Action of Allelochemicals on Algal Growth and Photosystem Ii Efficiency

Date of Graduation

Fall 1996


Master of Science in Biology



Committee Chair

Frank Einhellig


The action of 15 allelochemicals from 7 chemical classes was tested on unicellular algal growth and photosystem II (PSII) efficiency. Chlorella pyrenoidosa Chick and Selenastrum capricornutum Printz were the bioassay species. Fourteen of the 15 allelochemicals investigated resulted in a significant decrease in C. pyrenoidosa growth; 7 caused more than 10% reduction of PSII efficiency. All compounds suppressed the growth of S. capricornutum growth, and 8 of them inhibited efficiency of PSII more than 10%. In general, of S. capricornutum was more sensitive than C. pyrenoidosa. Artemisinin was the most inhibitory compound, suppressing growth at 1 μM. The growth-inhibition threshold for other sesquiterpene lactones, alkaloids, coumarins, flavonoids, and quinones ranged between 10 and 100 μM. The inhibition threshold was 100 μM or higher for benzoic and cinnamic acids. Sesquiterpene lactones were PSII inhibitors that had a positive correlation between growth suppression and PSII reduction, indicating that interference with photosynthesis is a major mechanism of their allelopathic action. Kaempferol, a flavonoid, also strongly affected PSII efficiency, but growth inhibition by another flavonoid (quercetin) did not. The slight inhibition on PSII observed with gramine, p-hydrobenzoic acid, vanillic acid, p-coumaric acid, ferulic acid and coumarin did not suggest effects on PSII were a factor affecting growth. The physiological responses and growth inhibition by allelochemicals on two tested algal species, suggested that the algal bioassay system applied in this research is useful in investigations of allelopathy.

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