Blue Light-emitting Diode Light Irradiation of Seedlings Improves Seedling Quality and Growth after Transplanting in Red Leaf Lettuce

Abstract

<jats:p>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<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup> of blue light, simultaneous irradiation with 50 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup> of blue light and 50 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup> of red light, and 100 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup> 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 <jats:italic>a</jats:italic>/<jats:italic>b</jats:italic> 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.</jats:p>

Species-specific differences in synthesis of flavonoids and phenolic acids under increasing periods of enhanced blue light

“…Total phenols, chlorogenic acid and anthocyanin concentrations in the seedlings of this cultivar were found to be significantly higher under bluecontaining LEDs (Johkan et al, 2010). There may exist a direct link between blue light biosynthesis of certain phenylpropanoids through photosynthesis.…”

Growth and antioxidant phenolic compounds in cherry tomato seedlings grown under monochromatic light-emitting diodes

“…In general, red light is known to play an important role in developing photosynthetic organs as well as leaf expansion, while blue light induces biomass accumulation, chloroplast formation, and increasing leaf thickness (Johkan et al, 2010;Saebo et al, 1995). Therefore, red and blue wavelengths of lights are essential for photosynthesis.…”

“…Tomato seedlings undergo both vegetative and reproductive growth at the same time so that the seedlings stage crucially affects the growth and yield of fruit of tomato plants (Buwalda et al, 2006). Moreover, sound seedlings can be well adapted when they are transplanted in fields or greenhouses (Johkan et al, 2010). To produce high-quality seedlings, control of environmental conditions, using proper growing medium, and cultural management skills are required.…”

Light signaling and plant responses to blue and UV radiations—Perspectives for applications in horticulture

“…Nevertheless, when blue light is present with other wavelengths, chl content tends to increase with the proportion of blue light in plant lighting (Hernández and Kubota, 2014;Hogewoning et al, 2010;Matsuda et al, 2007;Yorio et al, 2001). Independently of species, both monochromatic blue light and higher proportion of blue light in plant lighting tend to increase the chl a/b ratio (Abidi et al, 2013;Hogewoning et al, 2010;Johkan et al, 2010;Kopsell and Sams, 2013;Matsuda et al, 2007;Ohashi-Kaneko et al, 2007;Wang et al, 2014). When plants are exposed to UV-B radiations, chl content decreases (Nedunchezhian and Kulandaivelu, 1997;Ziska et al, 1993) due to high decrease in chlorophyll a content and, consequently, in chl a/b ratio (Lidon and Ramalho, 2011).…”