Rubisco Activity Research Articles

Sustainable transforming toxic sludge into amino acids via bacteria-algae consortium

The utilization of residual sludge by microalgae represents an environmentally sustainable method for resource recovery. In this study, Tetradesmus obliquus was cultured in hydrolysate derived from toxic sludge. Under symbiotic conditions with bacteria, Tetradesmus obliquus demonstrated enhanced toxin degradation capability and biomass accumulation, which exhibited a 1.39-fold increase in algal cell density, a 1.50-fold increase in Rubisco activity, and a total protein content of 341.83 ± 6.99 mg/L on the 30th day of cultivation. Metabolic utilization of substances in the hydrolysate by microalgae led to a toxicity removal rate of up to 60.43% by day 10. Phenylalanine showed the most significant increase among essential amino acids, and transcriptomic profiling identified genes (gene_16399, gene_16602) involved in phenylalanine enrichment. Macrotranscriptomics showed that bacteria upregulated the TCS system and tryptophan metabolism, supplying microalgae with more CO2 and IAA, which enhanced amino acid enrichment. This study established a non-toxic and biomass-accumulating bacterial-algal co-cultivation system.

Cyanobacterial Cultures, Cell Extracts, and Individual Toxins Decrease Photosynthesis in the Terrestrial Plants Lactuca sativa and Zea mays

Cyanobacterial harmful algal blooms (cHABs) are increasing due to eutrophication and climate change, as is irrigation of crops with freshwater contaminated with cHAB toxins. A few studies, mostly in aquatic protists and plants, have investigated the effects of cHAB toxins or cell extracts on various aspects of photosynthesis, with variable effects reported (negative to neutral to positive). We examined the effects of cyanobacterial live cultures and cell extracts (Microcystis aeruginosa or Anabaena flos-aquae) and individual cHAB toxins (anatoxin-a, ANA; beta-methyl-amino-L-alanine, BMAA; lipopolysaccharide, LPS; microcystin-LR, MC-LR) on photosynthesis in intact plants and leaf pieces in corn (Zea mays) and lettuce (Lactuca sativa). In intact plants grown in soil or hydroponically, overall net photosynthesis (Pn), but not Photosystem-II (PSII) electron-transport yield (ΦPSII), decreased when roots were exposed to cyanobacterial culture (whether with intact cells, cells removed, or cells lysed and removed) or individual toxins in solution (especially ANA, which also decreased rubisco activity); cyanobacterial culture also decreased leaf chlorophyll concentration. In contrast, ΦPSII decreased in leaf tissue vacuum-infiltrated with cyanobacterial culture or the individual toxins, LPS and MC-LR, though only in illuminated (vs. dark-adapted) leaves, and none of the toxins caused significant decreases in in vitro photosynthesis in thylakoids. Principal component analysis indicated unique overall effects of cyanobacterial culture and each toxin on photosynthesis. Hence, while cHAB toxins consistently impacted plant photosynthesis at ecologically relevant concentrations, the effects varied depending on the toxins and the mode of exposure.

Simulation of Defoliation Effects on Relay Strip Intercropping Soybean: Elucidating Foliar Shedding and Leaf-to-Nodule Growth Plasticity.

Extensive foliar shedding in monoculture soybeans post-anthesis negatively impacts yield, whereas relay strip intercropping prolongs leaf area duration, enhancing productivity. However, little is known about the causes of leaf shedding in monoculture and its impact on physiological functions and plasticity of source and sink organs, we conducted a 4-year field experiment and leaf-removal simulations in relay intercropped soybeans. Results revealed that monoculture soybeans experienced severe self-shading and defoliation, while relay intercropping maintained better light conditions, supporting higher leaf area, nodule numbers, and carbon allocation. Increasing leaf removal initially increased leaf area but eventually reduced it. Extensive leaf-removal reduced Rubisco and sucrose phosphate synthase (SPS) activity, as well as sucrose, malate, ATP, and energy charge (EC) in nodules, revealing a trade-off between leaf growth and nodule development. Moderate leaf-removal (L30), however, balanced compensation and consumption, increasing total non-structural carbohydrates (TNC) in roots and N and ureide in leaves and pods. Network analysis showed that L30 improved the synergies of functional traits in leaves and nodules, ultimately benefiting overall plant growth and nutrient accumulation in pods. This study elucidates a mechanism of foliar shedding and highlights how relay strip intercropping optimizes source-sink coordination to enhance photosynthesis and nitrogen fixation.

