Adding Far-Red to Red, Blue Supplemental Light-Emitting Diode Interlighting Improved Sweet Pepper Yield but Attenuated Carotenoid Content

"Metabolight": how light spectra shape plant growth, development and metabolism

Innovations in light technologies (i.e. Light Emitting Diodes; LED) and cover films with specific optical features (e.g. photo-selective, light-extracting) have revolutionized crop production in both protected environments and open fields. The possibility to modulate the light spectra, thereby enriching/depleting cultivated plants with targeted wavebands has attracted increasing interest from both basic and applicative research. Indeed, the light environment not only influences plant biomass production but is also a pivotal factor in shaping plant size, development and metabolism. In the last decade, the strict interdependence between specific wavebands and the accumulation of targeted secondary metabolites has been exploited to improve the quality of horticultural products. Innovation in LED lighting has also marked the improvement of streetlamp illumination, thereby posing new questions about the possible influence of light pollution on urban tree metabolism. In this case, it is urgent and challenging to propose new, less-impacting solutions by modulating streetlamp spectra in order to preserve the ecosystem services provided by urban trees. The present review critically summarizes the main recent findings related to the morpho-anatomical, physiological, and biochemical changes induced by light spectra management via different techniques in crops as well as in non-cultivated species. This review explores the following topics: (1) plant growth in monochromatic environments, (2) the use of greenhouse light supplementation, (3) the application of covering films with different properties, and (4) the drawbacks of streetlamp illumination on urban trees. Additionally, it proposes new perspectives offered by in planta photomodulation.

Intra-canopy LED lighting outperformed top LED lighting in improving tomato yield and expression of the genes responsible for lycopene, phytoene and vitamin C synthesis

Greenhouses located at high latitudes and in cloudy areas often experience a low quality and quantity of light, especially during autumn and winter. This low daily light integral (DLI) reduces production rate, quality, and nutritional value of many crops. This study was conducted on Sakhiya RZ F1 tomato plants to evaluate the impact of LED lights on the growth and nutritional value of tomatoes in a greenhouse with low daily light due to cloudy weather. The treatments included LED growth lights in three modes: top lighting, intra-canopy lighting, and combined top and intra-canopy lighting. The results showed that although the combined top and intra-canopy lighting reached the maximum increase in tomato yield, exposure to intra-canopy LED lighting alone outperformed in tomato fruit yield increase (28.46%) than exposure to top LED lighting alone (12.12%) when compared to no supplemental lighting during the entire production year. Intra-canopy exposure demonstrated the highest increase in tomato lycopene (31.3%), while top and intra-canopy lighting exhibited the highest increase in vitamin C content (123.4%) compared to the control. The LED light treatment also had a very positive effect on the expression of genes responsible for metabolic cycles, including Psy1, LCY-β, and VTC2 genes, which had collinearity with the increase in tomato fruit production.

Genetic Regulation, Environmental Cues, and Extraction Methods for Higher Yield of Secondary Metabolites in Capsicum

Capsicum (chili pepper) is a widely popular and highly consumed fruit crop with beneficial secondary metabolites such as capsaicinoids, carotenoids, flavonoids, and polyphenols, among others. Interestingly, the secondary metabolite profile is a dynamic function of biosynthetic enzymes, regulatory transcription factors, developmental stage, abiotic and biotic environment, and extraction methods. We propose active manipulable genetic, environmental, and extraction controls for the modulation of quality and quantity of desired secondary metabolites in Capsicum species. Specific biosynthetic genes such as Pun (AT3) and AMT in the capsaicinoids pathway and PSY, LCY, and CCS in the carotenoid pathway can be genetically engineered for enhanced production of capsaicinoids and carotenoids, respectively. Generally, secondary metabolites increase with the ripening of the fruit; however, transcriptional regulators such as MYB, bHLH, and ERF control the extent of accumulation in specific tissues. The precise tuning of biotic and abiotic factors such as light, temperature, and chemical elicitors can maximize the accumulation and retention of secondary metabolites in pre- and postharvest settings. Finally, optimized extraction methods such as ultrasonication and supercritical fluid method can lead to a higher yield of secondary metabolites. Together, the integrated understanding of the genetic regulation of biosynthesis, elicitation treatments, and optimization of extraction methods can maximize the industrial production of secondary metabolites in Capsicum.

Post-Harvest Red- and Far-Red-Light Irradiation and Low Temperature Induce the Accumulation of Carotenoids, Capsaicinoids, and Ascorbic Acid in Capsicum annuum L. Green Pepper Fruit

Environmental factors, such as light of different spectral compositions and temperature, can change the level of activated photoreceptors which, in turn, can affect the biosynthesis of secondary metabolites in the cells of green fruit. By briefly irradiating the harvested fruit of Capsicum annuum L. hot peppers with red light (RL, maximum 660 nm) and far-red light (FRL, maximum 730 nm) and by keeping them at a low temperature, we attempted to determine whether the state of phytochromes in fruit affects the biosynthesis of secondary metabolites. Using HPLC, we analysed the qualitative composition and quantitative content of the main carotenoids and alkaloids and the chlorophylls and ascorbate, in pepper fruit exposed to the above factors. We measured the parameters characterising the primary photochemical processes of photosynthesis and the transcript levels of genes encoding capsaicin biosynthesis enzymes. The total carotenoids content in the fruit increased most noticeably after 24 h of RL irradiation (more than 3.5 times compared to the initial value), and the most significant change in the composition of carotenoids occurred when the fruit was irradiated with FRL for 72 h. The capsaicin alkaloid content increased markedly after 72 h of FRL irradiation (more than 8 times compared to the initial value). It was suggested that decrease in the activity of phytochromes due to a low temperature or FRL may result in an increase in the expression of the PAL and CAM genes.

