RESPONSE TO SALINITY AND HEAT STRESS IN TWO HALOTOLERANT CHLOROPHYTE ALGAE¹

Abstract

Two new isolates of halotolerant chlorophyte algae from the Salt Plains National Wildlife Refuge in Oklahoma, USA, tentatively identified as Dunaliella sp. Teodoresco and Nannochloris sp. Naumann, were characterized with respect to interaction between growth salinity and short-term heat tolerance. Cells were cultured at 23-25 Њ C over a wide range of salinity. In both species, salinity alone had little effect on maximum photochemical yield (measured by pulse modulated fluorescence) and integrity of the light harvesting system (77 K fluorescence emission spectra). In contrast, Nannochloris exhibited decreasing growth rate ( ), light-saturated photosynthetic capacity ( ), respiration (R d ), light-harvesting efficiency ( ␣ cell ), and chl content with increasing salinity. Cultures were heated for 2 h near their upper temperature limits (41.5 Њ C for Dunaliella and 45 Њ C for Nannochloris grown at 50 psu). Dunaliella was progressively more heat-tolerant with increasing salinity. Photochemical yield of cells at 100 and 50 psu was inhibited by about 15% and 40%, respectively, and largely recovered within 30 min after return to 23 Њ C. Thermal inhibition of photochemical yield in Nannochloris was about 45% at both 50 and 100 psu, but recovery was slower at 100 psu. At 20 psu, both species were almost 90% inhibited by high temperature and required more than a day to recover. In both species, 2 h of heating increased the PSI:PSII fluorescence emission ratio (714:690 nm) at all salinities. This ratio largely recovered within 24 h in Dunaliella at 50 and 100 psu and partially recovered in Nannochloris at 100 psu, but cells of both species heated at 20 psu were chlorotic the next day. Abbreviations: ␣ cell , ␣ chl , initial slope of photosynthetic light-saturation (P-E) curve normalized per cell or chl; AS, artificial seawater; F o , F v , and F m , initial, variable, and maximum chl fluorescence measured after dark adaptation; F s and F m Ј , steady-state and maximum chl fluorescence measured in the light; , specific growth rate; PFR, photon fluence rate; , , light-saturated photosynthesis normalized per cell or chl; R d , dark respiration; SP, Salt Plains brine; SPNWR, Salt Plains National Wildlife Refuge P cell max P cell max P chl max 1

Performances of growth, photochemical efficiency, and stress tolerance of young sporophytes from seven populations of Saccharina japonica (Phaeophyta) under short-term heat stress

“…Six individuals from each of the seven populations were measured after being cultured for 72 h at different temperatures. Optimal chlorophyll fluorescence quantum yield was calculated according to the following equation: (Parkhill et al 2001;Henley et al 2002). F o and F m refer to the minimum fluorescence and the maximum fluorescence from dark adapted samples, respectively.…”

Effect of salinity on growth and chemical composition of the diatom Thalassiosira weissflogii at three culture phases

“…Environmental factors have been reported to influence the chemical composition of microalgae. For instance, the effect of light, nutrients, temperature, pH and salinity has been well documented (Richmond 1986;Henley et al, 2002). In addition, the growth phase has been reported as an intrinsic factor influencing the growth rate and biochemical composition of microalgae (Renaud et al, 2002).…”

Changes in photosynthesis, chlorophyll fluorescence, and antioxidant enzymes of mulberry (Morus ssp.) in response to salinity and high-temperature stress

“…Numerous studies have shown that salinity stress predisposes photosystem II (PSII) to photoinhibitory damage (Lu et al 2002;Maricle et al 2007;Hichem et al 2009;Qin et al 2010Qin et al , 2011Sui et al 2010). However, very little attention has been paid to the responses of PSII to salinity stress and high-temperature stress in combination (Henley et al 2002). It is obviously important from an ecophysiological viewpoint to study the combination of these two stresses, given that about one-third of the irrigated land worldwide is already experiencing increased salinity (Epstein et al 1980; Photosynthesis of mulberry at stress conditions 405 Epstein 1984).…”