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(3)Submerged aquatic plants
① Genus Myriophyllum
Fig. 6 Allelopathic abdane diterpenes from Potamogeton pectinatus [81]
Gross et al. reported that the acetone extract of Myriophyllum spicatum had remarkable inhibition on
many globular and fibrous cyanobacteria but was ineffective on many green algae and diatoms. The extract
analysis showed that hydrolytic tannins, ellagic acid (EA), and many polyphenols occupied the great
content, in which eugeniin as the main allelochemical was 1.5% of the dry weight of the extract[82].
Nakai et al. studied the leachate of Myriophyllum spicatum with similar results, especially discovered
the water-soluble inhibitory allelochemicals in the secretions, of which the molecular weights were less
than 1000 Dalton. Based on the analysis of HPLC and APCI-MS, pyrogallic acid (PA), gallic acid (GA),
(+)-catechin (CATECH) were identified[41]. At the earilier year, Planas et al. also pointed out the PA, GA,
and EA existed but CATECH was firstly discovered by Nakai in Myriophyllum spicatum[83]. Subsequently,
Nakai et al. investigated the left organic fraction obtained as above and nonanoic acid, tetradecanoic acid,
palmitic acid, octadecanoic acid and octadecenoic acid, a variety of fatty-acid-like allelochemicals were
identified in it, of which nonanoic acid, cis-6-octadecenoic, and cis-9-octadecenoic acids had the strongest
inhibitory activities[42]. Majority of the phenolic and fatty acids discovered above are by far the strongest
allelochemicals, of which EC50s were seen in Table 4.
Gross reported the plants of genus Myriophyllum, Myriophyllum alterniflorum and Myriophyllum
heterophyllum could excrete polyphenol-like alleochemicals like Myriophyllum verticillatum,
Myriophyllum brasiliense, and Myriophyllum spicatum to inhibit the growth of green algae and
cyanobacteria[84], which might be due to the close genetic relationship among the plant species in the
same genus (Gross et al, unpublished). In addition to polyphenols, α-asarone, phenylpropane
glycoside-like allolochemicals were identified from Myriophyllum verticillatum[85, 86].
Table 4 EC 50 values of allelochemicals from Myriophyllum spicatum on Microcystis aeruginosa
Allelochemicals EC 50(mg/L) References
gallic acid 1.0
pyrogallic acid 0.65
ellagic acid 5.1
(+)-catechin 5.5
nonanoic acid 0.5±0.3
cis-9-octadecenoic acids 1.6±0.4
cis-6-octadecenoic acids 3.3±0.4
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[41]
[42]