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Effects of Light Quality on the Growth, Development and Metabolism of Rice Seedlings (Oryza sativa L.)

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The V3 seedlings of two rice cultivars, IR1552 (purple leaf) and Taichung sen 10 (TS10, green leaf) were hydroponically cultured under 12 h photoperiod at 30/25°C (day/night), 70% relative humidity and 160 μmol m−2s−1 photon flux density under red light-emitting diodes (LEDs) (R), green LEDs (G), blue LEDs (B) and red + blue LEDs (RB) inside growth chambers for 14 days (starting 2 days after sowing). The results showed that shoot elongation was induced under the exposure of R and G. The maximum health index [(stem diameter/plant height) × biomass)] occurred under B because blue light inhibited shoot elongation. The root length under RB was the shortest. Different wavelengths mediated the chlorophyll (Chl) a/b ratio of the leaves.
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Research Journal of Biotechnology Vol. 9(4) April (2014)
Res. J. Biotech
15
Effects of Light Quality on the Growth, Development and
Metabolism of Rice Seedlings (Oryza sativa L.)
Chang-Chang Chen1, Meng-Yuan Huang2, Kuan-Hung Lin3, Shau-Lian Wong4, Wen-Dar Huang1*
and Chi-Ming Yang2
1. Department of Agronomy, National Taiwan University, Taipei 11106, TAIWAN
2. Biodiversity Research Center, Academia Sinica, Nankang, Taipei 11115, TAIWAN
3. Graduate Institute of Biotechnology, Chinese Culture University, Taipei 11110, TAIWAN
4. Endemic Species Research Institute, Chichi Township 552, Nantou County, TAIWAN
*wendar@ntu.edu.tw
Abstract
The V3 seedlings of two rice cultivars, IR1552 (purple
leaf) and Taichung sen 10 (TS10, green leaf) were
hydroponically cultured under 12 h photoperiod at
30/25°C (day/night), 70% relative humidity and 160
μmol m2s1 photon flux density under red
light-emitting diodes (LEDs) (R), green LEDs (G),
blue LEDs (B) and red + blue LEDs (RB) inside
growth chambers for 14 days (starting 2 days after
sowing). The results showed that shoot elongation was
induced under the exposure of R and G. The maximum
health index [(stem diameter/plant height) × biomass)]
occurred under B because blue light inhibited shoot
elongation. The root length under RB was the shortest.
Different wavelengths mediated the chlorophyll (Chl)
a/b ratio of the leaves.
The content of anthocyanin (Ant) in seedling leaves
was observed to be highest in RB but less in R and B,
the latter pair being even lower than in G. B light
LEDs enhanced effective quantum yield of PSII
photochemistry (ΦPSII) and photochemical quenching
(qP), but reduced non-photochemical quenching (NPQ)
of seedling leaves. B LEDs also showed higher total
protein content in the tested leaves compared to B plus
R. In summary, precise management of irradiance and
wavelength may hold promise in maximizing the
economic efficiency of plant growth, development and
metabolic potential of rice seedlings grown in
controlled environments.
Keywords: Light-emitting diode, Light quality, Rice,
Photomorphogensis, Metabolism.
Introduction
Light is the main energy source for plant photosynthesis
and is an environmental signal used to trigger growth and
structural differentiation in plants. Light quality, quantity
and photoperiod control the morphogenesis, growth and
differentiation of plant cells, tissue and organ cultures1.
Plant development is strongly influenced by light quality
which refers to the colors or wavelengths reaching a plant’s
surface2. Red (R) and blue (B) lights have the greatest
impact on plant growth because they are the major energy
sources for photosynthetic CO2 assimilation in plants. It is
well known that spectra have action maxima in the B and R
ranges3. The integration, quality, duration and intensity of
red light/far red light, blue light, mixed red and blue lights
(RB), UV-A (320500 nm) or UV-B (280320 nm) and
hormone signaling pathways have a profound influence on
plants by triggering or halting physiological reactions and
controlling the growth and development of plants4,5. Recent
studies reported that green (G) light also affects the
morphology, metabolism and photosynthesis of plants6,7.
Light sources such as fluorescent, metal-halide,
high-pressure sodium and incandescent lamps are generally
used for plant cultivation. These sources are applied to
increase photosynthetic photon flux levels but contain
unnecessary wavelengths that are located outside the
photosynthetically active radiation spectrum and are of low
quality for promoting growth8. Compared to those
conventional light sources, gallium-aluminum-arsenide
light-emitting diode (LED) lighting systems have several
unique advantages, including the ability to control spectral
composition, small size, durability, long operating lifetime,
wavelength specificity, relatively cool emitting surfaces
and photon output that is linear with electrical input current.
These solid-state light sources are therefore ideal for use in
plant lighting designs and allow wavelengths to be matched
to plant photoreceptors for providing more optimal
production and influencing plant morphology and
metabolism9-11.
The LED light spectra in many reported experiments were
inconsistent with light intensity being non-uniform because
the investigators were unable to precisely modulate and
quantify spectral energy parameters12. Furthermore,
experimental results may have been influenced in part by
differences in light intensity and this often presents a
problem when comparing results from experiments
conducted under inconsistent lighting parameters. While it
is widely understood that light intensity can positively
affect photochemical accumulation13,14, the effects of light
quality are more complex and mixed results have often
been reported.
Spectral light changes evoke different morphogenetic and
photosynthetic responses that can vary among different
plant species. Such photo responses are of practical
importance in recent plant cultivation technologies since
the feasibility of tailoring illumination spectra enables one
to control plant growth, development and nutritional quality.
