Heme is involved in the exogenous ALA-promoted growth and antioxidant defense system of cucumber seedlings under salt stress

Evaluate the physiological role of tetrapyrroles precursor on growth, yield and some biochemical composition of two cultivars of Vicia faba L

It is well known that 5-aminolevulinic acid (5ALA) is a non-protein amino acid and essential for the formation of biosynthesis of tetrahydropyrroles. So, two field experiments were carried out in a private farm at Sharkia Governorate to study effect of foliar spraying with 5ALA (1, 3, and 6 mgL-1) on both quality and economic characters of two cultivars of Vicia faba L. (Giza 843 and Nubaria 1). Results indicated that plants belong to Nubaria 1 cv. are characterized by significant increases in all components of photosynthetic pigments, indole acetic acid, free amino acids, seed yield /fed and straw yield/fed over those of Giza 843 cv. under control treatments. Notably, yielded seeds of Giza 843 cv. are characterized by significant increases in total carbohydrate and protein content than those of Nubaria 1 cv. Whereas, yielded seeds of Nubaria 1 cv. are characterized by significant increases in total phenolic content and vicine. Moreover, 5ALA treatments significantly increased most of all values of vegetative growth parameters, photosynthetic pigments, indole acetic acid, proline and free amino acids as well as seed and straw yield/fed, total carbohydrate and protein, and phenolic contents accompanied by significant decreases in vicine content of two faba bean cultivars relative to corresponding controls. On the other hand, the increments in most of investigated parameters were in opposite direction with concentration of 5ALA.The least concentration of 5ALA (1mg/L) was the most significant treatment in both cultivars. Since it increased seed yield by 17.86% and 72.27% in Giza 843 cv. and Nubaria 1 cv. respectively relative to corresponding controls. Regarding anti-nutritional substance called vicine, 5ALA at 3mg/L caused significant decrease in vicine content of Giza 843 cv. relative to control. It could be concluded that faba bean plants belong to Nubaria 1 cv. effectively responded to 5ALA at 1mg/L more than faba bean plants belong to Giza 843 cv.

Protective mechanisms of exogenous melatonin on chlorophyll metabolism and photosynthesis in tomato seedlings under heat stress

Elevated temperatures severely affect plant growth, reducing yield and quality. Melatonin (MT), a plant biomolecule, is known to enhance stress tolerance, but its role in heat resistance and underlying mechanisms require further exploration. This study investigates MT's regulatory effects on chlorophyll metabolism and photosynthesis in tomato seedlings under high-temperature stress (40°C). Tomato seedlings treated with 100 μmol MT showed improved physiological and photosynthetic performance under heat stress. MT application increased osmolytes (proline and soluble sugar), enhanced antioxidant enzyme activities [catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX)], and reduced oxidative damage markers (H2O2, O2 -, malondialdehyde, and conductivity). Photosynthetic parameters, including key enzyme activities [sedoheptulose-1,7-bisphosphatase (SBPase), ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and NADP-dependent glyceraldehyde-3-phosphate dehydrogenase (NADP-GAPDH)], photochemical efficiency [Fv/Fm and Y(II)], and photochemical quenching (Qp), were significantly improved, restoring the OJIP curve and enhancing photosynthesis. MT also regulated chlorophyll metabolism by promoting synthesis [increasing chlorophyll a and b, 5-aminolevulinic acid (ALA), Mg-protoporphyrin (Mg Proto), and protochlorophyllide (Pchlide) levels] and upregulating synthesis genes (SlHEMA1, SlPORB, SlPORC, and SlCHLI) while inhibiting degradation genes (SlCLH1, SlCLH2, SlPAO, SlPPH, and SlRCCR). These findings demonstrate that MT enhances tomato heat tolerance by protecting chlorophyll metabolism and photosynthesis, offering a theoretical basis for improving crop resilience to heat stress.

