Addition of White Light to Monochromatic Red and Blue Lights Alters the Formation, Growth, and Dormancy of In Vitro-grown Solanum tuberosum L. Microtubers

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  • 1 College of Agriculture, Nanjing Agricultural University, Nanjing 210095, China

Monochromatic light and wide-band white light both affect plant growth and development. However, the different effects between monochromatic light and addition white light to monochromatic light on the formation, growth, and dormancy of microtubers have not been fully explored. Therefore, we evaluated these effects using in vitro potatoes grown under pure blue and red lights and a combination of blue light and red light supplemented with white light, respectively. Current results suggested that light spectra influenced microtuber formation, growth, and dormancy by regulating potato plantlet morphogenesis, affecting the synthesis and transportation of photosynthetic metabolites, and altering the accumulation and distribution of biomass in various plant tissues. Monochromatic lights and the combined spectra had differing effects. For instance, monochromatic red light induced the growth of more microtubers, whereas addition white light to red light decreased number but increased weight of microtubers. Meanwhile, monochromatic blue light facilitated tuber growth, whereas addition white light to blue light decreased microtubers weight but increased microtuber number. In addition, composite lights of addition white light to monochromatic red and blue lights both extended the dormancy period, and monochromatic blue light shortened the dormancy period of microtubers >300 mg. Therefore, in microtuber agricultural production, specific light conditions may be applied at different growth stages of in vitro potatoes to increase the number of effective microtubers (>50 mg) and to satisfy storing requirement of seed microtubers.

Abstract

Monochromatic light and wide-band white light both affect plant growth and development. However, the different effects between monochromatic light and addition white light to monochromatic light on the formation, growth, and dormancy of microtubers have not been fully explored. Therefore, we evaluated these effects using in vitro potatoes grown under pure blue and red lights and a combination of blue light and red light supplemented with white light, respectively. Current results suggested that light spectra influenced microtuber formation, growth, and dormancy by regulating potato plantlet morphogenesis, affecting the synthesis and transportation of photosynthetic metabolites, and altering the accumulation and distribution of biomass in various plant tissues. Monochromatic lights and the combined spectra had differing effects. For instance, monochromatic red light induced the growth of more microtubers, whereas addition white light to red light decreased number but increased weight of microtubers. Meanwhile, monochromatic blue light facilitated tuber growth, whereas addition white light to blue light decreased microtubers weight but increased microtuber number. In addition, composite lights of addition white light to monochromatic red and blue lights both extended the dormancy period, and monochromatic blue light shortened the dormancy period of microtubers >300 mg. Therefore, in microtuber agricultural production, specific light conditions may be applied at different growth stages of in vitro potatoes to increase the number of effective microtubers (>50 mg) and to satisfy storing requirement of seed microtubers.

Potato tuber is rich in starch, proteins, and other important nutrients, making potato (Solanum tuberosum L.) one of the most important staple food and vegetable crops (Abelenda et al., 2019). However, potato crops are susceptible to viral and fungal infections, resulting in yield loss and crop quality deterioration (Chen et al., 2018). The production of virus-free microtubers in sterile environments may reduce the risk of viral infection (Park et al., 2009). The morphogenesis of potato plantlets and the subsequent growth of microtubers are influenced by light (Halterman et al., 2016). However, the artificial light environments for the production of seed microtuber in the sterile environments have not been fully explored.

It has been reported that monochromatic red and blue lights regulate the formation and growth of microtuber (Aksenova et al., 1989; Chen et al., 2018; Fixen et al., 2012). However, studies have yielded inconsistent or contradictory results regarding the effects of red light and blue light on microtuber formation and growth, which may be attributed to differences in the variety, intensity, and peak wavelength of lights used, resulting in a puzzling application in microtuber production. The research has reported that white light is conductive to the growth of cattleya hybrid (Cybularz-Urban et al., 2007), lettuce (Hunter and Burritt, 2004), and spinach (Toledo and Ueda, 2003) and beneficial for photosynthesis because more light could penetrate through the canopy to lower leaves compared with red and blue lights (Park et al., 2013). In addition, white light-emitting diode (LED) can also increase the fresh weight of individual microtuber (Chen et al., 2018). However, little attention is paid to the studies of addition white light to monochromatic light on microtuber formation and growth, and further research is required.

The yield of microtubers is directly determined by the quality of potato plantlets, and increased biomass in potato plantlets helps to induce high yield and quality of microtubers (Pelacho and Mingo-Castel, 1991). Furthermore, the carbohydrates produced by potato plantlets are an important material source for the growth of plantlets and microtubers. Tuberization is also known to be regulated by the availability of carbohydrates—in particular, sucrose, the transported form of sugar, required for starch synthesis (Abelenda et al., 2019). In addition, the distribution and transportation of sugar among leaves, stems, and microtubers regulates microtuber formation and growth. However, few studies have investigated this process in detail.

