The super-excess energy dissipation in diatom algae: comparative analysis with higher plants

Area of Science:

• Photosynthesis research
• Algal physiology
• Photoprotection mechanisms

Background:

• Diatom algae, like Phaeodactylum tricornutum, possess unique photoprotective mechanisms.
• Non-photochemical chlorophyll fluorescence quenching (NPQ) is a key process for managing excess light energy.
• Xanthophyll cycle pigments, such as diatoxanthin in diatoms, are crucial for NPQ.

Purpose of the Study:

• To investigate the magnitude and regulation of NPQ in Phaeodactylum tricornutum under intermittent light.
• To elucidate the role of the xanthophyll cycle and proton gradients (DeltapH) in diatom NPQ.
• To characterize spectral changes associated with NPQ and diatoxanthin cycling in diatoms.

Main Methods:

• Cultivation of Phaeodactylum tricornutum under intermittent light conditions.
• Measurement of chlorophyll fluorescence to quantify NPQ.
• Use of the uncoupler NH4Cl to assess DeltapH dependency.
• Spectrophotometric analysis of absorption changes related to the xanthophyll cycle.

Main Results:

• Diatoms exhibited 3-5 times higher NPQ than higher plants, sustained in the dark and linked to diatoxanthin.
• NPQ formation and reversal were strongly dependent on proton gradients (DeltapH), with uncouplers affecting both.
• Unique spectral changes (e.g., 522 nm absorption) correlated with NPQ kinetics, differing from higher plants.

Conclusions:

• The proton gradient is a critical trigger for NPQ in diatoms, potentially involving alternative proton sources like cyclic electron flow or chlororespiration.
• Diatom NPQ mechanisms differ spectrally from higher plants, with distinct absorption changes associated with the xanthophyll cycle.
• Phaeodactylum tricornutum displays a highly efficient and uniquely regulated NPQ system crucial for its survival in fluctuating light.