Fucoidans of Moroccan Brown Seaweed as Elicitors of Natural Defenses in Date Palm Roots

Abstract

Fucoidans from Moroccan brown seaweed Bifurcaria bifurcata and Fucus spiralis were tested for their elicitor activity after their purification and complete characterization. The fucoidans of B. bifurcata (BBF) and of F. spiralis (FSF) were extracted and purified then characterized by infrared spectroscopy, proton nuclear magnetic resonance spectroscopy and size exclusion chromatography. The results show that BBF and FSF are mainly sulfated with 45.49 and 49.53% (w/w) sulfate, respectively. Analysis of neutral sugars determined by gas chromatography-mass spectrometry showed that FSF and BBF were mainly composed of 64% and 91% fucose and 20% and 6% galactose, respectively, with a few other sugars such as glucose (8% in FSF), rhamnose (1% in BBF) and mannose (8% in FSF and, 2% in BBF). The eliciting activity of these sulfated polysaccharides in stimulating the natural defenses of the date palm was evaluated through the activity of phenylalanine ammonia-lyase (PAL), and the increase in phenols and lignin content in the roots. The results obtained clearly show that the two fucoidans early and intensely stimulate the natural defenses of the date palm after 24 h of treatments. This remarkable elicitor effect seems to be linked to the sulfated groups compared to non-sulfate alginates extracted from the same algae. These results open promising perspectives for a biological control approach against date palm diseases.

Keywords: natural defenses; phenolic metabolism; phenylalanine ammonia-lyase; sulfated polysaccharides.

Figure 1

¹H NMR spectra of sulfated polysaccharides from (A) B. bifurcata (BBF) and (B) F. spiralis (FSF) at 60 °C in D₂O solution.

Figure 2

ATR-FTIR spectra of sulfated polysaccharides from (A) B. bifurcata (BBF) and (B) F. spiralis (FSF).

Figure 3

Induction of phenylalanine ammonia-lyase (PAL) activity in date palm roots treated with sulfated polysaccharides of F. spiralis (FSF) and B. bifurcata (BBF). Based on Tukey’s test at 12 h, 24 h, 72 h and 96 h * Control vs. FSF: p < 0.05, at 24 h, 48 h, 72 h and 96 h * Control vs. BBF: p < 0.05.

Figure 4

Effect of F. spiralis (FSF) and B. bifurcata (BBF) fucoidans on the accumulation of phenolic compounds in date palm roots. Means values ± SE. Based on Tukey’s test at 12 h and 24 h * Control vs. BBF: p < 0.05, at 24 h, 48 h and 72 h * Control vs. FSF: p < 0.05.

Figure 5

Effect of sulfated polysaccharides from F. spiralis (FSF) and B. bifurcata (BBF) on the accumulation of lignin in date palm roots. Means values ± SE. Based on Tukey’s test at 12 h, 24 h, 48 h and 72 h * Control vs. FSF: p < 0.05, at 12 h, 48 h and 96 h * Control vs. BBF: p < 0.05.