Inhibition of nitrogen and photosynthetic carbon assimilation of maize seedlings by exposure to a combination of salt stress and potassium-deficient stress

Nitrogen Journey in Plants: From Uptake to Metabolism, Stress Response, and Microbe Interaction

Plants uptake and assimilate nitrogen from the soil in the form of nitrate, ammonium ions, and available amino acids from organic sources. Plant nitrate and ammonium transporters are responsible for nitrate and ammonium translocation from the soil into the roots. The unique structure of these transporters determines the specificity of each transporter, and structural analyses reveal the mechanisms by which these transporters function. Following absorption, the nitrogen metabolism pathway incorporates the nitrogen into organic compounds via glutamine synthetase and glutamate synthase that convert ammonium ions into glutamine and glutamate. Different isoforms of glutamine synthetase and glutamate synthase exist, enabling plants to fine-tune nitrogen metabolism based on environmental cues. Under stressful conditions, nitric oxide has been found to enhance plant survival under drought stress. Furthermore, the interaction between salinity stress and nitrogen availability in plants has been studied, with nitric oxide identified as a potential mediator of responses to salt stress. Conversely, excessive use of nitrate fertilizers can lead to health and environmental issues. Therefore, alternative strategies, such as establishing nitrogen fixation in plants through diazotrophic microbiota, have been explored to reduce reliance on synthetic fertilizers. Ultimately, genomics can identify new genes related to nitrogen fixation, which could be harnessed to improve plant productivity.

Potassium deficiency causes more nitrate nitrogen to be stored in leaves for low-K sensitive sweet potato genotypes

In order to explore the effect of potassium (K) deficiency on nitrogen (N) metabolism in sweet potato (Ipomoea batatas L.), a hydroponic experiment was conducted with two genotypes (Xushu 32, low-K-tolerant; Ningzishu 1, low-K-sensitive) under two K treatments (-K, <0.03 mM of K⁺; +K, 5 mM of K⁺) in the greenhouse of Jiangsu Normal University. The results showed that K deficiency decreased root, stem, and leaf biomass by 13%-58% and reduced whole plant biomass by 24%-35%. Compared to +K, the amount of K and K accumulation in sweet potato leaves and roots was significantly decreased by increasing root K⁺ efflux in K-deficiency-treated plants. In addition, leaf K, N, ammonium nitrogen (NH₄ ⁺-N), or nitrate nitrogen (NO₃ ^--N) in leaves and roots significantly reduced under K deficiency, and leaf K content had a significant quadratic relationship with soluble protein, NO₃ ^--N, or NH₄ ⁺-N in leaves and roots. Under K deficiency, higher glutamate synthase (GOGAT) activity did not increase amino acid synthesis in roots; however, the range of variation in leaves was larger than that in roots with increased amino acid in roots, indicating that the transformation of amino acids into proteins in roots and the amino acid export from roots to leaves were not inhibited. K deficiency decreased the activity of nitrate reductase (NR) and nitrite reductase (NiR), even if the transcription level of NR and NiR increased, decreased, or remained unchanged. The NO₃ ^-/NH₄ ⁺ ratio in leaves and roots under K deficiency decreased, except in Ningzishu 1 leaves. These results indicated that for Ningzishu 1, more NO₃ ^- was stored under K deficiency in leaves, and the NR and NiR determined the response to K deficiency in leaves. Therefore, the resistance of NR and NiR activities to K deficiency may be a dominant factor that ameliorates the growth between Xushu 32 and Ningzishu 1 with different low-K sensitivities.

Potassium: A track to develop salinity tolerant plants

Salinity is one of the major constraints to plant growth and development across the globe that leads to the huge crop productivity loss. Salinity stress causes impairment in plant's metabolic and cellular processes including disruption in ionic homeostasis due to excess of sodium (Na⁺) ion influx and potassium (K⁺) efflux. This condition subsequently results in a significant reduction of the cytosolic K⁺ levels, eventually inhibiting plant growth attributes. K⁺ plays a crucial role in alleviating salinity stress by recasting key processes of plants. In addition, K⁺ acquisition and retention also serve as the perquisite trait to establish salt tolerant mechanism. In addition, an intricate network of genes and their regulatory elements are involved in coordinating salinity stress responses. Furthermore, plant growth regulators (PGRs) and other signalling molecules influence K⁺-mediated salinity tolerance in plants. Recently, nanoparticles (NPs) have also been found several implications in plants with respect to their roles in mediating K⁺ homoeostasis during salinity stress in plants. The present review describes salinity-induced adversities in plants and role of K⁺ in mitigating salinity-induced damages. The review also highlights the efficacy of PGRs and other signalling molecules in regulating K⁺ mediated salinity tolerance along with nano-technological perspective for improving K⁺ mediated salinity tolerance in plants.

