Enhanced drought tolerance and photosynthetic efficiency in Arabidopsis by overexpressing phosphoenolpyruvate carboxylase from a single-cell C4 halophyte Suaeda aralocaspica

In crop genetic improvement, the introduction of C4 plants' characteristics, known for high photosynthetic efficiency and water utilization, into C3 plants has been a significant challenge. This study investigates the effects of the desert halophyte Suaeda aralocaspica SaPEPC1 gene from a single-cell C4 photosythetic pathway, on drought resistance and photosynthetic performance in Arabidopsis. We used transgenic Arabidopsis with Zea mays ZmPEPC1 from C4 plant with classic Kranz anatomical structure and Arabidopsis AtPEPC1 from C3 photosynthetic cycle plants as controls. The results demonstrated that C4 photosynthetic-type PEPCs could improve drought resistance in plants through stomatal closure, promoting antioxidant enzyme accumulation, and reducing reactive oxygen species (ROS) accumulation. Overexpression of SaPEPC1 was significantly more effective than ZmPEPC1 in enhancing drought tolerance. Notably, overexpressed SaPEPC1 significantly improved light saturation intensity, electron transport rate (ETR), photosynthetic rate (Pn), and photoprotection ability under intense light. Furthermore, overexpression SaPEPC1 or ZmPEPC1 enhanced the activity of key C4 photosynthetic enzymes, including phosphoenolpyruvate carboxylase (PEPC), pyruvate orthophosphate dikinase (PPDK) and NADP-malic enzyme (NADP-ME), and promoted photosynthetic product sugar accumulation. However, with AtPEPC1 overexpression showing no obvious improvement effect on drought and photosynthetic performance. Therefore, these results indicated that introducing C4-type PEPC into C3 plants can significantly enhance drought resistance and photosynthetic performance. However, SaPEPC1 from a single-cell C4 cycle plant exhibits more significant effect in ETR and PSII photosynthesis performance than ZmPEPC1 from a classical C4 anatomical structure plant, although the underlying mechanism requires further exploration.

Tolerance enhancement of Dendrobium officinale by salicylic acid family-related metabolic pathways under unfavorable temperature

BACKGROUND

Unfavorable temperatures significantly constrain the quality formation of Dendrobium officinale, severely limiting its food demand. Salicylic acid (SA) enhances the resistance of D. officinale to stress and possesses various analogs. The impact and mechanism of the SA family on improving the quality of D. officinale under adverse temperature conditions remains unclear.

RESULTS

Combined with molecular docking analysis, chlorophyll fluorescence and metabolic analysis after treatments with SA analogues or extreme temperatures are performed in this study. The results demonstrate that both heat and cold treatments impede several main parameters of chlorophyll fluorescence of D. officinale, including the ΦPSII parameter, a sensitive growth indicator. However, this inhibition is mitigated by SA or its chemically similar compounds. Comprehensive branch imaging of ΦPSII values revealed position-dependent improvement of tolerance. Molecular docking analysis using a crystal structure model of NPR4 protein reveals that the therapeutic effects of SA analogs are determined by their binding energy and the contact of certain residues. Metabolome analysis identifies 17 compounds are considered participating in the temperature-related SA signaling pathway. Moreover, several natural SA analogs such as 2-hydroxycinnamic acid, benzamide, 2-(formylamino) benzoic acid and 3-o-methylgallic acid, are further found to have high binding ability to NPR4 protein and probably enhance the tolerance of D. officinale against unfavorable temperatures through flavone and guanosine monophosphate degradation pathways.

CONCLUSIONS

These results reveal that the SA family with a high binding capability of NPR4 could improve the tolerance of D. officinale upon extreme temperature challenges. This study also highlights the collaborative role of SA-related natural compounds present in D. officinale in the mechanism of temperature resistance and offers a potential way to develop protective agents for the cultivation of D. officinale.

Molecular Insights into the Defense of Dioscorea opposita Cultivar Tiegun Callus Against Pathogenic and Endophytic Fungal Infection Through Transcriptome Analysis

