Effect of light regime on seedling development of eelgrass (Zostera marina L.)

Light plays a crucial role in plant development and growth. Plants use photoreceptors to perceive light of varying wavelengths and intensities, translating these signals into photoresponses. In the marine environments where seagrasses grow, blue light is predominant due to the absorption of longer wavelengths by water. To elucidate the photoresponses of seagrasses , we analyzed the photoresponses of young seedlings of eelgrass ( Zostera marina ), whose genome analysis has confirmed the presence of photoreceptors. When cultured under white, blue, green, or red light, the coleoptiles were shorter, and de-etiolated primary leaves were observed. Conversely, under dark conditions, coleoptiles were elongated, and primary leaves did not emerge. These findings indicate that light reduces coleoptile elongation and promotes the emergence and de-etiolation of primary leaves. The reduction in coleoptile elongation was enhanced under intense blue light but diminished under strong red light. Additionally, primary leaf emergence was lowered under high red light conditions. The expression of photoreceptor genes ( ZoPHYA, ZoPHYB , and ZoCRY1 ) was upregulated during seed germination , with ZoPHYA and ZoCRY1 expression being particularly elevated at the coleoptile tips. Our results imply that, in young eelgrass seedlings, red and blue light are perceived at the coleoptile tips, triggering the transition from embryonic to vegetative growth . However, this transition is attenuated by intense red light. This response is likely to be an adaptive mechanism, enabling eelgrass to grow at optimal depths where blue light dominates. • Light reduced eelgrass coleoptile elongation but promoted leaf emergence. • The transition to vegetative growth was attenuated under high red light. • The expression of photoreceptor genes was upregulated during seed germination.