Nitrogen differentially modulates photosynthesis, carbon allocation and yield related traits in two contrasting Capsicum chinense cultivars

Galactinol Regulates JA Biosynthesis to Enhance Tomato Cold Tolerance

Low temperatures can inhibit plant growth and development and reduce fruit yield. This study demonstrated that the expression of AnGolS1 from Ammopiptanthus nanus (A. nanus) encoding a galactinol synthase enhanced tomato cold tolerance. In AnGolS1-overexpressing plants, the jasmonic acid (JA) biosynthesis substrates 13-hydroperoxylinolenicacid and 12,13-epoxylinolenicacid were significantly accumulated, and the expression levels of the ethylene response factor (SlERF4-7) and serine protease inhibitor (SlSPI5) were increased. We speculated that there may be correlations among galactinol, ethylene signaling, the protease inhibitor, protease, and JA levels. The expression levels of SlERF4-7 and SlSPI5 as well as the JA content were significantly increased under exogenous galactinol treatment. Additionally, the expression of SlSPI5 was reduced in SlERF4-7-silenced plants, and SlERF4-7 was confirmed to bind to the dehydration-responsive element (DRE) of the SlSPI5 promoter. These results suggest that SlSPI5 is a target gene of the SlERF4-7 transcription factor. In addition, SlSPI5 interacted with cysteine protease (SlCPase), while SlCPase interacted with lipoxygenase (SlLOX5) and allene oxide synthase (SlAOS2). When SlCPase was silenced, JA levels increased and plant cold tolerance was enhanced. Therefore, galactinol regulates JA biosynthesis to enhance tomato cold tolerance through the SlERF4-7-SlSPI5-SlCPase-SlLOX5/SlAOS2 model. Overall, our study provides new perspectives on the role of galactinol in the JA regulatory network in plant adaptation to low-temperature stress.

Population genetic differentiation and phenotypic plasticity of Ambrosia artemisiifolia under different nitrogen levels

Rapid adaptive evolution and phenotypic plasticity are two mechanisms that often underlie invasiveness of alien plant species, but whether they can co-occur within invasive plant populations under altered environmental conditions such as nitrogen (N) enrichment has seldom been explored. Latitudinal clines in plant trait responses to variation in environmental factors may provide evidence of local adaptation. Here, we inferred the relative contributions of phenotypic plasticity and local adaptation to the performance of the invasive plant Ambrosia artemisiifolia under different soil N levels, using a common garden approach. We grew A. artemisiifolia individuals raised from seeds that were sampled from six invasive populations along a wide latitudinal cline in China (23°42' N to 45°43' N) under three N (0, 5, and 10 g N m-2 ) levels in a common garden. Results show significant interpopulation genetic differentiation in plant height, number of branches, total biomass, and transpiration rate of the invader A. artemisiifolia across the N treatments. The populations also expressed genetic differentiation in basal diameter, growth rate, leaf area, seed width, root biomass, aboveground biomass, stomatal conductance, and intercellular CO2 concentration regardless of N treatments. Moreover, plants from different populations of the invader displayed plastic responses in time to first flower, hundred-grain weight, net photosynthetic rate, and relative biomass allocation to roots and shoots and seed length under different N treatments. Additionally, individuals of A. artemisiifolia from higher latitudes grew shorter and allocated less biomass to the roots regardless of N treatment, while latitudinal cline (or lack thereof) in other traits depended on the level of N in which the plants were grown. Overall, these results suggest that rapid adaptive evolution and phenotypic plasticity in the various traits that we quantified may jointly contribute to invasiveness of A. artemisiifolia under different levels of N availability. More broadly, the results support the idea that phenotypic plasticity and rapid adaptive evolution can jointly enable invasive plants to colonize a wide range of environmental conditions.

High nitrogen inhibits biomass and saponins accumulation in a medicinal plant Panax notoginseng

