Analytical, Nutritional and Clinical MethodsA novel approach of LED light radiation improves the antioxidant activity of pea seedlings
Introduction
Light is not only an essential energy source for plant but also an important signal influencing the transition from etiolated to de-etiolated state, a stimulus for plant development, biosynthesis of cell components and gene expression throughout the life cycle of a plant (Clouse, 2001, Erdei et al., 2005). The integration, quality, duration and intensity of red light/far red light, blue light, UV-A (320–500 nm) or UV-B (280–320 nm) and hormone signaling pathways have a profound influence on plant by triggering on/off of physiological reactions and control the growth and development of plant (Briggs et al., 2001, Briggs and Olney, 2001, Clouse, 2001, Kevin, 2000).
The advantages of using light-emitting diode (LED) as artificial light source for controlled-environment plant growth applications including high energy-conversion efficiency, using DC power, small volume, longer life, wavelength specific, light intensity/quality adjustable and low thermal energy output (Okamoto et al., 1997, Schuerger et al., 1997). Some crops and flowers have been cultured by LED light radiation such as lettuce (Hoenecke et al., 1992, Okamoto et al., 1996), pepper (Brown, Schuerger, & Sager, 1995), wheat (Goins et al., 1997, Tripathy and Brown, 1995), spinach (Yanagi and Okamoto, 1997, Yanagi et al., 1996), and banana (Duong, Hong, Watanabe, Goi, & Tanaka, 2002). Red light is important for photosynthetic apparatus development and may increase starch accumulation in several plant species by inhibiting the translocation of photosynthesis out of leaves (Saebo, Krekling, & Appelgren, 1995). Blue light is important for chloroplast development, chlorophyll formation and stomata opening (Senger, 1982).
Etiolated seedlings constitute a major component of human diets (including salad, sandwich, Chinese dish and drink), especially as breakfasts and for vegetarians, providing fiber, vitamins and phytonutrients. β-Carotene and chlorophyll synthesized by all plants are components of photosynthesis and serve critical functions in plant biology including light harvesting, quenching of photooxidation, coloring of plants and providing nutritional benefits as precursor of essential vitamins and antioxidants for human beings. Photoinhibition results in many fold increase in the activity of superoxide dismutase and ascorbate peroxidase for protecting the seedlings against photooxidative damage (Sankhalkar & Sharma, 2002). Menezes-Benavente, Kernodle, Margis-Pinheiro, and Scandalios (2004) indicated that expression of antioxidant defense genes would be triggered to defend the cells against oxidative damage.
Recently, far-infrared radiation was reported to facilitate the antioxidant activity of rice hulls (Lee, Kim, Jeong, et al., 2003) and raw and cooked turkey breast (Lee, Kim, Nam & Ahn, 2003), suggesting the light radiation was contributory to the enhancement of nutrients in foods. In this study, red and blue LEDs were first utilized as light sources to understand the effect of LED radiation on the changes of antioxidant activity of radiated pea seedlings.
Section snippets
Materials
Peas (Pisum sativum L.), from Australia for seeding, were purchased from a local supermarket in Pingtung County. Ethanol of 95% (v/v) was the product of Taiwan Tobacco and Liquor Co., Taiwan. Each of acetonitrile, ethyl acetate, tetrahydrofuran, acetone, and acetic acid was HPLC grade and was purchased from Sigma (St. Louis, MO, USA); while trichloroacetic acid, potassium ferricyanide and FeCl2 were from Merck (Darmstadt, Germany). β-Carotene from Calbiochem (Darmstadt, Germany) was used for
Effect of LED on pea sprout growth
Pea seedings are one of popular vegetables in oriental countries and the effects of radiation on pea sprout growth and nutritional changes are rarely studied. The seedlings were 4 days incubated in dark and transferred for different LED light radiation. No difference was observed at stem diameter among dark-grown and light radiated seedlings, but stem length, leaf area and seedling weight were greatly affected by light quality (Table 1). Light radiation induced color change and significantly (p <
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