Using Light Quality for Growth Control of Cucumber Seedlings in Closed-Type Plant Production System

Effects of Red and Blue Light on the Growth, Photosynthesis, and Subsequent Growth under Fluctuating Light of Cucumber Seedlings

The effects of red and blue light on growth and steady-state photosynthesis have been widely studied, but there are few studies focusing on dynamic photosynthesis and the effects of LED pre-treatment on cucumber seedlings' growth, so in this study, cucumber (Cucumis sativus L. cv. Jinyou 365) was chosen as the test material. White light (W), monochromatic red light (R), monochromatic blue light (B), and mixed red and blue lights with different red-to-blue ratios (9:1, 7:3, 5:5, 3:7, and 1:9) were set to explore the effects of red and blue light on cucumber seedlings' growth, steady-state photosynthesis, dynamic photosynthesis, and subsequent growth under fluctuating light. The results showed that compared with R and B, mixed red and blue light was more suitable for cucumber seedlings' growth, and the increased blue light ratios would decrease the biomass of cucumber seedlings under mixed red and blue light; cucumber seedlings under 90% red and 10% blue mixed light (9R1B) grew better than other treatments. For steady-state photosynthesis, blue light decreased the actual net photosynthetic rate but increased the maximum photosynthetic capacity by promoting stomatal development and opening; 9R1B exhibited higher actual net photosynthetic rate, but the maximum photosynthetic capacity was low. For dynamic photosynthesis, the induction rate of photosynthetic rate and stomatal conductance were also accelerated by blue light. For subsequent growth under fluctuating light, higher maximum photosynthetic capacity and photoinduction rate could not promote the growth of cucumber seedlings under subsequent fluctuating light, while seedlings pre-treated with 9R1B and B grew better under subsequent fluctuating light due to the high plant height and leaf area. Overall, cucumber seedlings treated with 9R1B exhibited the highest biomass and it grew better under subsequent fluctuating light due to the higher actual net photosynthetic rate, plant height, and leaf area.

Synthesis and Biological Profiling of Novel Strigolactone Derivatives for Arabidopsis Growth and Development

The artificially synthesized strigolactone (SL) analogue GR24 is currently the most widely used reference compound in studying the biological functions of SLs. To elucidate the structure-activity relationship and find more promising derivatives with unique molecular profiles, we design and synthesized three series of novel GR24 derivatives and explored their activities in hypocotyl and root development of Arabidopsis. Among the 50 synthesized compounds, A11a, A12a, and A20d were found to have high activities comparable to GR24 for hypocotyl and/or primary root elongation inhibition in Arabidopsis. Some new analogues have been discovered to exhibit unique activities: (1) A20c, A21e, and A21o are specific inhibitors in primary root elongation; (2) A21c, A26c, and A27a exhibit a high promotion effect on Arabidopsis primary root elongation; and (3) A27e possesses the most unique profiles completely opposite to GR24 that promotes both hypocotyl elongation and primary root development. Moreover, we revealed that the AtD14 receptor does not affect the inhibitory effect of SL analogues in Arabidopsis root development. The ligand-receptor interactions for the most representative analogues A11a and A27e were deciphered with a long time scale molecular dynamics simulation study, which provides the molecular basis of their distinct functions, and may help scientists design novel phytohormones.

Growth of tomato and cucumber seedlings under different light environments and their development after transplanting

Selecting suitable light conditions according to the plant growth characteristics is one of the important approaches to cultivating high-quality vegetable seedlings. To determine the more favorable LED light conditions for producing high-quality tomato and cucumber seedlings in plant factories with artificial light (PFALS), the growth characteristics of tomato and cucumber seedlings under seven LED light environments (CK, B, UV-A, FR, B+UV-A, UV-A+FR, and B+FR) and the development of these seedlings after transplanting into a plastic greenhouse were investigated. The results showed that the seedling height and hypocotyl length increased in treatments with far-red light supplementation (FR, UV-A+FR, and B+FR), but decreased in the B treatment, in both varieties. The seedling index of tomato seedlings increased in the B+UV-A treatment, while that of cucumber seedlings increased in the FR treatment. After transplanting into a plastic greenhouse, tomato plants that radiated with UV-A had greater flower numbers on the 15th day after transplanting. In cucumber plants of the FR treatment, the flowering time was significantly delayed, and the female flower exhibited at a lower node position. By using a comprehensive scoring analysis of all detected indicators, light environments with UV-A and FR were more beneficial for improving the overall quality of tomato and cucumber seedlings, respectively.