Regulation of the activity of maize glutamate dehydrogenase by ammonium and potassium

Glutamate dehydrogenase (GDH) is an important enzyme in ammonium metabolism, the activity of which is regulated by multiple factors. In this study, we investigate the effects of ammonium and potassium on the activity of maize GDH. Our results show that both ammonium and potassium play multiple roles in regulating the activity of maize GDH, with the specific roles depending on the concentration of potassium. Together with the structural information of GDH, we propose models for the substrate inhibition of ammonium, and the elimination of substrate inhibition by potassium. These models are supported by the analysis of statistic thermodynamics. We also analyze the binding sites of ammonium and potassium on maize GDH, and the conformational changes of maize GDH. The findings provide insight into the regulation of maize GDH activity by ammonium and potassium and reveal the importance of the dose and ratio of nitrogen and potassium in crop cultivation.

Current Advances in Plant Growth Promoting Bacteria Alleviating Salt Stress for Sustainable Agriculture

Humanity in the modern world is confronted with diverse problems at several levels. The environmental concern is probably the most important as it threatens different ecosystems, food, and farming as well as humans, animals, and plants. More specifically, salinization of agricultural soils is a global concern because of on one side, the permanent increase of the areas affected, and on the other side, the disastrous damage caused to various plants affecting hugely crop productivity and yields. Currently, great attention is directed towards the use of Plant Growth Promoting Bacteria (PGPB). This alternative method, which is healthy, safe, and ecological, seems to be very promising in terms of simultaneous salinity alleviation and improving crop productivity. This review attempts to deal with different aspects of the current advances concerning the use of PGPBs for saline stress alleviation. The objective is to explain, discuss, and present the current progress in this area of research. We firstly discuss the implication of PGPB on soil desalinization. We present the impacts of salinity on crops. We look for the different salinity origin and its impacts on plants. We discuss the impacts of salinity on soil. Then, we review various recent progress of hemophilic PGPB for sustainable agriculture. We categorize the mechanisms of PGPB toward salinity tolerance. We discuss the use of PGPB inoculants under salinity that can reduce chemical fertilization. Finally, we present some possible directions for future investigation. It seems that PGPBs use for saline stress alleviation gain more importance, investigations, and applications. Regarding the complexity of the mechanisms implicated in this domain, various aspects remain to be elucidated.

Effects of imazethapyr spraying on plant growth and leaf surface microbial communities in Arabidopsis thaliana

Imazethapyr (IM) is an acetolactate synthase (ALS)-inhibiting herbicide that has been widely used in recent years. However, IM spraying can lead to the accumulation of herbicide residues in leaves. Here, we determined the effects of IM spraying on the plant growth and leaf surface microbial communities of Arabidopsis thaliana after 7 and 14 days of exposure. The results suggested that IM spraying inhibited plant growth. Fresh weight decreased to 48% and 26% of the control value after 7 and 14 days, respectively, of 0.035 kg/ha IM exposure. In addition, anthocyanin content increased 9.2-fold and 37.2-fold relative to the control content after 7 and 14 days of treatment, respectively. Furthermore, IM spraying destroyed the cell structures of the leaves, as evidenced by increases in the number of starch granules and the stomatal closure rate. Reductions in photosynthetic efficiency and antioxidant enzyme activity were observed after IM spraying, especially after 14 days of exposure. The diversity and evenness of the leaf microbiota were not affected by IM treatment, but the composition of community structure at the genus level was altered by IM spraying. Imazethapyr application increased the abundance of Pseudomonas, a genus that includes species pathogenic to plants and humans, indicating that IM potentially increased the abundance of pathogenic bacteria on leaves. Our findings increase our understanding of the relationships between herbicide application and the microbial community structures on plant leaves, and they provide a new perspective for studying the ecological safety of herbicide usage.

