Natural Variation in Photoprotection: Rapid NPQ Kinetics in Ferns
Land plants perform oxygenic photosynthesis but are unable to use all of the solar radiation that they absorb on a daily basis. To minimize the production of reactive oxygen species in excess light, photosynthetic organisms use non-photochemical quenching (NPQ) mechanisms to dissipate excess excitation energy. However, the on-off transition of these mechanisms is slower than the light fluctuations themselves. In high-to-low light transitions, this can be costly to the overall productivity and carbon gain of the organism across its lifetime, because useful light energy is wasted. Here, we characterize the rapid kinetics of NPQ found in species across the fern lineage. Most of the 23 examined fern species showed faster NPQ induction and faster and more complete NPQ relaxation. Curve fitting suggested that energy-dependent quenching was the dominant contributor to the kinetics. The xerophytic fern Astrolepis windhamii exhibited rapid, dithiothreitol-resistant accumulation of zeaxanthin during NPQ induction, and it maintained low residual NPQ after NPQ relaxation, which however was not associated with rapid re-epoxidation of zeaxanthin. Rapid NPQ kinetics might have been an adaptive trait as ferns radiated in sunflecked forest understories during angiosperm diversification and expansion during the Cretaceous.