Cent. Eur. J. Biol.• 6(5) • 2011 • 821-828
DOI: 10.2478/s11535-011-0059-z
Central European Journal of Biology
The impact of red and blue light-emitting diode
illumination on radish physiological indices
Research Article
Giedrė Samuolienė*, Ramūnas Sirtautas, Aušra Brazaitytė, Jurga Sakalauskaitė,
Sandra Sakalauskienė, Pavelas Duchovskis
Institute of Horticulture,
Lithuanian Research Centre for Agriculture and Forestry,
Lt-54333 Babtai, Kaunas, Lithuania
Received 20 January 2011; Accepted 19 May 2011
Abstract: The objective was to evaluate the effect of different combinations of red (638 nm) and blue (455 nm) light produced by solid-state
light-emitting diodes (LEDs) on physiological indices (net assimilation rate, hypocotyl-to-leaf ratio, leaf area, leaf dry weight, hypocotyl
length and diameter, plant length, developed leaves), variation of photosynthetic pigments and non-structural carbohydrates in radish
(Raphanus sativus L., var. ‘Faraon’). Lighting experiments were performed under controlled conditions (total PPFD - 200 µmol m-2 s-1;
16 h photoperiod; 14/18°C night/day temperature). The LED conditions: 638 nm; 638 + 5% 455 nm; 638 + 10% 455 nm; 638 + 10%
455 + 731 nm; 638 + 10% 455 + 731 + 669 nm. Our results showed that radishes grown under red (638 nm) alone were elongated,
and the formation of hypocotyl was weak. The net assimilation rate, hypocotyl–to–leaf ratio, and leaf dry weight also were low due to
the low accumulation of photosynthetic pigments and non-structural carbohydrates in leaves. The supplemented blue (455 nm) light
was necessary for the non–structural carbohydrates distribution between radish storage organs and leaves which resulted in hypocotyl
thickening. Red alone (638 nm) or in combination with far–red (731 nm), or red669 for radish generative development was required.
Keywords: Carbohydrates • Chlorophyll • Hypocotyl • Leaf dry weigh • Root:shoot ratio
© Versita Sp. z o.o.
1. Introduction
Light quality and quantity in the growth environment
through photosynthesis and photomorphogenetic
photoreceptors strongly influences plant development
and physiology [1-4]. One of the problems of controlled
environment crop production is the distribution of
adequate light for plant growth. Some electrically light
sources lack specific wavelengths required for natural
plant photomorphogenesis. Generally fluorescent, highpressure sodium, and metal halide lamps are used for
illumination in greenhouses or in other controlled growth
environment [5]. These lamps vary in terms of spectral
quality, which can result in differences in plant growth
and morphology [6]. Recently most studies are based
on solid-state light-emitting diodes (LEDs) lighting [7] as
a potential light source for successful growth [8] and to
determine if the requirements for plant photosynthesis
and photomorphogenesis are met [9,10].
It is known that the main role in photomorphogenesis,
through the photoreceptors, needs blue light and thus it
is essential for the growth and development of higher
plants [8,10]. In photomorphogenesis the attention falls
on the red far-red light-absorbing phytochromes, the
blue, UV-A light-absorbing cryptochromes and blue
light photoreceptors phototropins [4,11]. Photosynthetic
receptors, chlorophylls and carotenoids absorb at
red and blue light [8]. It is important to understand
the light competition between photosynthetic and
photomorphogenetic pigments and related processes.
According to literature data [9], plants can complete a
life cycle under red LEDs alone, but supplementing red
light with blue light promotes dry matter production in
several plant species [2,10], including radish [1]. The
trend of higher biomass production and photosynthetic
capacity due to blue and red light combinations was
observed in many papers [2,9,10]. The effect of light
quantity on plant development and physiological indices
is also important. Goins and co–workers [2] ascertained
that wheat grown under red LEDs supplemented with
blue light from fluorescent lamps (BF) were larger and
greater amounts of seed were produced. According to
* E-mail: [email protected]
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The impact of red and blue light-emitting diode
illumination on radish physiological indices
Yorio et al. [1] data, 10% of blue light from BF lamps and
red LEDs were still insufficient for achieving maximal
growth for radish, lettuce and spinach. Hogewoning
et al. [8] found that 7% of blue light during cucumber
growth is qualitatively required for normal photosynthetic
functioning and quantitatively mediates leaf responses
resembling those to irradiance intensity.
