Plants collect light for photosynthesis using light-harvesting complexes (LHCs)-an array of chlorophyll proteins that are able to reversibly switch from harvesting to energy-dissipation mode to prevent damage of the photosynthetic apparatus. LHC antennae as well as other members of the LHC superfamily evolved from cyanobacterial ancestors called high light-inducible proteins (Hlips). Here, we characterized a purified Hlip family member HliD isolated from the cyanobacterium Synechocystis sp. PCC 6803. We found that the HliD binds chlorophyll-a (Chl-a) and β-carotene and exhibits an energy-dissipative conformation. Using femtosecond spectroscopy, we demonstrated that the energy dissipation is achieved via direct energy transfer from a Chl-a Qy state to the β-carotene S1 state. We did not detect any cation of β-carotene that would accompany Chl-a quenching. These results provide proof of principle that this quenching mechanism operates in the LHC superfamily and also shed light on the photoprotective role of Hlips and the evolution of LHC antennae.

Twenty-two tropical seaweeds from the Rhodophyta, Phaeophyta and Chlorophyta were examined for their possible use as nutritional supplements. All seaweeds contained balanced Na/K and C/N ratio and high amounts of macroelements (Na, K, Ca, and Mg) as compared to the terrestrial vegetables. Among the microelements, Fe was the highest followed by Zn, Mn, Cu and other trace elements. Fatty acid distribution showed high level of n-6 and n-3 polyunsaturated fatty acids (PUFAs), and their ratios were within the WHO prescribed limits. The higher ratios of PUFA/SFA (>0.4) are in agreement with the recommendations of nutritional guidelines. Most of the species, especially the Chlorophyta and Phaeophyta, had permissible intake values of unsaturation, atherogenic and thrombogenic indexes comparable to milk-based products. Principal component analysis demonstrated a correlation between total phenolic content, total antioxidant activity, DPPH, and O 2 •− radical scavenging activity, suggesting polyphenols as the chief contributor to the antioxidant activity in seaweeds. These results indicate that these seaweeds could be a potential source of natural antioxidants, minerals and high-quality PUFAs and may be efficiently used as ingredients in functional foods.