Photosynthetic activity detected in the seed epidermis of Thalassia testudinum

• This is study evidences photosynthetic activity in Thalassia testudinum seeds.
• Seed photosynthetic descriptors were calculated: (higher α, lower P. max, Ek, and Ec).
• Seed photosynthesis is highly efficient and makes it well adapted to colonize habitats with reduced light availability.
• Taking the Chl a/b ratio into account, the T. testudinum seed can be considered as a “Shade plant”.
• The T. testudinum seed photo-adapt capability is very relevant in terms of possible settlement places where sink, characterized by different irradiance intensities.

Seagrasses are marine angiosperms that have evolved from terrestrial ancestors. Photosynthetic activity on seed has been studied before in Posidonia genus. T. testudinum and P. oceanica share some evolutionary aspects as they live in more stable environments. As in P. oceanica, T. testudinim seed is also green-coloured suggesting the presence of photosynthetic pigments. Here, the photosynthetic activity in the T. testudinum seed was examined. Measurements of photosynthetic production, pigment content and maximum PSII photochemical efficiency (Fv: Fm) were determined. Epifluorescence microscopy analysis was used to obtain evidence of photosynthetic structures within the seed. This study revealed photosynthetic activity in seed epidermis which increased linearly with increasing irradiance. T. testudinum seed displayed a higher Photosynthetic efficiency (α), and lower light saturated photosynthesis (P. max), saturation irradiance (Ek), and compensation irradiance (Ec) compared to adult leaves. Epifluorescence microscopy images of the seeds showed an epidermis composed of relatively small, regular cells, tending towards a rectangular shape, containing abundant chloroplasts. The photobiological behaviour results in the T. testudinum seed being strongly adapted to colonize environments with reduced light availability. Photosynthetic activity in T. testudinum seed shed some light on seagrass dispersal and expansion mechanisms.