Several studies have shown that biochemical
properties of photosynthesis (chlorophyll a, b contents
and ratios) are positively influenced by blue light [8].
Dougher and Bugbee [12] reported that with regard
to morphogenesis, dicotyledonous species tend to be
more sensitive to blue light than monocotyledonous
species. The regulation of photosynthesis is associated
with carbohydrate accumulation in leaves, [13] but there
still is not much literature data associated with light
treatments.
With concern to its economical importance, radish
(Raphanus sativus L.) has attracted the attention
of researchers studying whole plant responses to
environmental conditions [14]. A short growth cycle,
generally day–length neutral, regularly shaped leaves,
distribution of biomass and a division between leaves
and a below–ground storage organ (hypocotyl) make
radish a convenient experimental plant. It is useful as a
model crop for studying developmental characteristics
and for applications between major plant organs. The
aim of this study was to evaluate the effect of different
combinations of red and blue light produced by LEDs
on physiological indices, variation of photosynthetic
pigments and non-structural carbohydrates in radish
(Raphanus sativus L., ‘Faraon’).
2. Experimental Procedures
2.1 Chemicals
Raffinose, sucrose, fructose, mannose and glucose
were obtained from Sigma-Aldrich (Germany).
Acetone was obtained from Merck (Germany). Calcium
carbonate (CaCO3) was obtained from Lach-Ner
(Czech Republic). All standards and samples for HPLC
were filtered through 0.25 µm syringe filters (Albet®,
Germany).
2.2 Growth conditions and plant material
Lighting experiments were performed in the phytotron
chambers, under controlled environmental conditions.
The originally designed [15] light emitting diode based
lighting units, consisted of commercially available
wavelengths: red component (638 nm, delivered by
AlGaInP LEDs LuxeonTM type LXHL-MD1D, Lumileds
Lighting, USA) and additional blue (445 nm, LuxeonTM
type LXHL-LR5C, Lumileds Lighting, USA), red
(669 nm, L670-66-60, Epitex, Japan), and far red
(731 nm, L735-05-AU, Epitex, Japan) LEDs were
used. The LED combinations are presented in Table 1,
red (638 nm) light treatment was used as a control.
Total photosynthetic photon flux density of about
200 µmol m-2 s-1 and 16 h photoperiod were maintained
in LED treatments. The night/day temperature was
maintained at 14/18°C.
Radishes (Raphanus sativus L., ‘Faraon’)
were grown in peat (pH ≈ 7, accuracy ±0.01
pH units) substrate under the light conditions
described in Table 1. The amount of nutrients
(mg/l) in the substrate was as follows: N 60-80,
P 30, K 140-180, Ca 200-300, Mg 40-60. Electrical
conductivity varied between 1.0 and 2.5 mS cm-1
(±0.03 mS cm-1). Plants were fertilized with 0.2%
ammonium nitrate solution once a week. Analyses
were performed 25 days after germination when
rhizocarp was formed (vegetative state); and 50 days
after germination when the formation of generative
organs was observed (the differentiation of apical
meristems started).
2.3 Determination
carbohydrates
of
non–structural
Raffinose, sucrose, fructose, mannose and glucose were
measured by high performance liquid chromatography
(HPLC) method. About 1 g of fresh plant tissue (leaves
or hypocotyl) was ground and diluted with +70ºC 4 ml
double distilled water. The extraction was carried out
for 24 h. The samples were filtered using cellulose
acetate (pore diameter 0.25 µm) syringe filters. The
analyses were performed on Shimadzu HPLC (Japan)
chromatograph with refractive index detector (RID 10A),
oven temperature was maintained at +80ºC. Separation
of carbohydrates was performed with a Shodex SC-1011
column (300 x 4.6 mm) (Japan), mobile phase – double
distilled water. The sensitivity of the HPLC method was
established using a method validation protocol [16].
