Nitrate Uptake Kinetics and Clonal Variability in the Neritic Diatombiddulphia Aurita1

Nitrate uptake experiments were conducted at 18 and 25 C on subtropical and temperate isolates of the neritic diatomBiddulphia aurita(Lyngb.) Breb. & Godey. Two clones (STX‐88 and B1) were grown in a 12:12 LD cycle in NO3‐limited continuous cultures used for uptake experiments. The half‐saturation constant (Ks) and the maximum NO3‐ uptake rate (Vm) were measured under conditions in which external NO3‐ concentration controlled uptake rate. The kinetic constants for both clones were higher at the higher temperature. The subtropical clone (STX‐88) had lower kinetic values than temperate clone (B1) at both temperatures. The differences appear to be of adaptive significance since STX‐88 has a NO3‐ uptake system, described by its lower Ksvalue, which minimizes the double stress effects of high temperature‐low NO3‐ concentration conditions characteristic of its habitat. Cytoplasmic enzyme electrophoretic analyses were conducted on the clones. Differences in banding patterns and mobilities showed evidence of allelic substitution. The results suggest genetic variation at the intraspecific level.