Phosphoenolpyruvate Carboxylase Activity Research Articles

Nitrogen Sources Reprogram Carbon and Nitrogen Metabolism to Promote Andrographolide Biosynthesis in Andrographis paniculata (Burm.f.) Nees Seedlings.

Carbon (C) and nitrogen (N) metabolisms participate in N source-regulated secondary metabolism in medicinal plants, but the specific mechanisms involved remain to be investigated. By using nitrate (NN), ammonium (AN), urea (UN), and glycine (GN), respectively, as sole N sources, we found that N sources remarkably affected the contents of diterpenoid lactone components along with C and N metabolisms reprograming in Andrographis paniculata, as compared to NN, the other three N sources raised the levels of 14-deoxyandrographolide, andrographolide, dehydroandrographolide (except UN), and neoandrographolide (except AN) with a prominent accumulation of farnesyl pyrophosphate (FPP). These N sources also raised the photosynthetic rate and the levels of fructose and/or sucrose but reduced the activities of phosphofructokinase (PFK), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoenolpyruvate carboxylase (PEPC) and pyruvate dehydrogenase (PDH). Conversely, phosphoenolpyruvate carboxykinase (PEPCK) and malate enzyme (ME) activities were upregulated. Simultaneously, citrate, cis-aconitate and isocitrate levels declined, and N assimilation was inhibited. These results indicated that AN, UN and GN reduced the metabolic flow of carbohydrates from glycolysis into the TCA cycle and downstream N assimilation. Furthermore, they enhanced arginine and GABA metabolism, which increased C replenishment of the TCA cycle, and increased ethylene and salicylic acid (SA) levels. Thus, we proposed that the N sources reprogrammed C and N metabolism, attenuating the competition of N assimilation for C, and promoting the synthesis and accumulation of andrographolide through plant hormone signaling. To obtain a higher production of andrographolide in A. paniculata, AN fertilizer is recommended in its N management.

The complex stress of waterlogging and high temperature accelerated maize leaf senescence and decreased photosynthetic performance at different growth stages

AbstractThe greenhouse effect caused by global warming was becoming more and more obvious, resulting in increased frequency of high temperature and high humidity, which significantly affected maize productivity. However, it was poorly understood how the interactions of high temperature and high humidity affected leaf senescence, photosynthetic performance and yield of summer maize. Three stress treatments including (a) high temperature stress (T), (b) waterlogging stress (W) and (c) complex stress (T‐W) were set at the third leaf stage (V3), the sixth leaf stage (V6) and the tasselling stage (VT) in 2019–2020 to explore the influence mechanism of complex stress. Each stress treatment period lasted 6 days. Non‐stressed plants served as control. Yield, antioxidant enzyme activity, photosynthetic characteristics, and dry matter accumulation were determined. Our study found that the activity of antioxidant enzymes was significantly decreased, while malonyldialdehyde (MDA) accumulation was increased under each stress treatment. As a result, the photosynthetic characteristics were impaired, manifested in a significant decrease in net photosynthetic rate (Pn), enzyme activities of phosphoenolpyruvate carboxylase (PEPCase) and ribulose diphosphate carboxylase (RUBPCase). The decrease in photosynthetic intensity affected by each stress treatment led to a significant decrease in total dry matter accumulation and grain yield. The most significant effects of waterlogging and combined stresses on yield occurred at the V3 stage, followed by the V6 and VT stages. However, the most significant effects of high temperature occurred at the VT stage, followed by the V6 and V3 stages. Moreover, the compound stress exacerbated damage to leaf senescence and photosynthetic properties of summer maize compared to the single stress of high temperature or waterlogging.