Photosynthetically active flux density, µmol m-2 s-1
Treatments
Blue
445 nm
R
Red
638 nm
Far–red
731 nm
10
4
200
R+5B
5% 10
190
R+10B
10% 20
180
R+10B+FR
10% 20
176
R+10B+FR+R669
10% 20
166
Table 1.
Red
669 nm
4
The light-emitting diode combinations and photon flux
densities
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2.4 Determination of photosynthetic pigments
About 0.2 g of fresh leaf tissue was ground with 0.5 g
CaCO3, washed with pure acetone, and filtered through a
cellulose filter. The sample was diluted to 50 ml with 100%
acetone. Chlorophyll a, b and carotinoids were measured
by the specrophotometric method of Wetshtein [17]. The
spectrum of photosynthetic pigments was measured at
440.5 nm, 662 nm and 644 nm respectively.
2.5 Physiological indices
The development levels and growth parameters of
plants were evaluated.
The net assimilation rate (NAR) of a plant is defined
as its growth rate per unit leaf area for any given time
period (day). It can be calculated as: NAR (g cm-2 d-1)=(1/
LA)(dW/dt), where LA is leaf area (cm2) and dW/dt is the
change in plant dry mass per unit time.
Root–to–shoot ratio - is the distribution of biomass
between the below-ground storage organ (hypocotyl)
and the shoot (leaves). In this case it was expressed as
hypocotyl–to–leaf ratio.
The leaf area of the radish was measured by
“WinDias” leaf area meter (Delta-T Devices Lts, UK).
Leaves and hypocotyls were dried in a drying oven at
105°C for 24 h to determine the dry mass.
Development, %
2.6 Statistical analysis
The analyses were performed in seven (biometrical
measurements) or five (analytical measurements)
replications and data analysis was processed using oneway analysis of variance Anova, the Fisher’s LSD test to
trial mean at the confidence level P = 0.05. The standard
deviation of mean to express some carbohydrate values
was used.
3. Results
After 25 days, radishes grown under red (R) light alone
were elongated (Table 2). The length of the hypocotyl
and the total plant length differed significantly from the
mean, 33% and 19% respectively. Increasing the blue
(B) light fraction from 0% to 10% resulted in significantly
decreased plant length (both hypocotyl and leaves). The
addition of far–red (FR) or FR together with red 669 nm
(R669) light component resulted in significantly increased
hypocotyl diameter. 50 days growth duration and LED
treatment resulted in developmental differences. The
differentiation of apical meristems and the formation of
generative structures were observed in radishes grown
under R alone (36.7%) or under R in combination with FR
The length of
hypocotyl, cm
The diameter of
hypocotyl, cm
R
2.99B
0.50A
15.6B
3.9
R+5B
2.27
1.79
14.7
4.0
R+10B
1.74
1.45
10.7
3.3A
R+10B+FR
1.86
1.76B
12.4
4.0
R+10B+FR+R669
1.94
2.12
12.9
4.1B
0.38
0.22
0.9
0.2
Treatments
Total plant length, cm
The number of
developed leaves
25 days after germination
Vegetative state,
100 %
LSD 05
A
B
B
B
A
50 days after germination
Vegetative, 63.3 %
R
3.00
2.06A
15.0
4.3
Vegetative, 100.0 %
R+5B
2.71
3.13
16.8
5.3B
Vegetative, 100.0 %
R+10B
2.69
2.54
14.0
4.6
Vegetative, 62.5 %
R+10B+FR
2.83
2.91
15.0
4.7
Vegetative, 70.0 %
R+10B+FR+R669
2.76
2.73
13.2A
5.0
0.22
0.26
1.1
0.5
LSD 05
B
B
Generative, 36.7 %
R
2.78
0.64
11.5
4.8
Generative, 37.5 %
R+10B+FR
1.82
1.42
12.4
5.6
Generative, 30.0 %
R+10B+FR+R669
2.38
1.41
11.9
5.2
0.60
0.42
1.8
1.1
LSD 05
Table 2.