Research Journal of Biotechnology Vol. 9(4) April (2014)
Res. J. Biotech
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The effects of LED light sources on several plants such as
maize15, cotton16 and peas17 have been reported and
indicate that LED lights are more suitable for plant growth
than fluorescent lights.
Rice (Oryza sativa L.) is a staple food in Asia. During the
vegetative growth stage, rice plants grow better under RB
lights than under R alone18,19. The quality of V3 seedlings
during growth is therefore an important factor in rice
production, especially when mechanically transplanting
seedlings to the field. The seedlings incubated under RB
LEDs were more robust than when incubated under other
LED spectra in terms of root number, stem diameter, health
index and soluble sugars20. Therefore, in order to apply the
findings to rice seedling quality and production, we
considered it important to investigate the effects of light
quality when provided by R, B, G and RB LED systems to
meet different purposes. Hence, in this study, the growth,
development and quality of rice hydroponically grown
under various LEDs at the same light intensity were
investigated to determine the efficacy of this promising
radiation source.
In order to clarify the different response of green and
purple leaf rice, rice seedlings of two indica rice varieties,
IR1552 (purple leaf) and Taichung sen 10 (TS10, green
leaf), were cultivated under different light environments at
the same light density. Fourteen day old seedlings were
collected to investigate the effects of light quality on
growth and metabolism of rice seedlings. Controlled
climates and LEDs may be practical issue for rice seedling
stages before transplanting to field conditions. An optimal
strategy of light quality regulation will help in designing
growth chambers or greenhouse light environments to
obtain maximum economic benefit for rice growers.
Material and Methods
Plant materials and growth conditions: Seeds of indica
rice (Oryza sativa L.) cultivar, IR1552, were donated by Dr.
Su-Jein Chang, Miaoli District Agricultural Research and
Extension Station, Taiwan. IR1552 is famous for its purple
leaf. In addition, Taichung shen 10 (TS10, green leaf), one
of the most widely grown rice cultivars in Taiwan, was also
used in this study. Seeds were sterilized with 2% sodium
hypochlorite for 20 min, washed extensively with distilled
water and then germinated in Petri dishes with wetted filter
paper at 37°C in the dark. After 48 h of incubation,
uniformly germinated seeds were selected and cultivated in
a 250 ml beaker containing a half-strength Kimura B
nutrient solution with the following macro and
microelements: 182.3 μM (NH4)2SO4, 91.6 μM KNO3,
273.9 μM MgSO4·7H2O, 91.1 μM KH2PO4, 182.5 μM
Ca(NO3)2, 30.6 μM Fe-citrate, 0.25 μM H3BO3, 0.2 μM
MnSO4·H2O, 0.2 μM ZnSO4·7H2O, 0.05 μM CuSO4·5H2O
and 0.07 μM H2MoO4.
Nutrient solutions (pH 4.7) were replaced every 3 d.
Hydroponically cultivated rice seedlings were raised in
growth chambers with the LED lighting system set at 30°C
and 25°C for day and night respectively and 70% relative
humidity under a 12 h photoperiod.
Light treatments: LED lighting systems designed by GRE
Technology Co. (Taipei, Taiwan) were used to control light
quality. The spectral distribution of the relative energy of
the blue (peak at 460 nm), red (peak at 630 nm) and green
(peak at 530 nm) regions were measured using a
spectroradiometer (LI-COR1800, Lincoln, NE, USA) in the
300-800 nm range. These peak emissions of LEDs closely
coincide with the absorption peaks of chlorophylls a and b
and the reported wavelengths are at their respective
maximum photosynthetic efficiencies21. Light treatments
for rice seedlings, proliferation and differentiation included
red LEDs (R), blue LEDs (B), green LEDs (G) and red +
blue LEDs (RB) (Fig. 1), with photon flux density (PPFD)
being set at 160 μmol m-2s-1. The experiment was
independently performed three times for a randomized
design of growth conditions and measurements
representing the means of 15 plants (three reps consisting
of five plants each) were taken.
Plant growth parameters: Rice seedlings were sampled
after 14 d of growth after reaching the V3 stage according
to Counce et al22. Three seedlings for each beaker and 3
beakers for each light treatment were randomly selected for
growth analysis. Plant height and root length were
measured from the base of the seedling to the top of the
third leaf and from the root base to the seed root tip
respectively. Column diameter was measured in the
seedling base with a Vernier caliper. Fresh weights (FW)
and dry weights (DW) of seedlings were measured with an
electronic balance. To determine DW, seedlings were dried
at 80°C until constant weights were achieved. Moisture
content (%) was calculated as [1- (DW/FW)] × 100%. The
health index was calculated as (stem diameter / plant height)
× biomass according to Guo et al20.
Chlorophyll fluorescence measurements: Seedlings were
kept in the dark for approximately 20 min before
measurement. Chlorophyll fluorescence was measured at
the middle portion of the second leaf of the seedlings taken
at ambient temperatures with a Portable Chlorophyll
Fluorometer PAM-2100 (Walz, Effeltrich, Germany).
Actinic light and saturating light intensities were set at 280
μmol mol-2s-1 and 2500 μmol mol-2s-1 photosynthetically
active radiation (PAR) respectively. The maximal
photochemical efficiency of PSII (Fv/Fm), relative quantum
efficiency of PSII photochemistry (ΦPSII), photochemical
quenching (qP) and non-photochemical quenching (NPQ)
were measured and calculated according to the method
described previously23.
