Abstract
Anthocyanins are secondary metabolites that contribute to red, blue, and purple colors in plants and are affected by light, but the effects of low light on the physiological responses of purple pak-choi plant leaves are still unclear. In this study, purple pak-choi seedlings were exposed to low light by shading with white gauze and black shading in a phytotron. The responses in terms of photosynthetic properties, carbohydrate metabolism, antioxidant enzyme activity, anthocyanin biosynthetic enzyme activity, and the relative chlorophyll and anthocyanin content of leaves were measured. The results showed that chlorophyll b, intracellular CO2 content, stomatal conductance and antioxidant activities of guaiacol peroxidase, catalase and superoxide dismutase transiently increased in the shade treatments at 5 d. The malondialdehyde content also increased under low light stress, which damages plant cells. With the extension of shading time (at 15 d), the relative chlorophyll a, anthocyanin and soluble protein contents, net photosynthetic rate, transpiration rate, stomata conductance, antioxidant enzyme activities, and activities of four anthocyanin biosynthetic enzymes decreased significantly. Thus, at the early stage of low light treatment, the chlorophyll b content increased to improve photosynthesis. When the low light treatment was extended, antioxidant enzyme activity and the activity of anthocyanin biosynthesis enzymes were inhibited, causing the purple pak-choi seedlings to fade from purple to green. This study provides valuable information for further deciphering genetic mechanisms and improving agronomic traits in purple pak-choi under optimal light requirements.
Highlights
Light is one of the most important environmental factors and plays a critical function in plant development and metabolism [1,2]
The chlorophyll b content of TL2 and TL3 leaves greatly decreased at 10 d and 15 d by 9.11% and 51.51% respectively, compared with that of NL leaves at 5 d; the content was 30.30% and 51.42% lower, respectively, at 10 d; and 24.66% and 64.95% lower, respectively, at 15 d
Photosynthetic pigments play an important role in photosynthesis as they can assimilate and transfer light energy
Summary
Light is one of the most important environmental factors and plays a critical function in plant development and metabolism [1,2]. Low light was shown to substantially affect the agronomic traits of plants and inhibit physiological metabolic processes, including photosynthesis and antioxidant characteristics, as well as carbon and nitrogen fixation [3,4,5,6]. It causes slow growth, decrease of leaf weight and flower bud number. Anthocyanins, a class of secondary metabolites, contribute to the red, blue, and purple colors in flowers, fruits, and leaves [20] They act as antioxidants and protect DNA and the photosynthetic apparatus from damage due to high radiation fluxes [21]. The shading of stems and leaves of Eustoma grandiflorum resulted in a significant anthocyanin reduction in petal color [41], while incubation in
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