A
Growth parameters of radish plants.
The values with the same letters are not significantly different with P≤0.05 (n=7).
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The impact of red and blue light-emitting diode
illumination on radish physiological indices
(37.5%), or with FR and R669 (30.0%). Radishes grown
under R with 5% or 10% of B remained in a vegetative
state. Plants grown under R in combination with 5% B
were still elongated. However, these conditions were
sufficient for the formation of hypocotyl (Table 2).
Significantly thinner hypocotyl in both vegetative and
generative stages were formed under R lighting alone.
As there were no significant differences in the length of
hypocotyl, the significant decrease of total plant length
in a vegetative stage was observed under lighting
combination with R669, due to shorter leaves.
A significantly negative effect of R alone was observed
on assimilative indices of radish (Table 3). Under these
lighting conditions, after 25 days of treatment, NAR and
hypocotyl–to–leaf ratio was significantly lower. Moreover
after 50 days of treatment, a significant decrease in
leaf area was observed. The significant decrease in
leaf area under R in combination with 10% of B, after
both 25 and 50 days duration was observed, too. A
significant positive effect of R with 5% of B, and R with
10% of B supplemented by FR on assimilative indices
was noticed. After 50 days of treatment these spectral
conditions also had a significant positive effect on leaf
dry weight accumulation. However the addition of R669
resulted in significant decrease in leaf area and leaf dry
Treatments
Development
Net assimilation rate,
g cm-2 d-1
weight of radishes which remained in a vegetative state
(Table 3). After 50 days of treatment in the generative
stage, the NAR decreased 4.5 and 3.6 times under R
alone or in combination with 10% B, FR and R669, and
under R with 10% B, FR, respectively. However under
R with 10% B, FR treatment, the NAR in both the
vegetative and the generative stages were significantly
higher due to significantly bigger leaf area.
The significant decrease of chlorophyll (Chl) a
to b ratio due to significant decrease of Chl a and
increase of Chl b content after 25 days of treatment
under R alone in radish leaves was observed (Table 4).
Increasing the blue light fraction from 0% to 10% and
the addition of far–red light normalized the Chl a to b
ratio (3.02 – 3.37). However, only R+10B+FR+R669 LED
spectral combination lead to the significant increase of
photosynthetic pigment ratio and content. Such affect
lasted for 50 days under the above-mentioned spectral
combination treatment for radishes which remained in a
vegetative state. The addition of FR light had a positive
effect on radish development rate (37.5%) (Table 2) and
lead to significant increase of Chl a to b ratio, Chl a and
carotenoid content (Table 4).
Radishes grown under R alone or R supplemented
with 5% of blue light for 25 days accumulated a
Hypocotyl–to–leaf
ratio
Leaf area, cm-2
Leaf dry weight, g
25 days after germination
R
0.009
0.22A
90.5
0.19
R+5B
0.020
1.04
112.1B
0.25
0.018
0.83
65.9A
0.30B
R+10B+FR
0.015
1.04
92.1
0.19
100.0
0.20
11.2
0.09
A
Vegetative state
R+10B
R+10B+FR+R669
0.019
1.54
LSD 05
0.004
0.27
R
0.027A
2.34A
83.0A
0.28
R+5B
0.050
2.87
148.7
0.46B
0.033
3.66
72.2A
0.27A
R+10B+FR
0.058
B
3.73
112.4
0.38B
R+10B+FR+R669
0.026A
3.78
73.2A
0.25A
LSD 05
0.011
0.73
15.0
0.06
R
A
B
50 days after germination
R+10B
Vegetative state
B
B
B
0.006
0.96
38.5
0.21
0.016B
1.71
76.1B
0.26
R+10B+FR+R669
0.006
2.67
52.2
0.17
LSD 05
0.006
0.73
16.9
0.07
R+10B+FR
Table 3.