A shorter dormancy period is vital for potato production at sites restricted by short growing seasons (Eremeev et al., 2008), a longer dormancy is used to limit sprout growth during long-term storage of seed tubers for the subsequent season (Mølmann and Johansen, 2019). Therefore, the quantification of microtuber dormancy is necessary for potato production. Tuber dormancy is related to the size and dry matter content of the microtubers, thus determining storage behavior and sprouting potential (Haverkort et al., 1991). The environmental conditions to which the mother plant is exposed often affect seed dormancy (Zhao, 1995). When Arabidopsis is grown under a high ratio of red-to-far-red light (R/FR), seeds are able to germinate in the dark; however, when grown under a lower R/FR, seeds only germinate under light (Zhao, 1995). The preceding studies show that microtuber dormancy is related to the light environment of mother plant. However, how light spectra influence on microtuber dormancy period after harvesting has not been reported. The sugar content at harvest is one of the important parameters determining the maturity and sprouting vigor of seed potato (Rees and Morrell, 1990) and has a strong effect on crop performance (Donnelly et al., 2003). Whether light spectra influence on sugar content of microtuber and then change the dormancy period is not yet well known.

The preceding issues led us to hypothesize that the addition of white light to monochromatic red and blue lights could alter the formation, growth, and dormancy of microtubers, so we grew potato plantlets under four light spectra provided by LEDs to evaluate the formation, growth, and dormancy of potato microtubers. To assess the effects of the lights, the number, weight, and dormancy period of microtubers were observed. Biomass accumulation and distribution and carbohydrate levels of the potato plantlets and microtubers throughout microtuber production were also measured to assess the regulatory mechanism for microtuber formation, growth, and dormancy induced by different light spectra.

Materials and Methods

Plant materials and growth conditions.

The experiment was conducted in a tissue culture chamber at Nanjing Agricultural University, Nanjing, China. Solanum tuberosum L. cv. Favorita is one of the major varieties in China and is sensitive to light variation and was therefore used in this experiment. Potato plantlets were cut into 1- to 1.5-cm segments with a piece leaf and then inoculated into Murashige and Skoog medium (8% sucrose, 0.9% agar) in tissue culture bottles (the internal diameter and height of the bottle are 63 mm and 85 mm, respectively). There were five stem segments in each bottle and 200 bottles in total. These in vitro shoots were irradiated with white fluorescent lamps for the first 3 d, and then 180 bottles selected from the 200 bottles were divided into four groups for exposure to light spectra provided by LEDs (Opt-run Biotechnology Co., Nanjing, China): blue light with a peak wavelength of 460 nm (B460), composite light of white light and B460 (B460W), red light with a peak wavelength of 660 nm (R660), and composite light of white light and R660 (R660W). The total photosynthetic photon flux density (PPFD) of all light treatments was set to 65 µmol·m−2·s−1, where the PPFD of white light accounted for 20 µmol·m−2·s−1 in the treatments of B460W and R660W. Each treatment consisted of 45 bottles. The spectral distributions of white, blue, and red lights are shown in Fig. 1 and were measured by a spectroradiometer (OPT-2000; ABDPE Co., Beijing, China). The in vitro plantlets were grown under an 8-h light/16-h dark photoperiod, day/night temperatures of 22 ± 2 °C/18 ± 2 °C, a relative humidity of 75 ± 5%, and a CO2 concentration identical to that of the outdoor atmosphere.

Fig. 1.
Fig. 1.

Spectral distribution of white, blue, and red lights. PPFD = photosynthetic photon flux density.

Citation: HortScience horts 55, 1; 10.21273/HORTSCI14548-19

Morphology and dry weight determination.

Potato plantlets from three bottles of each treatment were randomly selected to measure plant height, stem diameter, leaf number, and microtuber number using standard methods. Plant height was measured using a ruler from the main stem base to the top of the plantlets. Using a vernier calipers (601-01; Links Inc., Harbin, China) to measure the diameter of the internode between the lower two leaves as stem diameter. All leaves, stems, and microtubers were dried at 80 °C to a constant weight, cooled to room temperature, and weighed with an electronic balance (LS 120 A, Precisa Gravimetrics AG, Dietikon, Switzerland) as dry weight. After weighing, the dry samples were used for determination of the carbohydrate.

Carbohydrate measurements.

The soluble sugar and starch content were measured using the anthrone method, and sucrose content was determined using the resorcinol method (Fairbairn, 1953; Martin et al., 2000).

Dormancy period determination.

The microtubers induced by different lights were classified and then placed into darkness at a temperature of 22 ± 2 °C after harvesting on day 90 of growth. Microtubers were checked every day for sprouts, and each group contained nine samples. Germination dates were recorded, and the elapsed time between harvest and germination was recorded as the dormancy period.

Statistical analysis.

After 20, 40, 60, 80, and 90 d of light irradiation, we randomly took the bottles first and then randomly took the plantlets from nine bottles per treatment at 09:00 on each date for analysis and measurement. Each measurement was repeated three times. The effects of light spectra were compared by analysis of variance using SPSS, version 20.0 (IBM, Armonk, NY) followed by Duncan’s test at P < 0.05 level. The correlations of between sugar contents and dormancy period of microtuber were determined on treatment means by Pearson’s correlation coefficient. The figures were mapped using Origin 2016 software (OriginLab, Northampton, MA).

Results

Microtuber number, weight, and size distribution.

As indicated in Table 1, the number of microtubers per bottle and per plantlet, and effective microtubers (those >50 mg) per bottle and per plantlet were higher under R660 than under R660W, whereas those parameters were higher under B460W than under B460. The effective microtuber rate under B460 was 100% and the highest. These results showed that red light favored a larger number of microtubers compared with blue light, and monochromatic red light seemed to be more effective in inducing microtubers than composite light of addition white light to monochromatic red light.

Table 1.

Effects of different light spectra on the number, weight, and size distribution of microtubers.

Table 1.