Chlorophyll (Chl), carotenoid (Car) and anthocyanin
(Ant) contents: Chl and Car contents were eluted from the
second leaf DW samples (0.01 g) with 5 ml of 80% acetone
at 4°C overnight and determined using the methods by
Research Journal of Biotechnology Vol. 9(4) April (2014)
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Porra et al24 and Holm25 respectively. Samples were then
centrifuged at 13,000 g for 5 min. Supernatants were tested
to determine the absorbances of Chl a, Chl b and Car in
acetone as measured with a spectrophotometer (U-2000,
Hitachi, Tokyo, Japan) at wavelengths of 663.6, 646.6 and
440.5 nm respectively. Concentrations (μg g-1 DW) of Chl
a, Chl b and Car were determined using the following
equations:
Chl a = (12.25 × OD663.6 2.55 × A646.6) × volume of
supernatant (ml) / sample weight (g)
Chl b = (20.31 × A646.6 4.91 × A663.6) × volume of
supernatant (ml) / sample weight (g)
Car = [(4.69 × A440.5 × volume of supernatant (ml) / sample
weight (g)) 0.267 × (Chl a + Chl b).
Ant content was measured according to the protocol of
Mancinelli et al26. A mixture of 80% methanol containing
1% HCl of solvent was used to extract the powder samples.
The mixture was then centrifuged at 4°C and 3,000 rpm for
5 min and the supernatant was used to measure the
absorbance at 530 nm and 657 nm. Ant content (μg g-1 DW)
was calculated as (A530 - 0.33 × A657 / 31.6) × volume of
supernatant (ml) / sample weight (g).
Free amino acid, soluble sugar and starch contents: DW
samples of the second leaf (0.05 g) were placed into 15 ml
tubes and then 5 ml of distilled water was added and mixed
in. The supernatant was collected after 30 min in a water
bath at 85°C. This step was repeated once and then distilled
water was added to obtain 10 ml of the extract for use in
determining soluble sugar and free amino acid contents (mg
g-1 DW). The soluble sugar content was determined using
the sulfuric acid anthrone method at a wavelength of 630
nm 27. Free amino acid content was determined using the
ninhydrin method at a wavelength of 570 nm 28. Starch was
extracted according to the procedures from Takahashi et
al29.
The residue obtained after distilled water extraction was
dried and then 1 ml of distilled water was added. The
mixture was placed in a water bath for 30 min at 100°C.
The gelatinized starch was digested after cooling with 1 ml
9.2 N perchloric acid for 10 min. Two ml of distilled water
was added and the mixture centrifuged at 8,000 g for 6 min.
After the extract was transferred to a 15 ml tube, 1 ml of
4.6N perchloric acid was added and stirred for 10 min.
Three ml of distilled water were added to the final volume
after centrifugation. Starch contents (mg g-1 DW) were
determined using the same method for soluble sugar.
Total protein content: Total proteins were measured using
the method of Bradford30. Samples (0.05 g FW) were
ground in a mortar with liquid nitrogen to which 3 ml of a
phosphate buffered solution (pH 7.0) was added. The
extract was centrifuged at 13,000 g for 15 min at 4°C and
0.1 ml of the supernatant was combined with 5 ml of
Coomassie brilliant blue G-250 solution (0.1 g l-1). The
soluble protein content (mg g-1 FW) was determined after 2
min at a wavelength of 595 nm.
Statistical analysis: All measurements were evaluated for
significance using analysis of variance (ANOVA) followed
by the least significant difference (LSD) test at the P < 0.05
level. All statistical analyses were conducted using SAS 9.2
(SAS Institute; Cary, NC, USA).
Results
Plant Growth and Morphology: The effects of light
quality treatments (T) on the two rice varieties (V) were
monitored by measuring changes in plant height, root
length, stem diameter, shoot and root biomasses, moisture
content and health index at 14 d seedling. In this
experiment, a factorial experiment design with a
completely randomized arrangement was used. Table 1
presents that all the measured components of growth
parameters were significant at the 5% level for the main
effects, except for plant height and shoot moisture content
in V and shoot biomass and root moisture content in both V
and T which showed negligible differences. Moreover,
when the V × T interaction was examined for significance,
all parameters significantly differed except the plant height,
shoot biomass, moisture content of shoot and root and
health index.
Plant heights of both varieties were significantly shorter
(12.9 and 13.1 cm) and stem diameters were larger (0.19
and 0.16 cm) under B than other lighting treatments (Table
1). Root lengths of both varieties were significantly shorter
(12.2 and 9.1 cm) under RB than under other lighting
conditions. However, shoot biomass and root moisture
contents were not significantly different among all lighting
environments. Different light quality treatments affected
the growth of rice seedlings and blue light likely inhibited
the elongation of rice seedlings. The shoot moisture content
of both varieties was lower (83.3 ~84.5%) under blue light
than without (85.0~ 86.2%) indicating that blue light could
increase water transport. Root biomass of TS10 was
significantly higher (0.019 g) under B compared to other
lighting environments. Lighting environments not only
affected shoot growth but also mediated root elongation
and root biomass accumulation.
The shoot/root dry weight ratios of TS10 under B (1.91)
and RB (2.16) were significantly lower than without blue
light, but there was no significant difference in the S/R DW
ratios of IR1552 among all treatments. A normal
appearance and compact morphology with vigorous roots
in TS10 seedlings treated with B LED light were observed.
However, seedlings grown under B light looked small or
even severely dwarfed (photos not shown). The health
index was used to describe the morphological quality of
rice seedlings and a higher index number contributed to
shorter shoot height and larger stem diameter. Under B
LED light, values were significantly higher (0.525 and
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Res. J. Biotech
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0.431) than under other lighting colors.