Dioscorea opposita cultivar Tiegun is an economically important crop with high nutritional and medicinal value. Plants can activate complex and diverse defense mechanisms after infection by pathogenic fungi. Moreover, endophytic fungi can also trigger the plant immune system to resist pathogen invasion. However, the study of the effects of endophytic fungi on plant infection lags far behind that of pathogenic fungi, and the underlying mechanism is not fully understood. Here, the black spot pathogen Alternaria alternata and the endophytic fungus Penicillium halotolerans of Tiegun were identified and used to infect calli. The results showed that A. alternata could cause more severe membrane lipid peroxidation, whereas P. halotolerans could rapidly increase the activity of the plant antioxidant enzymes superoxide dismutase, peroxidase, and catalase; thus, the degree of damage to the callus caused by P. halotolerans was weaker than that caused by A. alternata. RNA sequencing analysis revealed that various plant defense pathways, such as phenylpropanoid biosynthesis, flavonoid biosynthesis, plant hormone signal transduction, and the mitogen-activated protein kinase signaling pathway, play important roles in triggering the plant immune response during fungal infection. Furthermore, the tryptophan metabolism, betalain biosynthesis, fatty acid degradation, flavonoid biosynthesis, tyrosine metabolism, and isoquinoline alkaloid biosynthesis pathways may accelerate the infection of pathogenic fungi, and the ribosome biogenesis pathway in eukaryotes may retard the damage caused by endophytic fungi. This study lays a foundation for exploring the infection mechanism of yam pathogens and endophytic fungi and provides insight for effective fungal disease control in agriculture.

Effect of different LED-lighting quality conditions on growth and photosynthetic characteristics of saffron plants (Crocus sativus L.)

The effects of different light-emitting diode (LED) lights on saffron growth and photosynthetic characteristic were explored. Physiological mechanisms were explained by chlorophyll a fluorescence transient curves (OJIP) and JIP-test parameters. A decrease in the red to blue light ratio resulted in negative effects, particularly for monochromatic blue (B) LED light; saffron seedlings showed reduced chlorophyll accumulation, inhibited leaf elongation, and decreased photosynthetic performance. In the OJIP curve, the higher positive K-band observed for B LED light indicated that oxygen-evolving complex activation significantly decreased. B LED light inhibited the electron transport between primary quinone acceptor and secondary quinone acceptor as well as the existence of reducing plastoquinone centers, and increased energy dissipation of reaction centers. Otherwise, the red to blue light ratio of 2:1 had a positive effect on saffron cultivation, resulting in the longest leaf lengths, highest chlorophyll content, and photosynthetic characteristics. This study provides theoretical guidance for saffron agricultural practices.

Effect on the Growth and Photosynthetic Characteristics of Anthurium andreanum (‘Pink Champion’, ‘Alabama’) under Hydroponic Culture by Different LED Light Spectra

Anthurium andreanum was one of the best indoor ornamental plants. Two cultivars of Anthurium andreanum (Pink Champion, Alabama) were used to investigate the effects of light quality on physiological and biochemical indexes. There were six different light quality treatments: Fluorescent Daylight Lamp (CK), and RB (100% Blue, 60% R + 40% B, 70% R + 30% B, 80% R + 20% B, 100% Red) provided by light emitting diodes (LED). The results showed that blue light was beneficial to shoot growth and dry matter accumulation, photosynthetic rate, soluble sugar, and POD activities. Red light was beneficial for the synthesis and accumulation of soluble protein, and could promote root growth. ‘Pink Champion’ and ‘Alabama’ obtained the relatively better morphological parameters, chlorophyll contents, photosynthetic parameters, and antioxidant enzyme activities in 7:3 and 6:4 treatments. The antioxidant enzyme (POD, SOD) activities under composite light of red and blue treatments were better than that of monochromatic red, blue light treatments and CK on the whole. Comprehensive evaluation showed that the treatment of 7:3 was a suitable light environment indoors and could be used as the preferred light quality ratio in the production and application of Anthurium andreanum.

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.

Photosynthetic apparatus performance of tomato seedlings grown under various combinations of LED illumination

It is already known that the process of photosynthesis depends on the quality and intensity of light. However, the influence of the new light sources recently used in horticulture, known as Light Emitting Diodes (LEDs), on this process is not yet fully understood. Chlorophyll a fluorescence measurement has been widely used as a rapid, reliable, and noninvasive tool to study the efficiency of the photosystem II (PSII) and to evaluate plant responses to various environmental factors, including light intensity and quality. In this work, we tested the responses of the tomato photosynthetic apparatus to different light spectral qualities. Our results showed that the best performance of the photosynthetic apparatus was observed under a mixture of red and blue light (R7:B3) or a mixture of red, green and blue light (R3:G2:B5). This was demonstrated by the increase in the effective photochemical quantum yield of PSII (Y[II]), photochemical quenching (qP) and electron transport rate (ETR). On the other hand, the mixture of red and blue light with a high proportion of blue light led to an increase in non-photochemical quenching (NPQ). Our results can be used to improve the production of tomato plants under artificial light conditions. However, since we found that the responses of the photosynthetic apparatus of tomato plants to a particular light regime were cultivar-dependent and there was a weak correlation between the growth and photosynthetic parameters tested in this work, special attention should be paid in future research.