Generative state
A
B
Assimilative indices of radish.
The values with the same letters are not significantly different with P≤0.05 (n=7).
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Content of
chlorophyll b,
mg g-1 FM
Content of
carotenoids,
mg g-1 FM
The chlorophyll a to
b ratio
Content of
chlorophyll a,
mg g-1 FM
R
1.97A
0.54A
0.28B
0.17A
R+5B
3.37
0.74
0.22
0.22
Treatment
Development
25 days after germination
3.33
0.64
0.18
0.22
R+10B+FR
3.02
0.66
0.22
0.19A
R+10B+FR+R669
3.60B
0.90B
0.25
0.26B
LSD 05
0.34
0.05
0.03
0.02
R
2.47B
0.35
0.15
0.13
1.91
0.29
0.14
0.15
1.71
0.29
0.19
0.14
R+10B+FR
1.44
0.24
0.18
0.13A
R+10B+FR+R669
1.79
0.34B
0.23B
0.20B
LSD 05
0.23
0.04
0.05
0.02
R
2.25
A
0.33
0.16
0.16A
2.44B
0.50B
0.15
0.21B
R+10B+FR+R669
2.30
0.40
0.17
0.19
LSD 05
0.04
0.02
0.08
0.01
Vegetative state
R+10B
A
A
50 days after germination
R+5B
Vegetative state
R+10B
A
A
R+10B+FR
Table 4.
Generative state
A
The distribution of photosynthetic pigments in radish leaves.
The values with the same letters are not significantly different with P≤0.05 (n=5).
significant lower amount of total carbohydrates in both
hypocotyl and leaves (Table 5). 10% of blue light lead
to an increased fructose content in the whole plant. The
significant biggest content (about 2 times) of total non–
structural carbohydrates in both hypocotyl and leaves
was detected under R+10B LED spectral combination.
In contrast to leaves, a significant higher content of
monocarbohydrates and a lower amount of sucrose in
hypocotyl were detected. The addition of FR spectral
component influenced better accumulation of total
carbohydrates in leaves, but the total amount in the
hypocotyl was significantly lower. The R+10B+FR+R669
spectral composition conditioned the opposite
distribution of carbohydrates, and the statistically bigger
amounts of glucose and fructose were determined to
be in the hypocotyl. The same effect was found with
different LED lighting sustained for 50 days of treatment
for radishes which remained in a vegetative state. Also,
the total amount of hypocotyl carbohydrates increased
from 27.0% to 49.8%, especially due to bigger contents
of monocarbohydrates. The increase of total leaf
carbohydrates was due to an increased accumulation
of both hexoses, especially of sucrose. The distribution
of non–structural carbohydrates changed drastically
in plants grown under R alone, which started to form
generative organs. A significant increase of total content
of carbohydrates, especially of sucrose, in the hypocotyl
and leaves was observed, 1.7 and 2 times respectively
(Table 5).
4. Discussion
Some plants systems quite easy accept light-driven
manipulation [3]. As photosynthesis is the basis for
primary metabolite production, light also modulates
several metabolic pathways altering gene expression
which generates a physiological response [4,11].
