Effects of Irradiation with Light of Different Photon Densities on the Growth of Young Green Barley Plants

Abstract

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.