The frequency and phenological stage of foliar application of nutrients and biostimulant can increase sugarcane yield and biomass and bioenergy productions

AbstractThe impacts of sugarcane (Saccharum spp.) production include an extensive area of cultivation, high use of technology, and the generation of by‐products that must be utilized. Achieving higher productivity while reducing the expansion of cultivation is challenging. A potential strategy for increasing sugarcane yields and productivity is the foliar application of nutrients and biostimulants at different stages of sugarcane growth. The present study assessed the impact of the foliar application of nutrients (N, B, Cu, and Zn) and a growth regulator as biostimulant (indole butyric acid, gibberellic acid, and kinetin) on sugarcane metabolism, stalk and sugar production, and quality. Field experiments were performed at 17 sites during four growing seasons (2017–2018, 2018–2019, 2019–2020, and 2020–2021) using sugarcane with three harvest times (early, mid‐late, and late harvests). The treatments were as follows: (i) no foliar application of the biostimulant and nutrients (control), (ii) foliar application of the biostimulant and nutrients at the vegetative stage (VS) of sugarcane, (iii) foliar application of the biostimulant and nutrients at the maturation stage (MS) of sugarcane, and (iv) foliar application of the biostimulant and nutrients at both the vegetative and maturation stages (VMS). Foliar application did not increase ribulose 1,5‐bisphosphate carboxylase activity but increased phosphoenolpyruvate carboxylase activity and the activities of the antioxidant enzymes. Peroxidase and catalase activities were higher, >100% and 45%, respectively, in VMS, whereas superoxide dismutase activity increased by 54% in MS compared with control. Consistent with these results, sugarcane had low hydrogen peroxide and malondialdehyde contents in VMS. In addition, the plant biometric parameters were highest in VMS, which sugarcane produced 105, 92, and 86 Mg stalk h−1 in early, mid‐late, and late harvest seasons, respectively. In summary, the foliar application of the biostimulant and nutrients efficiently promoted the growth, productivity, and quality of early, mid‐late, and late harvest seasons. The positive effects of foliar application on the enzymatic and physiological responses of sugarcane can be achieved when applications are performed in both the VMS in all harvest seasons.

The distinctive level of interaction between carbon and nitrogen metabolisms in the leaves of submerged macrophytes plays a key role in ammonium detoxification

Possible ammonium detoxification mechanisms have been proposed recently, on submerged macrophytes, evidently illustrating that glutamate dehydrogenase (GDH) plays a greater role in ammonium detoxification compared to the primary glutamine synthetase/glutamate oxaloacetate transaminase (GS/GOGAT) pathway. In the current investigation, we cultured three submerged macrophytes to extreme concentrations of [NH4+-N] of up to 50 mg/L with the aim of clarifying the interaction between carbon and nitrogen metabolisms. The activities of carboxylation enzymes pyruvate orthophosphate dikinase (PPDK) and phosphoenolpyruvate carboxylase (PEPC), in lieu of Rubisco, increased almost two-fold for ammonium tolerant species P. maackianus and M. spicatum, compared with the sensitive species P. lucens. While these enzymes are well known for their central role in CO2 fixation, their inference in conferring resistance to ammonium stress has not been well elucidated before. In this study, we demonstrate that the overproduction of PEPC and PPDK led to improved photosynthesis, better ammonium assimilation and overall ammonium detoxification in M. spicatum and P. maackianus. These findings propose likelihood for the existence of a complementary ammonium detoxification pathway that targets carbon metabolism, thus, presenting a relatively efficient linkage between nitrogen and carbon metabolisms and identify candidate species for practical restoration of fresh water resources.

Root phosphoenolpyruvate carboxylase activity is essential for Sorghum bicolor tolerance to ammonium nutrition

Phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) is an enzyme family with pivotal roles in plant carbon and nitrogen metabolism. A main role for non-photosynthetic PEPC is as anaplerotic enzyme to load tricarboxylic acid (TCA) cycle with carbon skeletons that compensate the intermediates diverted for biomolecule synthesis such as amino acids. When plants are grown under ammonium (NH4+) nutrition, the excessive uptake of NH4+ often provokes a stress situation. When plants face NH4+ stress, N assimilation is greatly induced and thus, requires the supply of carbon skeletons coming from TCA cycle. In this work, we addressed the importance of root PEPC and TCA cycle for sorghum (Sorghum bicolor L. Moench), a C4 cereal crop, grown under ammonium nutrition. To do so, we used RNAi sorghum lines that display a decrease expression of SbPPC3 (Ppc3 lines), the main root PEPC isoform, and reduced root PEPC activity. SbPPC3 silencing provoked ammonium hypersensitivity, meaning lower biomass accumulation in Ppc3 respect to WT plants when growing under ammonium nutrition. The silenced plants presented a deregulation of primary metabolism as highlighted by the accumulation of NH4+ in the root and the alteration of normal TCA functioning, which was evidenced by the accumulation of organic acids in the root under ammonium nutrition. Altogether, our work evidences the importance of non-photosynthetic PEPC, and root TCA cycle, in sorghum to deal with high external NH4+ availability.