The microtuber weight per bottle, average microtuber weight, and effective average microtuber weight were higher under B460 than under B460W, R660, and R660W. Furthermore, the weight of microtuber was higher under B460 than under B460W. These indicators were the lowest under R660. These results indicate that monochromatic blue light favored the growth of microtubers. Furthermore, B460 clearly helped induce larger tuber-shaped potatoes, whereas B460W reduced the percentage of microtubers >300 mg compared with B460, confirming that blue light is important to induce large tuber-shaped potatoes and that the effect of blue light can be disturbed by white light. However, the percentages of microtubers >300 mg increased by R660W compared with R660. Under B460W, R660, and R660W, 11.2%, 4.8%, and 5.0% of microtubers were <50 mg, respectively. Conversely, virtually no microtubers <50 mg occurred under B460.

Microtuber formation and growth changes.

Microtubers were induced on day 60, and the number of microtubers was greatest under B460, followed by R660. Thus, the addition of white light to B460 and R660 reduced the rate of induction of microtubers on day 60. However, the number of microtubers and effective microtuber increased more rapidly under R660, R460W, and B460W than under B460 after day 60; the most microtubers were obtained under R660; and more effective microtubers were observed under B460W than under B460 on day 90 (Fig. 2A and B). The microtuber formation rate, rates of effective microtubers, microtuber weight per bottle, and average microtuber weight under B460 were consistently higher than under the other treatments from days 60 to 90 (Fig. 2C, D, and F), indicating that monochromatic blue light is beneficial to microtuber growth. The average microtuber weight increased more rapidly under R660W than under R660 from days 80 to 90 (Fig. 2E and F).

Fig. 2.
Fig. 2.

Effects of different monochromatic lights on (A) microtuber (MT) number, (B) effective microtuber (EMT) number, (C) MT formation rate, (D) effective MT rate, (E) MT weight per bottle, and (F) average MT (AMT) weight during different growth stages. Microtuber with a weight of >50 mg was defined as effective microtuber. Error bars indicate standard deviations. B460 = 460-nm blue light; B460W = the combined spectra of white light and 460-nm blue light; R660 = 660-nm red light; R660W = the combined spectra of white light and 660-nm red light. k = 1000.

Citation: HortScience horts 55, 1; 10.21273/HORTSCI14548-19

Plantlet morphology changes.

As indicated in Fig. 3A, a large number of leaves developed under B460 and B460W, fewer leaf numbers were induced by R660W than B460 and B460W. However, there were no leaves on plantlets grown under R660 treatment throughout the growth period (Fig. 4), suggesting that blue light is vital for leaf formation of plantlets. Additionally, the leaves under B460W and R660W withered on day 60, but leaves under B460 did not wither until the day 90 (Fig. 3A), implying that leaves were more prone to senescence when adding white light to monochromatic blue light. Plant heights under R660 and R660W were always higher than those under B460 and B460W from days 20 to 60, respectively. Interestingly, the plant heights under B460W and R660W were consistently higher than those under B460 and R660 after 60 d, respectively (Fig. 3B). Differences in stem diameter of different light treatments were similar to those of plant height (Fig. 3C).

Fig. 3.
Fig. 3.

Effects of different light spectra on leaf number (A), plantlet height (B), and stem diameter (C) of potato plantlets during different growth stages. Error bars indicate standard deviations. B460 = 460-nm blue light; B460W = the combined spectra of white light and 460-nm blue light; R660 = 660-nm red light; R660W = the combined spectra of white light and 660-nm red light.

Citation: HortScience horts 55, 1; 10.21273/HORTSCI14548-19

Fig. 4.
Fig. 4.

Images of potato plantlets grown on day 20 under different light spectra. B460 = 460-nm blue light; B460W = the combined spectra of white light and 460-nm blue light; R660 = 660-nm red light; R660W = the combined spectra of white light and 660-nm red light. Scale bar is 1 cm.

Citation: HortScience horts 55, 1; 10.21273/HORTSCI14548-19

Biomass accumulation and distribution changes in different organs.

The dry weights of leaves and stems were heavier under B460 than under B460W on day 20 but were less than weights from days 40 to 90 (Fig. 5A, C, E, G, and I). The dry weights of leaves and stems under R660 were not much different with R660W on day 20 but was consistently less than from days 40 to 90 (Fig. 5A, C, E, G, and I). The dry weight of stems observed under B460 was consistently lowest compared with other treatments from days 40 to 90 (Fig. 5C, E, G, I). Additionally, the average proportion of dry weight in microtubers under B460, R660, B460W, and R660W on day 60 was 59.4%, 13.6%, 3.6%, and 3.1%, respectively (Fig. 5F), demonstrating that white light temporarily inhibits dry matter in the microtubers. On day 90, the proportion of dry weight in the microtubers under these treatments was 80.0, 75.2, 67.6, and 65.0%, respectively (Fig. 5J). The proportion of dry weight in microtubers and the whole plant weight were consistently greater under B460 than the other lights (Fig. 5F, H, and J). These results showed that pure blue light favored distribution of the dry matter in microtuber and that the composite lights with the addition white light to blue or red light reserved a greater proportion of dry matter in stems and decreased the distribution rate of dry matter in microtubers.

Fig. 5.
Fig. 5.