Analysis of the Transcriptome Provides Insights into the Photosynthate of Maize Response to Salt Stress by 5-Aminolevulinic Acid

Salt stress is a significant environmental factor that impedes maize growth and yield. Exogenous 5-aminolevulinic acid (ALA) has been shown to mitigate the detrimental effects of various environmental stresses on plants. However, its regulatory role in the photosynthesis mechanisms of maize seedlings under salt stress remains poorly understood. Transcriptome sequencing and physiological index measurements were conducted on the leaves of the "Zhengdan 958" cultivar subjected to three different treatments. Differential expression analysis revealed 4634 differentially expressed genes (DEGs), including key transcription factor (TF) families such as NAC, MYB, WRKY, and MYB-related, across two comparisons (SS_vs_CK and ALA_SS_vs_SS). Significant enrichment was observed in the metabolic pathways related to porphyrin metabolism, photosynthesis-antenna proteins, photosynthesis, and carbon fixation in photosynthetic organisms. ALA treatment modulated the expression of photosynthesis-related genes, increased photosynthetic pigment content, and enhanced the activities of superoxide dismutase (SOD) and catalase (CAT), thereby mitigating the excessive accumulation of reactive oxygen species (ROS). Furthermore, ALA increased starch content under salt stress. These findings establish a foundational understanding of the molecular mechanisms through which ALA regulates photosynthesis under salt stress in maize seedlings. Collectively, exogenous ALA enhances maize's salt tolerance by regulating photosynthesis-related pathways.

MdFC2, a ferrochelatase gene, is a positive regulator of ALA-induced anthocyanin accumulation in apples

5-Aminolevulinic acid (ALA), a key biosynthetic precursor of tetrapyrrole compounds, significantly induces anthocyanin accumulation in apple (Malus × domestica Borkh.) as well as other fruits. Although the molecular mechanisms of ALA-induced anthocyanin accumulation have been reported, it remains unknown whether the metabolism of ALA is involved in ALA-induced anthocyanin accumulation. Here, we found that MdFC2, a gene encoding ferrochelatase (MdFC2), which catalyzes the generation of heme from protoporphyrin lX (PPIX), may play an important role in ALA-induced apple anthocyanin accumulation. Exogenous ALA induced the MdFC2 expression as well as anthocyanin accumulation in apple leaves, calli, and isolated fruits. MdFC2 overexpression in apple leaves or calli significantly enhanced anthocyanin accumulation as well as the expression of genes involved in anthocyanin biosynthesis, while RNA interference MdFC2 inhibited anthocyanin accumulation and the expression of genes involved in anthocyanin biosynthesis. When 2,2'-dithiodipyridine, an inhibitor of MdFC2, was added, ALA-induced anthocyanin accumulation was blocked. These results suggest that ALA-induced anthocyanin accumulation of apple may be regulated by heme or its biosynthesis, among which MdFC2 or MdFC2 may play a critical positive regulatory role. This finding provides a novel insight to explore the mechanisms of ALA-regulating physiological processes and better application of ALA in high-quality fruit production.

A combination of joint linkage and genome-wide association study reveals putative candidate genes associated with resistance to northern corn leaf blight in tropical maize

Northern corn leaf blight (NCLB), caused by Setosphaeria turcica, is a major fungal disease affecting maize production in sub-Saharan Africa. Utilizing host plant resistance to mitigate yield losses associated with NCLB can serve as a cost-effective strategy. In this study, we conducted a high-resolution genome-wide association study (GWAS) in an association mapping panel and linkage mapping with three doubled haploid (DH) and three F3 populations of tropical maize. These populations were phenotyped for NCLB resistance across six hotspot environments in Kenya. Across environments and genotypes, NCLB scores ranged from 2.12 to 5.17 (on a scale of 1-9). NCLB disease severity scores exhibited significant genotypic variance and moderate-to-high heritability. From the six biparental populations, 23 quantitative trait loci (QTLs) were identified, each explaining between 2.7% and 15.8% of the observed phenotypic variance. Collectively, the detected QTLs explained 34.28%, 51.37%, 41.12%, 12.46%, 12.11%, and 14.66% of the total phenotypic variance in DH populations 1, 2, and 3 and F3 populations 4, 5, and 6, respectively. GWAS, using 337,110 high-quality single nucleotide polymorphisms (SNPs), identified 15 marker-trait associations and several putative candidate genes linked to NCLB resistance in maize. Joint linkage association mapping (JLAM) identified 37 QTLs for NCLB resistance. Using linkage mapping, JLAM, and GWAS, several QTLs were identified within the genomic region spanning 4 to 15 Mbp on chromosome 2. This genomic region represents a promising target for enhancing NCLB resistance via marker-assisted breeding. Genome-wide predictions revealed moderate correlations with mean values of 0.45, 0.44, 0.55, and 0.42 for within GWAS panel, DH pop1, DH pop2, and DH pop3, respectively. Prediction by incorporating marker-by-environment interactions did not show much improvement. Overall, our findings indicate that NCLB resistance is quantitative in nature and is controlled by few major-effect and many minor-effect QTLs. We conclude that genomic regions consistently detected across mapping approaches and populations should be prioritized for improving NCLB resistance, while genome-wide prediction results can help incorporate both major- and minor-effect genes. This study contributes to a deeper understanding of the genetic and molecular mechanisms driving maize resistance to NCLB.