Priming with multiwalled carbon nanotubes improved biomass accumulation, biological activityand metabolism of four horticultural plants during the sprouting stage.

It is imperative to enhance the quality of sprouts since they are a rich source of various primary and secondary metabolites. The objective of this work was to examine how multiwalled carbon nanotubes (MWCNTs) priming at various concentrations affected the nutritional qualities of four horticultural plants (T. foenum-graecum, L. grandiflorum, L. sativum and A. graveolens) and their sprouting processes. Among the four applied concentrations (10-60 mgL-1), MWCNTs at 10 and 40 mg L⁻¹ induced the highest biomass accumulation in L. grandiflorum and T. foenum-graecum, respectively, while 60 mg L⁻¹ was most effective for L. sativum and A. graveolent. MWCNTs induced growth by enhancing photosynthesis, as shown by increased chlorophyll content and rubisco activity, which rose by 27%, 17%, 23% and 12% in T. foenum-graecum, L. grandiflorum, L. sativum, and A. graveolens, respectively. Enhanced photosynthesis by MWCNTs improved sugar metabolism as indicated by increased activity of sugar metabolic enzymes such as amylase, starch synthase and invertase. This also supplied the carbon necessary for the production of primary (amino acids, fatty acids and organic acids) and secondary (flavonoids and polyphenols) metabolites. There was consistently higher activity of antioxidant enzymes (catalase and peroxidase). Interestingly, species-specific reactions to MWCNT priming were observed, where L. sativum sprouts showed the highest antioxidant activity, followed by A. graveolens. MWCNT priming improves sprout growth and nutritional quality by boosting metabolic processes and antioxidant activity, presenting a promising approach for sustainable agriculture. © 2024 Society of Chemical Industry.

Rubisco activity and activation state dictate photorespiratory plasticity in Betula papyrifera acclimated to future climate conditions

Plant metabolism faces a challenge of investing enough enzymatic capacity to a pathway without overinvestment. As it takes energy and resources to build, operate, and maintain enzymes, there are benefits and drawbacks to accurately matching capacity to the pathway influx. The relationship between functional capacity and physiological load could be explained through symmorphosis, which would quantitatively match enzymatic capacity to pathway influx. Alternatively, plants could maintain excess enzymatic capacity to manage unpredictable pathway influx. In this study, we use photorespiration as a case study to investigate these two hypotheses in Betula papyrifera. This involves altering photorespiratory influx by manipulating the growth environment, via changes in CO2 concentration and temperature, to determine how photorespiratory capacity acclimates to environmental treatments. Surprisingly, the results from these measurements indicate that there is no plasticity in photorespiratory capacity in B. papyrifera, and that a fixed capacity is maintained under each growth condition. The fixed capacity is likely due to the existence of reserve capacity in the pathway that manages unpredictable photorespiratory influx in dynamic environments. Additionally, we found that B. papyrifera had a constant net carbon assimilation under each growth condition due to an adjustment of functional rubisco activity driven by changes in activation state. These results provide insight into the acclimation ability and limitations of B. papyrifera to future climate scenarios currently predicted in the next century.

