Formation of the guanine crystals regarding the light adaptation of dinoflagellate Amphidinium carterae
Abstract
For a long time, animals have been utilizing biogenic guanine crystals to manipulate light. These crystals have a plate-like arrangement and a high refraction index, which enable them to function as diffuse scatterers, reflectors, or image-forming mirrors.
Guanine crystals or similar purines have been found in crystalline inclusions in various photosynthetic microalgae, despite being phylogenetically unrelated [1]. In Amphidinium carterae guanine crystals serve as a long-term and high-capacity storage of nitrogen, although their role in light manipulation was speculated earlier in photosynthetic eukaryotes [2].
Confocal Raman microscopy was employed to visualize crystalline guanine in intact A. carterae cells, and it was found that the location of guanine crystals was influenced by the intensity of illumination. Regardless of the lighting conditions, the initial position of crystal formation is at the periphery of the cell membrane.
However, under low light intensity (5 µmol(photons) m-2 s-1), guanine crystals were produced closer to the center of the cell, functioning as photonic mirrors or diffusers to enhance photosynthesis efficiency. Conversely, high light intensity (range from 200-500 µmol(photons) m-2 s-1) resulted in the formation of substantial guanine crystal layers between the cell wall and plastids, providing protection against excessive illumination and regulating photosynthetic efficiency.
This study emphasizes the potential role of guanine crystals in regulating photosynthetic processes and safeguarding plastids against photo damage in A. carterae.