Formation and dynamics of the guanine crystals regarding the light adaptation of dinoflagellate Amphidinium carterae
Abstract
Biogenic guanine crystals are essential for light manipulation in animals and photosynthetic microalgae [1-4]. These crystals, with their high refractive index and plate-like arrangement, serve various functions such as scattering, reflection, and image formation [1]. Interestingly, similar crystalline inclusions have been found in unrelated photosynthetic microalgae [2]. In Amphidinium carterae, guanine crystals act as long-term nitrogen stores and potentially play a role in light manipulation [3,4].
Using confocal Raman microscopy, we studied guanine crystals in A. carterae cells under different light and nutritional conditions. Crystal formation typically occurs at the cell periphery, between the cell wall and plastids, regardless of light intensity. Even under prolonged darkness, nitrogen supplementation triggers guanine crystal formation at the periphery. However, the crystal position can change depending on light stress.
Under conditions of low light intensity and continuous inorganic nitrogen supply, cells adapt by increasing plastid abundance and depositing guanine crystals closer to the cell center. This positioning enhances photosynthetic efficiency by redirecting photons to the plastids. Conversely, under high light intensity, extensive guanine crystal layers form at the cell periphery, providing shielding to the plastids against excessive illumination. This suggests a regulatory role of guanine crystals in photosynthetic efficiency and protection against photodamage in A. carterae.
In summary, biogenic guanine crystals are crucial for light manipulation and nitrogen storage in various organisms. In A. carterae, these crystals contribute to regulating photosynthetic efficiency and safeguarding plastids under different light conditions