Chlorophyll (Chl), carotenoid (Car) and anthocyanin
(Ant) contents: ANOVA was used to uncover the main
effects of variety (V) and light quality treatment (T) and
their interaction effects (V × T) for different pigments as
summarized in table 2. All pigments displayed significant
differences (p< 0.05) for the main effects, with the
exception of Car levels. Only total Chl and Ant contents
constituted significant differences for the interaction effect.
Pigment content in leaves was influenced by different
lighting environments. Total Chl content in leaves of TS10
was not significantly different among all treatments but in
IR1552 it was highest (18.25 mg g-1 DW) under RB and
lowest (13.24 mg g-1 DW) under R condition (Table 2). The
Chl a/b ratio of both varieties was higher (2.81 and 2.47 mg
g-1 DW) under B than other lighting treatments.
The Car content in leaves of both varieties was not
significantly different among all lighting environments.
Changes in the Car/Chl ratio were therefore attributed to
the level of total Chl content in the leaves. The level of Ant
in the purple leaves of IR1552 was sensitive to lighting.
Ant content in IR1552 was significantly higher (150 μg g-1
DW) under RB as compared to other conditions, indicating
that light quality affected the synthesis of pigments (Chl
and Ant) in rice seedling leaves.
Chlorophyll (Chl) fluorescence: Chl fluorescence
components were used to indirectly measure the different
functional levels of photosynthesis. Figure 2 shows the
effects of light quality on Chl fluorescence in 14 d rice
leaves. The Fv/Fm ratios of both varieties were not
significantly different among all lighting conditions. In
healthy leaves, the Fv/Fm ratio is close to 0.8, a value
typical for uninhibited plants. A lower value indicates that a
portion of the PSII reaction center is damaged31,32. The
ΦPSII and qP of the two varieties under B were highest
(0.85~0.87) among all lighting treatments and those under
R and G were at similar levels. The exception was that the
qP of IR1552 under R (0.82) was significantly higher than
under G (0.71).
Therefore, blue light might promote the photosynthetic
potential of rice seedlings. The seedlings of TS10 under R
(1.4) and G (1.3) exhibited higher NPQ than those grown in
the blue light environment (1.0). This indicated thermal
energy dissipation in the antennae. In IR1552, there was no
significant difference in the NPQ among the R (1.0), G (0.8)
and B (0.8) lighting but NPQ under RB (1.2) was slightly
higher than under other lighting qualities. In general,
cultivars responded differently to light quality due to a
different photosynthetic apparatus and the Chl fluorescence
of two varieties varied in response to RB LED conditions.
Free amino acid, soluble sugar, starch and total protein
contents: ANOVAs for variety (V), light quality treatment
(T) and their interaction (V × T) for carbonnitrogen
metabolism in 14 d seedlings are tabulated in table 3. There
were significant differences in soluble sugar, free amino
acid and total protein content between the two varieties.
Moreover, total protein levels were significantly affected
by T and soluble sugar appeared to significantly differ in V
× T.
The soluble sugar content of IR1552 was significantly
greater in seedling leaves under R and G (47~48.6 mg g-1
DW) than under B and RB (37~38.7 mg g-1 DW) (Table 3).
A similar trend was observed in starch levels where R and
G (23~25.4 mg g-1 DW) were greater than B and RB
(14.0~15.4 mg g-1 DW), suggesting that R and G lights
might stimulate carbohydrate accumulation. The soluble
sugar content in TS10 seedling leaves was not significantly
different among all treatments but the starch content was
greatest (54.3 mg g-1 DW) when exposed to G. The only
significant difference in free amino acid content was the
value from TS10 seedling leaves under RB which showed
the lowest level (15.3 mg g-1 DW) among all lighting
qualities. The total protein of leaves was greatest (43.7 mg
g-1 DW) in IR1552 under B and lowest (33.1 mg g-1 DW)
in TS10 under R. Furthermore, total proteins of IR1552
under R (35.6 mg g-1 DW) were significantly lower in
comparison to other LED conditions (41.1~43.7 mg g-1 DW)
indicating that blue light might promote protein synthesis in
seedling leaves.
Discussion
Growth and morphological quality: Rice is widely grown
in Taiwan and its production is very important
economically and commercially. The spectral quality of
lighting is defined as the relative intensity and quantity of
different wavelengths emitted by a light source and
perceived by photoreceptors within a plant. Plant yields and
quality are the result of interactions of various
environmental factors under which plants are grown. The
present study examined the effects of different spectral
lighting conditions on growth parameters, pigments,
chlorophyll fluorescence and carbonnitrogen metabolism
of two genotypes of rice seedling plants grown under
identical environmental conditions. Plants showed distinct
growth responses to different light-quality treatments.
Results from table 1 demonstrated that light quality
influenced the growth and morphology of rice seedlings
and blue light inhibited shoot elongation. Seedling height
was shortest and stem diameter greatest under B LED
conditions.
Similar results were observed in rice seedlings20,
strawberry plantlets33, sprouting broccoli34, grapes35, roses1
and Cymbidium plantlets36. In addition, several
studies2,8,16,18,36-38 showed that blue and red mixed LEDs
increased biomass accumulation. In our study, however,
shoot biomass was unaffected by light quality. It is unlikely
that red and blue mixed LEDs could promote shoot
biomass. Root length was the shortest and root biomass the
lowest in seedlings of the two varieties under RB LED
Research Journal of Biotechnology Vol. 9(4) April (2014)
Res. J. Biotech
19
conditions. This agrees with the reports by Guo et al20 and
Nhut et al38 but differs from previous studies2,36,37 in which
red and blue mixed LEDs were shown to induce root
elongation.