Artificial humic acid promotes carbon sequestration in rice-soil system

Artificial humic acid (AHA) is a new exogenous organic material with enormous carbon sequestration potential. However, the effects and mechanisms of applying AHA under different irrigation regimes on carbon sequestration in rice-soil systems still need to be clarified. This study applied carbon isotope labeling technology to analyze the photosynthetic carbon sequestration capacity, the carbon transport capacity of the root, and greenhouse gas emission flux in the rice-soil system under different irrigation regimes and AHA application conditions. The results showed that as the amount of AHA applied increased, the leaf area and chlorophyll concentration gradually increased, the Rubisco activity first increased and then decreased under two irrigation regimes. In alternate wetting and drying irrigation with 300 mg kg-1 AHA treatment (DWI3), the photosynthetic carbon fixation ability was the highest, with Pn, Fv/Fm, and qP increasing by 65.35%, 214.85%, and 43.15% compared to alternate wetting and drying irrigation without applying AHA treatment (DWI0), respectively. Meanwhile, during DWI3 treatment, the organic acid concentration in root exudates, root biomass, root length, root surface area, and root length density were also the highest. In summary, among all treatments in this study, the content of 13C in soil under DWI3 treatment was highest, closely related to the strongest photosynthetic carbon fixation and root transport capacity under this treatment, as well as the lower greenhouse gas emission flux. Therefore, it is recommended to apply 300 mg kg-1 AHA with alternate wetting and drying irrigation for carbon sequestration, water conservation, and sustainable agricultural development.

Mitigating effects of Nigeria seaweed phytonutrients on biochemical and physiological conditions of Lycopersicon esculentum under heavy metal-induced abiotic stress

Abiotic stress has become a significant issue in recent years, affecting various physiological and biochemical aspects of crops and threatening food security. This study aimed to investigate the effects of seaweed on the biochemical and physiological conditions of Lycopersicon esculentum under heavy metal-induced abiotic stress. Lycopersicon esculentum plants were grown in greenhouse bags for four weeks and then exposed to 0.10M Pb Nitrate. They were divided into six groups: one control group sprayed with tap water and five experimental groups sprayed with different seaweed concentrations (0%, 20%, 40%, 60%, and 80%). Results showed that abiotic stress led to notable decreases in root length, shoot length, chlorophyll a, chlorophyll b, stomatal conductance, photosynthetic rate, Rubisco activity, and carotenoids by 48%, 47% 38%, 65%, 61%, 77%, 75%, and 68%, respectively. Seaweed treatment improved these indices, with the 80% seaweed group showing increases of 27%, 21%, 44%, 36%, 56%, and 48%, 54% after 21 days. Additionally, seaweed application enhanced antioxidant activities in the roots (SOD by 71%, CAT by 45%, POD by 51%, and APX by 92%) and in the leaves (SOD by 18%, CAT by 26%, POD by 34%, APX by 58%) compared to the control. The study concluded that seaweeds significantly mitigated oxidative stress in plants, boosting growth, antioxidant potential, mineral absorption, and osmotic protection. Nigeria seaweeds could be a promising tool to enhance food production by reducing oxidative stress in crops.

Enhancing cold tolerance in tobacco through endophytic symbiosis with Piriformospora indica.

Tobacco, a warm-season crop originating from the Americas, is highly susceptible to cold stress. The utilization of symbiotic fungi as a means to bolster crops' resilience against abiotic stresses has been proven to be a potent strategy. In this study, we investigated the effect of endophytic fungus Piriformospora indica on the cold resistance of tobacco. When exposed to cold stress, the colonization of P.indica in tobacco roots effectively stimulates the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX). This, in turn, reduces the accumulation of reactive oxygen species (ROS), thereby mitigating oxidative damage. Additionally, P. indica elevates the levels of osmolytes, such as soluble sugars, proline, and soluble proteins, thus facilitating the restoration of osmotic balance. Under cold stress conditions, P. indica also induces the expression of cold-responsive genes. Furthermore, this fungus not only enhances photosynthesis in tobacco by stimulating the synthesis of photosynthetic pigments, strengthening Rubisco activity, and elevating PSII efficiency, but also fortifies tobacco's nitrogen assimilation by inducing the expression of nitrate transporter gene and activating enzymes related to nitrogen assimilation. Consequently, this synergistic optimization of nitrogen and carbon assimilation provides a solid material and energetic foundation for tobacco plants to withstand cold stress. Our study demonstrates that a mycorrhizal association between P. indica and tobacco seedlings provides multifaceted protection to tobacco plants against low-temperature stress and offers a valuable insight into how P. indica enhances the cold tolerance of tobacco.

