# Photomorphogenic and Biochemical Effects of Radiation and Nitrate Availability on the Red Alga Plocamium cartilagineum

## TL;DR

This study explores how light and nitrate levels affect the red alga Plocamium cartilagineum's photosynthesis and biochemistry, revealing potential biotechnological applications.

## Contribution

The study introduces a novel experimental setup to simulate daily light cycles and investigates photomorphogenic responses in red algae under varying nitrate levels.

## Key findings

- Nitrate assimilation was higher in blue and green light treatments, possibly due to increased nitrate reductase activity.
- UV-A and blue radiations significantly influenced photosynthetic pigments and mycosporine-like amino acids over two weeks.
- Shinorine content increased under blue light with high nitrate, suggesting modulation by a blue light photoreceptor.

## Abstract

Non-photosynthetic photoreceptors detecting different wavelength ranges in the UV and visible region of spectra may trigger algal acclimation and homeostasis. We studied Plocamium cartilagineum responses based on the saturation of photosynthesis by Amber light and supplementation by different light qualities, applying an experimental design able to simulate a daily cycle in a fully automated system. Thalli were exposed to Amber, Amber + UV-A, Amber + Blue and Amber + Green radiation treatments under two nitrate levels (60 and 240 μM) for enrichment lasting two weeks. P. cartilagineum photosynthesis and biochemistry were measured during different experimental periods. Photosynthesis showed only slight variations, emphasizing that other response variations could be activated by photomorphogenic pathways. Nitrate assimilation was higher in the treatments containing blue and green lights, potentially caused by increasing nitrate reductase activity. Photosynthetic pigments and mycosporine-like amino acids were affected over the two weeks, being mostly influenced by UV-A and blue radiations with the highest nitrate concentration. The shinorine content of thalli under blue radiation with 240 μM of nitrate increased at day 7, possibly modulated by a blue light photoreceptor. The increase in the bioactive compounds in the short-term by specific light qualities under optimal photosynthetic performance was found to be a relevant biotechnological strategy.