Physiological and proteomic analyses of two Gracilaria lemaneiformis strains in response to high-temperature stress

The rhodophyte Gracilaria lemaneiformis is an important macroalga of great economic value, and is cultured on the southeastern coast of China. In this study, two G. lemaneiformis strains, 981 and 07-2, were cultured at three temperatures (25, 30 and 35 A degrees C) for 48 h. Analysis of the physiological parameters of the two strains under the heat treatments showed that the specific growth rates (SRGs) and photochemical efficiencies (F-v/F-m) were decreased in both strains with increasing temperatures. The decrease in the F-v/F-m in strain 07-2 was less than that in strain 981. However, the phycobiliprotein (PB) and soluble protein (SP) concentrations in strain 981 were decreased at 35 A degrees C throughout the experiment. The PB and SP concentrations in strain 07-2 exhibited initial decreases and then recovered under the heat treatments (25, 30 and 35 A degrees C). These findings suggest that the heat tolerance of strain 07-2, but not that of strain 981, is probably promoted by heat stress. Furthermore, proteomics analysis of the two strains at 35 A degrees C was conducted using 2-DE. Thirteen proteins were identified and classified into eight categories, including photosynthesis, energy metabolism, protein-folding catalysis, transcription, molecular chaperoning, and unknown function. The western blotting results demonstrated that cytosolic HSP70 expression was increased at 35 A degrees C in strain 07-2 and was stable in strain 981. These results indicate that this cytosolic heat shock protein plays an important role in ameliorating damage caused by heat stress and that strain 07-2 is more heat-resistant than strain 981.