5.2.1.1 Light
Light is one of the most important and obvious requirements for plant growth and
development, where the energy of sunlight and artificial light sources is mainly
used for photosynthesis. However, light is not only involved in the photosynthesis
process but also in the production of natural bioactive compounds, gene expression,
and synchronization of the circadian clock in the light/dark cycle (Larner et al.
2018). Changes in the light intensity, quality, direction, and duration are sensed by
specialized photoreceptors which are specially designed proteins that sense light,
triggering chain reactions that have been studied in terms of photomorphogenesis
and primary and secondary metabolites production (Alvarado et al. 2019).
Photoreceptors perceive specific light wavelengths of over a continuous spectral
range through a small cofactor or chromophore molecule (Burgie et al. 2014). Five
photosensory systems have been identified: phytochromes perceiving red (660–
700 nm) and far-red (700–750 nm), cryptochromes, phototropins, and members of
the Zeitlupe family perceiving blue (495–400 nm) and UV-A (400–315 nm), and
UV Resistance Locus 8 (UVR8) perceiving (315–280 nm) (Bantis et al. 2018;
Alvarado et al. 2019).
Recent investigation has focused on the effect of light technology in plant
growth, developmental traits, and primary and secondary metabolites by using one
or more light wavelengths, intensities, and photoperiods. It has been reported that
blue light increases phenolic compounds by promoting the production of malonyl
CoA and coumaroyl CoA, participating in the synthesis of phenolic compounds
(Qian et al. 2016). In addition, red and far-red wavelengths are perceived by the
phytochromes photoreceptors, which regulates biosynthetic pathways involved in
the synthesis of anthocyanins, molecules that belong to the phenolic compounds
known as flavonoids and have many functions in plants including pigmentation
(Alokam et al. 2002). In the same way, plants produce secondary metabolites such
as flavonoids and anthocyanins to cope with cell damage produced by UV radiation
(Jiang et al. 2017b). Serious damage to DNA, membrane, and proteins can be
caused by UV-B radiation, whereas UV-A induces DNA damage less efficiently
because of the activation of photoreactions forming reactive oxygen species
(ROS) (Hideg and Strid 2017; Häder et al. 2015).
Supplemental lighting has been accepted for improving horticultural crops.
Light-emitting diode (LED) technology has been linked to controlled environments
in horticulture for achieving crop yield, phytochemical content, nutritional value,
flowering control, transplant success, pre-harvest and postharvest product quality,
and production of regeneration material (Bantis et al. 2018; Alvarado et al. 2019).
LEDs have allowed a sustainable and highly efficient use of energy and reproduce
true spectral composition of blue, green, red, and far-red wavelengths that matches
with plant-specific photoreceptors (Singh et al. 2015). Other light technologies, as
high sodium pressure (HSP) and other high-intensity discharge (HID) lamps are still
used in greenhouse and plant experimentation, however, LED technology is
replacing these devices due to the various advantages LEDs offer. Table 5.1
summarizes some examples of the application of supplemental light on plants or
5 Role of Stress and Defense in Plant Secondary Metabolites …
155
Light is one of the most important and obvious requirements for plant growth and
development, where the energy of sunlight and artificial light sources is mainly
used for photosynthesis. However, light is not only involved in the photosynthesis
process but also in the production of natural bioactive compounds, gene expression,
and synchronization of the circadian clock in the light/dark cycle (Larner et al.
2018). Changes in the light intensity, quality, direction, and duration are sensed by
specialized photoreceptors which are specially designed proteins that sense light,
triggering chain reactions that have been studied in terms of photomorphogenesis
and primary and secondary metabolites production (Alvarado et al. 2019).
Photoreceptors perceive specific light wavelengths of over a continuous spectral
range through a small cofactor or chromophore molecule (Burgie et al. 2014). Five
photosensory systems have been identified: phytochromes perceiving red (660–
700 nm) and far-red (700–750 nm), cryptochromes, phototropins, and members of
the Zeitlupe family perceiving blue (495–400 nm) and UV-A (400–315 nm), and
UV Resistance Locus 8 (UVR8) perceiving (315–280 nm) (Bantis et al. 2018;
Alvarado et al. 2019).
Recent investigation has focused on the effect of light technology in plant
growth, developmental traits, and primary and secondary metabolites by using one
or more light wavelengths, intensities, and photoperiods. It has been reported that
blue light increases phenolic compounds by promoting the production of malonyl
CoA and coumaroyl CoA, participating in the synthesis of phenolic compounds
(Qian et al. 2016). In addition, red and far-red wavelengths are perceived by the
phytochromes photoreceptors, which regulates biosynthetic pathways involved in
the synthesis of anthocyanins, molecules that belong to the phenolic compounds
known as flavonoids and have many functions in plants including pigmentation
(Alokam et al. 2002). In the same way, plants produce secondary metabolites such
as flavonoids and anthocyanins to cope with cell damage produced by UV radiation
(Jiang et al. 2017b). Serious damage to DNA, membrane, and proteins can be
caused by UV-B radiation, whereas UV-A induces DNA damage less efficiently
because of the activation of photoreactions forming reactive oxygen species
(ROS) (Hideg and Strid 2017; Häder et al. 2015).
Supplemental lighting has been accepted for improving horticultural crops.
Light-emitting diode (LED) technology has been linked to controlled environments
in horticulture for achieving crop yield, phytochemical content, nutritional value,
flowering control, transplant success, pre-harvest and postharvest product quality,
and production of regeneration material (Bantis et al. 2018; Alvarado et al. 2019).
LEDs have allowed a sustainable and highly efficient use of energy and reproduce
true spectral composition of blue, green, red, and far-red wavelengths that matches
with plant-specific photoreceptors (Singh et al. 2015). Other light technologies, as
high sodium pressure (HSP) and other high-intensity discharge (HID) lamps are still
used in greenhouse and plant experimentation, however, LED technology is
replacing these devices due to the various advantages LEDs offer. Table 5.1
summarizes some examples of the application of supplemental light on plants or
5 Role of Stress and Defense in Plant Secondary Metabolites …
155