Effects of Spirulina platensis and C-phycocyanin on seed germination and seedling growth of two monocot and dicot plants

In laboratory bioassay the allelopathic effects of Spirulina platensis (Nordst) Geitl. were investigated on Chinese amaranth (Amaranthus tricolor L.), Chinese mustard (Brassica campestris var. chinensis), bamyardgrass (Echinochloa crus-galli [L.] Beauv.) and rice (Oryzva sativa L.). The seeds were germinated in Petri dishes with aqueous extract (0.625-5% concentrations) and crude organic extract (250-4000 ppm concentrations) distilled water used as control. All aqueous extracts influenced the seed germination and seedling growth of dicotyledons (A. tricolor and B. campestris). The aqueous extract of 1.25% and 2.50% concentration completely inhibited the germination in dicots. In monocots (barnyardgrass and rice), the aqueous extract of 2.50% concentration inhibited the root length, while the 5% concentration completely inhibited their germination and seedling shoot length. The UV-VIS spectra indicated that the aqueous extract contained C-phycocyanin (C-PC), with a purity ratio (A(620)/A(280)) of 1.17. The allelopathic activity of biologically active protein pigment, C-PC, was assayed on seed germination and seedling growth at 62.50-1000 ppm concentrations. At 1000 ppm, this compound was most inhibitory to shoot and root length of A. tricolor and B. campestris, but there was no effect on germination. The crude ethyl acetate extract was most inhibitory to dicots, but all three crude organic extracts were not inhibitory to monocots.