Effects of different light spectra on dry weight (DW) and proportion of DW in leaves, stems, and microtubers grown for (A, B) 20, (C, D) 40, (E, F) 60, (G, H) 80, and (I, J) 90 d. B460 = 460-nm blue light; B460W = the combined spectra of white light and 460-nm blue light; R660 = 660-nm red light; R660W = the combined spectra of white light and 660-nm red light.

Citation: HortScience horts 55, 1; 10.21273/HORTSCI14548-19

Carbohydrate content changes in different organs.

The data show that the starch content in leaves decreased sharply under B460 from days 20 to 40 and then remained stable, whereas it increased sharply under B460W and R660W from days 40 to 60 (Fig. 6A). The starch content in stems under B460 and R660 followed a similar trend (Fig. 6D). Under B460, B460W, and R660, the starch content in microtubers initially increased and then decreased from days 60 to 90, but the pattern was reversed under R660W (Fig. 6G). The highest starch content was under B460 and the second highest was under R660, whereas the addition of white light to red and blue lights reduced the starch content in microtubers on the 80th days (Fig. 6G).

Fig. 6.
Fig. 6.

Effects of different light spectra on starch, soluble sugar, and sucrose contents in leaves (A–C), stems (D–F), and microtubers (G–I) at various growth stages. B460 = 460-nm blue light; B460W = the combined spectra of white light and 460-nm blue light; R660 = 660-nm red light; R660W = the combined spectra of white light and 660-nm red light. Error bars indicate standard deviations.

Citation: HortScience horts 55, 1; 10.21273/HORTSCI14548-19

The soluble sugar in leaves increased throughout the growing period under B460, B460W, and R660W and was consistently lower under B460 and B460W than R660W (Fig. 6B). The soluble sugar content in stems decreased in all treatments from days 20 to 40 (Fig. 6E). The soluble sugar was consistently lower under B460 than under R660, and the addition of white light to red and blue lights reduced soluble sugar content in stems from days 20 to 40 (Fig. 6E). The soluble sugar content in microtubers initially decreased and then increased under R620, B460W, and R660W and increased under B460 from days 60 to 90 (Fig. 6H).

The sucrose content in leaves under B460 reached minimum and maximum values at days 40 and 80, respectively. The sucrose content in leaves was always the highest under R660W (Fig. 6C). In all treatments, the sucrose content in stems first decreased and then increased from days 20 to 90 and was significantly higher under B460 than the other treatments on day 80 (Fig. 6F). The sucrose content in microtubers decreased from days 60 to 90 under B460W and R660W, but the starch content in microtubers was initially stable, then increased under B460 and R660 from days 80 to 90 (Fig. 6I).

Microtuber dormancy.

As shown in Table 2, dormancy periods were influenced by light spectra. The dormancy periods under B460 and R660 were significantly shorter than under B460W and R660W, and the dormancy period of microtubers >300 mg under B460 was significantly shorter compared with the other treatments, indicating that monochromatic 460-nm blue light decreased the dormancy period for large microtubers. As shown in Table 3, correlation analysis revealed no significant relationship between average microtuber weight and dormancy period, and a correlation coefficient of r = –0.206 was recorded. However, there was a negative and highly significant correlation between microtuber starch content and dormancy period.

Table 2.

Effects of different light spectra on microtuber dormancy period.

Table 2.
Table 3.

Pearson correlation coefficients among sugar content in microtubers, average microtuber weight, and dormancy period after harvesting.

Table 3.

Discussion

Red light increases microtuber formation and blue light favors microtuber growth.

Light wavelengths, as environmental signals, stimulate various plant life activity, and light quantity of different wavelengths, as major energy sources, affects photosynthesis and thus alters plant growth (Li et al., 2018; Seabrook, 2005). Red and green lights have been shown to promote microtuber growth (Mohamed Ali and Esmail, 2011). In the current study, R660 facilitated microtuber formation in the middle and late growth stages (Fig. 2A and B). However, Aksenova et al. (1989) found that red light inhibited microtuber formation, which is inconsistent with the present study. The regulatory effects of light spectra on growth can be partly attributed to the regulation of phytohormone levels in plants (Kaufman, 1993). Endogenous hormones in potato are affected by light quality (Fixen et al., 2012). It has been reported that gibberellic acid (GA3) and abscisic acid (ABA) are closely related to tuber formation and that GA3 inhibits tuber formation whereas ABA promotes it (Lovell and Booth, 2010; Roumeliotis et al., 2012). GA3 concentrations decrease in leaves of grape grown under red light (Wang et al., 2017), and ABA concentrations induced by red light increased in hypocotyl of cucumber (Su et al., 2014). In the present study, red light facilitated microtuber formation, which might be correlated with decreased levels of GA3 and increased ABA concentrations in plantlets. Interestingly, composite light with the addition of white light to R660 slightly reduced the effect of R660, which may be caused by a decrease in PPFD of red light (R660 = 65 µmol·m−2·s−1; 45 µmol·m−2·s−1 < R660W < 65 µmol·m−2·s−1) and an increase of blue light in R660W. Compared with R660, B460 induced significantly fewer microtubers (Table 1), indicating that blue light does not favor the induction of microtubers compared with red light. Composite light with the addition of white light to B460 induced more microtubers than B460 (Table 1), perhaps through a decrease in PPFD of blue light and an increase of red light in B660W. Thus, red light is beneficial for the formation of microtubers, whereas blue light reverses the active effect.