Transcriptomic Insights: Phytogenic Modulation of Buffel Grass (Cenchrus ciliaris) Seedling Emergence

This study explores the impact of a novel phytogenic product containing citric acid, carvacrol, and cinnamaldehyde on buffel grass (Cenchrus ciliaris) seedling emergence. A dilution series of the phytogenic solution revealed a concentration range that promoted seedling emergence, with an optimal concentration of 0.5%. Transcriptomic analysis using RNA-seq was performed to investigate gene expression changes in seedlings under the influence of the phytogenic product. The results revealed that the phytogenic treatment significantly altered the gene expression, with a prevalent boost in transcriptional activity compared to the control. Functional analysis indicated the positive alteration of key metabolic pathways, including the tricarboxylic acid (TCA) cycle, glycolysis, and pentose phosphate pathways. Moreover, pathways related to amino acids, nucleotide biosynthesis, heme biosynthesis, and formyltetrahydrofolate biosynthesis showed substantial modulation. The study provides valuable insights into the molecular mechanisms underlying the phytogenic product's effects on grass seedling establishment and highlights its ability to promote energy metabolism and essential biosynthetic pathways for plant growth.

Comparative genomic analysis of Chryseobacterium species: deep insights into plant-growth-promoting and halotolerant capacities

Members of the genus Chryseobacterium have attracted great interest as beneficial bacteria that can promote plant growth and biocontrol. Given the recent risks of climate change, it is important to develop tolerance strategies for efficient applications of plant-beneficial bacteria in saline environments. However, the genetic determinants of plant-growth-promoting and halotolerance effects in Chryseobacterium have not yet been investigated at the genomic level. Here, a comparative genomic analysis was conducted with seven Chryseobacterium species. Phylogenetic and phylogenomic analyses revealed niche-specific evolutionary distances between soil and freshwater Chryseobacterium species, consistent with differences in genomic statistics, indicating that the freshwater bacteria have smaller genome sizes and fewer genes than the soil bacteria. Phosphorus- and zinc-cycling genes (required for nutrient acquisition in plants) were universally present in all species, whereas nitrification and sulphite reduction genes (required for nitrogen- and sulphur-cycling, respectively) were distributed only in soil bacteria. A pan-genome containing 6842 gene clusters was constructed, which reflected the general features of the core, accessory and unique genomes. Halotolerant species with an accessory genome shared a Kdp potassium transporter and biosynthetic pathways for branched-chain amino acids and the carotenoid lycopene, which are associated with countermeasures against salt stress. Protein-protein interaction network analysis was used to define the genetic determinants of Chryseobacterium salivictor NBC122 that reduce salt damage in bacteria and plants. Sixteen hub genes comprised the aromatic compound degradation and Por secretion systems, which are required to cope with complex stresses associated with saline environments. Horizontal gene transfer and CRISPR-Cas analyses indicated that C. salivictor NBC122 underwent more evolutionary events when interacting with different environments. These findings provide deep insights into genomic adaptation to dynamic interactions between plant-growth-promoting Chryseobacterium and salt 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.

