in this study. Furthermore, nonphosphorus lipids, selleck chemical phospholipid substitutions, are recently suggested as fundamental biochemical mechanisms to maintain phytoplankton growth in response to P limitation (Van Mooy et al. 2009). Van Mooy et al. (2009) found that marine phytoplankton showed different ability to substitute the nonphosphorus membrane
lipids for the phospholipids. Thus, further studies concerning the regulation of phospholipids and phospholipid substitutions are highly recommended to explore the interspecific effect of P deficiency on PUFAs in phytoplankton. The results discussed above suggest that the association of PUFAs with different types of lipids, e.g., TAGs, phospholipids, and phospholipid substitutions, should be considered
in further studies on RXDX-106 cost lipid biosynthesis under different nutrient supply. Moreover, advanced analytical techniques, e.g., HPLC/electrospray ionization–mass spectrometry (ESI-MS), have been recently used to improve the identification of different types of lipids in the ocean (Van Mooy et al. 2006, 2009, Van Mooy and Fredricks 2010). In conjunction with the advent of advanced techniques, this study will provide important empirical data for further studies on lipid biosynthesis of phytoplankton in changing oceans. In this study, significant effects of N or P deficiency on FAs in the three species were only observed at lower growth rates (20% or 40% of μmax). It has been suggested that nutrient limitation does not have direct effects on FA synthesis of phytoplankton, but a consequence of a limited growth rate leads to FA changes (Piepho et al. 2012). However, our study showed significant responses of FAs to N or P deficiency at the same growth rate
in all three species, while the effects of N and P deficiency became nonsignificant when growth rate increased. Our previous study demonstrated that high dilution rate (loss rate) could explain the limited flexibility of phytoplankton stoichiometry in natural communities (Bi et al. 2012). Thus, the optimal nutrient uptake ratio of phytoplankton at higher growth rates may explain the optimal N:P biomass Thymidylate synthase ratios, as well as the relative stability of FA contents, irrespective of N:P supply ratios. It is commonly accepted that total lipid content increases with decreasing growth rate (Borowitzka 1988, Sterner and Hessen 1994). This is probably due to the low requirement for synthesis of protein and instead a steady accumulation of lipid, mainly TAGs, when growth slows down (Siron et al. 1989, Reitan et al. 1994, Guschina and Harwood 2009). FA accumulation at lower growth rates has been found for several algal species in previous studies (e.g. Reitan et al. 1994, Otero and Fábregas 1997, Ferreira et al. 2011, Spijkerman and Wacker 2011). Also, in this study TFAs contents in both Rhodomonas sp. and I. galbana were relatively higher at lower growth rates. The lack of significant TFA response in P.