Potential Use of Extracts of Seaweeds Against Plant Pathogens 189
that activation of the JA-pathway could be a general feature of sulphated oligosaccharides. Nevertheless,
the role of other defence mechanisms is also entirely possible.
Treatment with laminarin and PS3 synergistically promoted an oxidative burst in tobacco cell
suspensions and induced the SA-signaling pathway in infiltrated tobacco and Arabidopsis thaliana leaf
tissues (Menard et al. 2005). This treatment was suggested to impart resistance in tobacco against TMV.
In transgenic PR1–β-glucuronidase (GUS) tobacco plants, PS3 increased the GUS activity in treated
tissues, as compared to the untreated (control) leaves. Interestingly, PS3 did not induce systemic acquired
resistance (SAR) to TMV, as reported in other studies. There was, however, increased expression of genes
encoding O-methyltransferases of the phenylpropanoid pathway in the tobacco plants. However, the
SA-dependent, acidic PR1 gene, or the ethylene-dependent, basic PR5 gene, were not affected in tobacco
plants. On the contrary, oligofucans prepared by enzymatic hydrolysis of fucan from the brown alga Pelvetia
canaliculata, induced both local and systemic defence responses in tobacco cell suspensions and marked
alkalinization of the extracellular medium, with associated release of hydrogen peroxide (Klarzynsci et al.
2003). Oligo-fucans are also reported to induce phenylalanine ammonia-lyase and lipoxygenase activity.
Additionally, local accumulation of salicylic acid (SA) and the phytoalexin scopoletin, were observed, along
with expression of several pathogenesis-related (PR) proteins. It was suggested that SA is required for the
establishment of oligo-fucan-induced resistance in plants such as tobacco against TMV. Vera et al. (2011a)
also showed that applications of sulphated galactan to tobacco and subsequent infection with TMV, resulted
in induction of the defence enzymes phenylalanine ammonia lyase and lipoxygenase, with a decrease in
the TMV-CP transcript level. Increased activity of defence-related enzymes with seaweed extract treatment
is another mechanism that operates to enhance plant resistance to pathogens. Disease resistance reported
after the use of a commercial aqueous extract from Sargassum wightii, against Xanthomonas campestris
pv. malvacearum in cotton, was associated with higher levels of total phenols and peroxidase activity in
the plant (Raghavendra et al. 2007). Goicoechea et al. (2004) further demonstrated that pepper grown in
an organic medium (COA H, containing SA, soluble ammonium salts, and A. nodosum extract) resulted
in an early accumulation of phenolics which were suggested to have contributed to disease resistance
and/or tolerance, exhibited by the seedlings against Verticillium dahliae. However, it was not clear which
component of the growing medium contributed the most towards disease suppression. Antioxidant properties
of polyphenols contained in some seaweed extracts may have acted against certain target pathogens (Zhang
et al. 2006). Phytoalexins produced in grapevines with seaweed extract treatment were associated with
reduced severity of grey mold (Jeandet et al. 1996). Laminarin from A. nodosum was also shown to elicit
a plant defence response by increasing anti-microbial phytoalexins (Patier et al. 1993).
Another study revealed that grapevine cells treated with laminarin resulted in an increased potential
calcium influx, alkalinization of the extracellular medium, production of an oxidative burst, activation
of mitogen-activated protein kinases (MAPKs), expression of defence-related genes, increased levels
of enzymes such as chitinase and B-1,3-glucanase and phytoalexins (i.e., resveratrol and E-viniferin).
This elicited defence response was attributed with protection of treated grapevines against B. cinerea
and Plasmopara viticola (Aziz et al. 2003). An oxidative burst was also attributed to be associated in the
protection of ulvan-primed wheat and rice cells that also correlated with a decrease of disease symptoms
in the infected plants (Paulert et al. 2010).
Treatment of carrots and cucumber, with a commercial A. nodosum extract, to suppress different
pathogens, indicated that enhanced activity of various defence-related enzymes and genes played various
roles at the molecular and biochemical level (Jayaraj et al. 2008). The plant defence mechanisms induced
by other macroalgal extracts, including polysaccharides, could also follow a similar response through
induction of defence genes or enzymes against pathogens. The A. nodosum extract and kappa, oligocarrageenan induced an increase in activity of the defence enzyme β-1,3-glucanase which is known to
have anti-fungal properties (Vera et al. 2011b). The polysaccharide fucoidan extracted from the blades
of Lessonia vadosa (Phaeophyta) showed significant activation of various defence enzymes such as
phenylalanine-ammonia lyase, lipooxygenase, and glutathione-S-transferase in tobacco (Chandia and
Matsuhiro 2008). Ethanol-soluble extracts from the red alga Gracilaria chilensis and L. trabeculata,
contained active compound(s) having polar characteristics, which either acted directly on the mycelial
growth of P. cinnamonni, or activated plant defence mechanisms to protect the plant tissues against
that activation of the JA-pathway could be a general feature of sulphated oligosaccharides. Nevertheless,
the role of other defence mechanisms is also entirely possible.
