Proline Dehydrogenase Activity Research Articles

Impact of Rapeseed Sequential Follow Paddy Crop on Its 2-Acetyl-1-pyrroline Biosynthesis and Economic Yield under the Double-Cropping System

Rapeseed–rice rotation is a cropping system that improves the land-use rate. The present study conducted a field experiment with winter planting of rapeseed as treatment (WR) and winter fallow as control (CK) to investigate the effects of winter planting of rapeseed on growth, yield formation, and 2-acetyl-1-pyrroline (2-AP) biosynthesis of fragrant rice in the two subsequent cropping seasons. The results show that WR treatment improved alkali-hydro nitrogen and rapidly available phosphorus contents in soil. Compared with CK, WR treatment significantly increased grain yield and effective panicle number per plant by 21.16–27.26% and 7.33–21.24%, respectively. Higher net photosynthetic rate, leaf area index, and dry matter accumulation of fragrant rice plants were recorded in WR treatment and CK. Furthermore, compared with CK, WR treatment significantly increased grain 2-AP content, which could be explained by increased content of pyrroline-5-carboxylic acid, methylglyoxal, 1-pyrroline, and enhanced activity of proline dehydrogenase. In addition, future studies should be conducted at a molecular level to reveal the regulation mechanism in 2-AP biosynthesis of fragrant rice under conditions of winter planting of rapeseed.

Ascorbic Acid Improves Tomato Salt Tolerance by Regulating Ion Homeostasis and Proline Synthesis.

In this study, processing tomato (Solanum lycopersicum L.) 'Ligeer 87-5' was hydroponically cultivated under 100 mM NaCl to simulate salt stress. To investigate the impacts on ion homeostasis, osmotic regulation, and redox status in tomato seedlings, different endogenous levels of ascorbic acid (AsA) were established through the foliar application of 0.5 mM AsA (NA treatment), 0.25 mM lycorine (LYC, an inhibitor of AsA synthesis; NL treatment), and a combination of LYC and AsA (NLA treatment). The results demonstrated that exogenous AsA significantly increased the activities and gene expressions of key enzymes (L-galactono-1,4-lactone dehydrogenase (GalLDH) and L-galactose dehydrogenase (GalDH)) involved in AsA synthesis in tomato seedling leaves under NaCl stress and NL treatment, thereby increasing cellular AsA content to maintain its redox status in a reduced state. Additionally, exogenous AsA regulated multiple ion transporters via the SOS pathway and increased the selective absorption of K+, Ca2+, and Mg2+ in the aerial parts, reconstructing ion homeostasis in cells, thereby alleviating ion imbalance caused by salt stress. Exogenous AsA also increased proline dehydrogenase (ProDH) activity and gene expression, while inhibiting the activity and transcription levels of Δ1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine-δ-aminotransferase (OAT), thereby reducing excessive proline content in the leaves and alleviating osmotic stress. LYC exacerbated ion imbalance and osmotic stress caused by salt stress, which could be significantly reversed by AsA application. Therefore, exogenous AsA application increased endogenous AsA levels, reestablished ion homeostasis, maintained osmotic balance, effectively alleviated the inhibitory effect of salt stress on tomato seedling growth, and enhanced their salt tolerance.

Enriching Iodine and Regulating Grain Aroma, Appearance Quality, and Yield in Aromatic Rice by Foliar Application of Sodium Iodide

Applying iodine fertilizers to cultivate iodine-rich crops for daily intake is an effective approach for iodine supplementation, especially for aromatic rice. Field experiments were conducted during the early growing seasons of 2021 and 2022 to evaluate the impacts of foliar application of iodine fertilizer on aromatic rice and to explore the optimal iodine fertilizer concentration. At the full heading stage, six different concentrations of sodium iodide solutions of 0% (CK), 0.010% (T1), 0.025% (T2), 0.050% (T3), 0.075% (T4), and 0.100% (T5) were applied to indica aromatic rice cultivars Meixiangzhan 2 and Xiangyaxiangzhan. The results showed that sodium iodide treatments significantly increased the iodine and sodium contents in both leaves and grains. Compared with the CK, the T1 and T2 treatments increased the 2-acetyl-1-pyrroline (2-AP) content in mature grains by 8.41%‒101.66% and 13.58%‒ 74.60%, respectively. Improvements in the contents of 1-pyrroline-5-carboxylic acid, proline, 1-pyrroline, and methylglyoxal, as well as the activity of proline dehydrogenase were also detected. Additionally, sodium iodide treatments remarkably decreased the chalky grain rate, chalkiness area, and chalkiness degree of aromatic rice, with the T2 treatment exhibiting a 17.79%‒47.42% decrease in chalkiness degree compared with the CK. Meanwhile, T1 and T2 treatments showed beneficial impacts on chlorophyll content, photosynthetic characteristics, and yield components, while T3, T4, and T5 treatments exhibited adverse effects on leaf and grain yields. The linear discriminant analysis revealed significant differences between treatments. The correlation analysis and piecewise structural equation modeling showed that the iodine and sodium influenced the photosynthetic characteristics and chlorophyll content of the leaves, thereby regulating the 2-AP biosynthesis and yield components, ultimately affecting the 2-AP content and yield. Overall, this study suggests that foliar application of 0.025% sodium iodide is an effective method to enrich the iodine content in rice grains, improve the grain aroma and appearance quality of aromatic rice, without detrimental effects on grain yield.