Liu et al12 reported that a different red to blue ratio affected
root morphology and an increase in blue radiation caused a
longer root length. The B:R (3:1) LED light was suitable
for rapeseed plantlet growth and can be used as a priority
light source in the rapeseed culture system39. In our study,
the energy distribution of RB LEDs was 80% red and 20%
blue in PPFD (data not shown). B LED light is important
for leaf expansion and enhances biomass production6,16,40.
Yorio et al41 also reported that there was higher dry weight
accumulation in lettuce grown under R light supplemented
with B light than in lettuce grown under R light alone.
These results indicate that plant responses to light quality
are species- or cultivar- dependent.
The morphological quality of rice seedlings can be
described by the S/R DW ratio and the health index. TS10
seedlings under B exhibited the lowest S/R ratio (1.91)
which contributed to an increase in root biomass. A higher
seedling root biomass supports shoot growth by fully
supplying the plant with water and mineral nutrition and
may increase successful transplantation into the field. Poor
roots cannot supply sufficient water for large shoots so
plants with high S/R ratios are unsuitable for active growth2.
In our study, the S/R DW in TS10 was not optimal under G
(2.80) compared to other light colors. This observation is
indicative of the poor growth of roots under G light and
also indicates that root induction is probably also dependent
on the spectral quality of lighting.
In addition, a growth-retarding effect might have been
caused by an insufficient quality of light. The seedling
health index was greatest under B which is in agreement
with Guo et al20. The higher health index under the blue
light environment contributed to the shorter shoot height
and larger stem diameter which can provide a higher
lodging resistance potential. Consequently, B LED light
was an effective light source for plant growth and
development and light spectra, intensities and durations can
easily be controlled by growers in artificial growing
environments.
Photosynthetic pigments and chlorophyll fluorescence:
Plant pigments have specific wavelength absorption
patterns known as absorption spectra. Biosynthetic
wavelengths for the production of plant pigments are
referred to as action spectra42. Chl and Car have high light
absorptions at 400500 and at 630680 nm respectively
and low light absorption at 530610 nm. Previous
studies2,12,20,33,36,37,43 demonstrated that blue light induces
the synthesis of Chl and Car. In our study, light quality also
affected photosynthetic pigments in rice seedling leaves
(Table 2). Total Chl in IR1552 seedling leaves under RB
was higher than other light conditions but Car in seedling
leaves was not responsive to different light qualities.
Although different quality lighting for all treatments were
applied at the same PPFD level, plants showed similar
absorption spectra of photosynthetic pigments, total Chl
and Car (Table 2).
Perhaps the applied PPFD level (160 μmol m2 s1) had
reached a certain minimum that is necessary for sufficient
synthesis and activity of photosynthetic pigments and
electron carriers. The Chl a/b ratio was mediated by
lighting treatments in seedling leaves of two varieties and
was higher under B compared to other lighting
environments. This result is consistent with those of
previous studies2,37,42,43. An increase in Chl a/b is usually
observed in higher irradiation environments44 suggesting it
as an indicator for estimating relative photosystem
stoichiometry45. Plants grown under all treatments appeared
to synthesize more Chl a because it has a wider spectrum
compared to that of Chl b and Chl a is the molecule that
makes photosynthesis possible46.
Furthermore, a change in the Chl a/b ratio is usually
correlated with variation in PSII light-harvesting antenna
size and PSII:PSI content47. This inference is strengthened
by our findings on Chl fluorescence (Fig. 2). The qP and
ΦPSII of the tested samples under B were higher than those
of under R and G which may indicate non-radiative
(thermal) energy dissipation. The thermal dissipation
process is called non-photochemical quenching (NPQ),
referring to the fact that the thermal dissipation of Chl's
excited states competes with fluorescence emission as well
as with photochemistry (i.e. photosynthesis). The decreases
in NPQ are associated with decreases in non-photochemical
quenching. PSII activity may regulate the response of
photosynthesis to light quality changes. Blue light
promoted the ΦPSII and qP of seedling leaves and is in
agreement with the findings by Wang et al42 who indicated
that the decrease in ΦPSII was due to the lower qP. This
might be caused by rate-limiting processes including the
PSI and cytochrome b6/f complex processes42. Yu and
Ong48 found a reduction of ΦPSII and qP in leaves under red
or yellow light compared with blue light.
In addition, blue light is essential for high light acclimation
and photoprotection in the diatom Phaeodactylum
tricornutum49. These results imply that the Chl fluorescence
parameters were genotype- and light quality-specific and
were not expressed solely in response to an increasing
excess of photon energy. Chloroplast development in TS10
may be particularly sensitive to blue lights. Electron
transport would be inhibited under conditions without blue
light and NPQ would increase in TS10 seedling leaves.
Both genotypes behaved similarly when their leaves were
developed at 30/25°C and 160 μmol m2s1 PPFD inside
growth chambers for 14 d and hence the genotypic
differences might be related to adaptation mechanisms
induced by light quality.
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20
Carbonnitrogen metabolism: The selected LED lights
differentially affected the metabolic system of the
investigated rice varieties. Seedlings under B were
observed to have higher total protein content in leaves than
under other monochromatic lights (Table 3) which is in
agreement with the findings by Lin et al43, Guo et al20,
Wang et al42 and Eskins et al50. Blue light influences nitrate
reductase activity for mediating the rate of nitrogen
assimilation in radish plants51. Ohashi-Kaneko et al18 and
Matsuda et al19 reported that a red light environment with a
supplemental blue light caused an increase in the total N
content of rice leaves. This included Rubisco, cytochrome f
and light-harvesting complex II and was positively
correlated with photosynthetic rate and stomatal
conductance. These results were consistent with our
findings on Chl a/b (Table 2) and Chl fluorescence (Fig. 2).
