Growth rate affects the responses of the green alga Tetraselmis suecica to external perturbations

We hypothesized that the duration of the perturbation relative to the reproduction rate influences the response mode to external perturbations and the degree of (organic) compositional homeostasis. Our findings are consistent with this hypothesis. When different growth rates were imposed to cells of the same species, the degree of compositional homeostasis following an external perturbation was significantly higher in the cells with slower growth rate. The ability to maintain a constant composition was however vinculated by the availability of sufficient energy. Acclimation to environmental changes involves a modification of the expressed proteome and metabolome. The reproductive advantage associated with the higher fitness that acclimation provides to the new conditions more than compensates for the costs of acclimation. To exploit such an advantage, however, the duration of the perturbation must be sufficiently long relative to the growth rate. Otherwise, a selective pressure may exist in favour of responses that minimize changes in carbon allocation and resource use and do not require reversal of the acclimation after the perturbation ceases (compositional homeostasis). We hypothesize that the choice between acclimation and homeostasis depends on the duration of the perturbation relative to the length of the cell cycle. To test this hypothesis, we cultured the green alga Tetraselmis suecica at two growth rates and subjected the cultures to three environmental perturbations. Carbon allocation was studied with Fourier transform infrared (FTIR) spectroscopy; elemental stoichiometry was investigated by total reflection X‐ray fluorescence (TXRF) spectroscopy. Our data confirmed that growth rate is a crucial factor for C allocation in response to external changes, with a higher degree of compositional homeostasis in cells with lower growth rate.