Carbon and energy metabolism for the mixotrophic culture of Chlorella vulgaris using sodium acetate as a carbon source.

There has been an emergence of a diversity of microalgal mixotrophic synergistic mechanisms due to substrate differences. In this study, the effects of the mixotrophic culture of Chlorella vulgaris were examined. The maximum values of cell density, specific growth rate, and cell dry weight of Chlorella vulgaris were 3.52*107 cells/mL, 0.75 d-1, and 3.48 g/L in the mixotrophic mode, respectively. These were higher than the corresponding values of photoautotrophic or heterotrophic modes. Moreover, it was found that the concentrations of sodium bicarbonate consumed by the Chlorella vulgaris under mixotrophic and photoautotrophic modes were 635 mg/L/d and 505 mg/L/d, respectively; the concentrations of sodium acetate consumed by the Chlorella vulgaris under mixotrophic and heterotrophic modes were 614 mg/L/d and 645 mg/L/d, respectively. The activity of Rubisco was 9.36 U/mL in the mixotrophic culture, which was 3.09 and 4.85 times higher than that of the photoautotrophic and heterotrophic modes, respectively. This indicated that the differences for the carbon source absorption efficiency of Chlorella vulgaris in the mixotrophy led to different internal metabolic efficiencies when compared to photoautotroph or heterotrophy. Additionally, Chlorella vulgaris exhibits a more rapid energy metabolism efficiency when operating in the mixotrophic mode.

C4 grasses employ distinct strategies to acclimate rubisco activase to heat stress.

Rising temperatures due to the current climate crisis will soon have devastating impacts on crop performance and resilience. In particular, CO2 assimilation is dramatically limited at high temperatures. CO2 assimilation is accomplished by rubisco, which is inhibited by the binding of inhibitory sugar phosphates to its active site. Plants therefore utilize the essential chaperone rubisco activase (RCA) to remove these inhibitors and enable continued CO2 fixation. However, RCA does not function at moderately high temperatures (42°C), resulting in impaired rubisco activity and reduced CO2 assimilation. We set out to understand temperature-dependent RCA regulation in four different C4 plants, with a focus on the crop plants maize (two cultivars) and sorghum, as well as the model grass Setaria viridis (setaria) using gas exchange measurements, which confirm that CO2 assimilation is limited by carboxylation in these organisms at high temperatures (42°C). All three species express distinct complements of RCA isoforms and each species alters the isoform and proteoform abundances in response to heat; however, the changes are species-specific. We also examine whether the heat-mediated inactivation of RCA is due to biochemical regulation rather than simple thermal denaturation. We reveal that biochemical regulation affects RCA function differently in different C4 species, and differences are apparent even between different cultivars of the same species. Our results suggest that each grass evolved different strategies to maintain RCA function during stress and we conclude that a successful engineering approach aimed at improving carbon capture in C4 grasses will need to accommodate these individual regulatory mechanisms.

Non-Foliar Photosynthesis in Pea (Pisum sativum L.) Plants: Beyond the Leaves to Inside the Seeds

In addition to leaves, photosynthesis can occur in other green plant organs, including developing seeds of many crops. While the majority of studies examining photosynthesis are concentrated on the leaf level, the role of other green tissues in the production of total photoassimilates has been largely overlooked. The present work studies the photosynthetic behavior of leaves and non-foliar (pericarps, coats, and cotyledons) organs of pea (Pisum sativum L.) plants at the middle stage of seed maturation. The Chl a fluorescence transient was examined based on OJIP kinetics using the FluorPen FP 110. A discrepancy was observed between the performance index (PIABS) for foliar and non-foliar plant tissues, with the highest level noted in the leaves. The number of absorbed photons (ABS) and captured energy flow (TRo) per reaction center (RC) were elevated in the non-foliar tissues, which resulted in a faster reduction in QA. Conversely, the energy dissipation flux per RC (DIo/RC and PHI_Do) indicated an increase in the overall dissipation potential of active reaction centers of photosystem II. This phenomenon was attributed to the presence of a higher number of inactive RCs in tissues that had developed under low light intensity. Furthermore, the expression of genes associated with proteins and enzymes that regulate ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) activity was observed, including chaperonins Cpn60α and Cpn60β, RuBisCO activase, as well as phosphoribulokinase. The expression of these genes was found to differ between foliar and non-foliar tissues, indicating that the activation state of RuBisCO may be modified in response to light intensity. Overall, the present study provides insights into the mechanisms by which non-foliar green tissues of plants adapt to efficient light capture and utilization under low light conditions.

