In recent years, young green barley has been increasingly used as a functional food ingredient. Studies have shown that cultivated young green barley has different levels of amino acids, vitamin C, and polyphenol content depending on the harvest time. Furthermore, some studies have investigated the effect of the growing conditions on cultivated barley in particular the use of light-emitting diodes (LED). Young green barley was exposed to three light sources of different wavelengths (sun light [ASL], light-emitting diode[LED] - Red 9 + Blue 1 [LED-R9:B1], LED - Red 4 + Green 1+ Blue 1 [LED-R4: G1:B1]). Under light with photon densities of 200 μmolmL-2·s-1, the dry weight of young green barley was not affected, while the differences were observed in the morphology of the underground portion of the plant (roots) depending on the light source. The roots of the plant grown in ASL weighed twice as much as those that were grown under LED irradiation. Furthermore, LED irradiation caused an increase in the amino acid content in plants; the amino acid content of plants grown under LED-R9:B1 was twice as much as that grown under ASL irradiation. Four kinds of cyanogenicglucosides (CGs) were isolated, identified, and their levels were measured. The plant grown under LED-RGB irradiation, including LED-G, produced approximately 20% more CGs as compared to the plants grown under the other two light sources. Thus, it was inferred that young green barley exhibited a stress response under LED-G light and accumulated CGs in the stems and leaves with prepare for any damage that may occur on the leaf surface. The nitrogen (N) content in the root was the lowest, while the CG content was the highest in the plant grown under LED-RGB irradiation. It is inferred that the N content decreased because N was eliminated from the roots to allow for accumulation of CGs response to stress. In general, the growth experiments to use an irradiation condition in which the distance between the light source and plant floor is fixed. It is not clear whether the photon density level received by the top leaves is fixed according to plant growth, by changing the height of plant growing shelf. Therefore, against this background, when the photon density was increased from 200 to 300 μmolmL-2·s-1 under ASL irradiation, only a minimal change was observed in the root weight, while the weight of the part of the plant above the ground surface (stems and leaves) increased by approximately 30%, with a 10% increase in the amino acid content.
In recent years, young green barley has been increasingly used as a functional food ingredient. The majority of studies on young green barley plants have focused on the antioxidant activity of secondary metabolites, such as phenolic compounds, whose primary components are flavonoids including saponarin and lutonarin [
Some studies have reported that there is a correlation between cyano glucoside (CGs) content and N content [
Our previous research showed that the amino acid content in plants increased when they were grown under LED-R9:B1 irradiation compared with that under natural sunlight and that the difference observed under the two light sources was related to the amount of amino nitrogen accumulated as well as the amount of CGs [
It is common, however, for growth experiments to use an irradiation condition in which the distance between the light source and plant floor is fixed. It is not clear whether the photon density level received by the top leaves is fixed according to plant growth, by changing the height of plant growing shelf. Therefore, against this background, we examined the effects of different irradiation conditions i.e., artificial sun light (ASL), LED-R9:B1, and LED-R4:G1:B1 under controlled same photon densities, on the growth and morphology of cultivated barley plants.
Two-rowed barley (Hordeum vulgare f. distichon) Nishinohoshi was harvested in 2014. Seeds were sown in planters (41 cm × 20 cm, soil area 820 cm2) containing organic fertilizers (SHOEI, Miyazaki, Japan) in a biotron growth chamber at 15˚C - 20˚C, 70% relative humidity.
LEDs (Model 3LH-256; Nippon Medical and Chemical Instrument Co., Ltd., Japan) tested in biotron chamber were shaded by an aluminum sheet. Artificial Sun-Lights (ASL: Model DR400/TL; Toshiba Lighting & Technology Components Corporation Ltd., Japan) was used as a control light in biotron growth chamber. Young green barley plants were divided into three groups, one group was the artificial sun-light (control group), and the other two groups were as treatment groups, first group growth under a mixture of 90% red + 10% blue LEDs light (LED-RB) and the second group growth under a mixture of 80% red + 10% green + 10% blue LEDs light (LED-RGB) (treatment groups). In the growth chamber the photoperiod was 12 h and 12 h dark per day during the whole experiment. Each group was harvested on the 5th, 10th day after germination, and the plant height and weight were quantified as growth parameters.
The three light sources were artificial sun light, LED-RB and LED-RGB. Red, green and blue LEDs have a peak emission at 660 nm, 550 nm and 450 nm, receptivity. ASL planters were placed on 85 cm steel shelves under ASL light in the biotron. Each LEDs light source was set at 20 cm from the surface of the planter soil. Photon density was measured (Model-101EG, Nippon Medical and Chemical Instrument Co., Led., Japan) at soil level of each planter. Response to the growth of the young green barley, adjustment once a day the position of the planter that the light intensity of three light sources were setting at 200 or 300 μmol ml−2・s−1 over the top of shoots, respectively.