Effect of Supplemental Inter-Lighting on Paprika Cultivated in an Unheated Greenhouse in Summer Using Various Light-Emitting Diodes

This study investigated the effects of supplemental inter-lighting on paprika (cv. Nagano RZ) in South Korea in summer using various LED light sources. The following LED inter-lighting treatments were used: QD-IL (blue + wide-red + far-red inter-lighting), CW-IL (cool-white inter-lighting), and B+R-IL (blue + red (1:2) inter-lighting). To investigate the effect of supplemental lighting on each canopy, top-lighting (CW-TL) was also used. Additionally, a control without supplemental lighting was included for comparison. Significant variations were observed in the plant growth indexes 42 days after treatment. The SPAD values and total chlorophyll content in the last period of cultivation were significantly higher than those of the control. In November, the marketable fruit yield was significantly higher than that of the control. QD-IL, CW-IL, and CW-TL resulted in significantly higher values of total soluble solids than the control, and CW-IL resulted in higher values of ascorbic acid content than the control. Regarding the economic analysis, CW-IL resulted in the highest net income rate (12.70%) compared with the control. Therefore, the light sources of CW-IL were assessed as suitable for supplemental lighting due to the highest total soluble solids, ascorbic acid content, and net income rate obtained.

Fruit quality and volatile compounds of greenhouse sweet peppers as affected by the LED spectrum of supplementary interlighting

BACKGROUND

Seasonal low light intensity and short photoperiods lead to decreased yield, size, and quality of fruits in the Northern Hemisphere. Recently, supplemental lighting using light-emitting diodes (LEDs) has been introduced to overcome such problems. However, most studies have focused on plant growth or fruit yield but not on taste. This study aimed to evaluate the quality and volatile compounds of greenhouse sweet pepper fruits under three different lighting conditions: natural light only (NL), NL with red/blue interlighting (RB), and NL with red/blue/far-red interlighting (RBFR).

RESULTS

The size, color, firmness, and soluble sugar concentration of the sweet pepper fruit were investigated, and sensory evaluation was conducted by nine trained panelists. Individual fruit fresh weights were higher in the order of RBFR, NL, and RB, with mean values of 219.1, 201.7, and 197.4 g, respectively. Additionally, the composition of volatile compounds demonstrated a distinct clustering pattern by light treatment, implying that the LED interlighting spectra affected the overall taste of sweet pepper fruits. Sensory evaluation indicated that sweetness was higher in the order of RBFR, RB, and NL, with values of 5.28, 4.36, and 3.72, respectively. The soluble sugar results showed the same order as that for the sensory evaluation of sweetness, i.e., RBFR, RB, and NL, with values of 5071, 4647, and 3978 μg ^-1 fresh weight, respectively.

CONCLUSION

Adding far-red to RB interlighting could improve the fruit quality attributes, fruit taste perception, and soluble sugars of sweet peppers compared to those under RB or solely NL. © 2023 Society of Chemical Industry.

Effects of light spectrum on the morphophysiology and gene expression of lateral branching in Pepino (Solanum muricatum)

In the present study, we determined the morphological and physiological indicators of Pepino to elucidate its lateral branching responses to different light qualities using a full-spectrum lamp (F) as the control and eight different light ratios using blue light (B) and red light (R). In addition, correlation analysis revealed that the gene expression patterns correlated with lateral branching under various light treatments. Compared with the F treatment, the R treatment increased the plant height and inhibited the elongation of lateral branches, in contrast with the B treatment. The number of lateral branches did not change significantly under different light quality treatments. Moreover, correlation analysis showed that the ratio of blue light was significantly positively correlated with the length of lateral branches and significantly negatively correlated with plant height, aboveground dry weight, and other indicators. We conducted transcriptome sequencing of the sites of lateral branching at three periods under different light quality treatments. The gene related to photodynamic response, cryptochrome (CRY), was the most highly expressed under B treatment, negatively regulated lateral branch length, and positively correlated with plant height. Branched 1, a lateral branch regulation gene, was upregulated under R treatment and inhibited branching. Overall, the red light facilitated internode elongation, leaf area expansion, plant dry weight increase, and inhibition of lateral branching. Soluble sugar content increased, and the lateral branches elongated under blue light. Different light qualities regulated lateral branching by mediating different pathways involving strigolactones and CRY. Our findings laid a foundation for further clarifying the response mechanism of Pepino seedlings to light and provided a theoretical reference for elucidating the regulation of different light qualities on the lateral branching of Pepino.