Comparative analysis of endogenous phytohormone profilings in different life stages of Haematococcus pluvialis by targeted metabolomics

Phytohormones play a crucial role in the growth and production of commercial microalgae, and are closely associated with their life stages. In the study, targeted metabolomics analysis was performed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) to investigate the phytohormone profiles of four life stages (zoospores, ZP; palmella, PL; palmella cell in transition to aplanospore, PAL; aplanospore, AL) of Haematococcus pluvialis. A total of 18 phytohormones were identified and quantified, including 4 auxins, 8 cytokinins (CKs), 2 jasmonates, 2 growth inhibitors, 1 abscisic acid (ABA), and 1 salicylic acid (SA). Indole-3-acetic acid (IAA) was the major auxin, with the highest content observed at the PL stage when biomass accumulation reaches its highest peak. Cis-zeatin (cZ) and cis-zeatin riboside (cZR) were the two predominant CKs, which increased significantly at the AL stage. Similarly, abscisic acid (ABA) content was the highest at the AL stage, which was associated with the accumulation of astaxanthin. The results provide important basic information for the development of plant growth regulators in the production of H. pluvialis.