2.3.1. Phenylalanine Amonia-Lyase (PAL) Activity

Given the involvement of the phenolic metabolism in the natural defenses in date palm roots against Foa [17], the mobilization of the phenlypropanoids pathway was demonstrated by studying PAL activity, as the main enzyme of this metabolic pathway. As shown in Figure 3, PAL activity was induced by both *F. spiralis* (FSF) and *B. bifurcata* (BBF) fucoidans. A total of 12 h of FSF treatment were sufficient to significantly increase PAL activity compared to the control treatment (*p* < 0.05). This increase stayed significantly different from control plants over 24 h. A second narrower peak was obtained at 96 h, this could be explained by the elicitor solutions (fucoidans) remained in permanent contact with the roots for the duration of the experiment (4 days), leading to a second wave of induction of PAL activity. The BBF treatment intensely and significantly increased PAL activity after 24 h of treatment, 4.8 times higher than the response noted in control plants (*p* < 0.05).

**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.
