has also been reported for many other microalgae including chlorophytes of the genera Chlorella, Scenedesmus, and Chlamydomonas and the euglenophyte Euglena (Wanka et al 1972, Ober 1975, Carré & Edmunds 1993, Lemaire et al 1999. In practice, the induction of synchronous (as opposed to merely phased) cell division by manipulation of the photoperiod is only possible when the length of the celldivision cycle closely approximates the length of the photoperiod (1 div.…”