The Effect of Supplementary LED Lighting on the Morphological and Physiological Traits of Miniature Rosa × Hybrida 'Aga' and the Development of Powdery Mildew (Podosphaera pannosa) under Greenhouse Conditions

We investigated the growth traits, flower bud formation, photosynthetic performance, and powdery mildew development in miniature Rosa × hybrida 'Aga' plants grown in the greenhouse under different light-emitting diode (LED) light spectra. Fluorescence-based sensors that detect the maximum photochemical efficiency of photosystem II (PS II) as well as chlorophyll and flavonol indices were used in this study. Five different LED light treatments as a supplement to natural sunlight with red (R), blue (B), white (W), RBW+FR (far-red) (high R:FR), and RBW+FR (low R:FR) were used. Control plants were illuminated only by natural sunlight. Plants were grown under different spectra of LED lighting and the same photosynthetic photon flux density (PPFD) (200 µmol m^-2 s^-1) at a photoperiod of 18 h. Plants grown under both RBW+FR lights were the highest, and had the greatest total shoot length, irrespective of R:FR. These plants also showed the highest maximum quantum yield of PS II (average 0.805) among the light treatments. Red monochromatic light and RBW+FR at high R:FR stimulated flower bud formation. Moreover, plants grown under red LEDs were more resistant to Podosphaera pannosa than those grown under other light treatments. The increased flavonol index in plants exposed to monochromatic blue light, compared to the W and control plants, did not inhibit powdery mildew development.

Effects of light quality on leaf growth and photosynthetic fluorescence of Brasenia schreberi seedlings

Brasenia schreberi J. F. Gmel, a perennial floating-leaved macrophyte with high economic value as an aquatic vegetable, has been listed as first-class endangered species in China, mainly due to its habitat loss. Protected cultivation is a potential strategy to meet the demand of both plant conservation and vegetable market, whereas pre-experiments are still needed before series of parameters can be properly set for the large-scale growth of the plants indoor. Light quality is one of the major factors controlling the development of plants and consequently becomes an important factor when planting B. schreberi indoor. This experiment used three artificial light sources to investigate the response of B. schreberi seedlings to different light qualities, including the red-blue LED light (red: blue = 5:1, RB-LED), the white LED light (W-LED) and the white fluorescent (W-Fluo). Our results indicated that the responses of B. schreberi towards varied light qualities differed from those of most terrestrial plants. The total leaf number of the RB-LED treatment was the highest; the number of the submerged leaf and the rolled leaf of the RB-LED treatment was higher than that of the other two treatments, but the number of floating leaves was the lowest. Both the specific leaf weight and the pigment contents per unit leaf area were the lowest in the RB-LED treatment. Quantum yield of PSⅡ (Φ_PSⅡ), electron transport rate (ETR) and photochemical quenching (qP) measured through light induction curves followed the sequence from high to low as W-Fluo > W-LED > RB-LED, whereas the trend of non-photochemical quenching (NPQ) reversed. The maximum potential ETR (P_s) and maximum ETR (ETR_m) derived from ETR curves further verified the trends.

Mechanisms Regulating the Dynamics of Photosynthesis Under Abiotic Stresses

Photosynthesis sustains plant life on earth and is indispensable for plant growth and development. Factors such as unfavorable environmental conditions, stress regulatory networks, and plant biochemical processes limits the photosynthetic efficiency of plants and thereby threaten food security worldwide. Although numerous physiological approaches have been used to assess the performance of key photosynthetic components and their stress responses, though, these approaches are not extensive enough and do not favor strategic improvement of photosynthesis under abiotic stresses. The decline in photosynthetic capacity of plants due to these stresses is directly associated with reduction in yield. Therefore, a detailed information of the plant responses and better understanding of the photosynthetic machinery could help in developing new crop plants with higher yield even under stressed environments. Interestingly, cracking of signaling and metabolic pathways, identification of some key regulatory elements, characterization of potential genes, and phytohormone responses to abiotic factors have advanced our knowledge related to photosynthesis. However, our understanding of dynamic modulation of photosynthesis under dramatically fluctuating natural environments remains limited. Here, we provide a detailed overview of the research conducted on photosynthesis to date, and highlight the abiotic stress factors (heat, salinity, drought, high light, and heavy metal) that limit the performance of the photosynthetic machinery. Further, we reviewed the role of transcription factor genes and various enzymes involved in the process of photosynthesis under abiotic stresses. Finally, we discussed the recent progress in the field of biodegradable compounds, such as chitosan and humic acid, and the effect of melatonin (bio-stimulant) on photosynthetic activity. Based on our gathered researched data set, the logical concept of photosynthetic regulation under abiotic stresses along with improvement strategies will expand and surely accelerate the development of stress tolerance mechanisms, wider adaptability, higher survival rate, and yield potential of plant species.