24-Epibrassinolide promoted growth and organic compounds accumulation in Dunaliella parva by enhancing photosynthesis

As a commonly used type of the sixth class of phytohormones brassinosteroids (BRs), 24-epibrassinolide (EBL) plays the important roles in plant growth and development. Dunaliella parva (D. parva) is an important lipid-producing microalga, and its growth and accumulation of organic compounds need to be further improved for higher application value. However, the effects of EBL on D. parva are still unclear now. In this study, D. parva was treated with different concentrations of 24-epibrassinolide (EBL) to evaluate its influence. Cell density of 0.5 mg/L EBL treated group was 1.28-fold of control at 18 d. The contents of chlorophyll, carotenoid, carbohydrate, starch, protein of 0.5 mg/L EBL treated group were 1.31-, 1.18-, 1.49-, 1.35-, and 1.54-fold of control. The highest mRNA levels of rbcS, rbcL, RuPE, PRK, TPI, FBPA, FBPase, SBPase, DpME, CA in EBL treated group were 1.94-, 2.43-, 2.14-, 1.76-, 1.97-, 2.21-, 1.48-, 1.96-, 2.06-, and 1.89-fold of control. The highest enzymatic activities of ME, CA and RuBisCO in EBL-treated group were 1.27-, 1.23-, and 1.37-fold of control. Lipid content of 0.4 mg/L EBL treated group was 1.44-fold of control. This study demonstrated the great potential of EBL to obtain higher biomass and organic compounds accumulation. Our study indicates that EBL treatment is valuable for the subsequent commercial production of biofuel and other high-value metabolites using microalgal biomass as raw material.

Response of blue light in different proportions on the growth & flowering in sunflower

Due to the light sensitivity of sunflowers, regulating spectral composition holds significant potential for optimizing sunflower growth and flowering to meet market demands. In this study, sunflower plants were exposed to white light (W200, control) and three levels of blue light (B40R80Fr80 with blue light intensity of 40 µmol m−2 s−1; B67R67Fr67 with blue light intensity of 67 µmol m−2 s−1; B100R50Fr50 with blue light intensity of 100 µmol m−2 s−1) under an overall irradiance level of 200 µmol m−2 s−1 for 60 days. The aim was to investigate the effects on sunflower morphology regulation, leaf growth, and flowering. Results demonstrated that the growth of sunflowers under B40R80Fr80 treatment with 20 % blue light inhibited plant height compared with B67R67Fr67 and B100R50Fr50 treatments. The highest total leaf dry weight was observed in sunflower leaves under the B100R50Fr50 treatment. Leaves under B67R67Fr67 treatment enhanced activities of Glyceraldehyde 3-phosphate dehydrogenase, Fructose-1,6-bisphosphate aldolase, and soluble starch synthase, along with a 10.4 % increase in Rubisco activity compared with B100R50Fr50 treatment. The sucrose and starch content under B67R67Fr67 treatment increased by 41.0 % and 19.1 % than those of B100R50Fr50 treatment, respectively. Sunflower plants under B67R67Fr67 treatment significantly improved flower disk diameter and No. of petal per flower compared with W200 treatment. Phenotype-assisted transcriptome analysis revealed that B67R67Fr67 treatment on sunflower leaves had positive effects on circadian rhythm-related genes associated with flowering [CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) and FLOWERING LOCUS T (FT)], compared with B100R50Fr50 treatment. Additionally, four genes related to GA metabolism were identified for flower development regulation; LOC110884159 and LOC110890361 (GID1B) were up-regulated under B67R67Fr67 treatment. Sunflower leaves under B67R67Fr67 treatment increased GA content and induced the GA pathway related to circadian rhythm, compared with those of B100R50Fr50 treatment. Consequently, the implementation of B67R67Fr67 treatment led to improved circadian rhythm and GA pathway activation, resulting in induced flowering to fulfill market demands for sunflowers.