Low red to far-red light ratio promotes salt tolerance by improving leaf photosynthetic capacity in cucumber

Soil salinity severely inhibits leaf photosynthesis and limits agricultural production. Red to far-red light ratio (R/FR) affects leaf photosynthesis under salt stress, however, its regulation mechanism is still largely unknown. This study investigated the effects of different R/FR on plant growth, gas exchange parameters, photosynthetic electron transport, Calvin cycle and key gene expression under salt stress. Cucumber seedlings were exposed to four treatments including 0 mM NaCl and R/FR=7 (L7, control), 0 mM NaCl and R/FR=0.7 (L0.7), 80 mM NaCl and R/FR=7 (H7) and 80 mM NaCl and R/FR=0.7 (H0.7) for 9 days in an artificial climate chamber. The results showed that compared to L7 treatment, H7 treatment significantly reduced relative growth rate (RGR), CO₂ assimilation rate (P _n), maximum photochemical efficiency PSII (F _v/F _m), most JIP-test parameters and total Rubisco activity, indicating that salt stress severely inhibited photosynthetic electron transport from PSII to PSI and blocked Calvin cycle in cucumber leaves. However, these suppressions were effectively alleviated by low R/FR addition (H0.7 treatment). Compared to H7 treatment, H0.7 treatment significantly increased RGR and P _n by 209.09% and 7.59%, respectively, enhanced F _v/F _m, maximum quantum yield for primary photochemistry (φ _Po), quantum yield for electron transport (φ _Eo) and total Rubisco activity by 192.31%, 17.6%, 36.84% and 37.08%, respectively, and largely up-regulated expressions of most key genes involved in electron transport and Calvin cycle. In conclusion, low R/FR effectively alleviated the negative effects of salt stress on leaf photosynthesis by accelerating photosynthetic electron transport from PSII to PQ pool and promoting Calvin cycle in cucumber plants. It provides a novel environmentally friendly light-quality regulation technology for high efficiency salt-resistant vegetable production.

Increasing the performance of cucumber (Cucumis sativus L.) seedlings by LED illumination

Light is one of the most important limiting factors for photosynthesis and the production of plants, especially in the regions where natural environmental conditions do not provide sufficient sunlight, and there is a great dependence on artificial lighting to grow plants and produce food. The influence of light intensity, quality, and photoperiod on photosynthetic pigments content and some biochemical and growth traits of cucumber seedlings grown under controlled conditions was investigated. An orthogonal design based on a combination of different light irradiances, ratio of LEDs and photoperiods was used. Treaments consisted of three light irradiance regimes (80, 100, and 150 µmol m⁻² s⁻¹) provided by light-emitting diodes (LEDs) of different ratios of red and blue (R:B) (30:70, 50:50, and 70:30) and three different photoperiods (10/14, 12/12, and 14/10 h). The white light was used as a control/reference. Plant height, hypocotyl length, stem diameter, leaf area, and soluble sugar content were highest when exposed to LM9 (150 µmol m⁻² s⁻¹; R70:B30; 12/12 h) light mode, while the lowest values for the above parameters were obtained under LM1 (80 µmol m⁻² s⁻¹; R30:B70; 10/14 h). Higher pigments contents (chlorophyll a, chlorophyll b, and carotenoid) were obtained when light regime LM9 (150 µmol m⁻² s⁻¹; R70:B30; 12/12 h) was applied. In general, cucumber seedlings grown under the LM9 regime showed a significant increase in growth as well as photosynthetic capacity. It seems that the content of photosynthetic pigments is the key factor responsible for the performance of cucumber seedlings grown under different lighting modes, compared to other traits studied. We recommend monitoring the content of chlorophyll a, b, and their ratio value when studying the light requirement of cucumber plants.

