Nanoparticles in agriculture have shown benefits related to physiological and
growth parameters. Moreover, the new knowledge related to its effect on secondary
metabolism has opened a field of possibilities in the production of bioactive
compounds with high commercial value using NPs. However, as with many elicitors, there is still a lack of knowledge about the type and size of nanoparticle and
appropriate concentrations to use depending on the species of interest. Furthermore,
a large part of the existing nanoparticles has not yet been studied and it is also
necessary to continue generating knowledge to understand the molecular mechanisms of elicitation with NPs.
Metal ions have been proposed as suitable elicitors of secondary metabolism in
cell cultures (Rudrappa et al. 2004), since they can make more efficient the tissue
culture techniques during the obtention of valuable secondary metabolites. Many
studies have proposed the use of different chemical metal species to enhance
bioactive compounds in plants. This tool is very attractive in the sense that, in
addition to producing these types of compounds, it can become an environmental
remediation technique. Also, the idea of producing specialized metabolites for later
extraction eliminates the risks associated with the potential health risks to the
consumers.
Among the study of new agricultural tools in the last decade, VOCs stands out
for being considered as an eco-friendly, cheap, and effective alternative. Even
genetically modified plants with altered VOC emission and synthetic formulations
of plant VOCs are been developed as a promising technology for agriculture and
horticulture (Rakshit et al. 2020). However, there are still many unknowns, especially about the mode of action of VOCs and about the molecular and biochemical
mechanisms related to eliciting responses of interest in plants.
The application of phytohormones in different phenological stages of plants,
including in the postharvest stage, induces the production of secondary metabolites
and is an effective strategy that uses defense mechanisms to mimic stress caused by
various environmental factors. This method can be used at the agronomic level to
improve the quality of plant products by increasing the content of bioactive
molecules. Defense plant response due to different types of stress depends on the
type of crosstalk (positive or negative) between the hormone signaling pathways
rather than on the individual contributions of each hormone (Verma et al. 2016).
This suggests that for future perspectives it should be taken into account that the
results of elicitation will depend on the synergy of the used phytohormones, the
concentration, the application conditions, and the type of cultivation. For example,
there is a balance between SA and JA to regulate biotic stress in tomato (Verma
et al. 2016). In the same way, SA and gibberellins have been used as elicitor and
biostimulant to enhance the production of steviol glycosides in stevia, producing
tall plants with a greater number of leaves and a larger stem diameter
(Vazquez-Hernandez et al. 2019).
Endophytic microbes have been shown to be able to promote plant growth,
induce tolerance and production of bioactive compounds (Lata et al. 2018).
Endophytic microbes generally reside in tissues and plants without causing
symptoms. However, they activate plant defense system and induce secondary
5 Role of Stress and Defense in Plant Secondary Metabolites …
183
growth parameters. Moreover, the new knowledge related to its effect on secondary
metabolism has opened a field of possibilities in the production of bioactive
compounds with high commercial value using NPs. However, as with many elicitors, there is still a lack of knowledge about the type and size of nanoparticle and
appropriate concentrations to use depending on the species of interest. Furthermore,
a large part of the existing nanoparticles has not yet been studied and it is also
necessary to continue generating knowledge to understand the molecular mechanisms of elicitation with NPs.
Metal ions have been proposed as suitable elicitors of secondary metabolism in
cell cultures (Rudrappa et al. 2004), since they can make more efficient the tissue
culture techniques during the obtention of valuable secondary metabolites. Many
studies have proposed the use of different chemical metal species to enhance
bioactive compounds in plants. This tool is very attractive in the sense that, in
addition to producing these types of compounds, it can become an environmental
remediation technique. Also, the idea of producing specialized metabolites for later
extraction eliminates the risks associated with the potential health risks to the
consumers.
Among the study of new agricultural tools in the last decade, VOCs stands out
for being considered as an eco-friendly, cheap, and effective alternative. Even
genetically modified plants with altered VOC emission and synthetic formulations
of plant VOCs are been developed as a promising technology for agriculture and
horticulture (Rakshit et al. 2020). However, there are still many unknowns, especially about the mode of action of VOCs and about the molecular and biochemical
mechanisms related to eliciting responses of interest in plants.
The application of phytohormones in different phenological stages of plants,
including in the postharvest stage, induces the production of secondary metabolites
and is an effective strategy that uses defense mechanisms to mimic stress caused by
various environmental factors. This method can be used at the agronomic level to
improve the quality of plant products by increasing the content of bioactive
molecules. Defense plant response due to different types of stress depends on the
type of crosstalk (positive or negative) between the hormone signaling pathways
rather than on the individual contributions of each hormone (Verma et al. 2016).
This suggests that for future perspectives it should be taken into account that the
results of elicitation will depend on the synergy of the used phytohormones, the
concentration, the application conditions, and the type of cultivation. For example,
there is a balance between SA and JA to regulate biotic stress in tomato (Verma
et al. 2016). In the same way, SA and gibberellins have been used as elicitor and
biostimulant to enhance the production of steviol glycosides in stevia, producing
tall plants with a greater number of leaves and a larger stem diameter
(Vazquez-Hernandez et al. 2019).
Endophytic microbes have been shown to be able to promote plant growth,
induce tolerance and production of bioactive compounds (Lata et al. 2018).
Endophytic microbes generally reside in tissues and plants without causing
symptoms. However, they activate plant defense system and induce secondary
5 Role of Stress and Defense in Plant Secondary Metabolites …
183