Screening capacity of UV-absorbing compounds in spores of Arctic Laminariales

Abstract

The functional significance of phlorotannins as ultraviolet radiation screens in brown algae is presented. Spectral analysis of zoospore suspensions of the three Arctic Laminariales Saccorhiza dermatodea, Alaria esculenta and Laminaria digitata showed strong absorption in the UV waveband, characteristic of phlorotannins. An induction in the synthesis of the UV-absorbing compound in zoospore suspensions of S. dermatodea and A. esculenta was observed as an increase in absorbance in the UV region after 8 h exposure to the whole light spectrum. Transmission of UVR was also negatively correlated with zoospore density in both these species but not in L. digitata. 'Biofilters' constructed from UV-transparent acrylic sheet, containing zoospore suspensions or solutions of phloroglucinol showed varying capacity to protect zoospore cultures from the lethal effects of ultraviolet radiation. Phloroglucinol protects the zoospores from damage by screening out the much harmful shorter UV-B spectra (280-290 nm). Cultured spores of A. esculenta and L. digitata after exposure to the whole light spectrum covered by filters containing phloroglucinol showed high rates of germination, unlike controls covered by seawater-only filters that showed 100% mortality. Biofilters containing zoospore suspensions act as buffers and showed variable UV-protection properties on the germination of its conspecies. At highest zoospore density (∼4 ×10 6 spores ml − 1 ), zoospores were observed to screen UV radiation maintaining viability among shielded spores in all species investigated. The protective function of zoospore film is, however, density-dependent in L. digitata. At lower spore density, UV-screening function in S. dermatodea and A. esculenta is attributed to their capacity to accumulate and release UV-absorbing compounds into the medium. Ultraviolet radiation transmission by zoospore suspensions of Saccorhiza and Alaria decreased during exposure to the whole light spectrum which is consistent with the earlier observation of enlarged phenolic vesicles following UVR exposure. The increase in vesicle size and the corresponding increase in UV-absorbing capacity may contribute to greater tolerance of UVR exposure in both species.

Seasonal photoacclimation patterns in the intertidal macroalga <em>Cystoseira tamariscifolia</em> (Ochrophyta)

“…High PAR irradiances and emersion have been associated with increasing phlorotannin release rates Jensen 1978, Carlson andCarlson 1984). In addition, phlorotannins in macroalgae are produced and released into seawater during periods of UVA stress and they are released but under UVB i.e at concentration of >0.84 g mL -1 , they reduce the impact of UVB exposure in UV-sensitive kelp meiospores (Roleda et al 2006. Taking into account that phlorotannins exhibit absorption maxima at 200 and 270 nm, the putative shielding capacity of phlorotannins would be more efficient in the case of DNA damage (caused mainly by UV-B wavelengths) than photosynthesis, for example, which is normally also affected by wavelengths in the UV-A region (Huovinen el at.…”

Photosynthetic performance, DNA damage and repair in gametes of the endemic Antarctic brown alga Ascoseira mirabilis exposed to ultraviolet radiation

“…Induction of phlorotannin synthesis is, however, species specific and is not only inducible by UV-B radiation but also by PAR and UV-A (Roleda et al 2006b,c). Mass released spores can screen each other serving as 'biofilter' and protect the lower layer of spores from excessive radiation (Roleda et al 2006c).…”

Isolate-specific effects of ultraviolet radiation on photosynthesis, growth and mycosporine-like amino acids in the microbial mat-forming cyanobacterium Microcoleus chthonoplastes

“…Cells and tissue of brown algae that contain UV-absorbing compounds have the potential to protect any underlying living cells from the harmful eVect of high levels of UVR. Among diVerent kelp species, release of a cloud of meiospores (with phlorotannin-containing physodes) could buVer each other eVectively acting as a UV-bioWlter (Roleda et al 2006). The superWcial meristoderm cells of a fucoid brown alga Hormosira banksii damaged by excess solar radiation was also observed to protect inner cells, remaining healthy, apparently shielded by the phlorotannin-rich dead tissue (Schoenwaelder 2002).…”