Modulation Effects of Sargassum pallidum Extract on Hyperglycemia and Hyperlipidemia in Type 2 Diabetic Mice.

The aim of this study was to investigate the antidiabetic effect of the extract from Sargassum pallidum (SPPE) on type 2 diabetes mellitus (T2DM) mice. SPPE treatment alleviated hyperglycemia, insulin resistance (IR), liver and pancreatic tissue damage, hyperlipidemia and hepatic oxidative stress resulting from T2DM. SPPE reversed phosphoenolpyruvate carboxylase (PEPCK) and hexokinase (HK) activities to improve gluconeogenesis and glycogen storage in the liver. Furthermore, SPPE modulated glucose metabolism by regulating the levels of mRNA expression involving the PI3K/Akt/FOXO1/G6pase/GLUT2 pathway and could inhibit fatty acid synthesis by reducing the gene expression levels of fatty acid synthase (FAS) and acetyl-CoA carboxylase-1 (ACC-1). A 16 sRNA analysis indicated that SPPE treatment also reversed gut dysbiosis by increasing the abundance of beneficial bacteria (Bacteroides and Lactobacillus) and suppressing the proliferation of harmful bacteria (Enterococcus and Helicobacter). Untargeted metabolomics results indicated that histidine metabolism, nicotinate and nicotinamide metabolism and fatty acid biosynthesis were significantly influenced by SPPE. Thus, SPPE may be applied as an effective dietary supplement or drug in the management of T2DM.

Effects of Vine Water Status on Malate Metabolism and γ-Aminobutyric Acid (GABA) Pathway-Related Amino Acids in Marselan (Vitis vinifera L.) Grape Berries.

Malic acid is the predominant organic acid in grape berries, and its content is affected by abiotic factors such as temperature (fruit zone microclimate) and water (vine water status). The objectives of this study were to explore the potential mechanisms behind the effects of vine water status on the biosynthesis and degradation of berry malic acid and the potential downstream effects on berry metabolism. This study was conducted over two growing seasons in 2021 and 2022, comprising three watering regimes: no water stress (CK), light water stress (LWS), and moderate water stress (MWS). Compared to CK, a significantly higher level of malic acid was found in berries from the MWS treatment when the berry was still hard and green (E-L 33) in both years. However, water stress reduced the malic acid content at the ripe berry harvest (E-L 38) stage. The activities of NAD-malate dehydrogenase (NAD-MDH) and pyruvate kinase (PK) were enhanced by water stress. Except for the E-L 33 stage, the activity of phosphoenolpyruvate carboxylase (PEPC) was reduced by water stress. The highest phosphoenolpyruvate carboxykinase (PEPCK) activity was observed at the berry veraison (E-L 35) stage and coincided with the onset of a decrease in the malate content. Meanwhile, the expression of VvPEPCK was consistent with its enzyme activity. This study showed that water stress changed the content of some free amino acids (GABA, proline, leucine, aspartate, and glutamate), two of which (glutamate and GABA) are primary metabolites of the GABA pathway.

A Carbonic Anhydrase, ZmCA4, Contributes to Photosynthetic Efficiency andModulates CO2 Signaling Gene Expression by Interacting with Aquaporin ZmPIP2;6 inMaize.