Foliar application of phenylalanine, tryptophan, and tyrosine in fragrant rice production: Aroma, yield, grain quality, and economic return

Phenylalanine, tryptophan, and tyrosine are amino acids that are important to the growth and development of crops. However, the application of these amino acids in fragrant rice (Oryza sativa L.) production has not been reported. The present study aimed to investigate the effects of exogenous amino acids on aroma, yield, grain quality, and economic return of fragrant rice. At the heading stage, phenylalanine, tryptophan, and tyrosine at 0.50, 1.00, and 2.00 g L−1 were foliar applied to fragrant rice plants respectively and the treatment sprayed with distilled water was taken as control. The results showed that the foliar application of these amino acids significantly increased grain yield and seed-setting rate of fragrant rice. The total return and net income of fragrant rice production increased due to amino acids and the highest or equally highest net income and benefit-cost ratio was recorded in phenylalanine treatments with 0.50 and 1.00 g L−1 and tryptophan with 1.00 g L−1. However, amino acids applied at 2.00 g L−1 significantly decreased the benefit-cost ratio. Foliar application of phenylalanine, tryptophan, and tyrosine significantly enhanced superoxide dismutase activity. Phenylalanine treatments also increased the chlorophyll content. Compared with control, phenylalanine and tryptophan treatments significantly increased the grain content of 2-acetyl-1-pyrroline (2-AP) which is the key volatile component of fragrant rice aroma. The increased 2-AP content was explained by enhanced activity of proline dehydrogenase which plays an important part in catalyzing the conversion from proline to 2-AP. In conclusion, foliar application of phenylalanine, tryptophan, and tyrosine improved yield formation and economic return of fragrant rice. Foliar application of phenylalanine and tryptophan also enhanced 2-AP biosynthesis in fragrant rice.

Evaluation of P5CS and ProDH activity in Paulownia tomentosa (Steud.) as an indicator of oxidative changes induced by drought stress.

The aim of the study was to investigate changes in proline metabolism in seedlings of tree species during drought stress. One month old Paulownia tomentosa seedlings were exposed to moisture conditions at various levels (irrigation at 100, 75, 50 and 25% of field capacity), and then the material (leaves and roots) was collected three times at 10-day intervals. The activity of enzymes involved in proline metabolism was closely related to drought severity; however, proline content was not directly impacted. The activity of pyrroline-5-carboxylate synthetase (P5CS), which catalyzes proline biosynthesis, increased in response to hydrogen peroxide accumulation, which was correlated with soil moisture. In contrast, the activity of proline dehydrogenase (ProDH), which catalyzes proline catabolism, decreased. Compared to proline, the activity of these enzymes may be a more reliable biochemical marker of stress-induced oxidative changes. The content of proline is dependent on numerous additional factors, i.e., its degradation is an important alternative energy source. Moreover, we noted tissue-specific differences in this species, in which roots appeared to be proline biosynthesis sites and leaves appeared to be proline catabolism sites. Further research is needed to examine a broader view of proline metabolism as a cycle regulated by multiple mechanisms and differences between species.