Previous studies found that the density, length and width of
stomata were enhanced in blue light-enriched
environments8,16,35,42.
In contrast, leaves in the blue light-enriched environments
of our study exhibited stronger water transport, contributing
to lower moisture content. The accumulation of
carbohydrates in IR1552 leaves was promoted significantly
under R and G LED conditions (Table 3). This outcome
was similar to those published for rice seedlings20,
Oncidium12 and upland cotton plantlets16 but was opposite
to the findings of Wang et al42 which indicated blue
light-induced carbohydrates were accumulated in leaves.
Red light induces the accumulation of carbohydrates which
is attributed to inhibiting the translocation of
photosynthetic products from leaves52.
IR1552 had the higher soluble sugar and starch contents
under R and G LEDs, so these light sources might be
beneficial for the accumulation of soluble sugars and
starches in plants. However, the amount of free amino acids
in all plant leaves showed no significant differences among
all treatments except for RB in TS10 leaves. This suggests
that the light spectrum might not be advantageous for free
amino acids synthesis.
Function of green light: Anthocyanins are one group of
polyphenols that are thought to protect plants against
unsuitable environments53. A study of red leaf lettuce
discovered that blue light induced the synthesis of Ant in
seedling leaves2. Our results showed that RB lighting also
induced Ant synthesis in purple leaf IR1552; however, the
efficiency of green light was higher than other
monochromatic lights (Table 2). Johkan et al6 tested the
effects of green light wavelengths on red leaf lettuce and
found that green LEDs (peak wavelength 510 nm) induced
Ant synthesis in baby lettuce leaves. In our study, G LEDs
had a peak wavelength of 525 nm and induced more Ant
synthesis than red or blue light (Fig. 1).
Furthermore, the morphology, photosynthetic pigments,
Chl fluorescence and metabolites under G performed
similarly to those under R (Tables 1, 2 and 3; Fig. 2), which
is in agreement with the trend that was observed in
cucumbers42. Green light acts as a signal source affecting
the development of wheat3 and the rosette architecture of
Arabidopsis7. However, the function of green light is not
clear54; hence the effect of green light on plants is worthy
of further evaluation. In addition, it will be interesting to
test more rice varieties and lines for seedling growth when
illuminated by various monochromatic light spectra and
combinations under a wide range of light intensities.
Table 1
The growth parameters of 14 d seedlings cultivated under different light environments.
Variety
Treatment
Plant
height
(cm)
Root
length
(cm)
Stem
diameter
(cm)
Shoot
biomass
(g)
Root
biomass
(g)
Shoot/Root
Ratio
(w/w)
Root
moisture
content (%)
Health
index
TS10
R
19.5a
13.7ab
0.16b
0.038a
0.015b
2.49b
92.3a
0.310c
G
20.1a
14.4a
0.17ab
0.036a
0.013c
2.80a
93.2a
0.310c
B
12.9c
14.1ab
0.19a
0.035a
0.019a
1.91c
93.1a
0.525a
RB
19.1a
12.2c
0.16b
0.036a
0.017b
2.16c
93.0a
0.307c
IR1552
R
19.6a
13.0bc
0.13c
0.034a
0.013c
2.66ab
92.4a
0.218d
G
19.5a
12.1c
0.12c
0.034a
0.013c
2.57ab
93.3a
0.221d
B
13.1c
11.9c
0.16b
0.036a
0.013c
2.79a
92.9a
0.431b
RB
16.8b
9.1d
0.15b
0.036a
0.013c
2.69ab
92.8a
0.340c
ANOVA F tests
Variety (V)
ns
<0.0001
<0.0001
ns
<0.0001
<0.0001
ns
0.0045
Treatment (T)
<0.0001
<0.0001
0.0003
ns
0.0016
0.0041
ns
<0.0001
V × T
ns
0.0489
0.0160
ns
0.0007
<0.0001
ns
ns
Biomass is the total weight of 3 seedlings. Values for ANOVA F tests are type I observed significance levels. Within columns,
means followed by the same letter are not significantly different according to LSD (0.05). ns, non-significant at P < 0.05.
Research Journal of Biotechnology Vol. 9(4) April (2014)
Res. J. Biotech
21
Table 2
The effect of light quality on pigments in 14 d seedling leaves.
nd, non-detectable. Values for ANOVA F tests are type I observed significance levels. Within columns,
means followed by the same letter are not significantly different according to LSD (0.05); ns, non-
significant at P < 0.05.
Table 3
Effects of light quality on the carbonnitrogen metabolism of seedling leaves collected from 14 d seedlings under
different light environments.
Values for ANOVA F tests are type I observed significance levels. Within columns, means followed by the same letter are not
significantly different according to LSD (0.05); ns, non-significant at P < 0.05.
Wavelength (nm)
300 400 500 600 700 800
Relative energy (Watt m-2 s-1)
0
10000
20000
30000
40000 R
G
B
RB
Fig. 1: The spectral distributions of different light treatments. Spectral scans were recorded at the top of the plant
canopy with a spectroradiometer.