Effects of LED photoperiods and light qualities on in vitro growth and chlorophyll fluorescence of Cunninghamia lanceolata

BACKGROUND

Cunninghamia lanceolata (C. lanceolata) is the main fast-growing timber species in southern China. As an alternative to conventional lighting systems, LED has been demonstrated to be an artificial flexible lighting source for commercial micropropagation. The application of LED can provide rapid propagation of C. lanceolata in vitro culture.

RESULTS

We applied two-factor randomized block design to study the effects of LED photoperiods and light qualities on the growth and chlorophyll fluorescence of C. lanceolata in vitro culture plantlets. In this study, plantlets were exposed to 20 μmol·m^- 2·s^- 1 irradiance for three photoperiods, 8, 16, and 24 h under the three composite lights, 88.9% red+ 11.1% blue (R/B), 80.0% red+ 10.0% blue+ 10.0% purple (R/B/P), 72.7% red+ 9.1% blue+ 9.1% purple+ 9.1% green (R/B/P/G), as well as white light (12.7% red+ 3.9% blue+ 83.4% green, W) as control. The results showed that: (1) Plant height, dry weight, rooting rate, average root number, length, surface area and volume, chlorophyll, and chlorophyll fluorescence parameters were significantly affected by photoperiods, light qualities and their interactions. (2) Plantlets subjected to photoperiod 16 h had longer root, higher height, rooting rate, root number, and the higher levels of chlorophyll, chlorophyll a/b, Y (II), qP, NPQ/4 and ETR_II compared to photoperiods 8 h and 24 h, while Fv/Fm during photoperiod 16 h was lower than 8 h and 24 h. Plantlets exposed to R/B/P/G generated more root and presented higher chlorophyll, Fv/Fo, Y (II), qP, and ETR_II than W during photoperiods 8 and 16 h. (3) Total chlorophyll content and ETR_II were significant correlated with rooting rate, root length and root volume, while Fv/Fm and ETR_II were significant correlated with plant height, average root number and root surface area. (4) 16-R/B/P/G is best for growing C. lanceolata plantlets in vitro.

CONCLUSIONS

This study demonstrated the effectiveness of photoperiods and light qualities using LEDs for micropropagation of C. lanceolata. The best plantlets were harvested under 16-R/B/P/G treatment. And there was a correlation between the growth and the chlorophyll and chlorophyll fluorescence of their leaves under different photoperiod and light quality. These results can contribute to improve the micropropagation process of this species.

Effects of Composite LED Light on Root Growth and Antioxidant Capacity of Cunninghamia lanceolata Tissue Culture Seedlings

We used the 12^th generation of the Cunninghamia (C.) lanceolata tissue culture seedlings, and white light emitting diode (LED) light as control (CK). We applied five composite LED light treatments, red-blue 4:1, 8:1 (4R1B and 8R1B), red-blue-purple 8:1:1 (8R1B1P), and red-blue-purple-green 6:1:1:1, 8:1:1:1 (6R1B1P1G and 8R1B1P1G), to study the effects of light quality on root growth characteristics and antioxidant capacity of C. lanceolata tissue culture seedlings. The results showed that: (1) rooting rate, average root number, root length, root surface area, and root activity were higher with 6R1B1P1G and 8R1B1P1G treatments compared to 4R1B, 8R1B, 8R1B1P and CK treatments; and the root growth parameters under the 8R1B1P1G treatment were as high as 95.50% for rooting rate, 4.63 per plant of the average number of root, 5.95 cm root length, 1.92 cm² surface area, and 145.56 ng/(g·h) root activity, respectively. (2) The composite lights of 4R1B, 8R1B, 8R1B1P, 6R1B1P1G, and 8R1B1P1G are beneficial for the accumulation of soluble sugar content (SSC) and soluble protein content (SPC), but not conducive for the increase of free proline content (FPC); the plants under 6R1B1P1G and 8R1B1P1G treatments had higher superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) activity and lower malondialdehyde (MDA), polyphenol oxidase (PPO) activity. (3) Redundancy analysis showed that POD activity positively correlated with root activity; SPC, SOD and CAT activities positively correlated with root growth parameters; while SSC, MDA content, APX and PPO activities negatively correlated with root growth parameters. These results suggest that the responses of root growth and antioxidant capacity of the C. lanceolata tissue culture seedlings to different light qualities vary. The relationship between root growth parameters and antioxidant capacity was closely related. Red-blue-purple-green was the most suitable composite light quality for root growth of C. lanceolata tissue culture seedlings, and 8:1:1:1 was the optimal ratio, under which the rooting rate, root activity and root growth of tissue culture seedlings peaked.