The interactive effects of diclofop-methyl and silver nanoparticles on Arabidopsis thaliana: Growth, photosynthesis and antioxidant system

Diclofop-methyl (DM), a common post-emergence herbicide, is frequently used in agricultural production. Silver nanoparticles (AgNPs) are one of the most widely used nanoparticles, and as such, have been detected and monitored in several environmental systems. Here we investigated the interactive effects of DM and AgNPs on the physiological morphology, photosynthesis and antioxidant system of Arabidopsis thaliana. Our results demonstrated that a 1.0 mg/L DM treatment had no significant effect on the fresh weight of plant shoots and the content of total chlorophyll and anthocyanin. However, a 0.5 mg/L AgNPs treatment was found to significantly inhibit plant growth and chlorophyll synthesis, and was found to cause more severe oxidative damage in plants compared to the effects observed in a hydroponic suspension in which DM and AgNPs were jointly present. Meanwhile, the relative transcript levels of photosynthesis related genes (psbA, rbcL, pgrl1A and pgrl1B) in the combined group were found to be slightly increased compared to transcript levels in the AgNPs group, in order to maintain ATP generation at relatively normal levels in order to repair light damage. One explanation for these observed antagonistic effects was that the existence of DM affects the stability of AgNPs and reduced Ag⁺ release from AgNPs in the mixed solution. Thereupon, the Ag⁺-content was found to decrease in shoots and roots in the combined group by 15.2% and 9.4% respectively, compared to the AgNPs group. The coexistence of herbicides and nanomaterials in aquatic environments or soil systems will continue to exist due to their wide usages. Our current study highlights that the antagonistic effects between DM and AgNPs exerted a positive impact on A. thaliana growth.

Cerium Improves Growth of Maize Seedlings via Alleviating Morphological Structure and Oxidative Damages of Leaf under Different Stresses

It had been indicated that cerium (Ce) could promote maize growth involving photosynthetic improvement under potassium (K) deficiency, salt stress, and combined stress of K⁺ deficiency and salt stress. However, whether the improved growth is related to leaf morphological structure, oxidative stress in maize leaves is not well understood. The present study showed that K⁺ deficiency, salt stress, and their combined stress inhibited growth of maize seedlings, affecting the formation of appendages of leaf epidermal cells, and stomatal opening, which may be due to increases in H₂O₂ and malondialdehyde levels, and reductions in Ca²⁺ content, ratios of glutathione/oxidized glutathione, ascorbic acid/dehydroascorbic acid, and the activities of superoxide dismutase, catalase, ascorbic acid peroxidase, guaiacol peroxidase, and glutathione reductase in leaves under different stresses. The adverse effects caused by combined stress were higher than those of single stress. Furthermore, our findings demonstrated that adding Ce³⁺ could significantly promote seedling growth, and alleviate morphological and structural damage of leaf, decrease oxidative stress and increase antioxidative capacity in maize leaves caused by different stresses.

Relationship between potassium fertilization and nitrogen metabolism in the leaf subtending the cotton (Gossypium hirsutum L.) boll during the boll development stage

The nitrogen (N) metabolism of the leaf subtending the cotton boll (LSCB) was studied with two cotton (Gossypium hirsutum L.) cultivars (Simian 3, low-K tolerant; Siza 3, low-K sensitive) under three levels of potassium (K) fertilization (K0: 0 g K2O plant(-1), K1: 4.5 K2O plant(-1) and K2: 9.0 g K2O plant(-1)). The results showed that total dry matter increased by 13.1-27.4% and 11.2-18.5% under K supply for Simian 3 and Siza 3. Boll biomass and boll weight also increased significantly in K1 and K2 treatments. Leaf K content, leaf N content and nitrate (NO3(-)) content increased with increasing K rates, and leaf N content or NO3(-) content had a significant positive correlation with leaf K content. Free amino acid content increased in the K0 treatment for both cultivars, due to increased protein degradation caused by higher protease and peptidase activities, resulting in lower protein content in the K0 treatment. The critical leaf K content for free amino acid and soluble protein content were 14 mg g(-1) and 15 mg g(-1) in Simian 3, and 17 mg g(-1) and 18 mg g(-1) in Siza 3, respectively. Nitrate reductase (NR), glutamic-oxaloace transaminase (GOT) and glutamic-pyruvic transaminase (GPT) activities increased in the K1 and K2 treatments for both cultivars, while glutamine synthetase (GS) and glutamate synthase (GOGAT) activities increased under K supply treatments only for Siza 3, and were not affected in Simian 3, indicating that this was the primary difference in nitrogen-metabolizing enzymes activities for the two cultivars with different sensitivity to low-K.