Variety
Treatment
Total Chl (mg g-1 DW)
Chl a/b
Car (mg g-1 DW)
Car/Chl
Ant (μg g-1 DW)
TS10
R
14.49bc
2.55bc
3.52ab
0.24ab
nd
G
14.02bc
2.77ab
3.70ab
0.26a
nd
B
13.45c
2.81a
3.52ab
0.26a
nd
RB
13.94bc
2.53bc
3.20ab
0.23ab
nd
IR1552
R
13.24c
2.19d
2.84b
0.22bc
15c
G
15.48b
2.20d
3.35ab
0.22b
33b
B
15.19b
2.47c
3.52ab
0.23ab
17c
RB
18.25a
2.06d
3.24ab
0.18c
150a
ANOVA F tests
Variety (V)
0.0015
<0.0001
ns
0.0006
<.0001
Treatment (T)
0.0083
0.0060
ns
0.0239
<.0001
V × T
0.0020
ns
ns
ns
<.0001
Variety
Treatment
Soluble sugar (mg g-1 DW)
Starch (mg g-1 DW)
Free amino acid (mg g-1 DW)
Total protein (mg g-1 FW)
TS10
R
50.3ab
23.1b
21.4a
33.1d
G
53.5ab
54.3a
19.2ab
34.7cd
B
52.3ab
21.5b
19.1ab
41.0ab
RB
57.6a
21.5b
15.3b
38.0bc
IR1552
R
48.6b
25.4b
19.6a
35.6cd
G
47.0b
23.0b
21.6a
41.1ab
B
37.0c
14.0c
21.4a
43.7a
RB
38.7c
15.4c
21.2a
41.7ab
ANOVA F tests
Variety (V)
<0.0001
ns
0.0362
0.0034
Treatment (T)
ns
ns
ns
0.0010
V × T
0.0162
ns
ns
ns
Research Journal of Biotechnology Vol. 9(4) April (2014)
Res. J. Biotech
22
Fig. 2: Effects of light quality on the relative value of chlorophyll fluorescence. Leaves were analyzed from 14 d
seedlings under different light environments. Values are the mean of ten plants from two replicates consisting of five
plants each. The values followed by the different letter show statistically significant differences at P < 0.05.
Conclusion
In agricultural production, yields and costs are the two most
important criteria by which optimization of environmental
factors are concerned. In the present study, we investigated
effective light quality with sufficient intensity for growing
healthier seedlings. Different wavelengths within the
visible spectrum influenced the growth, morphology,
photosynthetic potential and metabolism of rice seedlings
and different responses to lighting depended on the
varieties of rice that were tested. Particularly, blue light
increased the S/R ratio, health index, Chl a/b ratio, Chl
fluorescence and total protein in leaves and may optimize
seedling growth and development in a controlled-climate
setting. Bioregenerative and hydroponic culture systems
may satisfy commercial requirements for rapid, large-scale
and precise management of rice seedling production.
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... A feasibility of tailoring light spectra enables recent plant cultivation technologies and controls the plant growth, development, and nutritional quality. In our study, the growth and that Car levels were not responsive to light quality [20]. Tanaka et al. (1998) found that RL promoted Cymbidium leaf growth, but reduced Chl content. ...
... The concentrations of Chl and Car in coriander leaves were determined as described [20]. In Brief, leaf sample powder (0.01 g) was mixed with 80% acetone (5 mL) and incubated at 4°C overnight, and was centrifugation at 13,000 g for 5 min. ...
... The supernatants were transferred to a new tube, and then used to determine the Chl a and Chl b absorbance in acetone at 663.6 nm and 646.6 nm, respectively, using a spectrophotometer (Hitachi U-2000, Tokyo, Japan). Following equations were used to calculate the Chl a, Chl b, Chl a + b, and Car concentrations: The anthocyanin (Ant) concentrations of extracts were measured as described by Chen et al. (2014) [20]. The extraction buffer (99% methanol containing 1% HCl) was added to leaf sample powder and incubated at room temperature for 1 h. ...
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... Plants can sense and respond to a broad range of the light spectrum, from the UltraViolet-C (260 nm) to far-red (720-780 nm) regions (Carvalho et al. 2016). Red (R; 600-700 nm) and blue (B; 400-500 nm) light have the greatest impact on plant growth because they are the most important spectra for inducing photosynthesis (Chen et al. 2014). According to previous studies, plant growth and development require a combination of light with an appropriate ratio, rather than monochromatic light (Gupta et al. 2013;Johkan et al. 2010;Carvalho et al. 2016;Naznin et al. 2016;Gam et al. 2020). ...
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... As reported in the false scale color of the VIP scores, the highest increase in metabolites was observed in plants treated with B and G lights and, to a lesser extent, with R and W lights (Fig. 2C). Concerning amino acids, known in the bibliography to be generally affected by monochromatic light (Chen et al., 2014;Dhakal and Baek, 2014;Gao et al., 2022), the G and B light supplementation showed the highest relative abundance of beta-alanine, glutamine, glutamic acid, GABA, allothreonine and aspartic acid. On the contrary, during R supplementation only the glutamic acid was present in higher content than control, whereas in plants exposed to W light, in comparison to NS, an accumulation of serine, glutamine and GABA was observed (Fig. 2C). ...
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... Compared to a study on white and black glutinous rice sprouts grown under natural light (Tanprasit et al., 2019), the current results showed that the proximate compositions of purple seedings grown under the blue LEDs light were lower in carbohydrates, fat and energy, but higher in protein. Chen et al. (2014) also showed that indica rice seedlings (purple leaf) cultured under blue LEDs had a higher total protein content, compared to those exposed to red+blue LEDs. photon sources to produce high-value bioactive compounds in greenhouse conditions. ...
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... In the absence of light, a negative value is observed in the net photosynthesis rate because of the releasing CO 2 through dark respiration [7]. Shade tolerance refers to the capacity of a given photosynthetic organism to tolerate low light levels and it is typically characterized by a set of morphological and physiological traits such as decrease in growth rate, light compensation point, dark respiration rate, net photosynthetic rate and chlorophyll a/b ratio, increase in quantum yield, chlorophyll content (both area -1 and dry mass -1 basis) and carbohydrate storage together with many other traits [8]. ...
