Biosynthesis of 2-Acetyl-1-pyrroline in Fragrant Rice: Recent Insights into Agro-management, Environmental Factors, and Functional Genomics

The economic benefits, energy use efficiency, and carbon footprint of fragrant super rice and nonfragrant super rice under different planting methods and nitrogen levels

BACKGROUND

The objective of this study was to investigate the input and output of energy, carbon input and sequestration, and economic benefits of fragrant and nonfragrant rice under different crop management practices, with the aim of providing theoretical guidance for sustainable rice production. Two high-yield and popular rice varieties, Yuxiangyouzhan and Jiyou615, were grown under three nitrogen fertilizer levels (0, 150, and 220 kg ha-1) and three planting methods (manual transplanting, mechanical transplanting, and mechanical direct seeding) during 2018 and 2019.

RESULTS

The results showed that the economic, energy, and carbon benefits of the different rice varieties varied in response to the different fertilizations and planting methods. The average energy outputs of Yuxiangyouzhan and Jiyou615 were 214 423.26 and 218 474.90 MJ ha-1, respectively. The mean harvest index and mean energy use efficiency of Jiyou615 were slightly greater, at 4.21% and 3.93%, respectively, than those of Yuxiangyouzhan, while the mean carbon input-sequestration ratio of Yuxiangyouzhan was slightly greater, at 1.79%, than that of Jiyou615. Yuxiangyouzhan had a significantly greater mean benefit-cost ratio (5.76%) than Jiyou615. In addition, Yuxiangyouzhan had a significantly greater mean nominal economic return on energy input (12.21%), nominal economic return on energy output (13.20%), nominal economic return on carbon input (12.65%), and nominal economic return on carbon sequestration (11.31%) than Jiyou615.

CONCLUSION

The results suggest that suitable high-yield and high-quality varieties with better consumer demand and the synergistic effect of variety and crop management in sustainable rice production are highly meaningful. © 2025 Society of Chemical Industry.

Exogenous application of abscisic acid enhanced 2-acetyl-1-pyrroline biosynthesis, accumulation, and antioxidant activities in aromatic rice

BACKGROUND

Abscisic acid (ABA) is a crucial endogenous hormone in plants, regulating a myriad of processes integral to plant growth and development. However, there has been no reported impact on the production of aromatic rice following the application of exogenous ABA. Aromatic rice not only possesses intense aroma but also boasts higher nutritional value. 2-Acetyl-1-pyrroline (2-AP) is the primary compound responsible for the distinctive aroma of aromatic rice. A two-year field experiment was conducted to explore the impact of exogenous ABA application on the biosynthesis and accumulation of 2-AP, as well as the physiological characteristics, yield, and quality of aromatic rice varieties.

RESULTS

The two aromatic rice varieties, Meixiangzhan-2 (MXZ2) and Nanjingxiangzhan (NJXZ), underwent five applications of 20 mg/L abscisic acid (ABA) from the breakthrough stage, whereas the control group (CK) received deionized water sprays.The results indicated that the application of exogenous ABA significantly boosted the 2-AP content by 20.7%, primarily by enhancing the levels of its precursors and the activities of enzymes involved in 2-AP biosynthesis. Exogenous ABA also upregulated the transcription levels of ProDH, P5CS2, OAT, and DAO4 while downregulating BADH2 transcription. Furthermore, exogenous ABA strengthened the antioxidant activites (superoxide dismutase, peroxidase, and catalase) of aromatic rice, although it led to increased malondialdehyde content and slight decreases in yield and quality. Notably, compared with superior grains, exogenous ABA application had a more pronounced effect on enhancing the aroma of inferior grains in aromatic rice with fewer negative effects.

CONCLUSIONS

The exogenous application of ABA from the breakthrough stage notably elevated the biosynthesis and accumulation of 2-AP in aromatic rice production. This was achieved by augmenting the content of its precursors and the activities of related synthetic enzymes, along with an enhancement in antioxidant activities. However, the impact on the yield and quality of aromatic rice remained relatively modest.