Nevertheless, B460 had beneficial effects on microtuber growth (Fig. 2E and F). Similar effects of blue light on microtuber growth were reported by Chang et al. (2009). Compared with R660 treatment, which was characterized by no leaves on plantlets (Fig. 4), greater microtuber weights were observed under B460, B460W, and R660W (Table 1). These results can likely be attributed to the large number of leaves grown under these lights, confirming that blue light is vital to form leaves of potato plantlets and red light has an adverse effect on leaf germination. Leaves are the main site of photosynthesis, and a large number of leaves has greater photosynthetic potential (Arp, 2010), creating more opportunities for plantlet metabolism and microtuber growth. Additionally, leaves withered under B460W and R660W on day 60, whereas they withered under B460 on day 90 (Fig. 3A), which is closely related to research demonstrating senescence of leaves induced by red light but delayed by blue light (Borras et al., 2003; Causin et al., 2006; Wang et al., 2010; Zhang and Zhou, 2013). The longer photosynthesis lasts, the more carbohydrate that is produced (Shaaf et al., 2019), and thus the higher microtuber weight per bottle was obtained under B460 (Table 1). Likewise, composite light with the addition of white light to B460 decreased microtuber weight, but the addition of white light to R660 increased microtuber weight compared with R660 treatment, which had the lowest microtuber weight (Table 1). This may result from the positive effect of blue light and the adverse effect of red light on microtuber weight. Therefore, we can conclude that blue light favors microtuber growth, and red light can reverse the positive effect of blue light on microtuber growth.

The accumulation and transportation of substances determine microtuber growth.

Assimilates in leaves, as the main products of metabolism, are associated with increased photosynthetic activity and yield in sink organs (Kang et al., 2013; Malone et al., 2006). Blue light is essential for the development of photosynthetic organs (Wang et al., 2015). A similar result was observed in the present study (Figs. 3A and 4), which provides a good material foundation for the growth of the microtubers grown under B460. The transportation of carbohydrates depends on transportation distance and resistance (Lalonde et al., 2010). Shorter plant height and thicker stems with larger cross-sectional phloem area were found under blue light (Fig. 3B and C), suggesting that carbohydrates could be transported to tubers over a short distance and with low resistance and thus that rapid carbohydrate transportation facilitates microtuber growth under blue light. In addition, the distribution of biomass and metabolites determines the growth of various organs (Gautier et al., 1997; Moreira et al., 1997). It has reported that blue light causes a higher proportion of metabolites distributed in the stems of strawberry and sweet pepper plants (Xu et al., 2006; Yang et al., 2012). Similar effects caused by monochromatic blue light on sucrose in stems on days 60 to 90 was also observed (Fig. 6C). However, the lowest stem dry weight and the heaviest microtubers were observed under B460 from days 40 to 90 (Fig. 5C, E, G, and I). Hence, we deduced that the higher concentration sucrose in stems was not used for growth of the stems themselves but is transferred into microtubers from the leaves (Fig. 6F and I). In contrast, the sucrose content in leaves was consistently highest under R660W (Fig. 6C), and the sucrose content in stems maintains relatively stable levels on days 20 to 80 (Fig. 6F); however, the sucrose, soluble sugar, and starch contents in microtubers continuously declined (Fig. 6I), indicating that the transportation of sucrose in this treatment is inhibited from source to sink. Furthermore, higher starch contents were observed in the leaves of B460W and R660W (Fig. 6A), suggesting that, except for the composite light of R660W, the addition of white light to blue light also inhibits transportation of the carbohydrates, resulting in a portion of these metabolites being temporarily reserved as starch in leaves (Fig. 6A). Consequently, lighter microtubers under B460W and R660W compared with B460 were observed (Table 1). Sugar content in leaves reflects the supply potential of carbohydrate (Farrar et al., 2000; Kang et al., 2013). As leaves formed, more carbohydrate was produced under R660W (Fig. 6A–C), and the dry weight of leaves and stems irradiated with R660W was greater than the dry weight of stems under R660 from days 40 to 60 (Fig. 5C and E), ensuring sufficient supply potential of carbohydrate, and thus higher microtuber weight per bottle under R660W than R660 (Table 1).

Addition of white light extends microtuber dormancy.

Potato size was closely related with dry matter content, thus determining sprouting potential (Haverkort et al., 1991), while sprouting potential seem to be highly related to the maturity of the potato microtubers (Park et al., 2009). In the current study, the dormancy periods of microtubers >300 mg exposed to B460 were significantly shorter than under other treatments (Table 2). This confirmed that sprout production was correlated with dry matter and maturity of tubers (Wijewardana et al., 2018). In addition, sugar is an energy source for sprouting, and its content at harvest is an important factor in determining the maturity and sprouting vigor of seed potato (Rees and Morrell, 1990). In the present study, the starch, soluble sugar, and sucrose contents in microtubers grown under B460 and R660 were higher at harvest than under B460W and R660W, so shorter dormancy periods were observed, which provides further evidence for previous results (Park et al., 2009). A highly significant negative correlation between sucrose and starch contents and dormancy period suggested that the addition of white light extended the dormancy period by decreasing sucrose and starch contents in microtubers (Table 3).

Conclusions

Light spectra influenced the formation, growth, and dormancy of microtubers by regulating potato plantlet morphogenesis, affecting the synthesis, transportation, and storage of photosynthetic metabolites. Red light facilitated the induction of more microtubers, but blue light favored microtuber growth. Furthermore, blue light shortened the dormancy period of large microtubers, and addition of white light extended the dormancy period by decreasing sucrose and starch content in microtubers. Therefore, in potato agricultural production, specific light conditions may be applied at different growth stages of in vitro potatoes to increase the number of effective microtubers (>50 mg) and satisfy storage requirements of seed microtubers.