Carbonic anhydrase (CA) catalyzes the reversible CO2 hydration reaction that produces bicarbonate for phosphoenolpyruvate carboxylase (PEPC). This is the initial step for transmitting the CO2 signal in C4 photosynthesis. However, it remains unknown whether the maize (Zea mays L.) CA gene, ZmCA4, plays a role in the maize photosynthesis process. In our study, we found that ZmCA4 was relatively highly expressed in leaves and localized in the chloroplast and the plasma membrane of mesophyll protoplasts. Knock-out of ZmCA4 reduced CA activity, while overexpression of ZmCA4 increased rubisco activity, as well as the quantum yield and relative electron transport rate in photosystem II. Overexpression of ZmCA4 enhanced maize yield-related traits. Moreover, ZmCA4 interacted with aquaporin ZmPIP2;6 in bimolecular fluorescence complementation and co-immunoprecipitation experiments. The double-knock-out mutant for ZmPIP2;6 and ZmCA4 genes showed reductions in its growth, CA and PEPC activities, assimilation rate and photosystem activity. RNA-Seq analysis revealed that the expression of other ZmCAs, ZmPIPs, as well as CO2 signaling pathway homologous genes, and photosynthetic-related genes was all altered in the double-knock-out mutant compared with the wild type. Altogether, our study's findings point to a critical role of ZmCA4 in determining photosynthetic capacity and modulating CO2 signaling regulation via its interaction with ZmPIP2;6, thus providing insight into the potential genetic value of ZmCA4 for maize yield improvement.

Waterlogging restricted cotton fiber elongation by reducing osmolyte accumulation and cell wall biosynthesis

Waterlogging severely threatens the formation of cotton fiber quality, especially the length. However, the underlying mechanism is still incompletely understood. Here, the experiment (control: soil relative water content at (75 ± 5)%; treatment: waterlogging for 6 days) was conducted during the flowering and boll forming stage using two upland cotton cultivars (Dexiamian 1 and Yuzaomian 9110) to investigate the effects of waterlogging on fiber development from both transcriptomic and physiological levels. The transcriptome analysis of 10 days post anthesis cotton fiber showed that waterlogging significantly regulated the expression of genes associated with fiber elongation events including osmotic solutes accumulation, fiber cell wall biosynthesis, and cell wall remodeling and loosening. Waterlogging decreased the sucrose input into cotton fiber, resulting in reduced sucrose and hexose contents. Under waterlogging, the accumulation of malate and K+ in both cultivars was reduced by decreasing phosphoenolpyruvate carboxylase (PEPC) activity and potassium transporter genes (GhPOT) expression, respectively. Thus, the total concentration of osmolytes was reduced, which dampened cotton fiber elongation. Due to reduced sucrose synthase activity and uridine diphosphate glucose content, the cellulose biosynthesis was limited, leading to decreased fiber cell wall accumulation, which was adverse to fiber elongation. Besides, genes responsible for cell wall remodeling and loosening, including xyloglucan endotransglucosylase/hydrolase genes (GhXTH), α-expansin genes (GhEXPA), and pectin methylesterase genes (GhPME) were also responsive to waterlogging, but in different ways between cultivars. Overall, the shortened cotton fiber could be attributed to reduced osmolytes accumulation and cell wall biosynthesis, whilst the effects of waterlogging on cotton fiber cell wall loosening require further exploration.

Overexpressing plant ferredoxin-like protein enhances photosynthetic efficiency and carbohydrates accumulation in Phalaenopsis.

Crassulacean acid metabolism (CAM) is one of three major models of carbon dioxide assimilation pathway with better water-use efficiency and slower photosynthetic efficiency in photosynthesis. Previous studies indicated that the gene of sweet pepper plant ferredoxin-like protein (PFLP) shows high homology to the ferredoxin-1(Fd-1) family that belongs to photosynthetic type Fd and involves in photosystem I. It is speculated that overexpressing pflp in the transgenic plant may enhance photosynthetic efficiency through the electron transport chain (ETC). To reveal the function of PFLP in photosynthetic efficiency, pflp transgenic Phalaenopsis, a CAM plant, was generated to analyze photosynthetic markers. Transgenic plants exhibited 1.2-folds of electron transport rate than that of wild type (WT), and higher CO2 assimilation rates up to 1.6 and 1.5-folds samples at 4pm and 10pm respectively. Enzyme activity of phosphoenolpyruvate carboxylase (PEPC) was increased to 5.9-folds in Phase III, and NAD+-linked malic enzyme (NAD+-ME) activity increased 1.4-folds in Phase IV in transgenic plants. The photosynthesis products were analyzed between transgenic plants and WT. Soluble sugars contents such as glucose, fructose, and sucrose were found to significantly increase to 1.2, 1.8, and 1.3-folds higher in transgenic plants. The starch grains were also accumulated up to 1.4-folds in transgenic plants than that of WT. These results indicated that overexpressing pflp in transgenic plants increases carbohydrates accumulation by enhancing electron transport flow during photosynthesis. This is the first evidence for the PFLP function in CAM plants. Taken altogether, we suggest that pflp is an applicable gene for agriculture application that enhances electron transport chain efficiency during photosynthesis.