Genome-wide association analysis reveals regulatory genes for the metabolite synthesis of 2-acetyl-1-pyrroline in aromatic coconut (Cocos nucifera L.)

Coconut (Cocos nucifera L.) is a key tropical economic tree valued for its fruit flavor, particularly 2-acetyl-1-pyrroline (2AP), a vital aroma metabolite. To enhance high-aromatic coconut breeding efforts, it is essential to deeply understand the hereditary factors governing the production of 2AP. In this study, a genome-wide association analysis identifies 32 loci that exhibit significant associations with 2AP content based on single nucleotide polymorphism (SNP) variations from 168 aromatic coconut germplasm resources. Transcriptome analysis then pinpoints 22 candidate genes near significant loci involved in 2AP metabolism. Proteins encoded by these genes are involved in amino acid metabolism, glycolysis, and secondary metabolism. Among these, Asparagine synthetase coding gene ASN1, Gamma-glutamylcysteine synthetase coding gene GSH1, and UbiA prenyltransferase coding gene UBIA are enriched in the linkage region constructed by significant locus Chr04_61490504. In particular, the SNP mutation of CnASN1 leads to amino acid changes in the functional region of the coding protein, potentially resulting in differences in 2AP content among haplotype populations. Identifying variations in related candidate genes, particularly the gene CnASN1, provides molecular markers closely associated with 2AP synthesis for coconut breeding and offers further insights into the metabolic mechanisms of 2AP.

Transgenic rice with microbial high-temperature-resistant β-glucosidase gene significantly improved 2-acetyl-1-pyrroline content and edible quality

BACKGROUND

The content of 2-acetyl-1-pyrroline (2-AP) directly affects the aroma and taste of rice. Δ1-Pyrroline and methylglyoxal are the precursors of 2-AP synthesis, and β-glucosidase plays an important role in the synthesis of methylglyoxal. In this study, β-glucosidase gene cloned from Pyrococcus furiosus was molecularly modified to obtain the high-temperature-resistant β-glucosidase gene 371-β-glucosidase (T371A), which was transformed into kitaake varieties (Oryza sativa L. subsp. japonica) by Agrobacterium-mediated transformation method, and transgenic rice with heterologous expression of T371A was obtained. Experiments were conducted in transgenic rice to investigate whether this gene had an effect on the synthesis of 2-AP.

RESULTS

Under the optimum reaction temperature of 50°C and cooking temperature of 100°C, the enzyme activity of β-glucosidase in transgenic rice seeds was prominently increased by 260-280% and 419-426% over that of the control, respectively. The content of 2-AP in transgenic rice seeds significantly increased by 75-105% under normal temperature and high-temperature cooking conditions compared with the control. It was also found that transgenic rice increased the content of methylglyoxal and decreased the expression of betaine aldehyde dehydrogenase (BADH2).

CONCLUSION

The high-temperature-tolerant β-glucosidase gene obtained in this study provides an innovative technical strategy for molecular breeding of high-edible aroma crops and has wide application potential. © 2024 Society of Chemical Industry.

Changes in key volatile components associated with leaf quality of Pandanus amaryllifolius Roxb. alongside growth duration

Pandan (Pandanus amaryllifolius Roxb.) are one of the traditional food materials in Southeast Asian countries. However, there has long been a lack of understanding of the differences in volatile organic compounds (VOCs) of leaves at different growth periods. Gas chromatography-mass spectrometry (GC-MS) was used to identify and analyze VOCs in different leaf positions of Pandan in this study. The content of 2-Acetyl-1-pyrroline (2AP) was higher in L1-L3 and decreased with leaf growth, while squalene showed the opposite trend. The content of neophytadiene first increased and then decreased, reaching the highest in L15. L8 is the critical point at which the content of each major VOCs is balanced. Combining agronomic traits and VOCs content, leaves in L4-L25 position are suitable for harvesting. This study provides data support for scientific judgment of the harvesting site and time of Pandan, and provides theoretical basis for further utilization of VOCs of Pandan.

