Protoplasmic streaming of chloroplasts enables rapid photoacclimation in large diatoms

Abstract Long-term (2004–2020) studies showed yearly summer/autumn blooms in the NE Black Sea dominated by large (cell volume > 5000 ?m3) diatoms (Pseudosolenia calcar-avis and Proboscia alata). This phenomenon is characterized high (>250 W m?2 photosynthetically active radiation, PAR) insolation, low phosphorus concentrations (to analytical zero). These contained >100 chloroplasts per cell, which at irradiance are evenly distributed throughout cell. As light increases 1000 ?mol photons s?1 PAR), aggregate within 20 min, usually to center of In consequence, absorption coefficient decreased >3 fold. At elevated photon flux density (PFD), P. also shows a “conveyor” moving from cell periphery back. mechanism enables continuous fine-tuning cells’ ability absorb light, likely facilitating photo-damage repair. rapid photoacclimation allows minimize photodamage PFD acclimate well PFD. We hypothesize that competitive success conditions gradients aided this short-term enhancing growth rate while minimizing chloroplast repair costs, cells accumulate nutrients for synthesis.