Effects of exogenous melatonin on sugar and organic acid metabolism in early-ripening peach fruits.

To evaluated the effects melatonin (MT) on the sugar and acid metabolism of early-ripening peach fruits, the concentration of 150 μmol/L MT was sprayed on the leaves of peach trees. MT increased the contents of total soluble sugar and sucrose in peach fruits during the whole ripening period, and increased the contents of glucose and sorbitol at the mature stage. During the whole ripening period, MT also increased the activities of sucrose synthase, sucrose phosphate synthase, neutral invertase, and acidic invertase and the relative expression levels of sucrose synthase, sucrose phosphate synthase, neutral invertase, and acidic invertase genes, while decreased the activity of sorbitol oxidase and the relative expression level of sorbitol dehydrogenase to some extent. Moreover, MT decreased the contents of total organic acid, malic acid, and citric acid at mature stage. At mature stage, MT decreased the activities of citrate synthetase and phosphoenolpyruvate carboxylase and the relative expression levels of citrate synthetase and phosphoenolpyruvate carboxylase genes, while increased the relative expression levels of Nicotinamide adenine dinucleotide phosphate (NADP+)-malic enzyme, malate dehydrogenase, and aconitase genes. Therefore, MT promotes the sugar accumulation and organic acid degradation in early-ripening peach fruits.

Low soil available phosphorus level reduces cotton fiber length via osmoregulation.

Phosphorus (P) deficiency hinders cotton (Gossypium hirustum L.) growth and development, seriously affecting lint yield and fiber quality. However, it is still unclear how P fertilizer affects fiber length. Therefore, a two-year (2019-2020) pool-culture experiment was conducted using the split-plot design, with two cotton cultivars (CCRI-79; low-P tolerant and SCRC-28; low-P sensitive) as the main plot. Three soil available phosphorus (AP) contents (P0: 3 ± 0.5, P1: 6 ± 0.5, and P2 (control) with 15 ± 0.5 mg kg-1) were applied to the plots, as the subplot, to investigate the impact of soil AP content on cotton fiber elongation and length. Low soil AP (P0 and P1) decreased the contents of the osmotically active solutes in the cotton fibers, including potassium ions (K+), malate, soluble sugar, and sucrose, by 2.2-10.2%, 14.4-47.3%, 8.7-24.5%, and 10.1-23.4%, respectively, inhibiting the vacuoles from facilitating fiber elongation through osmoregulation. Moreover, soil AP deficiency also reduced the activities of enzymes participated in fiber elongation (plasma membrane H+-ATPase (PM-H+-ATPase), vacuole membrane H+-ATPase (V-H+-ATPase), vacuole membrane H+-translocating inorganic pyrophosphatase (V-H+-PPase), and phosphoenolpyruvate carboxylase (PEPC)). The PM-H+-ATPase, V-H+-ATPase, V-H+-PPase, and PEPC were reduced by 8.4-33.0%, 7.0-33.8%, 14.1-38.4%, and 16.9-40.2%, respectively, inhibiting the transmembrane transport of the osmotically active solutes and acidified conditions for fiber cell wall, thus limiting the fiber elongation. Similarly, soil AP deficiency reduced the fiber length by 0.6-3.0 mm, mainly due to the 3.8-16.3% reduction of the maximum velocity of fiber elongation (VLmax). Additionally, the upper fruiting branch positions (FB10-11) had higher VLmax and longer fiber lengths under low soil AP. Cotton fibers with higher malate content and V-H+-ATPase and V-H+-PPase activities yielded longer fibers. And the malate and soluble sugar contents and V-H+-ATPase and PEPC activities in the SCRC-28's fiber were more sensitive to soil AP deficiency in contrast to those of CCRI-79, possibly explaining the SCRC-28 fiber length sensitivity to low soil AP.