Pursuant to literature data [2], radishes grown under R
alone were elongated, the formation of hypocotyl was
weak (Table 2), the net assimilation rate and hypocotyl–
to–leaf ratio was low (Table 3), leaf dry weight also
was low due to the low accumulation of photosynthetic
pigments (Table 4) and non–structural carbohydrates
in leaves (Table 5). A wide variety of plant responses,
such as procession of flowering [18] or morphological
alterations [3], is the result of light activated phytochromes
or cryptochromes action. Besides, changes in the
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Treatment
Organs
Development
The impact of red and blue light-emitting diode
illumination on radish physiological indices
Raffinose,
mg g-1, FM
Sucrose,
mg g-1, FM
Glucose,
mg g-1, FM
Mannose,
mg g-1, FM
Fructose,
mg g-1, FM
Total,
mg g-1, FM
1.78A
10.33A
25 days after germination
5.71B
2.57A
R+5B
1.25A
2.21A
6.71B
10.18A
1.80A
12.14B
7.04B
20.97B
1.21A
8.01B
4.63A
13.85A
2.20
9.54
5.90
17.64B
0.02
0.01
0.01
0.02
2.57
1.64
A
0.29
4.51A
3.09A
1.05A
0.15
0.50B
8.20A
15.68B
2.38B
0.16B
0.53B
18.75B
8.84B
5.34A
3.03B
0.12A
0.63B
17.96B
R+10B+FR+R669
4.34A
2.67A
1.35A
0.16B
0.43A
8.96A
LSD 05
0.03
0.03
0.01
0.00
0.00
0.04
hypocotyl
R
R+10B
R+10B+FR+R669
LSD 05
R
R+5B
A
Vegetative state
R+10B+FR
3.41A
leaves
R+10B
A
R+10B+FR
0.27±0.00
B
B
A
50 days after germination
2.46A
11.69A
4.06A
18.21A
R+5B
4.27
10.59
A
2.95
17.81A
8.72B
14.94B
5.07B
28.73B
3.62A
9.20A
6.10B
22.73A
9.30B
21.70B
4.12A
35.12B
0.01
0.04
0.01
0.05
1.77
B
2.04
17.08A
0.31A
0.87A
14.61A
0.55A
21.43B
hypocotyl
R
R+10B
R+10B+FR+R669
LSD 05
R
R+5B
3.72±0.00
Vegetative state
R+10B+FR
10.92
A
R+10B+FR
R+10B+FR+R669
LSD 05
R
R+10B+FR
R+10B+FR+R669
LSD 05
Table 5.
leaves
LSD 05
R
Generative state
R+10B+FR+R669
hypocotyl
1.87±0.01
R+10B+FR
A
2.35
A
13.43A
leaves
R+10B
A
0.08±0.00
B
19.49B
1.39A
24.47B
3.14B
0.23A
1.48B
29.32B
13.24A
3.03B
0.79B
1.32
18.38A
0.04
0.00
0.00
0.01
0.04
15.84
9.85
0.18±0.00
A
2.63
30.36B
4.45A
14.44B
6.79B
25.67A
4.89A
13.80B
6.30B
24.99A
B
A
0.02
0.01
26.86B
5.22±0.01
0.02
0.02
0.13A
1.97B
34.18B
14.82A
2.86B
1.85A
19.54A
14.13A
1.70B
1.84A
17.67A
0.09
0.01
0.01
0.03
The distribution of non–structural carbohydrates in radish hypocotyl and leaves.
The values with the same letters are not significantly different with P≤0.05 (mean ± SD; n=5).
