Temperature adaptation in phaeodactylum tricornutum Bohlin: Photosynthetic rate compensation and capacity

Abstract

Two views of temperature adaptation in marine phytoplankton have been proposed. The first emphasizes that adaptation is manifest as a compensation of photosynthetic rate (some time after the initial chemical kinetic response to temperature shift) so that eventually cells are able to perform more or less at the same level over a wide temperature range. The second emphasizes that adaptation is manifest as a change in the maximum photosynthetic ability. In order to examine these two concepts concurrently, short-term light saturated photosynthetic rates per cell ( P m ) were examined as a function of temperature for Phaeodactylum tricornutum Bohlin grown at various temperatures in turbidostat cultures. Within the range from 10 to 25°C, when cells grown at a high temperature were transferred to a low temperature, P m decreased according to Arrhenius-type kinetics in the short term. However, prolonged exposure at the lower temperature led eventually to compensation which partly restored P m to its original value. Within the same temperature range, growth at lower temperatures resulted in higher maximum photosynthetic abilities (i.e. P m measured at the optimal assay temperature) which were positively correlated with in vitro activities of ribulose-l,5-bisphosphate carboxylase (RuBPCase). Within this temperature range, the amount of total protein per cell did not change but there was an increase in the amount of chlorophyll α per cell with temperature. It is suggested that the regulation of RuBPCase activity may perhaps be associated with the two manifestations of temperature adaptation exhibited by P. tricornutum: partial compensation of P m and change in maximum photosynthetic ability.