ASSESSING PHYSIOLOGICAL STRESS IN THALASSIOSIRA FLUVIATILIS (BACILLARIOPHYTA) AND DUNALIELLA TERTIOLECTA (CHLOROPHYTA) WITH DCMU‐ENHANCED FLUORESCENCE¹

Abstract

Exponentially growing cultures of Thalassiosira fluviatilis Hustedt and Dunaliella tertiolecta Butcher were exposed to 4 min temperature shocks of 5° to 20°C above ambient (20°C). Photosynthetic carbon fixation, changes in in vivo fluorescence and fluorescence on the addition of the herbicide DCMU (3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea) were measured over the subsequent 24 h. The fluorescence ratio (R, DCMU‐enhanced fluorescence/in vivo fluorescence) paralleled changes in photosynthesis over this period; both were significantly reduced (P < 0.05) by temperature shocks of +15° and +20° C, but +5° and +10° C treatments had no inhibitory effect on either relative to the control. The instantaneous response obtained with the fluorescence ratio indicates that the technique might be applicable to routine bioassay procedures and thus replace the time consuming methods now used for the estimation of 14C‐incorporation and growth rates.

Co-existence and survival of diatoms on sand grains

“…This ratio can be related to the maximum photochemical quantum efficiency (see Cullen, 1982;Falkowski & Kolber, 1995;Cullen & Davis, 2003), so has to be interpreted carefully because it can be influenced by a number of factors. Some of these have been discussed recently in relation to productivity of the oceans (see Cullen, 1982;Falkowski & Kolber, 1995;Cullen & Davis, 2003), nutrient conditions (Geider et al, 1993;Berges et al, 1996;Boyd et al, 1998;Young & Beardall, 2003) and temperature shock (Sellner et al, 1982). In this study, sand diatoms were silica limited from mid March until August, followed by nitrogen limitation through to late October.…”