Inhibitory Effects of the Lipophilic Extracts and An Isolated Meroditerpene of Brown Alga in Pasture Weeds in the Eastern Amazon Region
ABSTRACT: Two lipophilic extracts and atomaric acid (1), an isolated natural product, were obtained from the marine brown alga Stypopodium zonale (Dictyotaceae) to identify and characterize their potential inhibitory effects on the seed germination, radicle elongation, and hypocotyl development of the weeds Mimosa pudica and Senna obtusifolia. The extracts were prepared with hexane and dichloromethane, and atomaric acid (1) was isolated from hexane extract by way of conventional chromatographic methods. During a 15 days period, germination bioassays were performed at 25 oC with a 12 h photoperiod, whereas radicle elongation and hypocotyl development were assayed at 25 oC with a 24 h photoperiod. After, Petri dishes 9.0 cm in diameter were coated with qualitative filter paper, 25 seeds were placed in a germination chamber, while six pregerminated seeds were placed in the Petri dish for 2-3 days. After 10 days, radicle and hypocotyl extension were measured; and the inhibitory potential of the extracts was assessed at 10 ppm and that of the atomaric acid at 5, 10, 15, and 20 ppm. In both M. pudica and S. obtusifolia, dichloromethane extract achieved the greatest rates of inhibition during seed germination (34% and 22%, respectively), radical germination (38% and 30%, respectively), and hypocotyl development (29% and 22%, respectively). At a concentration of 20 ppm, atomaric acid (1) also demonstrated reduced inhibitory potential, with mean values of 58.67% for M. pudica and 48.67% for S. obtusifolia.