Salicylic acid mitigates 'Hayward' kiwifruit chilling injury by regulating hormone and proline metabolism, as well as maintaining cellular structure

The 'Hayward' kiwifruit is extremely susceptible to chilling injury (CI) during the late stages of cold storage, thus limiting its storage quality and life. Therefore, mitigating the losses caused by CI is imperative. Salicylic acid (SA) has been demonstrated to mitigate CI in fruit and vegetables. In this study, we conducted a comparative analysis of proline metabolism, key endogenous hormone levels, as well as the effects on cell structure and membrane lipid oxidation in kiwifruit treated with 1 mM SA during low-temperature storage. The results showed that SA could attenuate lipoxygenase (LOX) activity, enhance catalase (CAT) activity, suppress the elevation of malondialdehyde (MDA) content, mitigate starch granule degradation in cells, and preserve cell structure integrity. Moreover, SA was found to enhance proline biosynthesis by activating ornithine transaminase (OAT) and pyrroline-5-carboxylate synthase (P5CS) while concurrently suppressing proline dehydrogenase (PDH) activity. Additionally, exogenous SA increased endogenous levels of both SA and abscisic acid (ABA), while simultaneously decreasing the concentration of gibberellic acid (GA) in fruit. In conclusion, exogenous SA treatment could alleviate the development of CI in kiwifruit by maintaining cell structure, promoting proline synthesis, and balancing endogenous hormone content. Our study offers a theoretical foundation for understanding the mechanism by which SA mitigates cold damage in kiwifruit, and provides novel insights into the low-temperature preservation of kiwifruit.

Lipid signaling and proline catabolism are activated in barley roots (Hordeum vulgare L.) during recovery from cold stress

Previous findings have shown that phospholipase D (PLD) contributes to the response to long-term chilling stress in barley by regulating the balance of proline (Pro) levels. Although Pro accumulation is one of the most prominent changes in barley roots exposed to this kind of stress, the regulation of its metabolism during recovery from stress remains unclear. Research has mostly focused on the responses to stress per se, and not much is known about the dynamics and mechanisms underlying the subsequent recovery. The present study aimed to evaluate how PLD, its product phosphatidic acid (PA), and diacylglycerol pyrophosphate (DGPP) modulate Pro accumulation in barley during recovery from long-term chilling stress. Pro metabolism involves different pathways and enzymes. The rate-limiting step is mediated by pyrroline-5-carboxylate synthetase (P5CS) in its biosynthesis, and by proline dehydrogenase (ProDH) in its catabolism. We observed that Pro levels decreased in recovering barley roots due to an increase in ProDH activity. The addition of 1-butanol, a PLD inhibitor, reverted this effect and altered the relative gene expression of ProDH. When barley tissues were treated with PA before recovery, the fresh weight of roots increased and ProDH activity was stimulated. These data contribute to our understanding of how acidic membrane phospholipids like PA help to control Pro degradation during recovery from stress.

Biochar Regulates 2-Acetyl-1-Pyrroline, Grain Yield and Quality in Fragrant Rice Cropping Systems in Southern China

With the existing model of chemical fertilizer application faces, improving grain yield and quality is challenging. Fragrant rice is known for its distinctive aroma and flavor, but it generally produces less grain than non-fragrant rice varieties. Limited research has been conducted on the potential of biochar as a solution for increasing the grain yield of fragrant rice. In a two-year field trial conducted in 2022 and 2023, two fragrant rice cultivars, Meixiangzhan2 (MXZ2) and Xiangyaxiangzhan (XYXZ), were selected as the experimental materials. These rice cultivars were subjected to four different rates of biochar application: no biochar treatment(T1); biochar with 0.375 t ha−1 (T2); biochar with 0.75 t ha−1 (T3); and biochar with 1.50 t ha−1 (T4). The results showed that the grain yield of both cultivars increased to an extent in both 2022 and 2023 (an 8.57–33.77% increase for MXZ2; a 6.00–21.59% increase for XYXZ). Furthermore, under the T2, T3, and T4 treatments, there was an increase in the number of effective panicles, seed setting rate, 1000-grain weight, biomass accumulation, net photosynthetic rate, and intercellular CO2 concentration. However, the transpiration rate and stomatal conductance decreased. The content of 2-acetyl-1-pyrroline (2-AP) increased with an increased rate of biochar application, and the highest content was observed under the T4 treatment (153.54–178.32 µg kg−1 in 2022; 163.93–180.28 µg kg−1 in 2023). The activities of proline dehydrogenase (PDH) and 1-pyrrolin-5-carboxylic acid synthase (P5CS), as well as the contents of proline (PRO), 1-pyrrolin-5-carboxylic acid (P5C), ∆1-pyrroline, and methylglyoxal, were improved under the T2, T3, and T4 treatments compared to the T1 treatment. Moreover, under the T2, T3, and T4 treatments, the brown rice rate, milled rice rate, and head rice rate increased, while the chalkiness degree and chalk rice rate decreased. Our correlation analysis showed that grain yield was positively correlated with total biomass accumulation, the number of grains per panicle, and the seed setting rate. Additionally, the content of 2-AP showed positive correlations with PRO, P5C, ∆1-pyrroline and methylglyoxal, and the activities of PDH and P5CS. In conclusion, applying biochar at a rate of 1.5 t ha−1 can be more effective in increasing the grain yield and 2-AP content of fragrant rice.