Amino acids (except for tryptophan) in the young green barley plants on 15th day after germination cultivated under the three light sources were determined by a JLC-500/V automatic amino acid analyzer (JEOL Co., Ltd., Japan), and tryptophan in the young green barley was measured by an LC-20AD solvent delivery unit (Shimadzu Corporation, Ltd., Japan). The sample dry weight of ASL light plants (n = 207) was 4.6g, that of LED-RB plants (n = 358) was 7.2 g, and that of LED-RGB plants (n = 226) was 4.1 g.
The young green barley cultivated under three light sources was extracted with 30% Methanol, and extracts were subjected to MCI gel CHP-20P (75 - 150 μm, Mitsubishi Kasei Co., Japan) column chromatography and eluted with water and 10% methanol. Osmaronin and epidermin were obtained from 10% methanol fraction. Methanol eluted fractions were subjected to ODS column chromatography and eluted 5%, 7%, and 100% methanol. Epiheterodendrin was obtained from the fractions eluted with 5%, 7% methanol. Sutherlandin was obtained from fractions eluted with 5% methanol. Structures of these compounds were elucidated on the basis of 1H-NMR (JEOL, 500 MHz) and 13C-NMR (JEOL, 125 MHz) spectral data and with literature values [
No significant difference was found in the growth of the aboveground part of plants, such as stems and leaves (data not shown); however, distinct differences were found in the morphology and dry weight of roots (
Dry weight (g) | ||||
---|---|---|---|---|
RB-LEDs (200a) | RGB-LEDs (200a) | ASL (200a) | ASL (300a) | |
Leaves | 21.66 | 24.42 | 25.74 | 33.37 |
Roots | 6.71 | 6.51 | 13.02 | 12.26 |
a. The photon density of unit was μmol mL−2・s−1.
The amino acid content in barley grown under LED-RB irradiation was twice the amount of that in plants grown under ASL irradiation, and those grown under RGB irradiation had 1.5-fold higher amino acid content than that in the ASL-irradiated plants. A significant increase in amino acid content was found in plants grown under both LEDs compared with the plant grown under ASL irradiation (
Some studies conducted on corn plants have reported that CGs are involved in cell defense and can counter light stress [
Amino acid contents (g/100g dry weight) | ||||||
---|---|---|---|---|---|---|
ASL | RB-LEDs | RGB-LEDs | RB-LEDs | RGB-LEDs | RB-LEDs | |
ASL | ASL | RGB-LEDs | ||||
Arginine | 0.59 | 1.20 | 0.86 | 2.0 | 1.5 | 1.4 |
Lysine | 0.75 | 1.46 | 1.06 | 1.9 | 1.4 | 1.4 |
Histidine | 0.27 | 0.59 | 0.40 | 2.2 | 1.5 | 1.5 |
Phenylalanine | 0.59 | 1.09 | 0.87 | 1.8 | 1.5 | 1.3 |
Tyrosine | 0.40 | 0.77 | 0.59 | 1.9 | 1.5 | 1.3 |
Leucine | 0.93 | 1.74 | 1.33 | 1.9 | 1.4 | 1.3 |
Isoleucine | 0.47 | 0.91 | 0.67 | 1.9 | 1.4 | 1.4 |
Methionine | 0.23 | 0.41 | 0.31 | 1.8 | 1.3 | 1.3 |
Valine | 0.65 | 1.20 | 0.94 | 1.8 | 1.4 | 1.3 |
Alanine | 0.76 | 1.37 | 1.09 | 1.8 | 1.4 | 1.3 |
Glycine | 0.64 | 1.13 | 0.90 | 1.8 | 1.4 | 1.3 |
Proline | 0.55 | 1.01 | 0.79 | 1.8 | 1.4 | 1.3 |
Glutamic acid | 1.08 | 2.26 | 1.59 | 2.1 | 1.5 | 1.4 |
Serine | 0.54 | 0.97 | 0.76 | 1.8 | 1.4 | 1.3 |
Threonine | 0.54 | 1.04 | 0.80 | 1.9 | 1.5 | 1.3 |
Aspartic acid | 1.07 | 2.24 | 1.71 | 2.1 | 1.6 | 1.3 |
Tryptophan | 0.23 | 0.41 | 0.36 | 1.8 | 1.6 | 1.1 |
Cystine | 0.16 | 0.26 | 0.23 | 1.6 | 1.4 | 1.1 |
Moisture content (%) | 91.7 | 93.0 | 93.0 |
CGs | CGs contents (mg/100g fresh weight) | ||
---|---|---|---|
ASL | RB-LEDs | RGB-LEDs | |
Epiheterodendrin (1) | 12.3 | 14.5 | 19.4 |
Osmaronin (2) | 30.1 | 10.7 | 27.9 |
Sutherlandin (3) | 38.7 | 38.4 | 36.9 |
Epidermin (4) | 3.1 | 16.9 | 16.2 |
Total CGs (mg/100g) | 84.1 | 80.4 | 100.4 |
The percentage of total N content in young green barley was almost the same in plants grown under LED-RB and LED-RGB irradiation, while that in plants grown under ASL was approximately 70% of that in the LED condition (