Combined effect and mechanism of acidity and lead ion on soybean biomass

Heavy metal pollution and soil acidification are serious global environmental issues. The combined pollution from acidification and heavy metal has become a new environmental issue in regions where the two issues simultaneously occur. However, studies on combined pollution are still limited. In the current study, we investigated the combined effect and mechanism of acidity and heavy metal [lead ion (Pb(2+))] on soybean biomass as well as on growth, nitrogen nutrition, and antioxidant system in soybean roots. Results showed that the combined treatment with acidity and Pb(2+) decreased the soybean biomass. At pH 4.5, the soybean biomass in the combined treatment with acidity and 0.9 mmol L(-1) Pb(2+) was lower than that in the combined treatment with acidity and Pb(2+) at 0.3 or 1.5 mmol L(-1). This result was also observed at pH 3.5 and 3.0. The combined treatment with acidity and Pb(2+) also resulted in the following consequences: root growth inhibition; decrease in nitrate, ammonium, and malondialdehyde contents; increase in nitrite reductase activity; and decrease in peroxidase activity. The extent at which the test indexes decreased/increased in the combined treatment was higher than that in the single acidity treatment. The correlation analysis results indicated that the decrease in the soybean biomass in the combined treatment with acidity and Pb(2+) resulted from the decrease in the root growth, nitrate-nitrogen assimilation, and peroxidase activity.

Improvement of cerium on photosynthesis of maize seedlings under a combination of potassium deficiency and salt stress

Added Ce(3+) can partly substitute for Ca(2+) or Mg(2+) and improve photosynthesis under the deficiency of these elements, but very few studies focused on photosynthetic improvement in maize seedlings caused by K(+) deficiency, salt stress, especially a combination of K(+) deficiency and salt stress. In the present study, the effects of Ce(3+) on the photosynthesis of maize seedlings under the three different stresses were investigated. The results showed that added Ce(3+) under various stresses increased the ratios of free water/bound water and of K(+)/Na(+), the pigment contents, the values of Fv/Fm, Y(II), ETR(II), Y(NPQ), Qp, qL, NPQ, and qN of photosystem II (PSII), the values of Y(I) and ETR(I) of photosystem I (PSI) and the expression levels of LhcII cab1 and rbcL, and decreased the values of Y(NO) and Y(NA). This implied that added Ce(3+) depressed ion toxicity, photodamage of PSII, and acceptor side constraints of PSI, and enhanced adjustable energy dissipation, the responses of photochemistry, and carbon assimilation caused by K(+) deficiency, salt stress, and the combination of K(+) deficiency and salt stress. However, Ce(3+) mitigation of photosynthetic inhibition in maize seedlings caused by the combined stresses was greater than that of salt stress, and Ce(3+) mitigation under salt stress was greater than that under K(+) deficiency. In addition, the results also showed that Ce(3+) cannot improve photosynthesis and growth of maize seedlings under K(+) deficiency by substituting for K(+).

The critical role of potassium in plant stress response

Agricultural production continues to be constrained by a number of biotic and abiotic factors that can reduce crop yield quantity and quality. Potassium (K) is an essential nutrient that affects most of the biochemical and physiological processes that influence plant growth and metabolism. It also contributes to the survival of plants exposed to various biotic and abiotic stresses. The following review focuses on the emerging role of K in defending against a number of biotic and abiotic stresses, including diseases, pests, drought, salinity, cold and frost and waterlogging. The availability of K and its effects on plant growth, anatomy, morphology and plant metabolism are discussed. The physiological and molecular mechanisms of K function in plant stress resistance are reviewed. This article also evaluates the potential for improving plant stress resistance by modifying K fertilizer inputs and highlights the future needs for research about the role of K in agriculture.

Imazethapyr enantioselectively affects chlorophyll synthesis and photosynthesis in Arabidopsis thaliana

Imazethapyr (IM) is a chiral herbicide with reported enantioselective biological activities between its enantiomers. This report investigated the effect of enantioselectivity between R- and S-IM in Arabidopsis thaliana on chlorophyll synthesis and photosynthesis. The results suggest that R-IM inhibited the transcription of chlM to a greater extent than S-IM, which reduced chlorophyll synthesis. R-IM also showed a stronger inhibitory effect than S-IM on the transcription of photosynthesis-related genes, affecting linear electron transport and CO(2) fixation. IM stress enantioselectively induced transcriptional upregulation of the ndhH gene, a representative of the NDH complex. In contrast, the expression of pgr5 was downregulated, which demonstrated that IM stress enhanced adenosine 5'-triphosphate (ATP) synthesis by stimulating an NDH-dependent and not ferredoxin (FD)-independent route. This study suggested that R-IM has a greater toxic effect on photosynthesis than S-IM, affecting plant growth through chlorophyll synthesis.