A framework of artificial light management for optimal plant development for smart greenhouse application

Smart greenhouse farming has emerged as one of the solutions to global food security, where farming productivity can be managed and improved in an automated manner. While it is known that plant development is highly dependent on the quantity and quality of light exposure, the specific impact of the different light properties is yet to be fully understood. In this study, using the model plant Arabidopsis, we systematically investigate how six different light properties (i.e., photoperiod, light offset, intensity, phase of dawn, duration of twilight and period) would affect plant development i.e., flowering time and hypocotyl (seedling stem) elongation using an established mathematical model of the plant circadian system relating light input to flowering time and hypocotyl elongation outputs for smart greenhouse application. We vary each of the light properties individually and then collectively to understand their effect on plant development. Our analyses show in comparison to the nominal value, the photoperiod of 18 hours, period of 24 hours, no light offset, phase of dawn of 0 hour, duration of twilight of 0.05 hour and a reduced light intensity of 1% are able to improve by at least 30% in days to flower (from 32.52 days to 20.61 days) and hypocotyl length (from 1.90 mm to 1.19mm) with the added benefit of reducing energy consumption by at least 15% (from 4.27 MWh/year to 3.62 MWh/year). These findings could provide beneficial solutions to the smart greenhouse farming industries in terms of achieving enhanced productivity while consuming less energy.

Increasing the performance of Passion fruit (Passiflora edulis) seedlings by LED light regimes

Due to progress in the industrial development of light-emitting diodes (LEDs), much work has been dedicated to understanding the reaction of plants to these light sources in recent years. In this study, the effect of different LED-based light regimes on growth and performance of passion fruit (Passiflora edulis) seedlings was investigated. Combinations of different light irradiances (50, 100, and 200 µmol m⁻² s⁻¹), quality (red, green, and blue light-emitting LEDs), and photoperiods (10 h/14 h, 12 h/12 h and 14 h/10 h light/dark cycles) were used to investigate the photosynthetic pigment contents, antioxidants and growth traits of passion fruit seedlings in comparison to the same treatment white fluorescent light. Light irradiance of 100 µmol m⁻² s⁻¹ of a 30% red/70% blue LED light combination and 12 h/12 h light/dark cycles showed the best results for plant height, stem diameter, number of leaves, internode distance, and fresh/dry shoot/root weights. 14 h/10 h light/dark cycles with the same LED light combination promoted antioxidant enzyme activities and the accumulation of phenols and flavonoids. In contrast, lower light irradiance (50 µmol m⁻² s⁻¹) had negative effects on most of the parameters. We conclude that passion fruit seedlings' optimal performance and biomass production requires long and high light irradiances with a high blue light portion.

Effects of Light Spectral Quality on the Micropropagated Raspberry Plants during Ex Vitro Adaptation

This work focuses on developing light environments for the effective regulation of morphogenesis and ex vitro conditions adaptation in micropropagated raspberry plants on the basis of photomorphogenetic control of physiological processes using light-emitting diodes (LEDs). In experiments with cloned plants growing ex vitro in stressful conditions during acclimation, the effects of optical radiation of various spectral combinations from different photosynthetically active radiation (PAR) spectral regions were studied. The data on the plant development and state of the photosynthetic apparatus, features of photosynthetic gas exchange and transpiration, accumulation of photosynthetic pigments, light curves of photosynthesis, and data on growth processes in light modes using combined quasimonochromatic radiation (either mixture of red, green, and blue light or red, far-red, and blue light) with various ratio of the distinct spectral regions were obtained. Photosynthetic apparatus functional activity under different light conditions was studied with chlorophyll fluorescence determination, and plant stress responses to growing under artificial spectral light conditions were characterized. The experiments were accompanied by detailed plant phenotyping at the structural and functional levels. Plant acclimation and photosynthetic improvements in response to added far-red and green light wavelengths to the main red-blue spectrum have been elucidated.