Under ASL irradiation, differences in the growth of barley plants were compared when the photon density received at the tip of the longest leaf was controlled as 200 μmol mL−2・s−1 and 300 μmol mL−2・s−1. By increasing the photon density as 200 μmol mL−2・s−1 to 300 μmol mL−2・s−1, the plant growth rate increased by 4.2% and the weight increased by 15.8% on the day 10 (data not shown), and the amino acid content increased by 10% at a higher photon density level (
Nitrogen contents (g/100g dry weight) | |||
---|---|---|---|
ASL | RB-LEDs | RGB-LEDs | |
Total nitrogen | 1.9 | 2.8 | 2.6 |
Nitrogen contents (mg/1g dry weight) | |||
---|---|---|---|
ASL | RB-LEDs | RGB-LEDs | |
Leaves | 20.6 | 30.3 | 26.2 |
Roots | 9.2 | 12.9 | 9.5 |
Roots/leaves (%) | 44.7 | 42.6 | 36.3 |
Amino acid contents (g/100g dry weight) | |||
---|---|---|---|
ASL 200 μmol mL−2・s−1 | ASL 300 μmol mL−2・s−1 | ASL 300 | |
ASL 200 | |||
Arginine | 0.59 | 0.67 | 1.1 |
Lysine | 0.75 | 0.77 | 1.0 |
Histidine | 0.27 | 0.29 | 1.1 |
Phenylalanine | 0.59 | 0.66 | 1.1 |
Tyrosine | 0.40 | 0.45 | 1.1 |
Leucine | 0.93 | 1.03 | 1.1 |
Isoleucine | 0.47 | 0.51 | 1.1 |
Methionine | 0.23 | 0.23 | 1.0 |
Valine | 0.65 | 0.72 | 1.1 |
Alanine | 0.76 | 0.82 | 1.1 |
Glycine | 0.64 | 0.70 | 1.1 |
Proline | 0.55 | 0.60 | 1.1 |
Glutamic acid | 1.08 | 1.26 | 1.2 |
Serine | 0.54 | 0.58 | 1.1 |
Threonine | 0.54 | 0.60 | 1.1 |
Aspartic acid | 1.07 | 1.16 | 1.1 |
Tryptophan | 0.23 | 0.28 | 1.2 |
Cystine | 0.16 | 0.18 | 1.1 |
Moisture content (%) | 91.7 | 90.8 |
A significant morphological difference was observed in the underground part (root) of barley grown under ASL and LED irradiation, both of which had the same photon density. The amount of root growth under ASL irradiation was twice the amount of that under LED irradiation (
Amino acid content in young green barley grown under LED-RB irradiation was twice that of the plant grown under ASL irradiation, and 1.4 times more than that under LED-RGB irradiation, in which both the ASL and LED-RB irradiation had the same photon density at 200 μmol mL−2・s−1. Our previous report [
It was revealed that cultivation under LED irradiation caused an increase in the amount of amino acid content; however, some studies using corn plants have showed that cultivation under a limited range of wavelengths is stressful for the plant [
Meanwhile, Selmar et al. suggested that CGs may play an important role in primary metabolism as an N and glucose transporter [
It became clear that LED-RB was more effective at increasing amino acid synthesis in barley cultivation, compared with ASL, which imitates natural sun light, and LED-RBG whose wavelength is similar to that of sun light. The reason why the CG content was lowest in the plant grown under the LED-RB irradiation, was probably because the limited range of the LED-RB wavelength was stressful to barley plant, and as a result, amino acid content increased.
To clarify the effect of photon density on the growth of young green barley, a growth test was conducted under different photon densities, which were set as 200 and 300 μmol mL−2・s−1. The increases in the growth (4.2%) and the weight (15.8%) were found under irradiation where the photon density was increased by 100 μmol mL−2・s−1. Furthermore, the amino acid content increased by 10%. This result is consistent with that observed in rice plants, in which an increase in photon density brought about an increase in N content in rice leaf under LED-R9: B1 irradiation [
In barley cultivation, LED irradiation inhibited root growth, which accounted for the underground part of the plant. A significant increase in amino acid content was found in plants grown under both LEDs compared with the plant grown under ASL irradiation. And comparing the CG content in plants grown under different light sources, the CG content under LED-RB irradiation was approximately 20% less than that under LED-RGB irradiation, and approximately 4% less than that under ASL irradiation. The N contents of young green barley grown under the three sources of light irradiation were compared. It was supposed that the N content increased as plants degraded CGs to counter the light stress induced under LED-RB light, and that N accumulated in the stems and leaves through this process.