Abstract
Mesembryanthemum crystallinum is a succulent, facultative crassulacean acid metabolism (CAM) plant. Plant growth and photosynthetic characteristics were studied when M. crystallinum plants were grown indoor under light emitting diodes (LED)-lighting with adequate water supply. Plants were cultured aeroponically for a 16-h photoperiod at an equal photosynthetic photon flux density of 350 μmol m-2 s-1 under different red:blue LED ratios: (1) 100:0 (0B); (2) 90:10 (10B); (3) 80:20 (20B); (4) 70:30 (30B); (5) 50:50 (50B); and (6)100:0 (100B). M. crystallinum grown under 10B condition had the highest shoot and root biomass and shoot/root ratio while those grown under 0B condition exhibited the lowest values. Compared to plants grown under 0B condition, all other plants had similar but higher total chlorophyll (Chl) and carotenoids (Car) contents and higher Chl a/b ratios. However, there were no significant differences in Chl/Car ratio among all plants grown under different red- and blue-LEDs. Photosynthetic light use efficiency measured by photochemical quenching, non-photochemical quenching, and electron transport rate, demonstrated that plants grown under high blue-LED utilized more light energy and had more effective heat dissipation mechanism compared to plants grown under 0B or lower blue-LED. Statistically, there were no differences in photosynthetic O2 evolution rate, light-saturated CO2 assimilation rate (Asat), and light-saturated stomatal conductance (gssat) among plants grown under different combined red- and blue-LEDs but they were significantly higher than those of 0B plants. No statistically differences in total reduced nitrogen content were found among all plants. For the total soluble protein, all plants grown under different combined red- and blue-LEDs had similar values but they were significantly higher than that of plants grown under 0B condition. However, plants grown under higher blue-LEDs had significant higher ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) protein than those plants grown under lower blue-LED. High Asat and gssat but very low CAM acidity of all M. crystallinum plants during light period, imply that this facultative CAM plant performed C3 photosynthesis when supplied with adequate water. Results of this study suggest that compared to red- or blue-LED alone, appropriate combination of red- and blue-LED lighting enhanced plant growth and photosynthetic capacities of M. crystallinum.
Highlights
Mesembryanthemum crystallinum is a succulent, facultative crassulacean acid metabolism (CAM) plants native to Europe and South Africa
Compared to plants grown under 0B condition, all other plants grown under different combinations of redand blue-light emitting diodes (LED) generally had higher shoot/root ratio fresh weight (FW) and dry weight (DW) with the highest value obtained from 100:0 (0B); (2) 90:10 (10B) treatment (Figures 3C,F)
Plants grown under 0B had lower total Chl (Figure 4A), total Car contents (Figure 4C), and Chl a/b ratio (Figure 4B) by 27, 28, FIGURE 4 | Total Chl content (A), Chl a/b ratio (B), total Car content (C), and Chl/Car ratio (D) of M. crystallinum grown under different combinations of red- and blue-LED lightings for 21 days
Summary
Mesembryanthemum crystallinum (common name: ice plant) is a succulent, facultative crassulacean acid metabolism (CAM) plants native to Europe and South Africa. The edible leaves of the M. crystallinum plants contain high nutritional values and were successfully grown inside greenhouses in Japan and Taiwan under cool temperature The growth of these halophytic plants were mostly studied in different treatments of soil (Winter and Holtum, 2007). The abnormal morphological characteristics were eliminated when red-LED was supplemented with blue light (Bula et al, 1991; Yorio et al, 2001; Nhut et al, 2003; Li et al, 2013; Hernández and Kubota, 2016; Shengxin et al, 2016; Wang et al, 2016). In a recent developed highly energy-efficient laserilluminated growth chamber, Ooi et al (2016) showed that the application of diffused single-wavelength red and blue laser light is adequate for the growth and development of Arabidopsis thaliana
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