Effects of extracts and isolated molecules of two species of Gracilaria (Gracilariales, Rhodophyta) on early growth of lettuce

Abstract Crude extracts using hexane, dichloromethane, methanol, 80% methanol or water of two agarophytes ( Gracilaria caudata and Gracilaria domingensis ) and their phase partitions were evaluated on early growth of lettuce. Hexane, methanol, 80% methanol and aqueous extracts of G . caudata and dichloromethane and aqueous extracts of G . domingensis were biostimulants. Palmitic acid, the major compound of non-polar extracts and phase partition, showed a significant stimulant activity in the concentrations tested (ranging from 0.49 mM to 1.95 mM), increasing 83% of lettuce root length, comparing to control, at the highest concentration. The promoting effect of the aqueous extracts is probably related to the presence of agaran, a typical hydrocolloid polysaccharide from red algae, which is mostly an exclusive constituent of these extracts. The agarans of G . domingensis and G . caudata promoted an increase in lettuce root length of 60% and 40%, respectively (both at 1 mg·mL −1 of extract). Differences in the effects promoted by these two agarans are probably related to the different content of sulfate groups (higher for polysaccharide from G . domingensis ). These results suggest that structural features of agaran-type polysaccharides can elicit distinct responses. To the best of our knowledge, this is the first report on the identification of compounds with biostimulating potential from Gracilaria .