Nitrogen (N) is an important macronutrient and is comprehensively involved in the synthesis of secondary metabolites. However, the interaction between N supply and crop yield and the accumulation of effective constituents in an N-sensitive medicinal plant Panax notoginseng (Burkill) F. H. Chen is not completely known. Morphological traits, N use and allocation, photosynthetic capacity and saponins accumulation were evaluated in two- and three-year-old P. notoginseng grown under different N regimes. The number and length of fibrous root, total root length and root volume were reduced with the increase of N supply. The accumulation of leaf and stem biomass (above-ground) were enhanced with increasing N supply, and LN-grown plants had the lowest root biomass. Above-ground biomass was closely correlated with N content, and the relationship between root biomass and N content was negatives in P. notoginseng (r = -0.92). N use efficiency-related parameters, NUE (N use efficiency, etc.), N_C (N content in carboxylation system component) and P _n (the net photosynthetic rate) were reduced in HN-grown P. notoginseng. SLN (specific leaf N), Chl (chlorophyll), N_L (N content in light capture component) increased with an increase in N application. Interestingly, root biomass was positively correlated with NUE, yield and P _n. Above-ground biomass was close negatively correlated with photosynthetic N use efficiency (PNUE). Saponins content was positively correlated with NUE and P _n. Additionally, HN improved the root yield of per plant compared with LN, but reduced the accumulation of saponins, and the lowest yield of saponins per unit area (35.71 kg·hm^-2) was recorded in HN-grown plants. HN-grown medicinal plants could inhibit the accumulation of root biomass by reducing N use and photosynthetic capacity, and HN-induced decrease in the accumulation of saponins (C-containing metabolites) might be closely related to the decline in N efficiency and photosynthetic capacity. Overall, N excess reduces the yield of root and C-containing secondary metabolites (active ingredient) in N-sensitive medicinal species such as P. notoginseng.

Impact of Plant-Beneficial Bacterial Inocula on the Resident Bacteriome: Current Knowledge and Future Perspectives

The inoculation of plant growth-promoting bacteria (PGPB) as biofertilizers is one of the most efficient and sustainable strategies of rhizosphere manipulation leading to increased plant biomass and yield and improved plant health, as well as the ameliorated nutritional value of fruits and edible seeds. During the last decades, exciting, but heterogeneous, results have been obtained growing PGPB inoculated plants under controlled, stressful, and open field conditions. On the other hand, the possible impact of the PGPB deliberate release on the resident microbiota has been less explored and the little available information is contradictory. This review aims at filling this gap: after a brief description of the main mechanisms used by PGPB, we focus our attention on the process of PGPB selection and formulation and we provide some information on the EU regulation for microbial inocula. Then, the concept of PGPB inocula as a tool for rhizosphere engineering is introduced and the possible impact of bacterial inoculant on native bacterial communities is discussed, focusing on those bacterial species that are included in the EU regulation and on other promising bacterial species that are not yet included in the EU regulation.

Differential Effects of Ammonium (NH4+) and Potassium (K+) Nutrition on Photoassimilate Partitioning and Growth of Tobacco Seedlings

Plants utilize carbohydrates as the main energy source, but much focus has been on the impact of N and K on plant growth. Less is known about the combined impact of NH₄⁺ and K⁺ nutrition on photoassimilate distribution among plant organs, and the resultant effect of such distribution on growth of tobacco seedlings, hence this study. Here, we investigated the synergetic effect of NH₄⁺ and K⁺ nutrition on photoassimilate distribution, and their resultant effect on growth of tobacco seedlings. Soluble sugar and starch content peaks under moderate NH₄⁺ and moderate K⁺ (2-2 mM), leading to improved plant growth, as evidenced by the increase in tobacco weight and root activity. Whereas, a drastic reduction in the above indicators was observed in plants under high NH₄⁺ and low K⁺ (20-0.2 mM), due to low carbohydrate synthesis and poor photoassimilate distribution. A strong positive linear relationship also exists between carbohydrate (soluble sugar and starch) and the activities of these enzymes but not for invertase. Our findings demonstrated that NH₄⁺ and K⁺-induced ion imbalance influences plant growth and is critical for photoassimilate distribution among organs of tobacco seedlings.

Delayed autumnal leaf senescence following nutrient fertilization results in altered nitrogen resorption

Increased atmospheric nitrogen (N) deposition could create an imbalance between N and phosphorus (P), which may substantially impact ecosystem functioning. Changes in autumnal phenology (i.e., leaf senescence) and associated leaf nutrient resorption may profoundly impact plant fitness and productivity. However, we know little about how and to what extent nutrient addition affects leaf senescence in tree species, or how changes in senescence may influence resorption. We thus investigated the impacts of N and P addition on leaf senescence and leaf N resorption in 2-year-old larch (Larix principisrupprechtii) seedlings in northern China. Results showed that nutrient addition (i.e., N, P or N + P addition) significantly delayed autumnal leaf senescence, and decreased leaf N resorption efficiency (NRE) and proficiency (NRP), particularly in the N and N + P treatments. Improved leaf N concentrations were correlated with delayed leaf senescence, as indicated by the positive relationship between mature leaf N concentrations and the timing of leaf senescence. Following nutrient addition, larch seedlings shifted toward delayed onset, but more rapid, leaf senescence. Additionally, we observed an initial negative correlation between the timing of leaf senescence and NRE and NRP, followed by a positive correlation, indicating delayed and less efficient remobilization during the early stages of senescence, followed by accelerated resorption in the later stages. However, the latter effect was potentially impaired by the increased risk of early autumn frost damage, thus failed to fully compensate for the negative effects observed during the early stages of senescence. Improved soil P availability increased leaf N resorption and thus weakened the negative impact of delayed leaf senescence on leaf N resorption, so P addition had no significant impact on leaf N resorption. Overall, our findings clarify the relationship between nutrient addition-resorption and the linkage with leaf senescence, and would have important implications for plant nutrient conservation strategy and nutrient cycling.

