## 3 Results and Discussion
### Sulfated and Unsulfated Polysaccharides and Oligosaccharides in Olive Tree Leaves
Carrageenan, a sulfated galactan presented in the red algae, was found to be capable of activating the defense mechanisms against a large wide of pathogens in _Arabidopsis thaliana_, tobacco, and tomato plants [70; 71; 72; 73; 74; 75]. The sulfated heteropolsaccharides, ulvan, from the green seaweed have been shown to trigger the pathogenesis-related proteins gene expression, reactive oxygen species metabolism, and the octadecanoid pathway, leading to protection against _Zymosetporia tritici_ in wheat [76]. The treatment of _A. thaliana_ plants by ulvans with sulfate content of 18.9 to 36.6% reduced the severity of _Alternaria brassicicola_ and _Colletotrichum higginsianum_ independently of sulfation degree [77]. These findings are in accordance with those reported in this work and the previous work [27], in which the AGB and AGP showed similarities in responses despite their sulfation variation. Furthermore, several studies have investigated the elicitor effects of ulvans in several plants [21; 23; 78; 79; 80]. The ability of fucoidan to provide protection and enhance natural defenses in plants has been previously assessed only to a very limited extent. Fucoidans from the brown macroalgae _B. bifurcata_ and _F. spiralis_ stimulated PAL activity, polyphenols, and lignin content in the roots of the date palm [19]. Detached leaves of _Datura stramonium_ L. and _Nicotiana tabacum_ L. infected by potato virus X (PVX) and tobacco mosaic virus (TMV), respectively, exhibited an inhibition of the development of the virus during the first stage of infection after treatment with fucoidan extracted from the brown alga _F. evanescens_[81; 82]. In addition, fucoidan from _Lessonia vadosa_ activated the PAL, lipooxygenase and glutathione-S-transferase activities in tobacco plants [24]. Compared to alignes (ALCM and ALSM), the sulfated polysaccharides (AGP, AGB, and FUCCM) exhibited an elicitor capacity more effective at low concentrations (0.5 g/L and 1 g/L). In response to fucoidan at 0.5 g/L, the levels of the PAL activity, phenolic compounds, and lignin content were significantly higher compared to AGB, AGP, ALCM, and ALSM. The sulfate group and the low M\({}_{\rm w}\) seem to be the principal factors in this fluctuation of plant defense responses. It has been shown before that the elicitation by glucuronan (unsulfated polysaccharide) had no considerable effects on PAL activity of tomato seedlings, while ulvan (sulfated polysaccharides) exhibited significant levels [21]. In addition, the desulfation of ulvan has shown suppression of the elicitor effect in the leaves of tomato plants, indicating the main role of sulfate substituent in the elicitation efficiency [21]. Several studies have found that desulfation reduces biological activities [83; 84; 85; 86]. The use of polysaccharides extracted from seaweeds as olive resistance-inducers has been previously assessed only to a very limited extent. [PERSON] et al., have reported the evaluation of laminarin (Vacciplant 4.5 SL) efficiency, against olive leaf spot (OLS) disease, caused by _Fusicaldium oleagineum_ on six-month-old olive plants [87]. The application of laminarin suppressed the disease severity and no symptoms were detected, compared to copper pesticides used as reference treatments. Moreover, the expression of PAL, copper amine oxidase (Cuao), and major pollen allergen (Mpol) genes was induced in laminarin-treated plants [87]. Another study has involved the ability of ulvan to control verticillium wilt of olive (VWO) caused by _V. dahlia_[88]. In response to this elicitor, the phenolic metabolism (PAL, polyphenols, and lignin) was significantly enhanced, reducing the verticillium wilt in the twigs (10 cm) of the olive tree (Picholine Marocaine) [88]. To the best of our knowledge, no study to date has examined the ficoudan, alignates from the brown macroalgae _S. muticum_ and _C. myriophyloides_ and their derivatives, as well as the sulfated glycoprotein from the green seaweed _C. decoritatum_, as inducers of natural defenses in the leaves of the olive tree.