Atmospheric CO2 captured by biogenic polyamines is transferred as a possible substrate to Rubisco for the carboxylation reaction

Regulation of ethylene metabolism in tomato under salinity stress involving linkages with important physiological signaling pathways

The tomato is well-known for its anti-oxidative and anti-cancer properties, and with a wide range of health benefits is an important cash crop for human well-being. However, environmental stresses (especially abiotic) are having a deleterious effect on plant growth and productivity, including tomato. In this review, authors describe how salinity stress imposes risk consequences on growth and developmental processes of tomato through toxicity by ethylene (ET) and cyanide (HCN), and ionic, oxidative, and osmotic stresses. Recent research has clarified how salinity stress induced-ACS and - β-CAS expressions stimulate the accumulation of ET and HCN, wherein the action of salicylic acid (SA),compatible solutes (CSs), polyamines (PAs) and ET inhibitors (ETIs) regulate ET and HCN metabolism. Here we emphasize how ET, SA and PA cooperates with mitochondrial alternating oxidase (AOX), salt overly sensitive (SOS) pathways and the antioxidants (ANTOX) system to better understand the salinity stress resistance mechanism. The current literature evaluated in this paper provides an overview of salinity stress resistance mechanism involving synchronized routes of ET metabolism by SA and PAs, connecting regulated network of central physiological processes governing through the action of AOX, β-CAS, SOS and ANTOX pathways, which might be crucial for the development of tomato.

Patterns of physical, chemical, and metabolic characteristics of sugar maple leaves with depth in the crown and in response to nitrogen and phosphorus addition

Few previous studies have described patterns of leaf characteristics in response to nutrient availability and depth in the crown. Sugar maple has been studied for both sensitivity to light, as a shade-tolerant species, and sensitivity to soil nutrient availability, as a species in decline due to acid rain. To explore leaf characteristics from the top to bottom of the canopy, we collected leaves along a vertical gradient within mature sugar maple crowns in a full-factorial nitrogen by phosphorus addition experiment in three forest stands in central New Hampshire, USA. Thirty-two of the 44 leaf characteristics had significant relationships with depth in the crown, with the effect of depth in the crown strongest for leaf area, photosynthetic pigments, and polyamines. Nitrogen addition had a strong impact on the concentration of foliar N, chlorophyll, carotenoids, alanine, and glutamate. For several other elements and amino acids, N addition changed patterns with depth in the crown. Phosphorus addition increased foliar P and B; it also caused a steeper increase of P and B with depth in the crown. Since most of these leaf characteristics play a direct or indirect role in photosynthesis, metabolic regulation, or cell division, studies that ignore the vertical gradient may not accurately represent whole-canopy performance.

Chitosan-Modified Polyethyleneimine Nanoparticles for Enhancing the Carboxylation Reaction and Plants' CO2 Uptake

Increasing plants' photosynthetic efficiency is a major challenge that must be addressed in order to cover the food demands of the growing population in the changing climate. Photosynthesis is greatly limited at the initial carboxylation reaction, where CO₂ is converted to the organic acid 3-PGA, catalyzed by the RuBisCO enzyme. RuBisCO has poor affinity for CO₂, but also the CO₂ concentration at the RuBisCO site is limited by the diffusion of atmospheric CO₂ through the various leaf compartments to the reaction site. Beyond genetic engineering, nanotechnology can offer a materials-based approach for enhancing photosynthesis, and yet, it has mostly been explored for the light-dependent reactions. In this work, we developed polyethyleneimine-based nanoparticles for enhancing the carboxylation reaction. We demonstrate that the nanoparticles can capture CO₂ in the form of bicarbonate and increase the CO₂ that reacts with the RuBisCO enzyme, enhancing the 3-PGA production in in vitro assays by 20%. The nanoparticles can be introduced to the plant via leaf infiltration and, because of the functionalization with chitosan oligomers, they do not induce any toxic effect to the plant. In the leaves, the nanoparticles localize in the apoplastic space but also spontaneously reach the chloroplasts where photosynthetic activity takes place. Their CO₂ loading-dependent fluorescence verifies that, in vivo, they maintain their ability to capture CO₂ and can be therefore reloaded with atmospheric CO₂ while in planta. Our results contribute to the development of a nanomaterials-based CO₂-concentrating mechanism in plants that can potentially increase photosynthetic efficiency and overall plants' CO₂ storage.

Promotion of Carbon Dioxide Biofixation through Metabolic and Enzyme Engineering

Carbon dioxide is a major greenhouse gas, and its fixation and transformation are receiving increasing attention. Biofixation of CO2 is an eco–friendly and efficient way to reduce CO2, and six natural CO2 fixation pathways have been identified in microorganisms and plants. In this review, the six pathways along with the most recent identified variant pathway were firstly comparatively characterized. The key metabolic process and enzymes of the CO2 fixation pathways were also summarized. Next, the enzymes of Rubiscos, biotin-dependent carboxylases, CO dehydrogenase/acetyl-CoA synthase, and 2-oxoacid:ferredoxin oxidoreductases, for transforming inorganic carbon (CO2, CO, and bicarbonate) to organic chemicals, were specially analyzed. Then, the factors including enzyme properties, CO2 concentrating, energy, and reducing power requirements that affect the efficiency of CO2 fixation were discussed. Recent progress in improving CO2 fixation through enzyme and metabolic engineering was then summarized. The artificial CO2 fixation pathways with thermodynamical and/or energetical advantages or benefits and their applications in biosynthesis were included as well. The challenges and prospects of CO2 biofixation and conversion are discussed.

Polyamines: Α bioenergetic smart switch for plant protection and development

The present review highlights the bioenergetic role of polyamines in plant protection and development and proposes a universal model for describing polyamine-mediated stress responses. Any stress condition induces an excitation pressure on photosystem II by reforming the photosynthetic apparatus. To control this phenomenon, polyamines act directly on the molecular structure and function of the photosynthetic apparatus as well as on the components of the chemiosmotic proton-motive force (ΔpH/Δψ), thus regulating photochemical (qP) and non-photochemical quenching (NPQ) of energy. The review presents the mechanistic characteristics that underline the key role of polyamines in the structure, function, and bioenergetics of the photosynthetic apparatus upon light adaptation and/or under stress conditions. By following this mechanism, it is feasible to make stress-sensitive plants to be tolerant by simply altering their polyamine composition (especially the ratio of putrescine to spermine), either chemically or by light regulation.

Phosphate Enrichment Hampers Development of Juvenile Acropora digitifera Coral by Inhibiting Skeleton Formation

Coral reef degradation due to various local stresses, such as nutrient enrichment and terrestrial run-off into coastal waters, is an increasing global concern. Inorganic phosphates have been considered to possibly inhibit skeleton formation in corals. Despite many studies available on the effects of nutrients on corals, a clear consensus on how nutrients exert deteriorative effects on corals has not been established satisfactorily. In this study, we examined the effects of phosphates and nitrates on in vitro aragonite CaCO₃ formation by using biogenic polyamines and in vivo aragonite formation in the skeleton of juvenile Acropora digitifera corals. We showed that the phosphates at similar concentrations clearly inhibited both in vitro and in vivo CaCO₃ formation. In contrast, nitrates inhibited neither in vitro aragonite CaCO₃ formation nor in vivo aragonite formation in juvenile coral skeleton. Furthermore, our findings showed that inhibition of coral skeleton formation was due to absorption of phosphate on the skeleton, which inorganically inhibited normal development of juvenile coral skeleton.