Interactive effects of external manganese, the toxic metals copper and zinc, and light in controlling cellular manganese and growth in a coastal diatom
Limnol. Oceanogr., 43(7), 1998, 1467-1475 | DOI: 10.4319/lo.19126.96.36.1997
ABSTRACT: Manganese is a fundamental component of the photosystem 11 reaction center, and thus its requirement should be linked to light utilization. High levels of Cu and Zn antagonize Mn nutrition by inhibiting cellular Mn uptake. Experiments were conducted to examine the interactive effects of Mn, the toxic metals Cu and Zn, and light on cellular Mn, chlorophyll a (Chl a), and specific growth rate in Thalassiosiru pseudonana. Cu and Zn inhibition of growth rate occurred only at. low Mn ion concentrations, an effect that was independent of light intensity and was totally accounted for by inhibition of Mn uptake by these metals. Cells grown at growth-limiting low light intensities contained high levels of Mn and Chl a, which are needed for the synthesis of additional photosynthetic units during low-light acclimation. This additional Mn was not provided by higher cellular Mn uptake rates, since these rates were the same in light-saturated and light-limited cells. However, because steady-state cell Mn is equal to the uptake rate divided by the specific growth rate, the cells were able to accumulate the additional Mn needed for acclimation once light limitation caused growth rate to decline, a inherent negative feedback relation. In seawater, Mn and Cu may interact with light in controlling algal growth rate, since the free ion concentration of both metals is influenced by iight within the euphotic zone.