Volatile organic compound and endogenous phytohormone characteristics during callus browning in Aquilaria sinensis

Callus browning, a common feature in plant cell cultures, has hardly been explored in Aquilaria sinensis. Here, the volatile organic compounds (VOCs) were characterized during the browning of A. sinensis cells using Gas Chromatography-Mass Spectrometry (GC-MS), and total sesquiterpene accumulation was significantly induced and peaked during A. sinensis callus browning, after 60 days of callus growth. Additionally, 14 types of sesquiterpenes were detected in the browning A. sinensis callus, with greater sesquiterpene diversity than in the ones treated with methyl jasmonate and salicylic acid (SA) in a previous study. To further evaluate the mechanism of regulation of agarwood sesquiterpenes during cell browning in A. sinensis, changes on phytohormone concentrations were explored using ultra-performance liquid chromatography-electrospray tandem mass spectrometry system (UPLC-ESI-MS/MS). Both endogenous jasmonic acid and SA, key plant defense hormones, increased during A. sinensis callus browning. 1-aminocyclopropanecarboxylic acid, an ethylene (ET) precursor, decreased significantly after A. sinensis callus browning. Conversely, two primary growth hormones, auxin and cytokinin, exhibited opposite trends, suggesting that they also play roles in agarwood sesquiterpene accumulation. Our results potentially offer novel insights that could facilitate the production valuable phytochemical compounds such as agarwood sesquiterpenes, using plant cell cultures treated with appropriate phytohormone combinations.