Bio-optical properties of the marine diazotrophic cyanobacteria Trichodesmium spp. I. Absorption and photosynthetic action spectra

TY - JOUR

T1 - Bio-optical properties of the marine diazotrophic cyanobacteria Trichodesmium spp. I. Absorption and photosynthetic action spectra

AU - Subramaniam, Ajit

AU - Carpenter, Edward J.

AU - Karentz, Deneb

AU - Falkowski, Paul G.

PY - 1999/5

Y1 - 1999/5

N2 - The optical absorption, fluorescence excitation and emission, and photosynthetic action spectra were measured in vivo on intact colonies of Trichodesmium from the Caribbean Sea. The optical cross-sections were dominated by ultraviolet-A (UVA) absorption, which was a consequence of massive accumulations of mycosporinelike amino acids. The visible region of the spectrum was decomposed into several bands, among which chlorophyll a (Chl a), carotenoids, and individual phycobilipigments could be discerned. There was a clear diel periodicity in the ratio of the optical absorption cross-sections of phycourobilin (PUB) to phycoerythrobilin (PEB), increasing from around 1.7 at night to 2.1 at midmorning. The diel cycle in PUB/PEB is consistent with a reversible interconversion of the two pigments. The ratio of PUB/PEB was inversely correlated with the transfer of excitation energy to photosystem II (PSII). Light absorbed by PUB was not transferred to PSII with a high efficiency, but rather, a significant fraction was reemitted at 565 nm as fluorescence. These observations suggest that the PUBs and PEBs in Trichodesmium act as a dynamic biophysical energy valve that modify the rate of excitation energy delivered to PSII in response to changes in ambient light regime. The low-temperature (77 K) fluorescence emission spectra reveal an extremely weak 685-nm emission signal in relation to that at 730 nm. Based on a simple model, these data suggest that the ratio of PSI/PSII reaction centers in Trichodesmium is about 24:1. Such an extraordinary bias against PSII may help minimize damage to nitrogenase from O2 production in PSII, but it also reduces the photosynthesis-enhanced growth and makes Trichodesmium virtually undetectable by chlorophyll fluorescence. The unique bio-optical properties of Trichodesmium can be used to develop algorithms to study its temporal and spatial distributions from remotely sensed information.

AB - The optical absorption, fluorescence excitation and emission, and photosynthetic action spectra were measured in vivo on intact colonies of Trichodesmium from the Caribbean Sea. The optical cross-sections were dominated by ultraviolet-A (UVA) absorption, which was a consequence of massive accumulations of mycosporinelike amino acids. The visible region of the spectrum was decomposed into several bands, among which chlorophyll a (Chl a), carotenoids, and individual phycobilipigments could be discerned. There was a clear diel periodicity in the ratio of the optical absorption cross-sections of phycourobilin (PUB) to phycoerythrobilin (PEB), increasing from around 1.7 at night to 2.1 at midmorning. The diel cycle in PUB/PEB is consistent with a reversible interconversion of the two pigments. The ratio of PUB/PEB was inversely correlated with the transfer of excitation energy to photosystem II (PSII). Light absorbed by PUB was not transferred to PSII with a high efficiency, but rather, a significant fraction was reemitted at 565 nm as fluorescence. These observations suggest that the PUBs and PEBs in Trichodesmium act as a dynamic biophysical energy valve that modify the rate of excitation energy delivered to PSII in response to changes in ambient light regime. The low-temperature (77 K) fluorescence emission spectra reveal an extremely weak 685-nm emission signal in relation to that at 730 nm. Based on a simple model, these data suggest that the ratio of PSI/PSII reaction centers in Trichodesmium is about 24:1. Such an extraordinary bias against PSII may help minimize damage to nitrogenase from O2 production in PSII, but it also reduces the photosynthesis-enhanced growth and makes Trichodesmium virtually undetectable by chlorophyll fluorescence. The unique bio-optical properties of Trichodesmium can be used to develop algorithms to study its temporal and spatial distributions from remotely sensed information.

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U2 - https://doi.org/10.4319/lo.1999.44.3.0608

DO - https://doi.org/10.4319/lo.1999.44.3.0608

M3 - Article

SN - 0024-3590

VL - 44

SP - 608

EP - 617

JO - Limnology and Oceanography

JF - Limnology and Oceanography

IS - 3 I

ER -