Carbon monoxide/heme oxygenase system in plant: Roles in abiotic stress response and crosstalk with other signals molecules

Carbon monoxide (CO) has been recognized as a crucial gasotransmitter mainly produced by heme oxygenase (HO)-catalyzed heme degradation in plant. Recent studies have shown that CO plays an important role in regulating growth and development of plant, as well as and responding to a variety of abiotic stresses. Meanwhile, many studies have reported on CO working in combination with other signal molecules to mitigate abiotic stress. Here, we presented a comprehensive overview of recent developments in which CO reduces plant damage caused by abiotic stresses. The regulation of antioxidant system, photosynthetic system, ion balance and transport are the main mechanisms of CO-alleviated abiotic stress. We also proposed and discussed the relationship between CO and other signal molecules, including nitric oxide (NO), hydrogen sulfide (H2S), hydrogen gas (H2), abscisic acid (ABA), indole 3-acetic acid (IAA), gibberellin (GA), cytokine (CTK), salicylic acid (SA), jasmonic acid (JA), hydrogen peroxide (H2O2) and calcium ion (Ca2+). Furthermore, the important role of HO genes in alleviating abiotic stress was also discussed. We proposed promising and new research directions for the study of plant CO, which can provide further insights on the role of CO in plant growth and development under abiotic stress.

Effect of NaCl stress on exoproteome profiles of Bacillus amyloliquefaciens EB2003A and Lactobacillus helveticus EL2006H

Salt stress can affect survival, multiplication and ability of plant growth promoting microorganisms to enhance plant growth. Changes in a microbe's proteome profile is one of the mechanisms employed by PGPM to enhance tolerance of salt stress. This study was focused on understanding changes in the exoproteome profile of Bacillus amyloliquefaciens EB2003A and Lactobacillus helveticus EL2006H when exposed to salt stress. The strains were cultured in 100 mL M13 (B. amyloliquefaciens) and 100 mL De man, Rogosa and Sharpe (MRS) (L. helveticus) media, supplemented with 200 and 0 mM NaCl (control), at pH 7.0. The strains were then incubated for 48 h (late exponential growth phase), at 120 rpm and 30 (B. amyloliquefaciens) and 37 (L. helveticus) °C. The microbial cultures were then centrifuged and filtered sterilized, to obtain cell free supernatants whose proteome profiles were studied using LC-MS/MS analysis and quantified using scaffold. Results of the study revealed that treatment with 200 mM NaCl negatively affected the quantity of identified proteins in comparison to the control, for both strains. There was upregulation and downregulation of some proteins, even up to 100%, which resulted in identification of proteins significantly unique between the control or 200 mM NaCl (p ≤ 0.05), for both microbial species. Proteins unique to 200 mM NaCl were mostly those involved in cell wall metabolism, substrate transport, oxidative stress tolerance, gene expression and DNA replication and repair. Some of the identified unique proteins have also been reported to enhance plant growth. In conclusion, based on the results of the work described here, PGPM alter their exoproteome profile when exposed to salt stress, potentially upregulating proteins that enhance their tolerance to this stress.

Alleviation of arsenic toxicity in pepper plants by aminolevulinic acid and heme through modulating its sequestration and distribution within cell organelles

Aminolevulinic acid (ALA) is essential for chlorophyll and heme synthesis. However, whether heme interacts with ALA to elicit antioxidants in arsenic (As)-exposed plants is still unknown. ALA was applied daily to pepper plants for 3 days prior to beginning As stress (As-S). Then, As-S was initiated for 14 days by employing sodium hydrogen arsenate heptahydrate (0.1 mM AsV). Arsenic treatment decreased photosynthetic pigments (chl a by 38% and chl b by 28%), biomass by 24%, and heme by 47% content, but it elevated contents of malondialdehyde (MDA) by 3.3-fold, hydrogen peroxide (H₂O₂) by 2.3-fold, glutathione (GSH), methylglyoxal (MG), and phytochelatins (PCs) and electrolyte leakage (EL) by 2.3-fold along with enhanced subcellular As concentration in the pepper plant's roots and leaves. The supplementation of ALA to the As-S-pepper seedlings enhanced the amount of chlorophyll, heme content, and antioxidant enzyme activity as well as plant growth, while it reduced the levels of H₂O₂, MDA, and EL. ALA boosted GSH and phytochelates (PCs) in the As-S-seedlings by controlling As sequestration and rendering it harmless. The addition of ALA enhanced the amount of As that accumulated in the root vacuoles and reduced the poisonousness of the soluble As in the vacuoles. The ALA treatment facilitated the deposition and fixation of As in the vacuoles and cell walls, thereby reducing the transport of As to other cell organelles. This mechanism may have contributed to the observed decrease in As accumulation in the leaves. The administration of 0.5 mM hemin (H) (a source of heme) significantly enhanced ALA-induced arsenic stress tolerance. Hemopexin (Hx, 0.4 μg L^-1), a heme scavenger, was treated with the As-S plants along with ALA and ALA + H to observe if heme was a factor in ALA's increased As-S tolerance. Heme synthesis/accumulation in the pepper plants was reduced by Hx, which counteracted the positive effects of ALA. Supplementation of H along with ALA + Hx reversed the negative effects of Hx, demonstrating that heme is required for ALA-induced seedling As-S tolerance.