Critical stages in pea photosynthesis impaired by tetracycline as an environmental contaminant.

The widespread use of antibiotics in intensive animal husbandry, and the agricultural utilization of manure from such farms, imposes a significant burden on the environment. Consequently, the effects of antibiotics should be studied not only in animals and humans but also in all components of biocenoses and agrocenoses. In our study, we analyze the impact of four different concentrations of tetracycline present in soil (0, 5, 50, and 500mg/kg of soil) on the growth and key photosynthesis parameters of pea seedlings: chlorophyll concentration, aminolevulinic acid concentration, aminolevulinic acid dehydrogenase activity, and ribulose bisphosphate carboxylase-oxygenase (RuBisCO) activity. At the lowest tetracycline concentration, chlorophyll content decreased by 13% compared to the control (0 tetracycline), while at the highest antibiotic concentration, it decreased by as much as 27%. Similarly, the decrease in aminolevulinic acid (a chlorophyll precursor) concentration was significant, amounting to 34%. However, the activity of the dehydrogenase enzyme, which consumes this precursor, decreased even more drastically by 51%, indicating significant disturbances in the light phase of photosynthesis. However, the activity of RuBisCO in pea plants subjected to tetracycline was even more severely affected, dropping by 58%, 69%, and 70% in soils with increasing concentrations of tetracycline. The reduction in enzyme activity could only partially be explained by a less pronounced decrease in the quantity of RuBisCO (large subunit) protein, which amounted to 6.5%, 11%, and 35% for tetracycline concentrations of 5, 50, and 500mg/kg of soil, respectively.

Effects of LED polarized and vortex light on growth and photosynthetic characteristics of pepper (Capsicum annuum L.)

Most studies currently focus on traditional illuminant regulating plant growth, while less attention has been given to the LED internal luminescence. This study examined how polarized and vortex light affect the growth and photosynthetic traits of pepper plants, with LED light used as the control. The findings indicated that circular polarized light significantly increased the aboveground biomass of pepper. Additionally, both polarized and vortex light treatment significantly influenced the root development of pepper. In comparison to the control group, the chlorophyll content was highest under circular polarized light, while the Pn, Sc, Tr, and Ci values were highest under linear polarized light, and the enzyme activity of Rubisco was increased. Circular polarized light notably increased the activities of POD, CAT, and SOD, the activity of SOD reached its peak under the left vortex light. Moreover, the content of MDA was observed to be the lowest under linear and right vortex light treatments. The expressions of key genes for chlorophyll synthesis (CaHEMA1 and CaCAO) and antioxidant enzyme synthesis (CaPOD, CaSOD, and CaMDHAR) were significantly altered under varying polarized light conditions, The latter genes, which play crucial roles in antioxidant enzyme activity, also showed significant variations in response to different polarized light treatments. In conclusion, polarized light significantly impacts the growth of pepper and is anticipated to be utilized for plant growth, setting the stage for future research in this area.

Oxidation of sulfur, hydrogen, and iron by metabolically versatile Hydrogenovibrio from deep sea hydrothermal vents.

Chemolithoautotrophic Hydrogenovibrio are ubiquitous and abundant at hydrothermal vents. They can oxidize sulfur, hydrogen or iron, but none are known to use all three energy sources. This ability though would be advantageous in vents hallmarked by highly dynamic environmental conditions. We isolated three Hydrogenovibrio strains from vents along the Indian Ridge, which grow on all three electron donors. We present transcriptomic data from strains grown on iron, hydrogen or thiosulfate with respective oxidation and autotrophic CO2 fixation rates, RubisCO activity, SEM, and EDX. Maximum estimates of one strain's oxidation potential were 10, 24, and 952mmol for iron, hydrogen and thiosulfate oxidation and 0.3, 1, and 84mmol CO2 fixation, respectively, per vent per hour indicating their relevance for element cycling in-situ. Several genes were up- or downregulated depending on the inorganic electron donor provided. Although no known genes of iron-oxidation were detected, upregulated transcripts suggested iron-acquisition and so far unknown iron-oxidation-pathways.

