Complementary UV-absorption of mycosporine-like amino acids and scytonemin is responsible for the UV-insensitivity of photosynthesis in Nostoc flagelliforme.
Mycosporine-like amino acids (MAAs) and scytonemin are UV-screening compounds that have presumably appeared early in the history of life and are widespread in cyanobacteria. Natural colonies of the UV-insensitive Nostoc flagelliforme were found to be especially rich in MAAs (32.1 mg g DW(-1)), concentrated in the glycan sheath together with scytonemin. MAAs are present in the form of oligosaccharide-linked molecules. Photosystem II activity, measured using PAM fluorescence and oxygen evolution, was used as a most sensitive physiological parameter to analyse the effectiveness of UV-protection. Laboratory experiments were performed under controlled conditions with a simulated solar radiation specifically deprived of UV-wavebands with cut-off filters (295, 305, 320, 345 and 395 nm). The UV-insensitivity of N. flagelliforme was found to cover the whole UV-A (315-400 nm) and UV-B (280-320 nm) range and is almost certainly due to the complementary UV-absorption of MAAs and scytonemin. The experimental approach used is proposed to be suitable for the comparison of the UV-protection ability in organisms that differ in their complement of UV-sunscreen compounds. Furthermore, this study performed with a genuinely terrestrial organism points to the relevance of marine photoprotective compounds for life on Earth, especially for the colonization of terrestrial environments.
Ferroni
Lorenzo
L
Laboratory of Plant Cytophysiology, Department of Biology and Evolution, University of Ferrara, Corso Ercole I d'Este, 32, 44100 Ferrara, Italy. lorenzo.ferroni@unife.it
Klisch
Manfred
M
Pancaldi
Simonetta
S
Häder
Donat-Peter
DP
D000042:Absorption; D000596:Amino Acids / Q000737:chemistry* / Q000302:isolation & purification; D002681:China; D003511:Cyclohexanols / Q000737:chemistry / Q000302:isolation & purification; D003512:Cyclohexanones / Q000737:chemistry / Q000302:isolation & purification; D003514:Cyclohexylamines / Q000737:chemistry / Q000302:isolation & purification; D019610:Cytoprotection; D004307:Dose-Response Relationship, Radiation; D017753:Ecosystem; D007211:Indoles / Q000737:chemistry* / Q000302:isolation & purification; D046937:Nostoc / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects* / Q000648:ultrastructure; D010100:Oxygen / Q000032:analysis; D010636:Phenols / Q000737:chemistry* / Q000302:isolation & purification; D010788:Photosynthesis / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism / Q000528:radiation effects; D010860:Pigments, Biological / Q000502:physiology*; D013045:Species Specificity; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D014466:Ultraviolet Rays
D000596:Amino Acids; D003511:Cyclohexanols; D003512:Cyclohexanones; D003514:Cyclohexylamines; D007211:Indoles; D010636:Phenols; D045332:Photosystem II Protein Complex; D010860:Pigments, Biological; C083368:scytonemin; D010100:Oxygen