Differential Metabolic Responses of Lettuce Grown in Soil, Substrate and Hydroponic Cultivation Systems under NH4+/NO3− Application

Nitrogen (N) is an essential element for plant growth and development. The application of a balanced and optimal amount of N is required for sustainable plant yield. For this, different N sources and forms are used, that including ammonium (NH₄⁺) and nitrate (NO₃⁻). These are the main sources for N uptake by plants where NH₄⁺/NO₃⁻ ratios have a significant effect on the biomass, quality and metabolites composition of lettuce grown in soil, substrate and hydroponic cultivation systems. A limited supply of N resulted in the reduction in the biomass, quality and overall yield of lettuce. Additionally, different types of metabolites were produced with varying concentrations of N sources and can be used as metabolic markers to improve the N use efficiency. To investigate the differential metabolic activity, we planted lettuce with different NH₄⁺/NO₃⁻ ratios (100:0, 75:25, 50:50, 25:75 and 0:100%) and a control (no additional N applied) in soil, substrate and hydroponic cultivation systems. The results revealed that the 25% NH₄^+/75% NO₃⁻ ratio increased the relative chlorophyll contents as well as the biomass of lettuce in all cultivation systems. However, lettuce grown in the hydroponic cultivation system showed the best results. The concentration of essential amino acids including alanine, valine, leucine, lysine, proline and serine increased in soil and hydroponically grown lettuce treated with the 25% NH₄^+/75% NO₃⁻ ratio. The taste and quality-related compounds in lettuce showed maximum relative abundance with the 25% NH₄^+/75% NO₃⁻ ratio, except ascorbate (grown in soil) and lactupicrin (grown in substrate), which showed maximum relative abundance in the 50% NH₄^+/50% NO₃⁻ ratio and control treatments, respectively. Moreover, 1-O-caffeoylglucose, 1,3-dicaffeoylquinic acid, aesculetin and quercetin-3-galactoside were increased by the application of the 100% NH₄^+/0% NO₃⁻ ratio in soil-grown lettuce. The 25% NH₄^+/75% NO₃⁻ ratio was more suitable in the hydroponic cultivation system to obtain increased lettuce biomass. The metabolic profiling of lettuce showed different behaviors when applying different NH₄⁺/NO₃⁻ ratios. Therefore, the majority of the parameters were largely influenced by the 25% NH₄^+/75% NO₃⁻ ratio, which resulted in the hyper-accumulation of health-promoting compounds in lettuce. In conclusion, the optimal N applications improve the quality of lettuce grown in soil, substrate and hydroponic cultivation systems which ultimately boost the nutritional value of lettuce.

Metabolic differences of two constructive species in saline-alkali grassland in China

BACKGROUND

Salinization of soil is an urgent problem that restricts agroforestry production and environmental protection. Substantial accumulation of metal ions or highly alkaline soil alters plant metabolites and may even cause plant death. To explore the differences in the response strategies between Suaeda salsa (S. salsa) and Puccinellia tenuiflora (P. tenuiflora), two main constructive species that survive in saline-alkali soil, their metabolic differences were characterized.

RESULT

Metabolomics was conducted to study the role of metabolic differences between S. salsa and P. tenuiflora under saline-alkali stress. A total of 68 significantly different metabolites were identified by GC-MS, including 9 sugars, 13 amino acids, 8 alcohols, and 34 acids. A more detailed analysis indicated that P. tenuiflora utilizes sugars more effectively and may be saline-alkali tolerant via sugar consumption, while S. salsa utilizes mainly amino acids, alcohols, and acids to resist saline-alkali stress. Measurement of phenolic compounds showed that more C6C3C6-compounds accumulated in P. tenuiflora, while more C6C1-compounds, phenolic compounds that can be used as signalling molecules to defend against stress, accumulated in S. salsa.