The potential of seaweed extracts as a biostimulant for improving salt stress tolerance of Solanum lycopersicum L

The present investigation aimed to examine the effects of seaweed extracts (SWE) on tomato plants under saline conditions (50 mM of NaCl). The current findings have shown that the SWE obtained from Jania rubens (J. rubens) gave better results compared to those prepared from the other two seaweeds; Dictyota dichotoma (D. dichotoma) and Gelidium sesquipedale (G. sesquipedale). Indeed, under salt stress, the application of fresh seaweed at 2% significantly (p ≤ 0.05) increased the plant height (26.28 cm ± 0.95) compared with the non-treated stressed control (17.65 cm ± 1.04). Based on these results the effect of J. rubens on some biological and biochemical parameters of tomato plants was evaluated. In fact, increased contents of chlorophylls, total soluble sugars (TSS), and total free amino acids (TFAA) were observed in seaweed-treated plants compared to the control plants. Moreover, the treatment of stressed plants with SWE revealed a significant (p ≤ 0.05) improvement in antioxidant enzyme activities such as superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione S-transferase (GST). The extract also showed an increase in the enzyme activities of glutamate dehydrogenase (GDH) and phosphoenolpyruvate carboxylase (PEPC), which are implicated in the nitrogen and carbon metabolism, respectively. Furthermore, the analysis of the chemical composition of the liquid seaweed extracts (fresh and dried) has shown that they contain bioactive compounds such as polyphenols, flavonoids, soluble sugars, and amino acids, which can be responsible for the tomato's tolerance to salinity. Therefore, the SWE tested in the present study can be used as a biostimulant to enhance the salt stress tolerance of tomato plants.

Critical taste substances and regulatory pathways of fresh lotus seed pulps at different ripeness stages

Previous reports about measuring flavor substances in lotus seeds focus on the nutritional quality. Currently, no research is devoted to the taste quality of lotus seeds. In this study, fresh lotus seeds' pulp at different ripeness stages was used to explore the critical taste substances and related regulatory pathways affecting the suitability of lotus seeds for fresh eating. Sweetness and umami were the basic flavors of low maturity, and astringency mainly existed in high maturity fresh lotus seeds. Fructose is a crucial factor affecting the suitability of fresh lotus seeds. During the ripening of lotus seeds, the increase of fructokinase (FRK) activity and related gene expression caused the decrease in fructose content. In contrast, the decrease in phosphoenolpyruvate carboxylase (PEPC) and NAD-malate dehydrogenase (NAD-MDH) activity was related to the decline of malic acid content in low maturity lotus seeds. The present study revealed the crucial taste substances and regulatory pathways of lotus seeds, which laid a theoretical foundation for the study of the taste formation mechanism of fresh lotus seeds.

The molecular mechanism of propionate-regulating gluconeogenesis in bovine hepatocytes.

Cows that are nursing get around 80% of their glucose from liver gluconeogenesis. Propionate, a significant precursor of liver gluconeogenesis, can regulate the key genes involved in hepatic gluconeogenesis expression, but its precise effects on the activity of enzymes have not yet been fully elucidated. Therefore, the aim of this study was to investigate the effects of propionate on the activity, gene expression, and protein abundance of the key enzymes involved in the gluconeogenesis of dairy cow hepatocytes. The hepatocytes were cultured and treated with various concentrations of sodium propionate (0, 1.25, 2.50, 3.75, and 5.00 mM) for 12 h. Glucose content in the culture media was determined by an enzymatic coloring method. The activities of gluconeogenesis related enzymes were determined by enzyme linked immunosorbent assay kits, and the levels of gene expression and protein abundance of the enzymes were detected by real-time quantitative polymerase chain reaction and Western blot, respectively. Propionate supplementation considerably increased the amount of glucose in the culture medium compared to the control (p<0.05); while there was no discernible difference among the various treatment concentrations (p>0.05). The activities of cytoplasmic phosphoenolpyruvate carboxylase (PEPCK1), mitochondrial phosphoenolpyruvate carboxylase (PEPCK2), pyruvate carboxylase (PC), and glucose-6-phosphatase (G6PC) were increased with the addition of 2.50 and 3.75 mM propionate; the gene expressions and protein abundances of PEPCK1, PEPCK2, PC, and G6PC were increased by 3.75 mM propionate addition. Propionate encouraged glucose synthesis in bovine hepatocytes, and 3.75 mM propionate directly increased the activities, gene expressions and protein abundances of PC, PEPCK1, PEPCK2, and G6PC in bovine hepatocytes, providing a theoretical basis of propionate-regulating gluconeogenesis in bovine hepatocytes.