Effects of cadmium stress on the growth and physiological characteristics of sweet potato

This study evaluated the responses of sweet potatoes to Cadmium (Cd) stress through pot experiments to theoretically substantiate their comprehensive applications in Cd-polluted agricultural land. The experiments included a CK treatment and three Cd stress treatments with 3, 30, and 150 mg/kg concentrations, respectively. We analyzed specified indicators of sweet potato at different growth periods, such as the individual plant growth, photosynthesis, antioxidant capacity, and carbohydrate Cd accumulation distribution. On this basis, the characteristics of the plant carbon metabolism in response to Cd stress throughout the growth cycle were explored. The results showed that T2 and T3 treatments inhibited the vine growth, leaf area expansion, stem diameter elongation, and tuberous root growth of sweet potato; notably, T3 treatment significantly increased the number of sweet potato branches. Under Cd stress, the synthesis of chlorophyll in sweet potato was significantly suppressed, and the Rubisco activity experienced significant reductions. With the increasing Cd concentration, the function of PS II was also affected. The soluble sugar content underwent no significant change in low Cd concentration treatments. In contrast, it decreased significantly under high Cd concentrations. Additionally, the tuberous root starch content decreased significantly with the increase in Cd concentration. Throughout the plant growth, the activity levels of catalase, peroxidase, and superoxide dismutase increased significantly in T2 and T3 treatments. By comparison, the superoxide dismutase activity in T1 treatment was significantly lower than that of CK. With the increasing application of Cd, its accumulation accordingly increased in various sweet potato organs. The the highest bioconcentration factor was detected in absorbing roots, while the tuberous roots had a lower bioconcentration factor and Cd accumulation. Moreover, the transfer factor from stem to petiole was the highest of the potato organs. These results demonstrated that sweet potatoes had a high Cd tolerance and a restoration potential for Cd-contaminated farmland.

Low nitrogen priming enhances Rubisco activation and allocation of nitrogen to the photosynthetic apparatus as an adaptation to nitrogen-deficit stress in wheat seedling

Reducing nitrogen (N) application is crucial in addressing the low N utilization efficiency (NUE) and the risks of environmental pollution in wheat production. Improving low N (LN) tolerance in wheat can help balance the conflict between wheat growth and reduced N fertilization. Hydroponic experiments were conducted using Yangmai158 (LN-tolerant) and Zaoyangmai (LN-sensitive) cultivars to study whether LN priming (LNP) in the 3-leaf stage can improve the photosynthetic capacity of wheat seedlings under N-deficit stress at the 5-leaf stage. LNP increased the net photosynthetic rate (Pn), stomatal conductance (Gs), electron transfer rate (ETR), carboxylation efficiency (CE), maximum carboxylation rate (Vcmax), and the content and activity of Rubisco and Rubisco activase (RCA) in both cultivars, with Yangmai158 showing a greater increase than Zaoyangmai. After 14 days of N-deficit stress, the decreases in Pn, Gs, ETR, CE, Vcmax, and the content and activity of Rubisco and RCA of the two cultivars treated with LNP were significantly lower compared with those of the treatments without LNP. LNP improved the allocation proportion of leaf N to photosynthetic machinery, with the greatest increase in the carboxylation machinery. These results indicate that LNP can allocate more N to the photosynthetic apparatus, improving Rubisco content and activity to enhance the photosynthetic capacity and NUE of leaves under N-deficit stress.

