# Diurnal-Rhythmic Relationships between Physiological Parameters and Photosynthesis- and Antioxidant-Enzyme Genes Expression in the Raphidophyte Chattonella marina Complex

## TL;DR

This study explores how the harmful algal species Chattonella marina adjusts its photosynthesis and antioxidant genes in a daily cycle, revealing a biological clock that supports its growth.

## Contribution

The study identifies a diurnal rhythm and biological clock in Chattonella marina, linking it to efficient photosynthesis and cell growth.

## Key findings

- Fv/Fm and photosynthesis-related genes like psbA and psbD show increased expression during light periods.
- Oxidative stress levels and H2O2 scavenging remain stable with no clear link to antioxidant gene expression.
- Diurnal rhythms persist even in continuous darkness, indicating an internal biological clock.

## Abstract

Diurnal rhythms in physiological functions contribute to homeostasis in many organisms. Although relationships between molecular biology and diurnal rhythms have been well studied in model organisms like higher plants, those in harmful algal bloom species are poorly understood. Here we measured several physiological parameters and the expression patterns of photosynthesis-related and antioxidant-enzyme genes in the Chattonella marina complex to understand the biological meaning of diurnal rhythm. Under a light–dark cycle, Fv/Fm and expression of psbA, psbD, and 2-Cys prx showed significant increases in the light and decreases during the dark. These rhythms remained even under continuous dark conditions. DCMU suppressed the induction of psbA, psbD, and 2-Cys prx expression under both light regimes. Oxidative stress levels and H2O2 scavenging activities were relatively stable, and there was no significant correlation between H2O2 scavenging activities and antioxidant-enzyme gene expression. These results indicate that the Chattonella marina complex has developed mechanisms for efficient photosynthetic energy production in the light. Our results showed that this species has a diurnal rhythm and a biological clock. These phenomena are thought to contribute to the efficiency of physiological activities centered on photosynthesis and cell growth related to the diurnal vertical movement of this species.