Atmospheric pressure plasma treatment induces abscisic acid production, reduces stomatal aperture and improves seedling growth in Arabidopsis thaliana

Cold atmospheric pressure plasmas (CAPPs) have been widely used for pre-sowing treatment in agriculture to accelerate seed germination; however, information on their application to pre-transplant seedlings is scarce. The roles of the phytohormone abscisic acid (ABA) on guard cell aperture that control air exchange with the environment were investigated after CAPPs treatment. In this study, Arabidopsis thaliana seedling growth was evaluated under CAPPs treatment at different doses. Besides, the optimal growth stimulation dose was selected to further evaluate changes in ABA, ROS, Ca²⁺ and stomatal aperture during growth .The expression of most ABA signalling genes were aslo examined to investigate the mechanism. CAPPs treatment for 1 min significantly promoted Arabidopsis seedling growth; the ABA concentration in seedlings increased and peaked 48 h after treatment but was lower than in the control after 96 h. Transcript levels of most ABA signalling genes were markedly enhanced at 48 h, although their transcripts were significantly downregulated after 96 h. CAPPs treatment also reduced stomatal aperture after 24 h and accelerated ROS accumulation in guard cells. The Ca²⁺ concentration in the treatment group was markedly higher than in the control at 24 and 96 h. The results suggest that CAPPs treatment accelerates ABA accumulation in Arabidopsis at early growth stages and ABA regulates ROS and Ca²⁺ concentrations to affect stomatal aperture, and both ABA and stoma size are affected in CAPPs stimulation of Arabidopsis seedling growth.

Effects of light spectrum on morpho-physiological traits of grafted tomato seedlings

It is already known that there are many factors responsible for the successful grafting process in plants, including light intensity. However, the influence of the spectrum of light-emitting diodes (LEDs) on this process has almost never been tested. During the pre-grafting process tomato seedlings grew for 30 days under 100 μmol m-2 s-1 of mixed LEDs (red 70%+ blue 30%). During the post-grafting period, seedlings grew for 20 days under the same light intensity but the lightening source was either red LED, mixed LEDs (red 70% + blue 30%), blue LED or white fluorescent lamps. This was done to determine which light source(s) could better improve seedling quality and increase grafting success. Our results showed that application of red and blue light mixture (R7:B3) caused significant increase in total leaf area, dry weight (total, shoot and root), total chlorophyll/carotenoid ratio, soluble protein and sugar content. Moreover, this light treatment maintained better photosynthetic performance i.e. more effective quantum yield of PSII photochemistry Y(II), better photochemical quenching (qP), and higher electron transport rate (ETR). This can be partially explained by the observed upregulation of gene expression levels of PsaA and PsbA and the parallel protein expression levels. This in turn could lead to better functioning of the photosynthetic apparatus of tomato seedlings and then to faster production of photoassimilate ready to be translocated to various tissues and organs, including those most in need, i.e., involved in the formation of the graft union.

Green Light Improves Photosystem Stoichiometry in Cucumber Seedlings (Cucumis sativus) Compared to Monochromatic Red Light

It has been shown that monochromatic red and blue light influence photosynthesis and morphology in cucumber. It is less clear how green light impacts photosynthetic performance or morphology, either alone or in concert with other wavelengths. In this study, cucumber (Cucumis sativus) was grown under monochromatic blue, green, and red light, dichromatic blue-green, red-blue, and red-green light, as well as light containing red, green, and blue wavelengths, with or without supplemental far-red light. Photosynthetic data collected under treatment spectra at light-limiting conditions showed that both red and green light enhance photosynthesis. However, photosynthetic data collected with a 90% red, 10% blue, 1000 µmol photons m^-2 s^-1, saturating light show significantly lower photosynthesis in the green, red, and red-green treatments, indicating a blue light enhancement due to photosystem stoichiometric differences. The red-green and green light treatments show improved photosynthetic capacity relative to red light, indicating partial remediation by green light. Despite a lower quantum efficiency and the lowest ambient photosynthesis levels, the monochromatic blue treatment produced among the tallest, most massive plants with the greatest leaf area and thickest stems.