Effects of the ammonium stress on photosynthesis and ammonium assimilation in submerged leaves of Ottelia cordata - an endangered aquatic plant

Although ammonium (NH4+-N) is an important nutrient for plants, increases in soil nitrogen (N) input and atmospheric deposition have made ammonium toxicity a serious ecological problem. In this study, we explored the effects of NH4+-N stress on the ultrastructure, photosynthesis, and NH4+-N assimilation of Ottelia cordata (Wallich) Dandy, an endangered heteroblastic plant native to China. Results showed that 15 and 50 mg L−1 NH4+-N damaged leaf ultrastructure and decreased the values of maximal quantum yield (Fv/Fm), maximal fluorescence (Fm), and relative electron transport rate (rETR) in the submerged leaves of O. cordata. Furthermore, when NH4+-N was ≥ 2 mg L−1, phosphoenolpyruvate carboxylase activity (PEPC) and soluble sugar and starch contents decreased significantly. The content of dissolved oxygen in the culture water also decreased significantly. The activity of the NH4+-N assimilation enzyme glutamine synthetase (GS) significantly increased when NH4+-N was ≥ 10 mg L−1 and NADH-glutamate synthase (NADH-GOGAT) and Fd-glutamate synthase (Fd-GOGAT) increased when NH4+-N was at 50 mg L−1. However, the activity of nicotinamide adenine dinucleotide-dependent glutamate dehydrogenase (NADH-GDH) and nicotinamide adenine dinucleotide phosphate-dependent glutamate dehydrogenase (NADPH-GDH) did not change, indicating that GS/GOGAT cycle may play an important role in NH4+-N assimilation in the submerged leaves of O. cordata. These results show that short-term exposure to a high concentration of NH4+-N is toxic to O. cordata.

Effects of Citric Acid and Humic-like Substances on Yield, Enzyme Activities, and Expression of Genes Involved in Iron Uptake in Tomato Plants

Iron (Fe) deficiency is a common abiotic stress on plants growing in calcareous soils where low organic matter content, high carbonate–bicarbonate concentration, and high pH precipitate Fe in unavailable forms. Enzymatic activity is a mechanism for plants to access soil nutrients; enzymes such as H+-ATPase, phosphoenolpyruvate carboxylase (PEPC), and the intracellular enzyme ferric reduction oxidase (FRO) are involved in Fe absorption. The effects of the application of citric acid (CA) and humic-like substances (HLS) on the yield, H+-ATPase, PEPC, and FRO enzyme activity, and expression of LeHA1, LePEPC1, and LeFRO1 genes in tomato plants grown under calcareous soil were studied. CA and HLS improved the SPAD units and increased the number of harvested fruits and yield per plant. Temporary alterations in enzyme activity, which reduced PEPC and FRO activity in roots, were documented. In leaf tissue, CA resulted in lower expression of LeHA1 and LePEPC1 and the induction of LeFRO1 expression, whereas HLS application resulted in higher expression of LePEPC1 and LeFRO1. In roots, LeHA1 expression increased with HLS, whereas LePEPC1 and LeFRO1 showed lower expression with CA and HLS, respectively. The application of CA and HLS through a nutrient solution in combination with Fe-chelate can improve Fe nutrition in tomato plants potted in calcareous soil by inducing temporal alterations in PEPC and FRO enzyme activity and LeFRO1 and LeHA1 gene expression.

Phosphorus-induced greater enhancement in carbon supply and storage for oil synthesis during the crucial period made cottonseed kernel oil yield have a higher increment than protein