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... According to Chen et al. (2014), the spectral quality of light, as it effects the plant through the wavelengths absorbed by phytochrome through specific photoreceptors, activates enzymes associated with the synthesis of auxins, which affects several morphological (Tables 3, 4) and physiological aspects (Table 5). This improves the plant's initial development, increases shoot height and internode lengths, and promotes root growth, allowing faster acclimatization and increasing field survival rates. ...
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The effects of light generated by superbright blue and red LEDs on the growth of Cymbidium plantlets cultured in vitro have been studied. Leaf growth, chlorophyll content and shoot and root weights were affected by different LED irradiations. Red light promoted leaf growth but decreased chlorophyll content. This was reversed by blue light. The growth of Cymbidium plantlets in terms of increase in total shoot and root weights was comparable under red plus blue LEDs and the fluorescent systems. Generally, the response to different LED was similar for plantlets grown on sugar-free medium with or without CO2 enrichment and sugar-containing medium but without CO2 enrichment. The growth of Cymbidium plantlets was enhanced by CO2 enrichment. Our study demonstrates the effectiveness of a total irradiation system for Cymbidium plantlets growth in vitro. The significance of our findings in relation to the development of a suitable lighting system for plant tissue culture is discussed.
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Solid-state lighting based on the use of light-emitting diodes (LEDs) is potentially one of the biggest advancements in horticultural lighting in decades. LEDs can play a variety of roles in horticultural lighting, including use in controlled environment research, lighting for tissue culture, and supplemental and photoperiod lighting for greenhouses. LED lighting systems have several unique advantages over existing horticultural lighting, including the ability to control spectral composition, the ability to produce very high light levels with low radiant heat output when cooled properly, and the ability to maintain useful light output for years without replacement. LEDs are the first light source to have the capability of true spectral composition control, allowing wavelengths to be matched to plant photoreceptors to provide more optimal production and to influence plant morphology and composition. Because they are solid-state devices, LEDs are easily integrated into digital control systems, facilitating special lighting programs such as "daily light integral" lighting and sunrise and sunset simulations. LEDs are safer to operate than current lamps because they do not have glass envelopes or high touch temperatures, and they do not contain mercury. The first sustained work with LEDs as a source of plant lighting occurred in the mid-1980s to support the development of new lighting systems to be used in plant growth systems designed for research on the space shuttle and space station. These systems progressed from simple red-only LED arrays using the limited components available at the time to high-density, multicolor LED chip-on-board devices. As light output increases while device costs decrease, LEDs continue to move toward becoming economically feasible for even large-scale horticultural lighting applications.
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In this study, we determined the effects of raising seedlings with different light spectra such as with blue, red, and blue + red light-emitting diode (LED) lights on seedling quality and yield of red leaf lettuce plants. The light treatments we used were applied for a period of 1 week and consisted of 100 μmol.m-2.s-1 of blue light, simultaneous irradiation with 50 mmol.m-2.s-1 of blue light and 50 mmol.m-2.s-1 of red light, and 100 mmol.m-2.s-1 of red light. At the end of the light treatment, that is 17 days after sowing (DAS), the leaf area and shoot fresh weight (FW) of the lettuce seedlings treated with red light increased by 33% and 25%, respectively, and the dry weight of the shoots and roots of the lettuce seedlings treated with blue-containing LED lights increased by greater than 29% and greater than 83% compared with seedlings grown under a white fluorescent lamp (FL). The shoot/root ratio and specific leaf area of plants irradiated with blue-containing LED lights decreased. At 45 DAS, higher leaf areas and FWs were obtained in lettuce plants treated with blue-containing LED lights. The total chlorophyll (Chl) contents in lettuce plants treated with blue-containing and red lights were less than that of lettuce plants treated with FL, but the Chl a/b ratio and carotenoid content increased under blue-containing LED lights. Polyphenol contents and the total antioxidant status (TAS) were greater in lettuce seedlings treated with blue-containing LED lights than in those treated with FL at 17 DAS. The higher polyphenol contents and TAS in lettuce seedlings at 17 DAS decreased in lettuce plants at 45 DAS. In conclusion, our results indicate that raising seedlings treated with blue light promoted the growth of lettuce plants after transplanting. This is likely because of high shoot and root biomasses, a high content of photosynthetic pigments, and high antioxidant activities in the lettuce seedlings before transplanting. The compact morphology of lettuce seedlings treated with blue LED light would be also useful for transplanting.
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The light sources generally used for in vitro plant cultures are fluorescent lamps. To select a more efficient light source, the present study evaluated the effects of different light qualities on the growth and morphogenesis of rapeseed (Brassica napus L.) cultivar Westar plantlets in vitro. The plantlets were exposed to 60 μmol m−2 s−1 photosynthetic photon flux (PPF) for a 12 h photoperiod under the following six different light qualities: fluorescent lamps (FL), monochromic blue light-emitting diodes (LEDs) (B), monochromic red LED (R), and three mixtures of B plus R (3:1, 1:1, 1:3) LED. The proliferation rate was greater in plantlets that were cultured under B light than those under FL. The differentiation rate, fresh mass, dry mass, concentration of chlorophyll a, soluble sugar concentration, stem diameter, leaf stomata abaxial surface length, adaxial surface stomata frequency and transplantation survival rate were greater in plantlets that were cultured under B:R = 3:1 light than under FL. The concentration of starch and the spongy tissue length were higher in plantlets cultured under R light than those under FL. The B:R = 3:1 LED light was suitable for rapeseed plantlet growth in vitro and can be used as a priority light source in the rapeseed culture system according to its differentiation rate, proliferation rate, growth rate, and transplantation survival rate.