generated by pathogen attack can induce resistance to abiotic stress factors. The
biochemical response generated by the attack of the pathogen is similar to the
response generated by abiotic factors. Plants attacked by Verticillium dahliae
(pathogenic fungus) develop tolerance to drought due to the formation of xylem but
reducing the growth rate (Tani et al. 2018).
Viruses are considered symbiotes. They can behave as pathogens or mutualists
depending on the environmental conditions where the host is (Roossinck 2015).
Research suggests that the mutualistic behavior of a virus occurs when the titer
virus is low and the environmental disturbance is low (Bao and Roossinck 2013).
Plant viruses can have a positive effect like other pathogens. The presence of the
virus in the plant can increase its ability to cope with biotic and abiotic stress factors
because of the activation of the plant defense system. Metabolomic studies in
infected plants have shown a significant increase in the quantity and diversity of
secondary metabolites. This metabolic effect allows the plant to cope with the stress
caused by the infection, as well as other stressors present in the environment. For
example, Sade et al. (2015), reported a significant impact on the metabolome in
tomato plants infected with Tomato yellow leaf curl virus (TYLCV) where resistant
and susceptible cultivars showed a major expression of the phenylpropanoid
pathway which is related to the production of antioxidant compounds, among
others. In the same research, the expression in resistant cultivars was more significant in terms of the production of flavonoids and other antioxidants. On the other
hand, rice plants infected with Brome mosaic virus (BMV) and beet plants (Beta
vulgaris) infected with Cucumber mosaic virus (CMV) increased the accumulation
of osmoprotectants and antioxidant compounds, conferring drought tolerance to
both crops (Xu et al. 2008).
5.3.2 Fungi
Plants have a strong symbiosis relationship with some fungi and bacteria present in
the substrate where they are grown. These microorganisms, endophytes or exogenous, can induce eustress to the crop, increasing the production of specialized
metabolites, e.g.,Aspergillus sp. applied as an elicitor in Artemisia annua L. callus
culture, enhanced the production of artemisinin, an endoperoxide sesquiterpene
lactone and an effective antimalarial agent (Yuliani et al. 2018). Soil-borne beneficial microbes have shown a protecting potential against pathogens and herbivores
via the elicitation of plant responses e.g. plant growth-promoting fungi (PGPF) and
arbuscular mycorrhizal fungi (AMF) (Pappas et al. 2018). Fungal elicitation (including yeas extract) is one of the most used to enhance the production of secondary metabolites (Singh et al. 2018).
Fungi with a beneficial effect on plant development that associate to plant roots
are called PGPF and are considered the first prevention mechanism in the pathogen
infection. Plants need to detect PGPFs and take advantage of the presence of
5 Role of Stress and Defense in Plant Secondary Metabolites …
177
biochemical response generated by the attack of the pathogen is similar to the
response generated by abiotic factors. Plants attacked by Verticillium dahliae
(pathogenic fungus) develop tolerance to drought due to the formation of xylem but
reducing the growth rate (Tani et al. 2018).
Viruses are considered symbiotes. They can behave as pathogens or mutualists
depending on the environmental conditions where the host is (Roossinck 2015).
Research suggests that the mutualistic behavior of a virus occurs when the titer
virus is low and the environmental disturbance is low (Bao and Roossinck 2013).
Plant viruses can have a positive effect like other pathogens. The presence of the
virus in the plant can increase its ability to cope with biotic and abiotic stress factors
because of the activation of the plant defense system. Metabolomic studies in
infected plants have shown a significant increase in the quantity and diversity of
secondary metabolites. This metabolic effect allows the plant to cope with the stress
caused by the infection, as well as other stressors present in the environment. For
example, Sade et al. (2015), reported a significant impact on the metabolome in
tomato plants infected with Tomato yellow leaf curl virus (TYLCV) where resistant
and susceptible cultivars showed a major expression of the phenylpropanoid
pathway which is related to the production of antioxidant compounds, among
others. In the same research, the expression in resistant cultivars was more significant in terms of the production of flavonoids and other antioxidants. On the other
hand, rice plants infected with Brome mosaic virus (BMV) and beet plants (Beta
vulgaris) infected with Cucumber mosaic virus (CMV) increased the accumulation
of osmoprotectants and antioxidant compounds, conferring drought tolerance to
both crops (Xu et al. 2008).
5.3.2 Fungi
Plants have a strong symbiosis relationship with some fungi and bacteria present in
the substrate where they are grown. These microorganisms, endophytes or exogenous, can induce eustress to the crop, increasing the production of specialized
metabolites, e.g.,Aspergillus sp. applied as an elicitor in Artemisia annua L. callus
culture, enhanced the production of artemisinin, an endoperoxide sesquiterpene
lactone and an effective antimalarial agent (Yuliani et al. 2018). Soil-borne beneficial microbes have shown a protecting potential against pathogens and herbivores
via the elicitation of plant responses e.g. plant growth-promoting fungi (PGPF) and
arbuscular mycorrhizal fungi (AMF) (Pappas et al. 2018). Fungal elicitation (including yeas extract) is one of the most used to enhance the production of secondary metabolites (Singh et al. 2018).
Fungi with a beneficial effect on plant development that associate to plant roots
are called PGPF and are considered the first prevention mechanism in the pathogen
infection. Plants need to detect PGPFs and take advantage of the presence of
5 Role of Stress and Defense in Plant Secondary Metabolites …
177