Effects of Hevea brasiliensis Intercropping on the Volatiles of Pandanus amaryllifolius Leaves

Pandanus amaryllifolius Roxb. is a special tropical spice crop resource with broad development prospects. It is widely cultivated under a Hevea brasiliensis (Willd. ex A. Juss.) Muell. Arg. canopy to improve the comprehensive benefits to Hevea brasiliensis plantations in Hainan Provence, China. However, the effects of intercropping with Hevea brasiliensis on the component number and relative contents of volatile substances in different categories in the Pandanus amaryllifolius leaves are still unknown. Therefore, a Hevea brasiliensis and Pandanus amaryllifolius intercropping experiment was set up to clarify the differences between several cultivated patterns on volatile substances in the Pandanus amaryllifolius leaves, and the key regulatory factors of volatile substances. The results showed that the soil pH was significantly decreased, while soil bulk density, alkali-hydrolyzable nitrogen and available phosphorus contents were significantly increased under the intercropping pattern. The component numbers of esters in volatile substances were increased by 6.20%, while the component numbers of ketones were decreased by 4.26% under the intercropping pattern. Compared with the Pandanus amaryllifolius monoculture, the relative contents of pyrroles, esters and furanones were significantly increased by 8.83%, 2.30% and 8.27%, respectively, while the relative contents of ketones, furans and hydrocarbons were decreased by 1.01%, 10.55% and 9.16% under the intercropping pattern, respectively. The relative contents of pyrroles, esters, furanones, ketones, furans and hydrocarbons were associated with changes in soil pH, soil available phosphorus content and air temperature. The results indicated that the reduction in soil pH and enhancement in soil-available phosphorus may be the main reasons for promoting the relative content of pyrroles and reducing the relative content of hydrocarbons under an intercropping pattern. Overall, Hevea brasiliensis intercropping with Pandanus amaryllifolius could not only improve soil properties, but also significantly increase the relative contents of the main volatile substances in Pandanus amaryllifolius leaves, which could provide a theoretical basis for the application and promotion of high-quality production patterns of Pandanus amaryllifolius.

Analysis of Physiological Indicators Associated with Drought Tolerance in Wheat under Drought and Re-Watering Conditions

Wheat (Triticum aestivum L.) production is severely threatened by an increase in the frequency of drought events. It is crucial to determine stable and effective morphological, physiological, and associated oxidative stress indicators, to evaluate the drought tolerance of wheat for breeding and cultivation. Therefore, the cultivars Luohan 22 (LH 22, drought-tolerant) and Zhengmai 366 (ZM 366, drought-sensitive) were used as experimental materials to analyze the changes in 12 physiological and biochemical indicators, as well as the yield, when the stress was prolonged to different times. Re-watering after 6 days of drought can effectively alleviate the associated oxidative stress of drought to wheat. The physiological responses of plants were reversible when they were re-watered in the range of 6 to 12 days after drought. The degree of recovery of LH 22 was higher than that of ZM 366. Afterwards, seven indicators, including stomatal conductance, proline, malondialdehyde, soluble sugar, hexokinase, glucose, and the non-photochemical quenching parameter, were screened out to characterize tolerance of wheat to drought using the multivariate statistical analytical method. This study further investigated the method of evaluating and indexing tolerance of wheat to drought, from the physiological and biochemical levels. This study can provide a theoretical basis and reference for the selection of wheat cultivars to breed and cultivate against drought stress.