Progresses in biosynthesis pathway, regulation mechanism and potential application of 2-acetyl-1-pyrroline in fragrant rice

The formation of rice aroma is a complex process that is influenced by genetic and environmental factors. More than 500 fragrance compounds have been documented in fragrant rice, among which 2-AP dominates the aroma of rice. This paper introduced the identification of OsBadh2 in the biosynthesis of 2-AP in rice. Then, non-enzymatic and enzymatic pathways of the 2-AP biosynthesis have been comprehensively investigated. In detail, 2-AP biosynthesis-associated enzyme, such as OsBADH2, OsP5CS, OsGAD, OsGAPDH, OsProDH, OsOAT, OsODC and OsDAO, have been summarized, while MG and fatty acids are also implicated in modulating the biosynthesis of 2-AP by providing the acetyl groups. Moreover, extensive collections of traditional fragrant rice varieties have been collated, together with the OsBadh2 haplotypes of 312 fragrant rice germplasm in China. And finally, genetic engineering of OsBadh2 and other genes in the 2-AP biosynthesis to develop fragrant rice are discussed.

Salicylic Acid and Melatonin Synergy Enhances Boron Toxicity Tolerance via AsA-GSH Cycle and Glyoxalase System Regulation in Fragrant Rice

Background: Boron is an essential micronutrient for plant growth and productivity, yet excessive boron leads to toxicity, posing significant challenges for agriculture. Fragrant rice is popular among consumers, but the impact of boron toxicity on qualitative traits of fragrant rice, especially aroma, remains largely unexplored. The individual potentials of melatonin and salicylic acid in reducing boron toxicity are less known, while their synergistic effects and mechanisms in fragrant rice remain unclear. Methods: Thus, this study investigates the combined application of melatonin and salicylic acid on fragrant rice affected by boron toxicity. One-week-old seedlings were subjected to boron (0 and 800 µM) and then treated with melatonin and salicylic acid (0 and 100 µM, for 3 weeks). Results: Boron toxicity significantly impaired photosynthetic pigments, plant growth, and chloroplast integrity while increasing oxidative stress markers such as hydrogen peroxide, malondialdehyde, methylglyoxal, and betaine aldehyde dehydrogenase. Likewise, boron toxicity abridged the precursors involved in the 2-acetyl-1-pyrroline (2-AP) biosynthesis pathway. However, individual as well as combined application of melatonin and salicylic acid ameliorated boron toxicity by strengthening the antioxidant defense mechanisms-including the enzymes involved during the ascorbate-glutathione (AsA-GSH) cycle and glyoxalase system-and substantially improved 2-AP precursors including proline, P5C, Δ1-pyrroline, and GABA levels, thereby restoring the 2-AP content and aroma. These findings deduce that melatonin and salicylic acid synergistically alleviate boron toxicity-induced disruptions on the 2-AP biosynthesis pathway by improving the 2-AP precursors and enzymatic activities, as well as modulating the physio-biochemical processes and antioxidant defense system of fragrant rice plants. Conclusions: The findings of this study have the potential to enhance rice productivity and stress tolerance, offering solutions to improve food security and sustainability in agricultural practices, particularly in regions affected by environmental stressors.

Revealing the aromatic sonata through terpenoid profiling and gene expression analysis of aromatic and non-aromatic coconut varieties

Aromatic coconut represents an exceptional variety of coconut known for its distinct and delightful flavor and aroma, both of which are highly cherished by consumers. Despite its popularity, there has been a lack of systematic research on aroma components and the associated synthetic genes. In this report, we developed the metabolite profiles of terpenoids by targeted metabolomics and obtained the expression profile of genes related to terpenoid biosynthesis by RNA-seq during different coconut fruit developmental stages. Totally, we separated 26 different terpenoids in aromatic coconut pulp, among which, geranyl acetate and (-)-isosyngene emerged as the most abundant. The integrated analysis of metabolism and RNA-seq data showed that HMGS2, HMGS3, IPI/IDI1, HMGR1, HMGR3, and CMK2 as potentially key genes involved in the synthesis of terpenoids in aromatic coconut. To validate these findings, qRT-PCR was conducted on terpenoid-related genes. These findings lay a foundation for understanding aroma formation and the molecular mechanism of terpenoids in coconut fruit.