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  • Kang, G.Z., Liu, G.Q., Peng, X.Q., Wei, L.T., Wang, C.Y., Zhu, Y.J., Ma, Y., Jiang, Y.M. & Guo, T.C. 2013 Increasing the starch content and grain weight of common wheat by overexpression of the cytosolic AGPase large subunit gene Plant Physiol. Biochem. 73 93 98

    • Search Google Scholar
    • Export Citation
  • Kaufman, L.S. 1993 Transduction of blue-light signals Plant Physiol. 102 333

  • Lalonde, S., Tegeder, M., Throne-Holst, M., Frommer, W.B. & Patrick, J.W. 2010 Phloem loading and unloading of sugars and amino acids Plant Cell Environ. 26 37 56

    • Search Google Scholar
    • Export Citation
  • Li, R.N., Huang, W.W., Wang, X.X., Liu, X.Y. & Xu, Z.G. 2018 Effects of yellow, green, and different blue spectra on growth of potato plantlets in vitro HortScience 53 541 546

    • Search Google Scholar
    • Export Citation
  • Lovell, P.H. & Booth, A. 2010 Effects of GA on growth, tuber formation and carbohydrate distribution in Solanum tuberosum New Phytol. 66 525 537

  • Malone, J.G., Mittova, V., Ratcliffe, R.G. & Kruger, N.J. 2006 The response of carbohydrate metabolism in potato tubers to low temperature Plant Cell Physiol. 47 1309 1322

    • Search Google Scholar
    • Export Citation
  • Martin, A.B., Cuadrado, Y., Guerra, H., Gallego, P., Hita, O., Martin, L., Dorado, A. & Villalobos, N. 2000 Differences in the contents of total sugars, reducing sugars, starch and sucrose in embryogenic and nonembrogenic calli from Medicago arborea L Plant Sci. 154 143 151

    • Search Google Scholar
    • Export Citation
  • Mohamed Ali, F.H. & Esmail, M.A. 2011 The impact of in vitro light quality on potato microtuberization from single-node cuttings Acta Hort. 923 73 77

    • Search Google Scholar
    • Export Citation
  • Mølmann, J.A. & Johansen, T.J. 2019 Sprout growth inhibition and photomorphogenic development of potato seed tubers (Solanum tuberosum L.) under different LED light colours Potato Res. 1 17

    • Search Google Scholar
    • Export Citation
  • Moreira, D.A., Silva, M.H. & Debergh, P.C. 1997 The effect of light quality on the morphogenesis of in vitro cultures of Azorina vidalii (Wats.) Feer Plant Cell Tissue Organ Cult. 51 187 193

    • Search Google Scholar
    • Export Citation
  • Park, S.W., Jeon, J.H., Kim, H.S., Hong, S.J., Aswath, C. & Joung, H. 2009 The effect of size and quality of potato microtubers on quality of seed potatoes in the cultivar ‘Superior’ Scientia Hort. 120 127 129

    • Search Google Scholar
    • Export Citation
  • Park, Y.G., Oh, H.J. & Jeong, B.R. 2013 Growth and anthocyanin concentration of perilla frutescens var. acuta Kudo as affected by light source and DIF under controlled environment Hort. Environ. Biotechnol. 54 103 108

    • Search Google Scholar
    • Export Citation
  • Pelacho, A.M. & Mingo-Castel, A.M. 1991 Jasmonic acid induces tuberization of potato stolons cultured in vitro Plant Physiol. 97 1253 1255

  • Rees, T. & Morrell, S. 1990 Carbohydrate metabolism in developing potatoes Amer. Potato J. 67 835 847

  • Roumeliotis, E., Visser, R.G. & Bachem, C.W. 2012 A crosstalk of auxin and GA during tuber development Plant Signal. Behav. 7 1360 1363

  • Seabrook, J.E.A. 2005 Light effects on the growth and morphogenesis of potato (Solanum tuberosum) in vitro: A review Amer. J. Potato Res. 82 353 367

    • Search Google Scholar
    • Export Citation
  • Shaaf, S., Bretani, G., Biswas, A., Fontana, I.M. & Rossini, L. 2019 Genetics of barley tiller and leaf development J. Integr. Plant Biol. 61 226 256

  • Su, N., Wu, Q. & Cui, J. 2014 Effects of monochromatic LED light quality on endogenous hormone content in leaves and hypocotyl of Cucumis sativus L Chin. J. Appl. Environ. Biol. 20 45 49

    • Search Google Scholar
    • Export Citation
  • Toledo, M.E.A. & Ueda, Y. 2003 L-aseorbic acid metabolism in spinach during postharvest storage in light and dark Postharvest Biol. Technol. l 47 57

    • Search Google Scholar
    • Export Citation
  • Wang, H.B., Wang, S., Wang, X.T., Shi, X.B., Wang, B.L., Zheng, X.C., Wang, Z.Q. & Liu, F.Z. 2017 Effects of light quality on leaf senescence and endogenous hormones content in grapevine under protected cultivation Ch. J. Appl. Ecol. 11 3535 3543

