Changes in cell density and chlorophyll fluorescence with salinity stress in two Isochrysis galbana strains (P rymnesiophyceae)
Liang, Ying; Cao, Chunhui; Tian, Chuanyuan; Sun, Minghui
In order to demonstrate whether chlorophyll fluorescence can be used as a potential tool for salinity tolerance in microalgae, fluorescence parameters, cell densities and relative chlorophyll contents were investigated for Isochrysis galbana 3011 and for I. galbana 8701 (Prymnesiophyceae), after exposure to different salinities (1–90 psu) for different times (12h, 24h and 48h). The results showed that both low ( 70 psu) salinity stress caused a strong depression of the photosynthetic activity in I. galbana 3011 and 8701. The maximal photochemical efficiency of PSII (Fv/Fm), the potential activity of PSII (Fv/Fo), the actual photochemical efficiency of PSII in the light (φPSII), the relative electron transport rate (rETR) and the photochemical quenching (qP) decreased significantly with the degree of salinity stress. The non-photochemical quenching (NPQ) significantly increased in I. galbana 3011, while in I. galbana 8701 it first increased and then decreased under salinity stress. Salinity stress also resulted in a decrease of cell densities and chlorophyll contents of both I. galbana strains. Some fluorescence parameters, cell densities and chlorophyll contents all showed significant correlations with salinity. The pattern and strength of the correlations varied with salinity range and microalgal strains. Moreover, there were significant positive correlations between fluorometer parameters (Fv/Fm, Fv/Fo, φPSII, rETR and qP) and cell densities, as well as between chlorophyll contents and cell densities. The responsive mechanism of the two microalgal strains to salinity stress as well as the possibility of determining the salinity resistance in microalgae using chlorophyll fluorescence induction kinetics was also discussed in this paper.