The kinetic study of 2-acetyl-1-pyrroline accumulation in the model system: An insight into enhancing rice flavor through the Maillard reaction

Controlling the Maillard reaction may affect the generation of 2-acetyl-1-pyrroline, the key aroma compound in rice. In this study, the kinetics of 2-acetyl-1-pyrroline accumulation in the glucose/proline model system was comprehensively investigated and extra methylglyoxal or glyoxal was added to enhance 2-acetyl-1-pyrroline concentrations during rice cooking. Using the multi-response kinetic modeling to derive kinetic parameters, the formation of glyoxal, as the reactive intermediate, was rate-determining for the overall generation rate of 2-acetyl-1-pyrroline. Besides, although 2-acetyl-1-pyrroline generation was easier to occur with lower activation energy, much higher depletion rates of 2-acetyl-1-pyrrroline at 120 °C and 140 °C led to maximal 2-acetyl-1-pyrroline accumulation at the lower temperature of 100 °C. Furthermore, the inclusion of 0.05 μmol/kg additional methylglyoxal in cooked rice significantly enhanced 2-acetyl-1-pyrroline generation. The work suggested that the development of rice products with superior flavor quality may be achieved by the slight accumulation of intermediates prior to thermal processing.

Multiomics analysis reveals a substantial decrease in nanoplastics uptake and associated impacts by nano zinc oxide in fragrant rice (Oryza sativa L.)

Nanoplastics (NPs) have emerged as global environmental pollutants with concerning implications for sustainable agriculture. Understanding the underlying mechanisms of NPs toxicity and devising strategies to mitigate their impact is crucial for crop growth and development. Here, we investigated the nanoparticles of zinc oxide (nZnO) to mitigate the adverse effects of 80 nm NPs on fragrant rice. Our results showed that optimized nZnO (25 mg L-1) concentration rescued root length and structural deficits by improving oxidative stress response, antioxidant defense mechanism and balanced nutrient levels, compared to seedlings subjected only to NPs stress (50 mg L-1). Consequently, microscopy observations, Zeta potential and Fourier transform infrared (FTIR) results revealed that NPs were mainly accumulated on the initiation joints of secondary roots and between cortical cells that blocks the nutrients uptake, while the supplementation of nZnO led to the formation of aggregates with NPs, which effectively impedes the uptake of NPs by the roots of fragrant rice. Transcriptomic analysis identified a total of 3973, 3513 and 3380 differentially expressed genes (DEGs) in response to NPs, nZnO and NPs+nZnO, respectively, compared to the control. Moreover, DEGs were significantly enriched in multiple pathways including biosynthesis of secondary metabolite, phenylpropanoid biosynthesis, amino sugar and nucleotide sugar metabolism, carotenoid biosynthesis, plant-pathogen interactions, MAPK signaling pathway, starch and sucrose metabolism, and plant hormone signal transduction. These pathways could play a significant role in alleviating NPs toxicity and restoring fragrant rice roots. Furthermore, metabolomic analysis demonstrated that nZnO application restored 2-acetyl-1-pyrroline (2-AP) pathways genes expression, enzymatic activities, and the content of essential precursors related to 2-AP biosynthesis under NPs toxicity, which ultimately led to the restoration of 2-AP content in the leaves. In conclusion, this study shows that optimized nZnO application effectively alleviates NPs toxic effects and restores both root structure and aroma production in fragrant rice leaves. This research offers a sustainable and practical strategy to enhance crop production under NPs toxicity while emphasizing the pivotal role of essential micronutrient nanomaterials in agriculture.