Treatment with laminarin and PS3 synergistically promoted an oxidative burst in tobacco cell
suspensions and induced the SA-signaling pathway in infiltrated tobacco and Arabidopsis thaliana leaf
tissues (Menard et al. 2005). This treatment was suggested to impart resistance in tobacco against TMV.
In transgenic PR1–β-glucuronidase (GUS) tobacco plants, PS3 increased the GUS activity in treated
tissues, as compared to the untreated (control) leaves. Interestingly, PS3 did not induce systemic acquired
resistance (SAR) to TMV, as reported in other studies. There was, however, increased expression of genes
encoding O-methyltransferases of the phenylpropanoid pathway in the tobacco plants. However, the
SA-dependent, acidic PR1 gene, or the ethylene-dependent, basic PR5 gene, were not affected in tobacco
plants. On the contrary, oligofucans prepared by enzymatic hydrolysis of fucan from the brown alga Pelvetia
canaliculata, induced both local and systemic defence responses in tobacco cell suspensions and marked
alkalinization of the extracellular medium, with associated release of hydrogen peroxide (Klarzynsci et al.
2003). Oligo-fucans are also reported to induce phenylalanine ammonia-lyase and lipoxygenase activity.
Additionally, local accumulation of salicylic acid (SA) and the phytoalexin scopoletin, were observed, along
with expression of several pathogenesis-related (PR) proteins. It was suggested that SA is required for the
establishment of oligo-fucan-induced resistance in plants such as tobacco against TMV. Vera et al. (2011a)
also showed that applications of sulphated galactan to tobacco and subsequent infection with TMV, resulted
in induction of the defence enzymes phenylalanine ammonia lyase and lipoxygenase, with a decrease in
the TMV-CP transcript level. Increased activity of defence-related enzymes with seaweed extract treatment
is another mechanism that operates to enhance plant resistance to pathogens. Disease resistance reported
after the use of a commercial aqueous extract from Sargassum wightii, against Xanthomonas campestris
pv. malvacearum in cotton, was associated with higher levels of total phenols and peroxidase activity in
the plant (Raghavendra et al. 2007). Goicoechea et al. (2004) further demonstrated that pepper grown in
an organic medium (COA H, containing SA, soluble ammonium salts, and A. nodosum extract) resulted
in an early accumulation of phenolics which were suggested to have contributed to disease resistance
and/or tolerance, exhibited by the seedlings against Verticillium dahliae. However, it was not clear which
component of the growing medium contributed the most towards disease suppression. Antioxidant properties
of polyphenols contained in some seaweed extracts may have acted against certain target pathogens (Zhang
et al. 2006). Phytoalexins produced in grapevines with seaweed extract treatment were associated with
reduced severity of grey mold (Jeandet et al. 1996). Laminarin from A. nodosum was also shown to elicit
a plant defence response by increasing anti-microbial phytoalexins (Patier et al. 1993).
Another study revealed that grapevine cells treated with laminarin resulted in an increased potential
calcium influx, alkalinization of the extracellular medium, production of an oxidative burst, activation
of mitogen-activated protein kinases (MAPKs), expression of defence-related genes, increased levels
of enzymes such as chitinase and B-1,3-glucanase and phytoalexins (i.e., resveratrol and E-viniferin).
This elicited defence response was attributed with protection of treated grapevines against B. cinerea
and Plasmopara viticola (Aziz et al. 2003). An oxidative burst was also attributed to be associated in the
protection of ulvan-primed wheat and rice cells that also correlated with a decrease of disease symptoms
in the infected plants (Paulert et al. 2010).
Treatment of carrots and cucumber, with a commercial A. nodosum extract, to suppress different
pathogens, indicated that enhanced activity of various defence-related enzymes and genes played various
roles at the molecular and biochemical level (Jayaraj et al. 2008). The plant defence mechanisms induced
by other macroalgal extracts, including polysaccharides, could also follow a similar response through
induction of defence genes or enzymes against pathogens. The A. nodosum extract and kappa, oligocarrageenan induced an increase in activity of the defence enzyme β-1,3-glucanase which is known to
have anti-fungal properties (Vera et al. 2011b). The polysaccharide fucoidan extracted from the blades
of Lessonia vadosa (Phaeophyta) showed significant activation of various defence enzymes such as
phenylalanine-ammonia lyase, lipooxygenase, and glutathione-S-transferase in tobacco (Chandia and
Matsuhiro 2008). Ethanol-soluble extracts from the red alga Gracilaria chilensis and L. trabeculata,
contained active compound(s) having polar characteristics, which either acted directly on the mycelial
growth of P. cinnamonni, or activated plant defence mechanisms to protect the plant tissues against