    • Search Google Scholar
    • Export Citation
  • Wang, H., Jiang, Y.P., Shi, K., Zhou, Y.H. & Yu, J.Q. 2010 Effects of light quality on leaf senescence and activities of antioxidant enzymes in cucumber plants Sci. Agr. Sinica 43 529 534

    • Search Google Scholar
    • Export Citation
  • Wang, X.Y., Xu, X.M. & Cui, J. 2015 The importance of blue light for leaf area expansion, development of photosynthetic apparatus, and chloroplast ultrastructure of Cucumis sativus grown under weak light Photosynthetica 53 213 222

    • Search Google Scholar
    • Export Citation
  • Wijewardana, C., Reddy, K.R., Shankle, M.W., Meyers, S. & Wei, G. 2018 Low and high-temperature effects on sweet potato storage root initiation and early transplant establishment Scientia Hort. 240 38 48

    • Search Google Scholar
    • Export Citation
  • Xu, K., Guo, Y.P., Zhang, S.L., Dai, W.S. & Fu, Q.G. 2006 Effects of different light quality on growth and development of fengxiang strawberry J. Fruit Sci. 23 818 824

    • Search Google Scholar
    • Export Citation
  • Yang, Z.Q., Zhao, X., Su, T.X., Zhou, Z.L., Zhu, K. & Peng, X.D. 2012 Effects of light quality on dry matter production and distribution index of sweet pepper in greenhouse J. Ecol. 31 1117 1122

    • Search Google Scholar
    • Export Citation
  • Zhang, H.S. & Zhou, C.J. 2013 Signal transduction in leaf senescence Plant Mol. Biol. 82 539 545

  • Zhao, D.L. 1995 Effects of light on seed dormancy and germination Chin. J. Biol. 7 24 25

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Contributor Notes

This work was funded by the National Natural Science Foundation of China (11674174).

Z.X. and X.L. are the corresponding authors. E-mail: xuzhigang@njau.edu.cn or liuxy@njau.edu.cn.

  • View in gallery

    Spectral distribution of white, blue, and red lights. PPFD = photosynthetic photon flux density.

  • View in gallery

    Effects of different monochromatic lights on (A) microtuber (MT) number, (B) effective microtuber (EMT) number, (C) MT formation rate, (D) effective MT rate, (E) MT weight per bottle, and (F) average MT (AMT) weight during different growth stages. Microtuber with a weight of >50 mg was defined as effective microtuber. Error bars indicate standard deviations. B460 = 460-nm blue light; B460W = the combined spectra of white light and 460-nm blue light; R660 = 660-nm red light; R660W = the combined spectra of white light and 660-nm red light. k = 1000.

  • View in gallery

    Effects of different light spectra on leaf number (A), plantlet height (B), and stem diameter (C) of potato plantlets during different growth stages. Error bars indicate standard deviations. B460 = 460-nm blue light; B460W = the combined spectra of white light and 460-nm blue light; R660 = 660-nm red light; R660W = the combined spectra of white light and 660-nm red light.

  • View in gallery

    Images of potato plantlets grown on day 20 under different light spectra. B460 = 460-nm blue light; B460W = the combined spectra of white light and 460-nm blue light; R660 = 660-nm red light; R660W = the combined spectra of white light and 660-nm red light. Scale bar is 1 cm.

  • View in gallery

    Effects of different light spectra on dry weight (DW) and proportion of DW in leaves, stems, and microtubers grown for (A, B) 20, (C, D) 40, (E, F) 60, (G, H) 80, and (I, J) 90 d. B460 = 460-nm blue light; B460W = the combined spectra of white light and 460-nm blue light; R660 = 660-nm red light; R660W = the combined spectra of white light and 660-nm red light.

  • View in gallery

    Effects of different light spectra on starch, soluble sugar, and sucrose contents in leaves (A–C), stems (D–F), and microtubers (G–I) at various growth stages. B460 = 460-nm blue light; B460W = the combined spectra of white light and 460-nm blue light; R660 = 660-nm red light; R660W = the combined spectra of white light and 660-nm red light. Error bars indicate standard deviations.

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  • Kang, G.Z., Liu, G.Q., Peng, X.Q., Wei, L.T., Wang, C.Y., Zhu, Y.J., Ma, Y., Jiang, Y.M. & Guo, T.C. 2013 Increasing the starch content and grain weight of common wheat by overexpression of the cytosolic AGPase large subunit gene Plant Physiol. Biochem. 73 93 98

    • Search Google Scholar
    • Export Citation
  • Kaufman, L.S. 1993 Transduction of blue-light signals Plant Physiol. 102 333

  • Lalonde, S., Tegeder, M., Throne-Holst, M., Frommer, W.B. & Patrick, J.W. 2010 Phloem loading and unloading of sugars and amino acids Plant Cell Environ. 26 37 56

    • Search Google Scholar
    • Export Citation
  • Li, R.N., Huang, W.W., Wang, X.X., Liu, X.Y. & Xu, Z.G. 2018 Effects of yellow, green, and different blue spectra on growth of potato plantlets in vitro HortScience 53 541 546

    • Search Google Scholar
    • Export Citation
  • Lovell, P.H. & Booth, A. 2010 Effects of GA on growth, tuber formation and carbohydrate distribution in Solanum tuberosum New Phytol. 66 525 537

  • Malone, J.G., Mittova, V., Ratcliffe, R.G. & Kruger, N.J. 2006 The response of carbohydrate metabolism in potato tubers to low temperature Plant Cell Physiol. 47 1309 1322