Aromatic compound 2-acetyl-1-pyrroline coordinates nitrogen assimilation and methane mitigation in fragrant rice

Rice paddy has been the main source of anthropogenic methane (CH4) emissions, with significant variations among rice varieties. 2-Acetyl-1-pyrroline (2-AP) is the key component of the pleasant aroma in fragrant rice. Here, we show that fragrant rice is metabolically active in nitrogen assimilation and exhibits high levels of 2-AP and that CH4 fluxes at the booting stage and cumulative emissions are 25.5% and 14.8% lower, respectively, in fragrant rice paddies compared with nonfragrant rice paddies. Three precursors involved in 2-AP synthesis-proline, glutamic acid, and ornithine-are identified as crucial nitrogen compounds that significantly promote CH4 oxidation in the rhizosphere. Augmenting 2-AP synthesis, either through foliar spraying or by utilizing CRISPR-Cas9 technology to generate knockout lines of BETAINE ALDEHYDE DEHYDROGENASE 2 gene, effectively enhances CH4 oxidation and reduces CH4 fluxes. Our findings reveal that the 2-AP metabolic pathway coordinates the carbon/nitrogen cycle to improve nitrogen assimilation along with high 2-AP levels and mitigate CH4 emissions in paddy ecosystems.

Metabolome and Transcriptome Unveil the Correlated Metabolites and Transcripts with 2-acetyl-1-pyrroline in Fragrant Rice

Fragrance is a valuable trait in rice varieties, with its aroma significantly influencing consumer preference. In this study, we conducted comprehensive metabolome and transcriptome analyses to elucidate the genetic and biochemical basis of fragrance in the Shangsixiangnuo (SSXN) variety, a fragrant indica rice cultivated in Guangxi, China. Through sensory evaluation and genetic analysis, we confirmed SSXN as strongly fragrant, with an 806 bp deletion in the BADH2 gene associated with fragrance production. In the metabolome analysis, a total of 238, 233, 105 and 60 metabolic compounds exhibited significant changes at the seedling (S), reproductive (R), filling (F), and maturation (M) stages, respectively. We identified four compounds that exhibited significant changes in SSXN across all four development stages. Our analyses revealed a significant upregulation of 2-acetyl-1-pyrroline (2AP), the well-studied aromatic compound, in SSXN compared to the non-fragrant variety. Additionally, correlation analysis identified several metabolites strongly associated with 2AP, including ethanone, 1-(1H-pyrrol-2-yl)-, 1H-pyrrole, and pyrrole. Furthermore, Weighted Gene Co-expression Network Analysis (WGCNA) analysis highlighted the magenta and yellow modules as particularly enriched in aroma-related metabolites, providing insights into the complex aromatic compounds underlying the fragrance of rice. In the transcriptome analysis, a total of 5582, 5506, 4965, and 4599 differential expressed genes (DEGs) were identified across the four developmental stages, with a notable enrichment of the common pathway amino sugar and nucleotide sugar metabolism in all stages. In our correlation analysis between metabolome and transcriptome data, the top three connected metabolites, phenol-, 3-amino-, and 2AP, along with ethanone, 1-(1H-pyrrol-2-yl)-, exhibited strong associations with transcripts, highlighting their potential roles in fragrance biosynthesis. Additionally, the downregulated expression of the P4H4 gene, encoding a procollagen-proline dioxygenase that specifically targets proline, in SSXN suggests its involvement in proline metabolism and potentially in aroma formation pathways. Overall, our study provides comprehensive insights into the genetic and biochemical mechanisms underlying fragrance production in rice, laying the foundation for further research aimed at enhancing fragrance quality in rice breeding programs.

Lipidomic analysis of grain quality variation in high quality aromatic japonica rice

To maintain the purity of the seeds and rice quality of the high-quality rice varieties, five lines with similar field and yield traits were selected from the Nanjing46 population in Liyang and used as study materials, and the original progeny were used as the control material for comparing rice quality and lipid metabolites in this study. The rice quality of the five lines still differed compared to CKN1. The Badh2-E2 gene was detected in all five lines, but its 2-AP content differed. The C11:0 content in CKN1 and VN1 was significantly greater than that in the other four lines. Most of the differentially abundant metabolites were phospholipids, including PA(16:0/18:2), PC(15:0/16:0) and PG(16:0/16:0). These metabolites can be used as potential metabolic markers for identifying quality variation. This study presents a novel methodology and theoretical framework for investigating varietal degradation and ensuring seed purity authentication.

