Phytoplankton extracellular phosphatases: Investigation using the ELF (enzyme labelled fluorescence) technique

Abstract

Phosphorus deficiency is frequently the limiting factor in phytoplank- ton growth and the major source of selective pressure on single populations in a variety of aquatic environments. Phytoplankton spe- cies have several mechanisms that allow them to overcome phosphorus starvation, such as high-affinity uptake of orthophosphate (P i ), stand-by energy metabolism or utilization of phosphorus from stored polyphosphates. This short review is focused on the production of extracellular phosphatases that is usually ac- companied by high-affinity uptake of P i . Ex- tracellular phosphatases are localized on the cell membrane, where they catalyze the lib- eration of P i from various organic compounds that are too large to be directly transported into the cell. The production of extracellu- lar phosphatases is not a general response to starvation in phytoplankton; it is a species- specific or cell-specific feature. The ELF (En- zyme Labelled Fluorescence) technique enables direct visualization of the sites of enzymatic activity and therefore gives detailed informa- tion about the physiological status of natural phytoplankton.