    • Search Google Scholar
    • Export Citation
  • Martin, A.B., Cuadrado, Y., Guerra, H., Gallego, P., Hita, O., Martin, L., Dorado, A. & Villalobos, N. 2000 Differences in the contents of total sugars, reducing sugars, starch and sucrose in embryogenic and nonembrogenic calli from Medicago arborea L Plant Sci. 154 143 151

    • Search Google Scholar
    • Export Citation
  • Mohamed Ali, F.H. & Esmail, M.A. 2011 The impact of in vitro light quality on potato microtuberization from single-node cuttings Acta Hort. 923 73 77

    • Search Google Scholar
    • Export Citation
  • Mølmann, J.A. & Johansen, T.J. 2019 Sprout growth inhibition and photomorphogenic development of potato seed tubers (Solanum tuberosum L.) under different LED light colours Potato Res. 1 17

    • Search Google Scholar
    • Export Citation
  • Moreira, D.A., Silva, M.H. & Debergh, P.C. 1997 The effect of light quality on the morphogenesis of in vitro cultures of Azorina vidalii (Wats.) Feer Plant Cell Tissue Organ Cult. 51 187 193

    • Search Google Scholar
    • Export Citation
  • Park, S.W., Jeon, J.H., Kim, H.S., Hong, S.J., Aswath, C. & Joung, H. 2009 The effect of size and quality of potato microtubers on quality of seed potatoes in the cultivar ‘Superior’ Scientia Hort. 120 127 129

    • Search Google Scholar
    • Export Citation
  • Park, Y.G., Oh, H.J. & Jeong, B.R. 2013 Growth and anthocyanin concentration of perilla frutescens var. acuta Kudo as affected by light source and DIF under controlled environment Hort. Environ. Biotechnol. 54 103 108

    • Search Google Scholar
    • Export Citation
  • Pelacho, A.M. & Mingo-Castel, A.M. 1991 Jasmonic acid induces tuberization of potato stolons cultured in vitro Plant Physiol. 97 1253 1255

  • Rees, T. & Morrell, S. 1990 Carbohydrate metabolism in developing potatoes Amer. Potato J. 67 835 847

  • Roumeliotis, E., Visser, R.G. & Bachem, C.W. 2012 A crosstalk of auxin and GA during tuber development Plant Signal. Behav. 7 1360 1363

  • Seabrook, J.E.A. 2005 Light effects on the growth and morphogenesis of potato (Solanum tuberosum) in vitro: A review Amer. J. Potato Res. 82 353 367

    • Search Google Scholar
    • Export Citation
  • Shaaf, S., Bretani, G., Biswas, A., Fontana, I.M. & Rossini, L. 2019 Genetics of barley tiller and leaf development J. Integr. Plant Biol. 61 226 256

  • Su, N., Wu, Q. & Cui, J. 2014 Effects of monochromatic LED light quality on endogenous hormone content in leaves and hypocotyl of Cucumis sativus L Chin. J. Appl. Environ. Biol. 20 45 49

    • Search Google Scholar
    • Export Citation
  • Toledo, M.E.A. & Ueda, Y. 2003 L-aseorbic acid metabolism in spinach during postharvest storage in light and dark Postharvest Biol. Technol. l 47 57

    • Search Google Scholar
    • Export Citation
  • Wang, H.B., Wang, S., Wang, X.T., Shi, X.B., Wang, B.L., Zheng, X.C., Wang, Z.Q. & Liu, F.Z. 2017 Effects of light quality on leaf senescence and endogenous hormones content in grapevine under protected cultivation Ch. J. Appl. Ecol. 11 3535 3543

    • Search Google Scholar
    • Export Citation
  • Wang, H., Jiang, Y.P., Shi, K., Zhou, Y.H. & Yu, J.Q. 2010 Effects of light quality on leaf senescence and activities of antioxidant enzymes in cucumber plants Sci. Agr. Sinica 43 529 534

    • Search Google Scholar
    • Export Citation
  • Wang, X.Y., Xu, X.M. & Cui, J. 2015 The importance of blue light for leaf area expansion, development of photosynthetic apparatus, and chloroplast ultrastructure of Cucumis sativus grown under weak light Photosynthetica 53 213 222

    • Search Google Scholar
    • Export Citation
  • Wijewardana, C., Reddy, K.R., Shankle, M.W., Meyers, S. & Wei, G. 2018 Low and high-temperature effects on sweet potato storage root initiation and early transplant establishment Scientia Hort. 240 38 48

    • Search Google Scholar
    • Export Citation
  • Xu, K., Guo, Y.P., Zhang, S.L., Dai, W.S. & Fu, Q.G. 2006 Effects of different light quality on growth and development of fengxiang strawberry J. Fruit Sci. 23 818 824

    • Search Google Scholar
    • Export Citation
  • Yang, Z.Q., Zhao, X., Su, T.X., Zhou, Z.L., Zhu, K. & Peng, X.D. 2012 Effects of light quality on dry matter production and distribution index of sweet pepper in greenhouse J. Ecol. 31 1117 1122

    • Search Google Scholar
    • Export Citation
  • Zhang, H.S. & Zhou, C.J. 2013 Signal transduction in leaf senescence Plant Mol. Biol. 82 539 545

  • Zhao, D.L. 1995 Effects of light on seed dormancy and germination Chin. J. Biol. 7 24 25

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