Regulation of 2-Acetyl-1-pyrroline Content in Fragrant Rice under Different Temperatures at the Grain-Filling Stage

2-Acetyl-1-pyrroline (2-AP) is a key volatile organic compound in fragrant rice aroma. However, the effects of temperature on 2-AP biosynthesis in fragrant rice and its regulation mechanism have been rarely reported. In the present study, three fragrant rice varieties were used as plant materials, and four temperature treatments during the grain-filling stage, i.e., (T1) 22/17 °C, (T2) 27/22 °C, (T3) 32/27 °C, and (T4) 37/32 °C, were adopted. The results showed that grain contents of 2-AP, proline, and γ-aminobutyric acid (GABA) significantly (P < 0.05) increased with decreased temperature, while the lowest and highest 2-AP contents were recorded in the T4 and T1 treatments, respectively. Higher pyrroline-5-carboxylic acid (P5C) content was recorded in low-temperature treatments (T1 and T2) than in high-temperature treatments (T3 and T4). The transcript levels of genes BADH2, PRODH, and OAT significantly (P < 0.05) decreased with decreased temperature. Lower transcript levels of genes P5CR, P5CS2, DAO2, DAO4, and DAO5 were recorded in low-temperature treatments (T1 and T2) than in high-temperature treatments (T3 and T4). In conclusion, low temperature increased 2-AP content and high temperature decreased 2-AP content in fragrant rice. We deduced that temperature regulated 2-AP biosynthesis through the metabolism of proline and GABA.

Transcription Factor OsbZIP60-like Regulating OsP5CS1 Gene and 2-Acetyl-1-pyrroline (2-AP) Biosynthesis in Aromatic Rice

The most important volatile in determining the aroma of fragrant rice is 2-Acetyl-1-pyrroline (2-AP); however, the transcriptional regulation mechanism of 2-AP biosynthesis in fragrant rice is still unclear. In this study, Osp5cs1 knockout mutant lines and OsP5CS1 over-expression lines were constructed by the genetic transformation of the Indica rice cultivar, i.e., 'Zhonghua11', which knocks out OsBADH2 to produce fragrance in aromatic rice. The OsP5CS1 gene was also identified as a key gene in the 2-AP biosynthesis pathway of aromatic rice. The OsP5CS1 promoter was used as bait, and the OsbZIP60-like transcription factor was screened by yeast one-hybrid assays. The OsbZIP60-like transcription factor specifically bound to the OsP5CS1 gene. The dual luciferase reporting system found that the OsbZIP60-like transcription factor promoted the transcriptional activation of OsP5CS1. Compared with the wild type, OsP5CS1 gene expression was significantly down-regulated in the Osbzip60-like mutant and resulted in a substantial reduction in 2-AP biosynthesis. Moreover, the OsP5CS1 gene expression was significantly up-regulated in OsbZIP60-like over-expressed plants, and the 2-AP concentrations were also increased, whereas the Osbzip60-like mutants were found to be sensitive to Zn deficiency. Overall, the OsbZIP60-like transcription factor promoted the 2-AP accumulation. This study provides a theoretical basis for the transcriptional regulation mechanism of 2-AP biosynthesis and explores the function of the OsbZIP transcription factor in fragrant rice.

l-Glutamate Seed Priming Enhances 2-Acetyl-1-pyrroline Formation in Fragrant Rice Seedlings in Response to Arsenite Stress

