Regulation of Fatty Acid Production and Release in Benthic Algae: Could Parallel Allelopathy Be Explained with Plant Defence Theories?

Abstract

Many organisms produce chemical compounds, generally referred as secondary metabolites, to defend against predators and competitors (allelopathic compounds). Several hypotheses have been proposed to explain the interaction between environmental factors and secondary metabolites production. However, microalgae commonly use simple metabolites having a role in primary metabolism as allelopathic compounds. The aim of this study was to determine whether classical theories of plant chemical defences could be applied to microalgae producing allelochemicals derived from the primary metabolism. Our study was designed to investigate how growth phase, algal population density, nutrient limitation and carbon assimilation affect the production and release of allelopathic free fatty acids (FFAs) among other FFAs. The model species used was Uronema confervicolum, a benthic filamentous green alga that produces two allelopathic FFAs (linoleic and α-linolenic acids) inhibiting diatom growth. FFAs have been quantified in algal biomass and in culture medium. Our results were analysed according to two classical plant defence theories: the growth-differentiation balance hypothesis (GDBH) and the optimal defence theory (ODT), based on the metabolic capacities for defence production and on the need for defence, respectively. While a higher production of allelopathic compounds under increased light conditions supports the use of GDBH with this microalga, the observation of a negative feedback mechanism mostly supports ODT. Therefore, both theories were insufficient to explain all the observed effects of environmental factors on the production of these allelochemicals. This highlights the needs of new theories and models to better describe chemical interactions of microalgae.

Allelopathic and Bloom-Forming Picocyanobacteria in a Changing World

“…Allelopathy is considered as one of the factors promoting and maintaining the massive cyanobacterial and algal blooms in freshwater, brackish and marine ecosystems around the world [ 93 , 94 , 95 , 96 ]. Therefore, the number of reports about the allelopathic effects of different species of cyanobacteria and microalgae has been steadily increasing (e.g., [ 95 , 96 , 97 , 98 , 99 ]). However, only little information on picocyanobacterial allelopathy or their harmful effects on other organisms has been described ( Table 2 ).…”

Allelopathic activity of the bloom‐forming picocyanobacterium Synechococcus sp. on the coexisting microalgae: The role of eutrophication

“…Other authors also observed that some cyanobacteria can cause allelopathy under non‐limiting nutrient conditions (Allen et al, ; Bittencourt‐Oliveira et al, ; Brutemark et al, ; Dias et al, ; Leflaive & Ten‐Hage, ). Allen et al () showed that allelopathic compounds produced by green algae Uronema confervicolum were the highest in the treatment with the highest nutrient level and were much lower in the unbalanced nutrients treatments. These results confirm the reports obtained on the same species and other green algae (Leflaive & Ten‐Hage, ).…”

“…One of the principal effects of eutrophication due to the anthropogenic supply of biogenic elements (especially nitrogen and phosphorus) is the excessive growth of phytoplankton. Recent studies suggest that the availability of nitrogen and phosphorus could affect cyanobacterial and microalgal allelopathy (Allen et al, ; Antunes et al, ) which, in turn, might be implied in the maintenance of harmful blooms (Figueredo, Giani, & Bird, ). Therefore, determining the effect of the increased availability of nutrients on the appropriate aspects should be a priority for present and future research.…”

“…Summarizing, the availability of nutrients may affect the production of cyanobacterial allelochemicals (Allen et al, 2017;Antunes et al, 2012). At the same time, unbalanced nutrient conditions are a problem in several coastal areas due to eutrophication (Chislock, Doster, Zitomer, & Wilson, 2013;Granéli et al, 2008).…”

Allelopathic effects and mechanisms of Cochlodinium geminatum isolated from the Pearl River Estuary

“…Furthermore, the allelopathic effect can be influenced by abiotic factors, such as irradiation, temperature, and salinity. Uronema confervicolum (Chlorophyta) had a higher production of allelopathic compounds under higher light intensity (Allen et al 2017). The allelopathic effect is also temperature-dependent, as toxic Microcystis aeruginosa (Cyanobacteria) strains inhibited the growth of Chlorella vulgaris (Chlorophyta) more at high temperatures (≥ 25°C) (Ma et al 2015).…”