Results
Light quality influenced the vegetative growth parameters of potato plantlets in vitro. Light treatments with mixtures of RB or RBG were more beneficial to the vegetative growth of potato plantlets in vitro than the FL treatment (Table 2, Fig. 1). Moreover, the addition of G to the composite spectrum of R and B was favorable for the vegetative growth of potato plantlets in vitro and increased stem diameter, leaf area, DM, health index and root activity (Table 2, Fig. 1). Stem height under R630B and R660B was significantly lower than that under FL, but stem height under R630BG and R660BG approximated stem height under FL, indicating that the addition of G contributed to increased stem height.The combined spectra containing R660 was better for the vegetative growth of potato plantlets in vitro than that containing R630.The combined spectra R660B and R660BG significantly increased leaf area, SLM, health index, and root activity (Table 2, Fig. 1).Chl accumulation in potato plantlets in vitro was significantly influenced by light quality, and the addition of G promoted Ch lac cumulation (Fig. 2). In addition, the highest Chla, Chlb, and total Chl contents were found in the R660BG treatment, which indicated that the combined spectrum containing R660was more favorable for Chl accumulation than R630in potato plantlets in vitro.The soluble sugar, soluble protein, and starch contents in potato plantlets in vitro were significantly higher in all of the LED treatments than under FL (Fig. 3). The addition of G promoted the accumulation of carbohydrates and proteins. The highest soluble sugar, starch and soluble protein contents were observed in the R660BG treatments; a result suggesting the combined spectrum Fig containing R660 enhanced the accumulation of carbohydrates and proteins more than R630in potato plantlets in vitro.The greatest stomata density of potato plantlets in vitro was under FL (56 mm−2) followed by R630B (48 mm−2) and R660B(46 mm−2), and the lowest value was observed in the R660BG treatment (Table 3). The stomata of potato plantlets in vitro in the FL treatment were elliptical in shape and small in size, while the stomata under R630BG and R660BG treatments were elliptical in shape with a narrower pore and were larger in size than under FL (Fig. 4).Under R660BG, a clearly defined upper epidermis developed in the leaves. In addition, the palisade cells were neatly arranged under R630BG and R660BG. The spaces between the spongy mesophyll cells in potato leaves were the smallest under R660BG.Compared with the combined spectrum containing G (R630BG and R660BG), the palisade cells were arranged more loosely, and the spaces between the spongy mesophyll cells were larger under the spectra of RB (R630B and R660B). In the FL treatment, a less conspicuous upper epidermis and loosely arranged palisade cells were observed, and the largest spaces were between the palisade cells