Introduction
Microcystis aeruginosa is the most common algae in water blooms, and can release toxic and harmful algal toxins into the environment[1-4]. There are two kinds of glutathione in algal cells, one is reduced glutathione (GSH), the other is oxidized glutathione (GSSG).However, glutathione in algal cells exists in the form of reduced glutathione (GSH) in most cases, and GSH has high reducibility [5-8]. Under certain conditions, oxidized glutathione (GSSG) and reduced glutathione (GSH) can be transformed into each other [9-11]. When stressed, there will be reactive oxygen species (ROS) in microalgae cells, which can cause GSH to be oxidized to GSSG [12-14].As the most abundant free mercaptan in microalgae cells, GSH maintains the best intracellular oxidation environment to play the normal function of cell proteins [15]. In general, the level of GSH in microalgae cells will affect the redox status of the cells[16].
GSH in microalgae cells can also be converted into phytochelating peptides (PC) and ascorbic acid (ASA) with the participation of various enzymes [17-20]. Under the action of phytochelating peptidases (PCs), GSH can be synthesized into PC to form low-molecular-weight complexes, which are then further converted into high-molecular-weight multimeric complexes and preserved in Microcystis aeruginosa cells [21]. GSH exerts its important antioxidant stress role through the ascorbic acid-glutathione (ASA-GSH) cycle [22-24].
Therefore, under the influence of environmental changes, glutathione and enzymes in algal cells undergo some synergistic changes and interact with each other [25, 26], but with the progress of metabolism, it is difficult to accurately detect and analyze the changes of each living substance by existing biochemical methods. In this study, we investigated the changes of GSH in different growth stages of Microcystis aeruginosa and its correlation with the synergistic changes of phycocyanin and enzymes, and analyzed the changes of carboxylated biomolecules in the growth and metabolism of Microcystis aeruginosa by covalent coupling method, mainly including the changes of GSH, phycocyanin and SOD enzymes. The distribution of GSH content in different stages was clear, no other interference in the system, good correlation, changes in the number of peaks and peak area of GSH content in the three-dimensional fluorescence spectral region, and the maximum GSH content in the algal cells at d 50. There are physiological activities between GSH synthesis, GSH/GSSG interconversion, synthesis of phytochelating peptide (PC), ASA-GSH cycle and metabolism in algae. The interaction between GSH synthesis, GSH/GSSG interconversion, phytochelating peptide (PC) synthesis, ASA-GSH cycling and metabolism was found to maintain the antioxidant properties of microalgae.