Light Sheet Microscopy Imaging of Light Absorption and Photosynthesis Distribution in Plant Tissue

Area of Science:

• Plant Physiology
• Photosynthesis Research
• Aquatic Macrophyte Biology

Background:

• In vivo measurements of photosystem II (PSII) quantum yields in optically dense tissues are complicated by light scattering and absorption, creating steep internal light gradients.
• Surface-based measurements may not accurately represent the photophysiological status of cells deeper within tissues, leading to potential under- or overestimations of effective PSII quantum yields.

Purpose of the Study:

• To investigate the impact of natural tissue light gradients on measured PSII quantum yields in the aquatic macrophyte *Fucus vesiculosus*.
• To develop and present a method for correcting apparent PSII electron transport rates by accounting for depth-resolved photon absorption.
• To explore strategies for optimizing photon absorption in aquatic macrophytes based on their unique absorption profiles.

Main Methods:

• Applied actinic irradiance perpendicular to *Fucus vesiculosus* thallus cross sections using laser light sheets.
• Imaged variable chlorophyll fluorescence with a microscope-mounted pulse amplitude-modulated imaging system.
• Combined fluorescence profiles with integrating sphere measurements (reflectance, transmittance) to calculate depth-resolved photon absorption.

Main Results:

• PSII quantum yields are significantly affected by light gradients within plant tissues.
• Traditional surface-based measurements can lead to substantial under- or overestimations of PSII efficiency.
• Absorption profiles in *Fucus vesiculosus* differ from terrestrial leaves, suggesting unique light absorption strategies.

Conclusions:

• Accurate in vivo PSII quantum yield measurements require correction for internal light gradients.
• The developed method allows for the calculation of depth-resolved photon absorption to refine electron transport rate estimations.
• Understanding and optimizing photon absorption through structural modulation is crucial for enhancing photosynthetic efficiency in aquatic environments.