Iodine in Seaweeds - Physiological Significance and Implications for Climate and Health
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2013-01-18Author
Nitschke, Udo
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Abstract
Iodine-rich macroalgae inhabit the subtidal on coasts in temperate regions. The
algae-driven release of iodine into the environment has major implications for the
biogeochemical iodine cycle a ffecting atmospheric chemistry and probably human
health. This thesis has focused on interactions between Laminaria digitata and
its environment, with emphasis on impacts of emersion, irradiance intensity, temperature and salinity on the release of iodine. The research also included an examination of the physiological role of iodine accumulation. L. digitata was further
investigated as potential antiproliferative agent in human mammary carcinoma
studies in vitro.
Sporophytes of L. digitata were strong emitters of molecular iodine (I2) during
emersion, but intra-thallus variations in I2 emission rates were observed. During
submersion iodide (I-) was released into seawater from meristematic areas of L.
digitata. Increased temperatures and dying resulted in elevated I2 emission rates,
whereby death and decomposition led to high quantities of I- released into the
seawater. These results, in addition to local field biomass assessments, suggest
that both living and dead biomass of L. digitata are fundamental elements in a
coastal iodine cycle.
The external salinity regime controlled the release of I- into seawater. Lowest
I- release rates from L. digitata were detected at highest salinities. When present
in seawater, I- was effi ciently incorporated by L. digitata and prevented the to-date well-established mannitol accumulation of this species when exposed to high
salinities. This suggests that I- acts as an inorganic osmolyte in L. digitata.
Exudates and extracts from L. digitata potently induced apoptosis in human
mammary carcinoma cells, but highest antiproliferative activities were observed
from low-iodine containing exudates. In some cases, high-iodine containing extracts
enhanced proliferation of human mammary carcinoma cells in vitro. The
results indicate that anti-carcinoma activities of L. digitata, where detected, cannot
solely be attributed to iodine levels, but may be associated with the large
variety of chemical constituents present in this species.
The results highlight the important role of L. digitata in coastal iodine
fluxes with implications for climate research, and potential impacts for human health.