CONCLUSIONS

Our observations suggest that S. salsa resists the toxicity of saline-alkali stress using aboveground organs and that P. tenuiflora eliminates this toxicity via roots. S. salsa has a stronger habitat transformation ability and can provide better habitat for other plants.

Metabolic Variation among Fruits of Different Chili Cultivars (Capsicum spp.) Using HPLC/MS

Chilies are widely cultivated for their rich metabolic content, especially capsaicinoids. In our study, we determined individual sugars, organic acids, capsaicinoids, and total phenolic content in pericarp, placenta, and seeds of Capsicum annuum L., Capsicum chinense Jacq. and Capsicum baccatum L. by HPLC/MS. Dry weight varied in the cultivar 'Cayenne', with the first fruit having the lowest dry weight, with 4.14 g. The total sugar content and organic acid content did not vary among the fruits of all three cultivars. The cultivar 'Cayenne' showed differences in total phenolic and capsaicinoid content between fruits in the placenta, with the first fruit having the highest content of total phenolics (27.85 g GAE/kg DW) and total capsaicinoids (16.15 g/kg DW). Of the three cultivars studied, the cultivar 'Habanero Orange' showed the least variability among fruits in terms of metabolites. The content of dihydrocapsaicin, nordihydrocapsaicin, homocapsaicin, and homodihydrocapsaicin in the seeds of the second fruit was higher than that of the first fruit of the cultivar 'Bishop Crown'. The results of our study provided significant insight into the metabolomics of individual fruits of the same chili plant. We have thus increased our understanding of how certain metabolites are distributed between fruits at different levels of the same plant and different parts of the fruit. This could be further investigated when chilies are exposed to different environmental stresses.

Metabolic shifts during fruit development in pungent and non-pungent peppers

Fruit pungency is caused by the accumulation of capsaicinoids, secondary metabolites whose relation to primary metabolism remains unclear. We have selected ten geographically diverse accessions of Capsicum chinense Jacq with different pungency levels. A detailed metabolic profile was conducted in the fruit placenta and pericarp at 20, 45, and 60 days after anthesis aiming at increasing our understanding of the metabolic changes in these tissues across fruit development and their potential connection to capsaicin metabolism. Overall, despite the variation in fruit pungency among the ten accessions, the composition and metabolite levels in both placenta and pericarp were uniformly stable across accessions. Most of the metabolite variability occurred between the fruit developmental stages rather than among the accessions. Interestingly, different metabolite adjustments in the placenta were observed among pungent and non-pungent accessions, which seem to be related to differences in the genetic background. Furthermore, we observed high coordination between metabolites and capsaicin production in C. chinense fruits, suggesting that pungency in placenta is adjusted with primary metabolism.

Sucrose Utilization for Improved Crop Yields: A Review Article

Photosynthetic carbon converted to sucrose is vital for plant growth. Sucrose acts as a signaling molecule and a primary energy source that coordinates the source and sink development. Alteration in source-sink balance halts the physiological and developmental processes of plants, since plant growth is mostly triggered when the primary assimilates in the source leaf balance with the metabolic needs of the heterotrophic sinks. To measure up with the sink organ's metabolic needs, the improvement of photosynthetic carbon to synthesis sucrose, its remobilization, and utilization at the sink level becomes imperative. However, environmental cues that influence sucrose balance within these plant organs, limiting positive yield prospects, have also been a rising issue over the past few decades. Thus, this review discusses strategies to improve photosynthetic carbon assimilation, the pathways actively involved in the transport of sucrose from source to sink organs, and their utilization at the sink organ. We further emphasize the impact of various environmental cues on sucrose transport and utilization, and the strategic yield improvement approaches under such conditions.

Specific leaf area is modulated by nitrogen via changes in primary metabolism and parenchymal thickness in pepper

Nitrogen promotes changes in SLA through metabolism and anatomical traits in Capsicum plants. Specific leaf area (SLA) is a key trait influencing light interception and light use efficiency that often impacts plant growth and production. SLA is a key trait explaining growth variations of plant species under different environments. Both light and nitrogen (N) supply are important determinants of SLA. To better understand the effect of irradiance level and N on SLA in Capsicum chinense, we evaluated primary metabolites and morphological traits of two commercial cultivars (Biquinho and Habanero) in response to changes in both parameters. Both genotypes showed increased SLA with shading, and a decrease in SLA in response to increased N supply, however, with Habanero showing a stable SLA in the range of N deficiency to sufficient N doses. Correlation analyses indicated that decreased SLA in response to higher N supply was mediated by altered amino acids, protein, and starch levels, influencing leaf density. Moreover, in the range of moderate N deficiency to N sufficiency, both genotypes exhibited differences in SLA response, with Biquinho and Habanero displaying alterations on palisade and spongy parenchyma, respectively. Altogether, the results suggest that SLA responses to N supply are modulated by the balance between certain metabolites content and genotype-dependent changes in the parenchyma cells influencing leaf thickness and density.