2-Acetyl-1-pyrroline (2-AP) is a fragrance compound and flavor in fragrant rice whose precursors are generally glutamate (Glu) and proline (Pro). Our previous study revealed that exogenous Glu enhanced the arsenic (As) tolerance in fragrant rice by improving the ascorbic acid-glutathione cycle and the Pro content in roots. However, less is known about how Glu is involved in 2-AP biosynthesis in fragrant rice under As stress. Herein, a hydroponic experiment of L-Glu seed priming with 0, 100, and 500 μM l-glutamic acid solutions was conducted with two fragrant rice varieties. After that, the 10-day-old seedlings were cultured under 0 and 100 μM arsenite stress for 10 d. Results showed that the 2-AP and Pro contents were increased by 18-30% and 21-78% under As100 μM-Glu100 μM treatment in comparison to the control As100 μM to Glu0 μM, while the activities of pyrroline-5-carboxylate synthetase (P5CS) and proline dehydrogenase (ProDH) were increased by 19-46% and 3-19%, respectively. Furthermore, the 2-AP, Pro contents, and P5CS activity were correlated positively. Correspondingly, a significant abundance of differential expressed metabolites (18) and differential expressed genes (26) was observed in amino acid metabolism and glutathione metabolism pathways. In addition, several essential genes were verified and grouped into the pathways of glutathione metabolism, proline, and arginine metabolism with antioxidant defense system to comodulate 2-AP biosynthesis and stress detoxification. Therefore, the Glu seed priming treatment had a positive impact on the 2-AP biosynthesis of fragrant rice under 100 μM arsenite toxicity.

Impact and mitigation of lead, cadmium and micro/nano plastics in fragrant rice

Heavy metals (HMs) and micro(nano)plastics (MNPs), represent a significant risk to global food supply as well as a potential risk to humankind. Over 50% of the worldwide population eat rice every day, and rice aroma is a significant qualitative trait that is highly valued by consumers and fetches premium prices in the global market. Despite the huge commercial importance of fragrant rice, limited studies were directed to investigate the influence of HMs and MNPs on yield related traits and 2-Acetyl-1-pyrroline (2-AP) compound, mainly responsible for aroma production in fragrant rice. In this review, we found that the interaction of HMs and MNPs in fragrant rice is complex and accumulation of HMs and MNPs was higher in root as compared to the grains. Nutrients and phytohormones mediated mitigation of HMs and MNPs were most effective sustainable strategies. In addition, monitoring the checkpoints of 2-AP biosynthesis and its interaction with HMs and MNPs is challenging. Finally, we explained the potential challenges that fragrant rice faces considering the continuous rise in environmental pollutants and discussed the future avenues of research to improve fragrant rice's yield and qualitative traits.

Nitric oxide confers cadmium tolerance in fragrant rice by modulating physio-biochemical processes, yield attributes, and grain quality traits

Cadmium (Cd) stress causes serious disruptions in plant metabolism, physio-biochemical processes, crop yield, and quality characters. Nitric oxide (NO) improves the quality features and nutritional contents of fruit plants. However, how NO confers Cd toxicity in fragrant rice plants, is sparse. Hence, the present study investigated the effects of 50 µM NO donor sodium nitroprusside (SNP) on physio-biochemical processes, plant growth attributes, grain yield, and quality traits of fragrant rice under Cd stress (100 mg kg^-1 soil). The results revealed that Cd stress diminished rice plant growth, impaired photosynthetic apparatus and antioxidant defense system, and deteriorated the grain quality traits. However, foliar application of SNP mitigated Cd stress by improving plant growth and gas exchange attributes. Higher electrolyte leakage (EL) was accompanied with elevated levels of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) under Cd stress; however, exogenous application of SNP reduced them. The activities and relative expression levels of enzymatic antioxidants; superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) and non-enzymatic antioxidants, glutathione (GSH) contents were reduced by Cd stress, while SNP application regulated their activity and transcript abundances. SNP application improved fragrant rice grain yield and 2-acetyl-1-pyrroline content by 57.68 % and 75.54 % respectively, which is concomitant with higher biomass accumulation, photosynthetic efficiency, photosynthetic pigment contents, and an improved antioxidant defense system. Collectively, our results concluded that SNP application regulated the fragrant rice plant physio-biochemical processes, yield traits and grain quality characters under Cd-affected soil.