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. 2020 Feb 17;20(1):78.
doi: 10.1186/s12870-020-2282-0.

Photosynthetic characteristics and chloroplast ultrastructure of welsh onion (Allium fistulosum L.) grown under different LED wavelengths

Song Gao  1   2   3   4 , Xuena Liu  1   2   3   4 , Ying Liu  1   2   3   4 , Bili Cao  1   2   3   4 , Zijing Chen  1   2   3   4 , Kun Xu  5   6   7   8
Affiliations

Photosynthetic characteristics and chloroplast ultrastructure of welsh onion (Allium fistulosum L.) grown under different LED wavelengths

Song Gao et al. BMC Plant Biol. .

Abstract

Background: The optimized illumination of plants using light-emitting diodes (LEDs) is beneficial to their photosynthetic performance, and in recent years, LEDs have been widely used in horticultural facilities. However, there are significant differences in the responses of different crops to different wavelengths of light. Thus, the influence of artificial light on photosynthesis requires further investigation to provide theoretical guidelines for the light environments used in industrial crop production. In this study, we tested the effects of different LEDs (white, W; blue, B; green, G; yellow, Y; and red, R) with the same photon flux density (300 μmol/m2·s) on the growth, development, photosynthesis, chlorophyll fluorescence characteristics, leaf structure, and chloroplast ultrastructure of Welsh onion (Allium fistulosum L.) plants.

Results: Plants in the W and B treatments had significantly higher height, leaf area, and fresh weight than those in the other treatments. The photosynthetic pigment content and net photosynthetic rate (Pn) in the W treatment were significantly higher than those in the monochromatic light treatments, the transpiration rate (E) and stomatal conductance (Gs) were the highest in the B treatment, and the intercellular CO2 concentration (Ci) was the highest in the Y treatment. The non-photochemical quenching coefficient (NPQ) was the highest in the Y treatment, but the other chlorophyll fluorescence characteristics differed among treatments in the following order: W > B > R > G > Y. This includes the maximum photochemical efficiency of photosystem II (PSII) under dark adaptation (Fv/Fm), maximum photochemical efficiency of PSII under light adaptation (Fv'/Fm'), photochemical quenching coefficient (qP), actual photochemical efficiency (ΦPSII), and apparent electron transport rate (ETR). Finally, the leaf structure and chloroplast ultrastructure showed the most complete development in the B treatment.

Conclusions: White and blue light significantly improved the photosynthetic efficiency of Welsh onions, whereas yellow light reduced the photosynthetic efficiency.

Keywords: Chloroplast ultrastructure; Light; Photosynthetic characteristics; Welsh onion (Allium fistulosum L.).

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Conflict of interest statement

The authors declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1
a Characteristics of the respective LED irradiance spectra in the different treatments; b the different LED light treatments tested
Fig. 2
Fig. 2
Photosynthetic parameters of Welsh onions under different light conditions, including: a net photosynthetic rate (Pn); b transpiration rate (E); c stomatal conductance (Gs); and d intercellular CO2 concentration (Ci). These photosynthetic parameters were measured under white, blue, red, green, and yellow light for about 5 min each. Values are means of 5 replicates ± SD. Different letters (a, b, c, d) in the same column indicate significant differences among treatments at P ≤ 0.05 according to Duncan’s new multiple range test. W: white light; B: blue light; G: green light; Y: yellow light; R: red light. n = 5
Fig. 3
Fig. 3
Chlorophyll fluorescence parameters of Welsh onions under different light conditions, including: a maximum photochemical efficiency of PSII under dark adaptation (Fv/Fm); b maximum photochemical efficiency of PSII under light adaptation (Fv’/Fm′); c photochemical quenching coefficient (qP); d actual photochemical efficiency (ΦPSII); e apparent electron transport rate (ETR); and f non-photochemical quenching coefficient (NPQ) = 1-(Fm′-Fo’)/(Fm-Fo). Values are means of 5 replicates ± SD. Different letters (a, b, c, d) in the same column indicate significant differences among treatments at P ≤ 0.05 according to Duncan’s new multiple range test. W: white light; B: blue light; G: green light; Y: yellow light; R: red light. n = 5
Fig. 4
Fig. 4
Chlorophyll fluorescence imaging analysis of Welsh onion leaves different light conditions, including the maximum photochemical efficiency of PSII under dark adaptation (Fv/Fm) in them
Fig. 5
Fig. 5
Leaf anatomy of Welsh onions under different light conditions. The fistular lamina of Welsh onion (Allium fistulosum L.) leaves changes from being solid to hollow during development, and the cells around the cavity break up until the remaining 1–2 layers of cells from the palisade layer show cell wall residues (‘arrowheads’) [30]. E: epidermis; PT: palisade tissue; ST: spongy tissue; VB: vascular bundle; W: white light; B: blue light; G: green light; Y: yellow light; R: red light. Scale bars = 50 μm
Fig. 6
Fig. 6
Chloroplast ultrastructure of Welsh onions under different light conditions. Transmission electron microscopy observations of mesophyll cells in Welsh onion leaves exposed to W Light (w1-w3) and B, G, Y, R Light (b1-r3). The bars shown are 10 μm, 2 μm, 1 μm, respectively. The size and arrangement density of chloroplasts could be clearly seen at 10 μm and 2 μm, and the grana lamella and stroma lamella of chloroplasts could be clearly seen at 1 μm. Ch: chloroplast; GL: grana lamella; SL: stroma lamella; white arrow: osmiophilic particles; W: white light; B: blue light; G: green light; Y: yellow light; R: red light
Fig. 7
Fig. 7
RuBPCase activity of Welsh onions under different light conditions. The ribulose-1,5-bisphosphate carboxylase (RuBPCase) activity of RuBisCo was determined using an ELISA kit (Suzhou Keming). Values are means of 5 replicates ± SD. Different letters (a, b, c, d) in the same column indicate significant differences among treatments at P ≤ 0.05 according to Duncan’s new multiple range test. W: white light; B: blue light; G: green light; Y: yellow light; R: red light. n = 5
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