FLAVODOXIN AS AN IN-SITU MARKER FOR IRON STRESS IN PHYTOPLANKTON

A fundamental issue in marine science is the identification of the fac tors controlling biological uptake of CO2 in high nitrate, low-chlorop hyll regions(1-10). A recent in situ iron fertilization experiment dem onstrated that iron limitation is responsible for low phytoplankton st ocks in the equatorial Pacific(4), Here we show that flavodoxin, a bio chemical marker of iron limitation, can be used to map the degree of i ron stress in natural populations. Flavodoxin assays along a 900-km ea st-west transect in the northeastern subarctic Pacific revealed a pron ounced increase in iron stress in the region west of the 135 degrees W meridian. Addition of dissolved iron alleviated this stress. Immunost aining of single cells from the most western station showed that flavo doxin is present specifically within the chloroplasts of diatoms. Our approach provides a rapid means of defining the extent of iron stress in the ocean(5) and supports the hypothesis that diatoms are iron stre ssed in the northeast Pacific(6,10).