Effect of light regime and provenance on leaf characteristics, growth and flavonoid accumulation in Cyclocarya paliurus (Batal) Iljinskaja coppices

Cyclocarya paliurus (Batal) Iljinskaja, commonly called “sweet tea tree” because of the flavor of its leaves, is a sole species from Cyclocarya genus and is widely distributed in sub-tropical regions of China (Fang et al. 2006). Leaves of this plant are traditionally used in China as a medicine or nutraceutical tea (Birari and Bhutani 2007; Fang et al. 2011). Many studies have demonstrated that C. paliurus possesses a variety of bioactivities, including antihypertensive activity, hypoglycemic activity, enhancement of mental efficiency, anticancer, anti-HIV-1, and antioxidant activity (Kurihara et al. 2003; Xie et al. 2010, 2013; Zhang et al. 2010). These beneficial effects have been partly attributed to its content of several chemical components, including proteins, polysaccharides, triterpenoids, flavonoids, steroids, saponins, phenolic compounds, and minerals (Xie et al. 2010, 2013; Li et al. 2011; Fang et al. 2011). Owing to its multiple beneficial effects on human health, a huge production of leaves is required for C. paliurus tea production and for medical use. However, most studies on C. paliurus were focused on extraction procedures and low molecular weight substances, such as triterpenoids, flavonoids, steroids, saponins, and other compounds present in this plant, whereas less attention was paid to the silvics of the species (Deng et al. 2012, 2015).

Flavonoids are a large group of phenolic constituents of plants, and the bioavailability of flavonoids varies greatly among different subgroups and compounds (Erlund 2004). Some beneficial bioactivities of flavonoids have been proved, such as antibacterial, anticarcinogenic, antioxidant, antimutagenic, anti-inflammatory, antiallergic, antiobesity, and antidiabetic activities (Peterson and Dwyer 1998; Erlund 2004; Zhang et al. 2010). Quercetin and its glycoside derivatives, such as isoquercitrin, have been found to promote human health through cytoprotective effects, including reducing lipid peroxidation, protein carbonylation and radical oxygen species (ROS) production (Ciancolini et al. 2013; Palazzolo et al. 2012), while kaempferol was found to have remarkable antioxidant potential and has the capacity to lower the risks of coronary heart disease (Schmidt et al. 2010). According to Iwashina (2000), biosynthesis of flavonoids is mostly carried out by plant, with a few exceptions of animals and fungi.

The content of phytochemicals in plants is affected by numerous internal and external factors that occur during the growing period (Graham 1998; Björkman et al. 2011; Cui et al. 2013; Liu et al. 2015). Thus, factors influencing the phytochemical content and profile in the production of plants are worth considering for improved cultivation. Recently, attempts have been made to develop plantations of C. paliurus as a functional food or ingredient to be used in traditional Chinese medicine. Fang et al. (2011) investigated the genetic and temporal variations in the flavonoid (quercetin, kaempferol, and isoquercitrin) content in leaves of C. paliurus, while Deng et al. (2012) explored the effects of environment and fertilization on growth and flavonoid content of C. paliurus. Xie et al. (2015) had examined the effects of plant growth regulating substances on growth and phytochemical content of C. paliurus leaves. Björkman et al. (2011) indicated that factors that influence plant growth and phytochemical content may interact, and it is now possible to design multifactorial experiments that simulate their combined effects. However, very little is known about the influences of interaction between genetic and environmental factors on plant growth and phytochemical contents of C. paliurus leaves, especially the mechanism of flavonoid accumulation in C. paliurus plants.

For these reasons, it is necessary to investigate the integrated influences of provenance and light intensity on plant growth, leaf characteristics, accumulation of total flavonoid and key health promoting flavonoids (quercetin, kaempferol, and isoquercitrin) in the leaves of C. paliurus. The information provided by this study would be of great value for understanding the light-regulating mechanism for different provenances of C. paliurus, and contribute to establishing optimal cropping strategies for C. paliurus plants.