Cottonseed has a high utilization value due to its luxuriant oil and protein, but low phosphorus (P) in cropland reduces its yield and quality. A limited understanding of the physiological mechanism underlying these results restricted the exploration of P efficient management in cotton cultivation. A 3-year experiment was performed with Lu 54 (low-P sensitive) and Yuzaomian 9110 (low-P tolerant) under 0 (deficient-P), 100 (critical-P), and 200 (excessive-P) kg P2O5 ha−1 in a field having 16.9 mg kg−1 available P to explore the key pathway for P to regulate cottonseed oil and protein formation. P application markedly increased cottonseed oil and protein yields, with the enhanced acetyl-CoA and oxaloacetate contents during 20–26 days post anthesis being a vital reason. Notably, during the crucial period, decreased phosphoenolpyruvate carboxylase activity weakened the carbon allocation to protein, making malonyl-CoA content increase greater than free amino acid; Meanwhile, P application accelerated the carbon storage in oil but retarded that in protein. Consequently, cottonseed oil yield increased more than protein. Oil and protein synthesis in Lu 54 was more susceptible to P, resulting in greater increments in oil and protein yields than Yuzaomian 9110. Based on acetyl-CoA and oxaloacetate contents (the key substrates), the critical P content in the subtending leaf to cotton boll needed by oil and protein synthesis in Lu 54 (0.35%) was higher than Yuzaomian 9110 (0.31%). This study provided a new perception of the regulation of P on cottonseed oil and protein formation, contributing to the efficient P management in cotton cultivation.

Panicle removal delays plant senescence and enhances vegetative growth improving biomass production in switchgrass

Switchgrass (Panicum virgatum L.) shows great bioenergy potential and provides multiple ecological services. However, its severe seed shedding causes biomass waste and seed diffusion risk. Questions arise as to the production performance of switchgrass after panicle removal (PR), which remains unknown. We revealed switchgrass growth responses to PR and illustrated physiological reasons. Compared to the untreated switchgrass, PR significantly stimulated stem elongation (32.13%) and increased tiller number (39.70%), as well as aboveground biomass (24.69%). Importantly, PR significantly increased contents of nonstructural carbohydrates (NSCs) in the stem, which was directly beneficial to the ethanol conversion, and in the rhizome and root. The chlorophyll contents, net photosynthetic efficiency, and photochemical quantum efficiencies of flag leaf increased significantly. PR switchgrass allocated more assimilates into the stem, root, rhizome, and NSCs. Activities of phosphoenolpyruvate carboxylase, ribulose-1, 5-diphosphate carboxylase, sucrose phosphate synthase (SPS) in flag leaf and adenosine diphosphate glucose pyrophosphorylase (AGPase) and SPS in the stem and rhizome all increased significantly. In contrast, activities of the AGPase in flag leaf and sheath decreased significantly. Contents of zeatin nucleoside, gibberellins, and indoleacetic acid in flag leaf, stem, and rhizome all increased. Abscisic acid contents in flag leaf and stem decreased significantly while increased significantly in the rhizome. In conclusion, growth-promoting hormones delayed plant senescence, enhanced leaf photosynthesis, and enhanced vegetative growth through regulating assimilates-metabolism-related enzymes, which increased biomass accumulation in PR switchgrass. This work provided new insights for yield and digestibility improvement in switchgrass through field management practices, hormones regulation, or genetic modification strategies.

Effects of filter mud applications on growth, physiological characteristics, and nutrient transfer pattern of sugar beet seedlings

Filter mud is an industrial waste produced by sugar crops during the sugar production process, which contains N, P, K, organic matter, and a variety of trace elements required for plant growth. Therefore, a soil cultivation experiment was devised to verify the effects of applying diverse proportions of filter mud on the growth and physiological variations of sugar beet (Beta vulgaris L. subsp. vulgaris) seedlings. For this study, sugar mill filter mud equivalent to 1%, 3%, 5%, 7%, 9%, 11%, and 13% of the dry weight of neutral black soil was used. Sugar beet seeds were planted in soil with filter mud and their growth, nutrient, and physiological indexes are measured after they grew into sugar beet seedlings. After the application of filter mud, the growth status of sugar beet seedlings increased significantly compared to the non-application of filter mud. Soil application of filter mud increases the content of inorganic N, available P, available K, and organic matter in the soil. And the most pronounced growth of sugar beet seedlings was achieved at 7% of the applied filter mud. In addition, the content of chlorophyll, transpiration rate, net photosynthetic rate, stomatal conductance, and phosphoenolpyruvate carboxylase activity all increased significantly. As a result, it was determined that filter mud from sugar beet waste was an effective soil improver material, a certain percentage of filter mud can promote the growth of sugar beet seedlings. This has important implications for the improvement of sugar beet yields and the recycling of agricultural wastes.