Plant-Originated Kaempferol and Luteolin as Allelopathic Algaecides Inhibit Aquatic Microcystis Growth Through Affecting Cell Damage, Photosynthetic and Antioxidant Responses

Abstract

Harmful algal blooms dominated by cyanobacterium Microcystis aeruginosa increasingly occur in freshwaters worldwide, and adversely threat ecosystem functioning. Plant allelopathic effects can be applied as an emerging biological option to control and remediate HABs pollution. This study aimed to explore the growth-inhibition effects of plant-originated kaempferol and luteolin on bloom-forming Microcystis aeruginosa (FACHB-915 strain) and elucidate their anti-algal mechanisms from the views of photosynthesis, antioxidant responses and cell oxidative damage. Results showed that kaempferol and luteolin stress on M. aeruginosa growth were dose-and time-dependent. In contrast to 0.5~4 mg/L dose, 16~32 m/L kaempferol and luteolin significantly inhibited growth after 6 days-exposure and achieved 92.05% ~95.20% and 74.40%~85.35% inhibition, respectively, by day 14, partially caused by inhibited chlorophyll-a content at late phase. On day 4 and 8, stimulated photosynthetic responses (except phycocyanin content on day 4) at 32 mg/L kaempferol and stimulated superoxide dismutase activity at 16~32 mg/L kaempferol and 32 mg/L luteolin acted as adaptive and antioxidant defense against oxidative stress. Despite these, enhanced oxidative damage at 16~32 mg/L kaempferol and 32 mg/L luteolin and inhibited phycobiliproteins (e.g., phycocyanin, allophycocyanin) synthesis at 16~32 luteolin throughout the test and/or during mid-late phase still caused inhibited growth. Innovatively, this study for the first time to reveal that plant-originated kaempferol and luteolin at 16~32 mg/L could inhibit M. aeruginosa growth due to enhanced cell oxidative damage and/or inhibited photosynthesis despite activated antioxidant responses and could be potentially developed as algaecides for efficient M. aeruginosa bloomremoval and bioremediation.