The Combined Application of Urea and Fulvic Acid Regulates Apple Tree Carbon and Nitrogen Metabolism and Improves Anthocyanin Biosynthesis

Improving apple peel color has been an important objective in apple production. To better understand the effect and mechanism of the combined application of urea and FA (fulvic acid) regulation of anthocyanin biosynthesis, a field experiment was performed in 2022 and 2023, respectively, under five treatments of urea + FA (CK, urea only; FA50, urea + 50 kg ha−1 FA; FA100, urea + 100 kg ha−1 FA; FA150, urea + 150 kg ha−1 FA; FA200, urea + 200 kg ha−1 FA), using isotope (13C and 15N) marking to analyze the changes in carbon (C) and nitrogen (N) nutrient distribution as well as anthocyanin biosynthesis in fruits. We observed that, under FA application conditions, anthocyanin content in the peel was elevated in both years, with increases of 15.98~52.88% in 2022 and 15.93~52.94% in 2023. The best promotion effects were observed under FA150 treatment. Apart from the expression levels of anthocyanin biosynthesis-related genes and transcription factors in the apple peel, this positive effect on anthocyanin content induced by FA addition was also found to be associated with the optimization of C and N distribution in leaves and fruits. On the one hand, the application of FA not only enhanced leaf photosynthetic-related indexes (such as Pn, Gs, and Rubisco activity) and influenced (increased) S6PDH, SPS, and SS activities in leaves, but also elevated fruit sugar metabolism-related enzyme (SDH, SS-c, AI, and NI) activity and upregulated fruit stalk sugar transporter (MdSOT1, MdSOT3, MdSUT1 and MdSUT4) gene expression, which ultimately promoted the synthesis and the leaf to fruit transport of photosynthates, thus promoting 13C-photosynthate accumulation in fruits. On the other hand, FA application elevated leaves’ N metabolism-related enzyme (GS and GOGAT) activity and optimized 15N distribution in leaves and fruits. Moreover, we also observed that FA application altered the fate of N fertilizer in apple orchards, showed an elevation in apple tree 15NUE and soil 15N residuals and showed a decrease in soil 15N loss. In summary, the appropriate application of FA150 (urea + 150 kg ha−1) synergistically optimized C and N nutrient distribution, and promoted anthocyanin biosynthesis in apple trees.

Native arbuscular mycorrhizal fungi drive ecophysiology through phenotypic integration and functional plasticity under the Sonoran desert conditions.

Knowledge is scarce to what extent environmental drivers and native symbiotic fungi in soil induce abrupt (short-term), systemic (multiple traits), or specific (a subset of traits) shifts in C3 plants' ecophysiological/mycorrhizal responses. We cultivated an emblematic native C3 species (Capsicum annuum var. glabriusculum, "Chiltepín") to look at how the extreme heat of the Sonoran desert, sunlight regimes (low = 2, intermediate = 15, high = 46 mol m2 d-1) and density of native arbuscular mycorrhizal fungi in soil (low AMF = 1% v/v, high AMF = 100% v/v), drive shifts on mycorrhizal responses through multiple functional traits (106 traits). The warming thresholds were relentlessly harsh even under intensive shade (e.g. superheat maximum thresholds reached ranged between 47-63°C), and several pivotal traits were synergistically driven by AMF (e.g. photosynthetic capacity, biomass gain/allometry, and mycorrhizal colonization traits); whereas concurrently, sunlight regimes promoted most (76%) alterations in functional acclimation traits in the short-term and opposite directions (e.g. survival, phenology, photosynthetic, carbon/nitrogen economy). Multidimensional reduction analysis suggests that the AMF promotes a synergistic impact on plants' phenotypic integration and functional plasticity in response to sunlight regimes; however, complex relationships among traits suggest that phenotypic variation determines the robustness degree of ecophysiological/mycorrhizal phenotypes between/within environments. Photosynthetic canopy surface expansion, Rubisco activity, photosynthetic nitrogen allocation, carbon gain, and differential colonization traits could be central to plants' overall ecophysiological/mycorrhizal fitness strengthening. In conclusion, we found evidence that a strong combined effect among environmental factors in which AMF are key effectors could drive important trade-offs on plants' ecophysiological/mycorrhizal fitness in the short term.