Light intensity affects the uptake and metabolism of glycine by pakchoi (Brassica chinensis L.)

Fluorescent-Dye-Labeled Amino Acids for Real-Time Imaging in Arabidopsis thaliana

Amino acid is the main transport form of reduced nitrogen in plants. To investigate the uptake and source–sink translocation process of plants to help understand their physiological roles and transport mechanisms, we designed and synthesized three fluorescent-dye-labeled amino acids as tools to visualize amino acid transportation in Arabidopsis thaliana; these amino acids consist of amino acids linked to the fluorophore nitrobenzoxadiazole (NBD) with excellent optical properties. Furthermore, we incubated Arabidopsis thaliana with these NBD fluorescent-dye-labeled amino acids for real-time imaging along with fluorescence enhancement for 24 h. The results showed that Arabidopsis thaliana could absorb them directly from the roots to the leaves. Therefore, our fluorescent-dye-labeled amino acids provide a de novo tool and strategy for visualizing amino acid absorption and transportation in plants.

Soil organic nitrogen: an overlooked but potentially significant contribution to crop nutrition

BACKGROUND

For more than a century, crop N nutrition research has primarily focused on inorganic N (IN) dynamics, building the traditional model that agricultural plants predominantly take up N in the form of NO₃ ^- and NH₄ ⁺. However, results reported in the ecological and agricultural literature suggest that the traditional model of plant N nutrition is oversimplified.

SCOPE

We examine the role of organic N (ON) in plant N nutrition, first by reviewing the historical discoveries by ecologists of plant ON uptake, then by discussing the advancements of key analytical techniques that have furthered the cause (stable isotope and microdialysis techniques). The current state of knowledge on soil ON dynamics is analyzed concurrently with recent developments that show ON uptake and assimilation by agricultural plant species. Lastly, we consider the relationship between ON uptake and nitrogen use efficiency (NUE) in an agricultural context.

CONCLUSIONS

We propose several mechanisms by which ON uptake and assimilation may increase crop NUE, such as by reducing N assimilation costs, promoting root biomass growth, shaping N cycling microbial communities, recapturing exuded N compounds, and aligning the root uptake capacity to the soil N supply in highly fertilized systems. These hypothetical mechanisms should direct future research on the topic. Although the quantitative role remains unknown, ON compounds should be considered as significant contributors to plant N nutrition.

Combined application of citric acid and 5-aminolevulinic acid improved biomass, photosynthesis and gas exchange attributes of sunflower (Helianthus annuus L.) grown on chromium contaminated soil

Phytoremediation is an important technique to remove heavy metals from contaminated soils due to its efficiency and cost-effectiveness. The present study was conducted to assess the synergistic role of 5-aminolevulinic acid (ALA) and citric acid (CA) in improving the phyto-extraction of chromium (Cr) by sunflower. Sunflower plants were grown in soil, spiked with different concentrations of Cr (0, 5, 10, 20 mg kg^-1). Various concentrations of 5-ALA (0, 10, 20 mg L^-1) and CA (0, 2.5, 5 mM) were applied exogenously at juvenile stage. A significant decrease was observed in biomass and agronomic traits of sunflower under Cr stress alone. Further, Cr toxicity significantly decreased the plant growth, soluble proteins and photosynthetic pigments. However, exogenously applied ALA and CA significantly improved the plants' physiological as well as agronomic attributes by lowering the production of reactive oxygen species and reducing electrolyte leakage. Moreover, Cr uptake was increased with increasing concentration of Cr in spiked soil, which was further enhanced by combined application of ALA and CA.

Exogenous glycine inhibits root elongation and reduces nitrate-N uptake in pak choi (Brassica campestris ssp. Chinensis L.)

Nitrogen (N) supply, including NO3--N and organic N in the form of amino acids can influence the morphological attributes of plants. For example, amino acids contribute to plant nutrition; however, the effects of exogenous amino acids on NO3--N uptake and root morphology have received little attention. In this study, we evaluated the effects of exogenous glycine (Gly) on root growth and NO3--N uptake in pak choi (Brassica campestris ssp. Chinensis L.). Addition of Gly to NO3--N agar medium or hydroponic solution significantly decreased pak choi seedling root length; these effects of Gly on root morphology were not attributed to the proportion of N supply derived from Gly. When pak choi seedlings were exposed to mixtures of Gly and NO3--N in hydroponic culture, Gly significantly reduced 15NO3--N uptake but significantly increased the number of root tips per unit root length, root activity and 15NO3--N uptake rate per unit root length. In addition, 15N-Gly was taken up into the plants. In contrast to absorbed NO3--N, which was mostly transported to the shoots, a larger proportion of absorbed Gly was retained in the roots. Exogenous Gly enhanced root 1-aminocyclopropane-1-carboxylic acid synthase (ACS) and oxidase (ACO) activities and ethylene production. The ethylene antagonists aminoethoxyvinylglycine (0.5 μM AVG) and silver nitrate (10 μM AgNO3) partly reversed Gly-induced inhibition of primary root elongation on agar plates and increased the NO3--N uptake rate under hydroponic conditions, indicating exogenous Gly exerts these effects at least partly by enhancing ethylene production in roots. These findings suggest Gly substantially affects root morphology and N uptake and provide new information on the specific responses elicited by organic N sources.

