Photoacclimation of the polar diatom Chaetoceros neogracilis at low temperature

Abstract

Polar microalgae face two major challenges: 1- growing at temperatures (-1.7 to 5°C) that limit enzyme kinetics; and 2- surviving and exploiting a wide range of irradiance. The objective of this study is to understand the adaptation of an Arctic diatom to its environment by studying its ability to acclimate to changes in light and temperature. We acclimated the polar diatom Chaetoceros neogracilis to various light levels at two different temperatures and studied its growth and photosynthetic properties using semi-continuous cultures. Rubisco content was high, to compensate for low catalytic rates, but did not change detectably with growth temperature. Contrary to what is observed in temperate species, in C. neogracilis, carbon fixation rate (20 min 14C incorporation) equaled net growth rate (μ) suggesting very low or very rapid (<20 min) re-oxidation of the newly fixed carbon. The comparison of saturation irradiances for electron transport, oxygen net production and carbon fixation revealed alternative electron pathways that could provide energy and reducing power to the cell without consuming organic carbon which is a very limiting product at low temperatures. High protein contents, low re-oxidation of newly fixed carbon and the use of electron pathways alternative to carbon fixation may be important characteristics allowing efficient growth under those extreme environmental conditions.

Photosynthetic processes in Antarctic sea ice during the spring melt

“…The high ratios of NBP L : GBP ($ 0.5-1.0) were similar to ratios of 0.6-0.9 observed during a coastal seawater spring bloom of diatoms in the western Antarctic Peninsula (Goldman et al 2015) and in cultured polar phytoplankton (Lacour et al 2022). High ratios suggest high assimilation efficiency of fixed carbon in polar waters.…”

Sustained xanthophyll pigments-related photoprotective NPQ is involved in photoinhibition in the haptophyte Tisochrysis lutea

“…Most studies on the effect of growth conditions on photoprotection were performed under a stable intensity during the light period or even under continuous light (i.e. 24 h Light:0 h Dark with constant light) 15,28 . However, natural light cycle regulates most of the cellular processes of all photosynthetic organisms in the ocean, including cell division, pigment synthesis, nutrient capture and carbon fixation 55,56 .…”

“…However, NPQ relaxation kinetic is highly variable across taxa and is dependent on growth conditions. In particular, prolonged low temperatures (overwintering evergreen plants: Verhoeven 11 , Míguez et al 12 , Demmig-Adams et al 13 ; diatoms: Lacour et al 14 , Lacour et al 15 , Wu et al 16 ), high irradiance (diatoms: Lavaud and Lepetit 17 ) and general harsh environmental conditions 18,19 are often associated with sustained NPQ (NPQs, slowly relaxing NPQ, see the review by García-Plazaola et al 20 ). In many studies, NPQs often comprises/overlaps with other types of NPQ named qI, qZ or qH, depending on the authors and the corresponding measurements performed.…”