Effects of Supplemental Lighting on Growth and Medicinal Compounds of Japanese Honeysuckle (Lonicera japonica Thunb.)

Japanese honeysuckle (Lonicera japonica Thunb.) is an evergreen climbing vine, naturally distributed in Japan and East Asia. Its dried buds and leaves are used as a traditional crude drug in Japan and many Asian countries (Pradhan et al., 2009; Wang et al., 2009; Park et al., 2012). In Japan, these drugs are known as ‘Kinginka’ (flower buds) and ‘Nindou’ (leaves). The majority of crude drugs used in Japan, including those produced from Japanese honeysuckle, are imported from overseas, i.e., China, as wild plants. However, the price of crude drugs in China has recently risen due to the increase in prices of farm and natural products, the shortage of labor, and the rise of labor cost (Kang, 2008; 2011). Additionally, the increased demand for crude drugs in China and European countries has caused a severe shortage of crude drug resources (Kang, 2008; Koike et al., 2012). Recently, fresh buds and leaves of Japanese honeysuckle have been recognized as an important medicinal remedy (Kang et al., 2010; Seo et al., 2012) and they are used in the food and cosmetic industries (Dung et al., 2011; Shang et al., 2011) worldwide. The main medicinal compounds in the flower buds of Japanese honeysuckle are polyphenols such as chlorogenic acid and luteolin (Lee et al., 2010). These compounds have numerous functions (Shang et al., 2011), including antiviral, anticancer (Pradhan et al., 2009; Park et al., 2012), anti-inflammatory (Kang et al., 2010), and antioxidant activities (Dung et al., 2011; Ohno et al., 2012; Seo et al., 2012). It is well known that the contents of many secondary metabolites (medicinal compounds) present in fresh plants decrease through the process of drying. Therefore, high concentrations of medicinal compounds in fresh plants of Japanese honeysuckle have been recognized as valuable. However, wild Japanese honeysuckle withers and lacks flower buds during the winter season. A year-round cultivation of Japanese honeysuckle for fresh flower buds and leaves is expected to solve these problems by providing a stable supply of these resources on the world market. Greenhouse cultivation is an effective method for steady production of medicinal plants because, through the control of optimal environmental conditions, plant growth is promoted, harvest period is prolonged, and the quality of medicinal compounds is stabilized. Additionally, the amount of agro-chemicals (pesticides and fungicides) applied during the cultivation of medicinal plants is reduced, resulting in high-quality crude drugs. Furthermore, greenhouse cultivation of Japanese honeysuckle, if possible, will allow altering the concentration and composition of medicinal compounds by controlling the environmental factors. The main flowering season of wild Japanese honeysuckle grown in the fields in China is from May to September (Wang et al., 2009), suggesting that Japanese honeysuckle is neither a short-day nor a long-day plant.