Elevated CO2 levels enhance the uptake and metabolism of organic nitrogen

The effects of elevated CO₂ (eCO₂ ) on the relative uptake of inorganic and organic nitrogen (N) are unclear. The uptake of different N sources by pak choi (Brassica chinensis L.) seedlings supplied with a mixture of nitrate, glycine and ammonium was studied using ¹⁵ N-labelling under ambient CO₂ (aCO₂ ) (350 ppm) or eCO₂ (650 ppm) conditions. ¹⁵ N-labelled short-term uptake and ¹⁵ N-gas chromatography mass spectrometry (GC-MS) were applied to measure the effects of eCO₂ on glycine uptake and metabolism. Elevated CO₂ increased the shoot biomass by 36% over 15 days, but had little effect on root growth. Over the same period, the N concentrations of shoots and roots were decreased by 30 and 2%, respectively. Elevated CO₂ enhanced the uptake and N contribution of glycine, which accounted for 38-44% and 21-40% of total N uptake in roots and shoots, respectively, while the uptake of nitrate and ammonium was reduced. The increased glycine uptake resulted from the enhanced active uptake and enhanced metabolism in the roots. We conclude that eCO₂ may increase the uptake and contribution of organic N forms to total plant N nutrition. Our findings provide new insights into plant N regulation under eCO₂ conditions.

Hexavalent chromium stress enhances the uptake of nitrate but reduces the uptake of ammonium and glycine in pak choi (Brassica chinensis L.)

Chromium (Cr) pollution affects plant growth and biochemical processes, so, the relative uptake of glycine, nitrate, and ammonium by pak choi (Brassica chinensis) seedlings in treatments with 0mgL^-1 and 10mgL^-1 Cr (VI) were detected by substrate-specific ¹⁵N-labelling in a sterile environment. The short-term uptake of ¹⁵N-labelled sources and ¹⁵N-enriched amino acids were detected by gas chromatography mass spectrometry to explore the mechanism by which Cr stress affects glycine uptake and metabolism, which showing that Cr stress hindered the uptake of ammonium and glycine but increased significantly the uptake of nitrate. Cr stress did not decrease the active or passive uptake of glycine, but it inhibited the conversion of glycine to serine in pak choi roots, indicating that the metabolism of glycine to serine in roots, rather than the root uptake, was the limiting step in glycine contribution to total N uptake in pak choi. Since Cr affects the relative uptake of different N sources, a feasible way to reduce Cr-induced stress is application of selective fertilization, in particular nitrate, in pak choi cultivation on Cr-polluted soil.

Effects of glucose on the uptake and metabolism of glycine in pakchoi (Brassica chinensis L.) exposed to various nitrogen sources

BACKGROUND

Plants can absorb amino acids as a nitrogen (N) source, and glucose is an important part of root rhizodeposition and the soil sugar pool, which participates in the regulation of plant growth and uptake. In pakchoi, the effect of glucose concentration on the glycine N uptake from a nutrient mixture composed of glycine, ammonium, and nitrate, or from a single N solution of glycine alone was studied using specific substrate 15N-labeling and 15N-gas chromatography mass spectrometry.

RESULTS

The optimal glucose concentration for plant growth was 4.5 μM or 25 μM when supplied with glycine alone or the N mixture, respectively, and resulted in a >25% increase in seedling biomass. The addition of glucose affected the relative contribution from organic or inorganic sources to overall N uptake. When glucose was added at optimal concentrations, glycine was preferentially used as an N source, while the relative contribution from nitrate was reduced. The limiting step for glycine N contribution was active uptake in the roots in high glucose and single-N-source conditions; however, root metabolism of glycine to serine was limiting in high-glucose and mixed-N-source conditions.

CONCLUSIONS

The addition of low concentrations of glucose increased the relative uptake of organic nitrogen and reduced the uptake of nitrate, suggesting a feasible way to decrease nitrate content and increase the edible quality of vegetables.