Improvement of Growth and Morphology of Vegetable Seedlings with Supplemental Far-Red Enriched LED Lights in a Plant Factory

Although light-emitting diode (LED) lamps have been broadly applied in horticultural production to improve plant yield and quality, compared to natural light there is a disadvantage in the lack of far-red light in the LED spectrum. Far-red light has been studied widely to control plant growth and development. Therefore, this study aimed to find the effect of supplemental far-red-enriched LED lights to control the growth of tomato, red pepper, cucumber, gourd, watermelon and bottle gourd seedlings. The treatments were cool white LED:far-red LED at ratios of 5:0, 5:1, 5:2 and 5:3. The growth of tomato and red pepper seedlings, including hypocotyl length, was correlated to far-red light and light intensity. The phytochrome photostationary state (PSS) value of maximum hypocotyl length by supplemental far-red-enriched light ranged from 0.69 to 0.77 in tomato and red pepper seedlings. Although hypocotyl lengths of cucumber and watermelon were greatly affected by PSS, the PSS value for maximum hypocotyl length was lower than for tomato and red pepper. These results show that manipulating supplemental far-red enrichment can be used to control vegetable seedling growth with some variation among plant species.

Leaf development and energy yield of hydroponic sweetpotato seedlings using single-node cutting as influenced by light intensity and LED spectrum

Vine cuttings with six to eight unfolded leaves are utilized as is conventional in sweetpotato (Ipomoea batatas (L.) Lam.) seedling production. However, most vine cuttings wilt after transplanting into the field. Moreover, few researchers have examined the influence of photon flux density (PFD) provided by white or white plus red light-emitting diodes (LEDs) on sweetpotato plantlets. In this study, hydroponic sweetpotato (cv. Beniharuka) seedlings using single-node cutting were grown under 20 combinations of five levels of PFDs of 150, 200, 250, 300, and 350 μmol m^-2 d^-1 and four light qualities: white LEDs with a red light to blue light ratio (R:B ratio) of 0.9, white plus red LEDs with R:B ratios of 1.2 and 2.2, respectively, and fluorescent lamp with an R:B ratio of 1.8 as control, for 20 days under a controlled enviroment. Results showed that the number of newly developed leaves on hydroponic sweetpotato seedlings increased with time in a quadratic function, regardless of light quality. Fluorescent lamps led to greater numbers of new leaves on hydroponic sweetpotato seedlings compared with those grown under LEDs. Plant height, leaf area, and fresh and dry weights increased initially and then decreased with increasing daily light integral (DLI) in quadratic funcitons with a highest value under a PFD of 250 μmol m^-2 d^-1. However, no significant differences were observed in fresh and dry weights of hydroponic sweetpotato seedlings grown under PFDs of 200 and 250 μmol m^-2 s^-1. The quantum yield of photosystem II (ФPSII) decreased linearly as DLI increased from 8.6-20.2 mol m^-2 d^-1. Power consumptions based on fresh and dry weights were lowest in sweetpotato seedlings grown under a PFD of 200 μmol m^-2 s^-1 provided by white LEDs with an R:B ratio of 0.9. White LEDs also showed higher light energy use efficiency than white plus red LEDs. In summary, it is recommended that a PFD of 200 μmol m^-2 s^-1 with DLI at 11.5 mol m^-2 d^-1 provided by white LEDs with an R:B ratio of 0.9 is suitable for hydroponic sweetpotato (cv. Beniharuka) seedling production under a controlled environment.