## 3 Results and Discussion
### Sulfated and Unsulfated Polysaccharides and Oligosaccharides in Olive Tree Leaves  
To evaluate the potential effect of the seven saccharide fractions on the natural defenses of the olive tree, leaf discs of 5 mm were used as a model system and were treated for 24 h with different concentrations. The PAL and TAL activities, the phenolic compounds, and the lignin content were then measured. To our knowledge, no study has reported the capacity of alginate (unsulfated polysaccharides), LMW alginates, fucoidan, and sulfated arabincalatan-rich protein to induce the natural defense of olive trees. PAL and TAL are monofunctional enzymes belonging to the plant aromatic amino-acid-lyase family [60]. The PAL catalyzes the deamination of L-phenylalanine into _trans_-cinnamic acid, while the TAL converts the L-tyrosine yielding _trans_-_p_-comarate. PAL is the most widely studied enzyme in plant phenolic synthesis. However, TAL is another enzyme involved in this pathway, that has rarely been investigated. This is the first report exploring the activity of TAL in the leaves of the olive tree. 5.1 Evaluation of Enzyme Activities and Secondary Metabolism Synthesis in the Leaf Discs of the Olive Tree in Response to Alginates and Their Oligomers  
The application of alignates with different molecular weights, ALCM (202 kDa), ALSM (76 kDa), OACM (19 kDa), and the oligomers OASM (3 kDa), significantly induced the PAL and TAL activities, the phenolic compounds, and the lignin content in the leaves of the olive tree depending on the concentration of saccharide solutions (_p_ < 0.05). After treatment with OASM, the PAL and TAL activities revealed a considerable increase at different concentrations, reaching an upward trend at 2 g/L. The polyphenols followed a similar pattern and rose at 0.5 g/L and 1 g/L, while no significant increment was observed in lignin content. Compared to their native polymer (ALSM) at 2 g/L, the oligoalginates (OASM) showed the induction of PAL and TAL activities, 1.4-1.6 times higher (Figure 4), as well as efficiency at a low concentration (0.5 g/L). On the other hand, the accumulation of polyphenols and lignin in the leaves was significantly increased after the treatment with ALSM polymers. The elicitor activity of the LMW alginates (OACM) was less important compared to the other fractions. In response to the native alginate polymers, ALCM showed significant stimulation of PAL and TAL activities at a low concentration (0.5 g/L) compared to ALSM, while the secondary metabolites (lignin and polyphenols) were strongly promoted after the application of ALSM (Figure 5). Lignin was only promoted in response to high molecular weight alginates polymers (ALCM and ALSM). In this study, the PAL and TAL activities showed a similar trend. In contrast, a considerable fluctuation was observed. All fractions reported a PAL/TAL ratio < 1 to, ranging from 0.34 to 0.77, indicating the high expression of TAL in the leaves of the olive tree compared to PAL. As mentioned before, PAL and TAL are the key regulatory enzymes associated with the biosynthesis of various secondary metabolites via the shikimic pathway [61]. Nevertheless, PAL is the most occurs in plants [60], while TAL enzyme is commonly found in Gramineae such as wheat and maize [62; 63; 64; 65]. Recently, TAL has been detected in other plants such as orchids, strawberry fruits, and leaves, ginger and soybean leave in response to biotic and abiotic stresses [66; 67; 68; 61]. As reported by [PERSON] et al., the treatment of soybean by chitin and chitosan oligomers significantly induced the PAL, TAL, and phenolic compounds in leaf tissues, which the specific activity of TAL was lower compared to PAL [67]. In this study, the elicitor capacities of alginate polymers and their derivatives depended on many factors such as concentration, nature of polymers, and chain length. The OASM (3 kDa), ALCM (76 kDa), and OACM (19 kDa) were more effective due to their abilities to activate the PAL and TAL at a low concentration (0.5 g/L) compared to ALSM (202 kDa).