AUTHOR=Wang Renjun , Wang Chao , Liu Xiuxia , Chen Junfeng , Liu Chunchen , Song Yuhao , Ding Ning , Gao Peike 

TITLE=Responses of Karenia mikimotoi to allelochemical linoleic acid: Growth inhibition, photosynthetic damage, oxidative stress and cell apoptosis

JOURNAL=Frontiers in Marine Science

VOLUME=10

YEAR=2023

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1105956

DOI=10.3389/fmars.2023.1105956

ISSN=2296-7745

ABSTRACT=<p>Linoleic acid (LA), a potentially algae-inhibiting chemical released by macroalgae, has been shown to hinder the growth of numerous bloom-forming species. The allelopathic effects of LA (varying from 100 μg/L to 900 μg/L) on harmful microalgae <italic>K. mikimotoi</italic> were examined using population growth dynamics and physiological levels of <italic>K. mikimotoi</italic>. LA (&gt;500 μg/L) strongly inhibited algal growth with most cells halted at the S and G2 phases and an evident drop in photosynthetic pigments (chlorophyll a (chl a), chlorophyll c (chl c) and carotenoids). Furthermore, chlorophyll fluorescence parameters such as F<sub>v</sub>/F<sub>m</sub>, PI, ETo/RC showed a declining trend whereas ABS/RC, DIo/RC, TRo/RC showed an increasing trend with increasing LA exposure concentrations. The level of intracellular reactive oxygen species (ROS) was considerably higher, indicating that LA promoted oxidative stress in <italic>K</italic>. <italic>mikimotoi</italic>. Excessive ROS promoted apoptosis in <italic>K. mikimotoi</italic>, which was noted by increased activity of caspase-3, caspase-9, and flow cytometry (FCM) data. Furthermore, N-acetylcysteine (NAC) and N-Acetyl-Asp-Glu-Val-Asp-CHO (Ac-DEVD-CHO) lowered the apoptotic rates of the LA-treated algal cells, indicating that the aforementioned inhibitors delayed <italic>K. mikimotoi</italic> apoptosis under LA treatment. To summarize, cell cycle arrest of <italic>K. mikimotoi</italic> is less sensitive to ROS, but the overproduction of ROS generated by LA activated caspase-3 and caspase-9, which further promoted the apoptosis of <italic>K. mikimotoi.</italic> This research showed that LA might have great potential and application prospects in controlling the outbreak of harmful algae.</p>