Chemical Constituents Of The Seaweed Gracilaria Lemaneiformis And Their Allelopathic Effects On Skeletonema Costatum

Allelochemicals were extracted, isolated and identified from seaweed Gracilaria lemaneiformis. Preliminary allelopathy mechanism of the G. lemaneiformis on Skeletonema costatum was studied. The main results are as follows:In order to investigate the chemical constituents of G. lemaneiformis, a variety of absorbing materials and separation approaches (including pressure silica gel column chromatography, reverse silica gel column chromatography, Sephadex LH-20 gel column chromatography, D101 macroporous resin, and HPLC) were assessed. Fifteen compounds from G.lemaneiformis were isolated from the 95% ethanol extract by various column chromatographies. On the basis of various modern spectroscopic and literature data, fifteen compounds were identified, and one of them,8-Hydroxy-4E,6E-octadien-3-one was identified as a new compound. Fifteen compounds were isolated from G. lemaneiformis for the first time. Among these compounds, there are three Glycolipid compounds:1-O-Palmitoyl-3-O-β-D-galactopyranosyl glycerol (1),1-O-Palmitoyl-2-O-palmitoleoyl-3-O-β-D-galactopyranosyl glycerol (2),1-O-Palmitoyl-2-O-oleoyl-3-O-β-D-galactopyranosyl glycerol (3); two fatty acid compounds:Palmitic acid (4), Linoleic acid (5); two nucleosides:Uridine (6), Adenosine (7); three amides:Squamolone (10), 2-ethylidene-3-methylsuccinimide(11), N-Phenethylacetamide (12); two phenolic compounds: Butylisobutyl phthalate (8),1,4-Dibenzoyloxybenzene (9); two terpenoids:Loliolide (13), 3β-hydroxy-5α,6α-epoxy-7-megastigmen-9-one (14); one other compound: 8-Hydroxy-4E,6E-octadien-3-one (15).The inhibition of activity screening of allelochemicals on Skeletonema costatum showed that the strongest inhibitory allelochemical was Linoleic acid, and the lowest 2-ethylidene-3-methylsuccinimide. According to inhibition rate of different concentrations of linoleic acid on S. costatum, ICso value was 23.17μmol/L. While the inhibitory effect of 2-ethylidene-3-methylsuccinimide on S. costatum was only 19.8% at the concentration of 330μmol/L.The chloroplast, SOD, MDA and intracellular organelles of S. costatum were tested under external stress of linoleic acid. The result showed that when exposure to linoleic acid, the inhibition effect of linoleic acid on S. costatum increased at low concentration (1μmolL-1) and gradually decreased with the increase of the concentration and the extend of exposure time. After 72 h, the cell densities of S. costatum exposed to 100μmolL-1 of linoleic acid were 16% of the controls. The results showed that the SOD and MDA level were rapidly increased after a short exposure, and gradually decreased with the increase of the concentrations and culture time.The ultrastructure of algal cells was observed with transmission eletron microscopy (TEM). The results showed that linoleic acid damaged the cell membrane, chloroplast, mitochondria and nucleolus of S.costatum.