surplus photosynthetic antennae complexes underlie diagnostics of iron limitation in a cyanobacterium盈余光合天线复合物构成诊断的铁限制藻青菌.pdfVIP

Surplus Photosynthetic Antennae Complexes Underlie Diagnostics of Iron Limitation in a Cyanobacterium Paul S. Schrader, Allen J. Milligan, Michael J. Behrenfeld* Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon, United States of America Abstract Chlorophyll fluorescence from phytoplankton provides a tool to assess iron limitation in the oceans, but the physiological mechanism underlying the fluorescence response is not understood. We examined fluorescence properties of the model cyanobacterium Synechocystis PCC6803 and a DisiA knock-out mutant of the same species grown under three culture conditions which simulate nutrient conditions found in the open ocean: (1) nitrate and iron replete, (2) limiting-iron and high-nitrate, representative of natural high-nitrate, low-chlorophyll regions, and (3) iron and nitrogen co-limiting. We show that low variable fluorescence, a key diagnostic of iron limitation, results from synthesis of antennae complexes far in excess of what can be accommodated by the iron-restricted pool of photosynthetic reaction centers. Under iron and nitrogen co- limiting conditions, there are no excess antennae complexes and variable fluorescence is high. These results help to explain the well-established fluorescence characteristics of phytoplankton in high-nutrient, low-chlorophyll ocean regions, while also accounting for the lack of these properties in low-iron, low-nitrogen regions. Importantly, our results complete the link between unique molecular consequences of iron stress in phytoplankton and global detection of iron stress in natural populations from space. Citation: Schrader PS, Milligan AJ, Behrenfeld MJ (2011) Surplus Photosynthetic Antennae Complexes Underlie Diagnostics of Iron Limitation in a Cyanobacterium. PLoS ONE 6(4): e18753. doi:10.1371/journal