Effect of ammonium and nitrate supplies on nitrogen and sucrose metabolism of Cabernet Sauvignon (Vitis vinifera cv.)

BACKGROUND

The quality of wine is highly dependent on the quality of berries. Development of berries is influenced by the type and ratio of different nitrogen supplies in the soil. To understand the impact of varying sources and levels of nitrate and ammonium on sucrose and nitrogen metabolism of Vitis vinifera cv. Cabernet Sauvignon, we tested nutrient solutions with four NO₃ ^- -N:NH₄ ⁺ -N ratios (100:0, 75:25, 50:50, 0:100) through the root system.

RESULTS

The form and quantity of nitrogen affected berries and leaves with source-sink relationships. Soluble sugar levels were significantly higher in plants treated with mixed nitrogen sources (75:25 and 50:50) compared to single nitrogen sources (100:0 and 0:100). In particular, treating plants with mixed nitrogen source at a 75:25 ratio resulted in 22% higher fructose levels in berries compared to the 50:50 treatment. In addition, mixed nitrogen treatments resulted in significantly higher amino acid levels and protein content. Mixed nitrogen substrates also increased the expression of enzymes involved in both nitrogen and sucrose metabolism.

CONCLUSION

Plants did not maximize the nitrogen supply when single form nitrogen was provided, and the mixed nitrogen substrates consistently increased the amount of available carbon and nitrogen in the berries and leaves. We found that NO₃ ^- -N:NH₄ ⁺ -N ratio of 75:25 was the optimum formula for improving nitrogen and sucrose metabolism, and reducing the competition between nitrogen and sucrose. By examining the nutrient utilization of plants cultivated with different nitrogen forms, the present study provides insights into improving cultivation and production practices. © 2020 Society of Chemical Industry.

Integrated analysis on biochemical profiling and transcriptome revealed nitrogen-driven difference in accumulation of saponins in a medicinal plant Panax notoginseng

The medicinal plant Panax notoginseng is considered a promising source of secondary metabolites due to its saponins. However, there are relatively few studies on the response of saponins to nitrogen (N) availability and the mechanisms underlying the N-driven regulation of saponins. Saponins content and saponins -related genes were analyzed in roots of P. notoginseng grown under low N (LN), moderate N (MN) and high N (HN). Saponins was obviously increased in LN individuals with a reduction in β-glucosidase activity. LN facilitated root architecture and N uptake rate. Compared with the LN individuals, 2872 and 1122 genes were incorporated into as differently expressed genes (DEGs) in the MN and HN individuals. Clustering and enrichment showed that DEGs related to "carbohydrate biosynthesis", "plant hormone signal transduction", "terpenoid backbone biosynthesis", "sesquiterpenoid and triterpenoid biosynthesis" were enriched. The up-regulation of some saponins-related genes and microelement transporters was found in LN plants. Whereas the expression of IPT3, AHK4 and GS2 in LN plants fell far short of that in HN ones. Anyways, LN-induced accumulation of C-based metabolites as saponins might derive from the interaction between N and phytohormones in processing of N acquisition, and HN-induced reduction of saponins might be result from an increase in the form of β-glucosidase activity and N-dependent cytokinins (CKs) biosynthesis.

Source Strength Modulates Fruit Set by Starch Turnover and Export of Both Sucrose and Amino Acids in Pepper

Fruit set is an important yield-related parameter, which varies drastically due to genetic and environmental factors. Here, two commercial cultivars of Capsicum chinense (Biquinho and Habanero) were evaluated in response to light intensity (unshaded and shaded) and N supply (deficiency and sufficiency) to understand the role of source strength on fruit set at the metabolic level. We assessed the metabolic balance of primary metabolites in source leaves during the flowering period. Furthermore, we investigated the metabolic balance of the same metabolites in flowers to gain more insights into their influence on fruit set. Genotype and N supply had a strong effect on fruit set and the levels of primary metabolites, whereas light intensity had a moderate effect. Higher fruit set was mainly related to the export of both sucrose and amino acids from source leaves to flowers. Additionally, starch turnover in source leaves, but not in flowers, had a central role on the sucrose supply to sink organs at night. In flowers, our results not only confirmed the role of the daily supply of carbohydrates on fruit set but also indicated a potential role of the balance of amino acids and malate.