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partitioning of photoassimilates may be involved by
photomorphogenetic responses [4]. Acording to our data,
R light was sufficient for flowering induction, 36.7% of
plants formed the generative organs (Table 2). Acording
to Goins and co–workers [2] data, wheat grown under red
LEDs alone also were elongated, shoot dry matter and
net leaf photosynthesis rate were decreased compared
to plants grown under supplemental blue fluorescent
light (from 1% to 10%). Yorio and co–workers [1] also
stated that radish, lettuce, and spinach grown under
red LEDs alone accumulated significantly less total dry
weight than when grown under cool-white fluorescent
light or R LEDs supplemented with 10%B fluorescent
light. According to our data, the addition of 5% blue light
to red LEDs improved the hypocotyl thickening (Table 2),
and leaf area significantly increased (Table 3), but plants
were still elongated and there was no positive effects
on photosynthetic pigment (Table 4) and non–structural
carbohydrate (Table 5) accumulation. In this case, B and
R light radiation was insufficient for photosynthetic and
photomorphogenetic responses, although chlorophylls
and carotenoids accumulated abundantly in plant tissue
as compared to photomorphogenetic photoreceptors
[11]. Hogewoning and co–workers [8] stated that 7% of
B light to R LEDs was sufficient enough to prevent any
overt dysfunctional photosynthesis. The authors noticed
that an increase of photosynthetic capacity associated
with an increase in leaf mass per unit leaf area, Chl
content per area continued to increase with increasing
B percentage up to 50%. In agreement with literature
data [8], our results demonstrated that Chl content
on leaf dry weight basis was not affected by blue light
percentage (Tables 2 and 3). In contrary to Yorio and co–
workers [1], radish grown under R LEDs supplemented
with 10% B LEDs accumulated significantly higher
leaf dry weight (Table 3) due to significantly increased
leaf carbohydrates contents (Table 5). Moreover, in
contrary to wheat development [2], the blue light did not
influence the generative growth of radish and all plants
remained in a vegetative state (Table 2). According to
our data, supplementation of R and B LEDs with FR
or R669 components had a positive effect on radish
development, and the significant hypocotyl thickening
was observed (Table 2). Such transition to flowering
might be influenced by integrated phytochromes and
cryptochromes action. As leaves filter out B and R light
and transmit far-red, there is a reduction in B and R
light leading to the decrease of photosynthetically active
radiation and light competitiveness [19]. So, due to light
quality and interaction between photomorphogenetic
and photosynthetic receptors, plants can change
the pattern of development during vegetation. FR
light significantly positively affected the assimilative
indices of radish (Table 3). Parks et al. [20] stated that
a decrease in stem elongation and an increase in leaf
expansion light activated phytochrome action. Dillard
and co–workers [21] also noticed that radish grown
under red, green, and blue supplemented by FR light
partitioned significantly more biomass than plants grown
without FR light. The significant hypocotyl–to–leaf ratio
under R+10%B+FR+R669 (Table 3) was observed and it
correlated with carbohydrates distribution in the hypocotyl
and leaves of radish (Table 5). Thus the response of
radish growth and biomass partitioning was linked to
patterns of non–structural carbohydrate distribution
between plant organs. As it is known, the sufficient doses
of photosynthetically active radiation are crucial for the
formation of assimilates and thus the accumulation of
biomass [9,22]. But spectral composition of light controls
formative processes and may initiate developmental
processes during plant growth [2,23]. Moreover, as
photomorphogenesis is the process by which light
regulates many plant development aspects, so some
metabolites which are produced by photosynthesis are
used in photomorphogenesis [11]. Our results showed
that for radish generative development, red alone
(638 nm) or combination with FR, or R669 was required
(Table 2). However, for hypocotyl formation a minimum
5% of blue light was necessary (Table 2). Besides, the
indirect effect of light spectral composition on hypocotyl
growth via formation and distribution of assimilates was
observed. The discussed data is in agreement with
Ballaré and Casal [4], where they state that stem growth
and dry matter partitioning are correlated, notwithstanding
changes in dry matter allocation are not entirely the
result of changes in stem elongation. This indicates
that photomorphogenetic responses, depend on the
interaction of photosynthetic and photomorphogenetic
photoreceptors. The co-operation of both signals,
chlorophyll and phytochrome, cryptochrome action,
control the morphology, development and distribution
of photoassimilates. Also an intense accumulation of
mannose in radish leaves inhibited sucrose synthesis
(Table 5). In agreement with Harris et al. [24], mannose
perturbs normal metabolic processes of glucose,
inhibits sucrose synthesis, moreover it distinguishes in
photosynthetic toxicity. Whereas high levels of raffinose,
synthesized from sucrose, are present under normal
and/or stressful conditions act as an antioxidant and
together with glucose, fructose and sucrose efficiently
scavenge hydroxyl radicals [25].
In summary, blue light has been shown to be
necessary for non–structural carbohydrates distribution
between radish storage organs and leaves resulting
in hypocotyl thickening. But it was not required for
generative development.
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The impact of red and blue light-emitting diode
illumination on radish physiological indices
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