Light quality affects the proliferation of in vitro cultured plantlets of Camellia oleifera Huajin

Abstract

Background: Camellia oleifera is an important oil-yielding woody plant native to China. Tea oil extracted from the seeds is rich in health-beneficial compounds. Huajin is a high-yielding elite variety of C. oleifera, with large fruits and remarkable resilience, widely cultivated in southern China; however, its seedling quality tends to be uneven. At present, techniques such as grafting, and cuttings are primarily adopted to propagate C. oleifera. These approaches are susceptible to environmental constraints owing to the long growth period, resulting in the lack of C. oleifera seedlings. Methods to make the cultivation more economical are warranted; this can be facilitated by tissue culture technology to provide good-quality seedlings in a short time.

Methods: In vitro cultured plantlets of C. oleifera Huajin were exposed to red light (RL), blue light (BL), red:blue light at a 4:1 ratio (R4:B1), and red:blue light at a 1:4 ratio (R1:B4); white light (WL) was used as the control treatment. To investigate the influence of light spectral quality on the proliferation coefficient, photosynthetic pigments, soluble proteins, plant height, leaf shape, Rubisco enzyme activity, and stomata and leaf anatomical features.

Results: The highest proliferation coefficient was observed under combined red and blue (4:1) light. In addition, this treatment resulted in the second highest chlorophyll content, the thickest palisade and spongy tissues, and consequently, the thickest leaves. The same treatment resulted in the second highest stomatal density, albeit concomitantly with the smallest average stomatal length and width.

Discussion: These results indicate that high-quality propagation of Huajin shoots can be achieved by culturing the plants in vitro under a combination of red and blue (4:1) lights. Previous studies have shown that red and blue lights improve rooting and transplanting rates of tissue culture seedlings. Hence, future research should focus on the effect of light quality on rooting and transplanting of tissue culture plantlets of Huajin and its specific molecular mechanisms.

Keywords: Camellia oleifera; In vitro culture; Light quality; Light-emitting diode; Proliferation.

Figure 1. Spectral distribution of LED light sources utilised (data obtained using a Hopocolor OHSP-350SF Spectral Colour Luminance Meter).

Each line indicates the wavelength of the test light quality. WL is white light, R4:B1 is red:blue ratio is 4:1; BL is blue light, R1:B4 is red-blue 1:4; RL is red light.

Figure 2. Growth of Huajin tissue-cultured plantlets under various light treatments.

(A) White light (WL, control); (B) red and blue (R4:B1); (C) blue light (BL); (D) red and blue (R1:B4); (E, F) red light (RL). Scale bar = 1 cm.

Figure 3. Stomatal growth under various light treatments.

(A) White light (WL); (B) red:blue (R4:B1); (C) blue light (BL); (D) red:blue (R1:B4); (E) red light (RL). Scale bar = 50 µm.

Figure 4. Leaf anatomy. Cross-section of the middle part of the leaf blade of Camellia oleifera cultured under light of different spectral quality, photographs were taken at 20 × magnification.

Photographs were taken at 20 × magnification. (A) White light (WL); (B) red:blue (R4:B1); (C) blue light (BL); (D) red:blue (R1:B4); (E) red light (RL). UE, upper epidermis; LE, lower epidermis; PT, palisade mesophyll tissue; ST, spongy mesophyll tissue. Scale bar = 50 µm.