Bioinformatics and expression analysis of proline metabolism-related gene families in alfalfa under saline-alkali stress

Regulation of the proline metabolic pathway is essential for the accumulation of proline under abiotic stress and for the amelioration of plant stress resistance. Δ1-pyrroline-5-carboxylate synthase (P5CS), pyrroline-5-carboxylate reductase (P5CR), ornithine transaminase (δ-OAT), proline dehydrogenase (PDH), pyrroline-5-carboxylate dehydrogenase (P5CDH), and proline transporter (ProT) are the key enzymes in the proline metabolic pathway. However, the gene families responsible for proline metabolism have not yet been identified or reported in alfalfa. In this study, a total of 12 MsP5CSs, 4 MsP5CRs, 3 MsOATs, 6 MsPDHs, 2 MsP5CDHs, and 5 MsProTs were identified in the genome of alfalfa, and the members of the same subfamily had similar gene structures and conserved motifs. Analysis of cis-regulatory elements revealed the presence of light-responsive, hormone-regulated, and stress-responsive elements in the promoter regions of alfalfa proline metabolism-related genes. Following treatment with saline-alkali, the expression of MsP5CSs, MsP5CRs, MsOATs, and MsProTs was significantly upregulated, whereas the expression of MsPDH1.1, MsPDH1.3, and MsP5CDH was significantly downregulated. The proline content and enzyme activity of P5CS gradually increased, whereas the enzyme activity of PDH gradually decreased as the duration of stress increased. Root growth rates decreased upon MsP5CS1a suppression (MsP5CS1a-RNAi) in the hairy roots of alfalfa compared to the empty vector line under saline-alkali stress. These results show that proline metabolism-related genes play an important role in the saline-alkali stress tolerance of alfalfa and provide a theoretical basis for further research on the functions of proline metabolism-related genes in alfalfa in response to saline-alkali stress.

Melatonin mobilizes the metabolism of sugars, ascorbic acid and amino acids to cope with chilling injury in postharvest pear fruit

Chilling injury manifesting as internal browning is an irreversible physiological disorder in cold-stored ‘Yali’ pear fruit, which seriously restricts postharvest handling and commercialization of pear fruit. This study investigated the impact of melatonin (MN) treatment on chilling injury and the metabolism of sugars, ascorbic acid (AsA), proline, and γ-aminobutyric acid (GABA) during chilling injury development in ‘Yali’ pears. The findings revealed that MN-treated pear fruit exhibited considerably improved tolerance to chilling stress compared with untreated control fruit. MN application augmented proline accumulation, likely owing to increased activities and transcriptional concentrations of Δ1-pyrroline-5-carboxylate synthase and ornithine-δ-aminotransferase as well as diminished activity and transcriptional level of proline dehydrogenase. MN immersion increased enzyme activities and gene expression related to the GABA shunt pathway, leading to increased GABA concentrations in cold-stored pear fruit. Furthermore, MN treatment elevated AsA concentrations in the fruit, exerting protective effects against cell membrane damage and mitigating oxidative stress damage caused by chilling. Compared with the control group, MN-treated fruit exhibited reduced neutral invertase enzyme activity and gene expression. Additionally, MN treatment increased both sucrose-phosphate synthase and sucrose synthase activities and gene expression in pear fruit. These observations indicated that the enhanced chilling tolerance of ‘Yali’ pear fruit following MN treatment may be associated with the regulation of proline, GABA, AsA, and soluble sugars metabolism.

Postharvest Melatonin Application Preserves Quality and Imparts Chilling Tolerance in Peaches

Peach being a climacteric fruit has a limited shelf life. Cold storage of peaches is an essential measure to maintain their quality. However, prolonged exposure to cold temperatures causes chilling injury in peaches, resulting in significant economic losses. Approximately, 40% of the produced commodity is lost in postharvest handling in which chilling injury contributes to about 25%. Melatonin can be a green solution and plays a key role in protecting peaches from chilling injury. Therefore, this experiment aimed to determine the effect of melatonin on the “Silver King” peaches by dipping them in 100 μM melatonin for 2 hours followed by storing them at chilling temperatures of 2 ± 1°C and 90–95% relative humidity for 21 d. The results showed that while control fruit experienced chilling injury and poor fruit quality, increased respiration rate, and enhanced senescence, 100 μM melatonin treatment was successful in preserving the fruit quality at chilling temperatures and was associated with the delayed respiration rate and lower malondialdehyde levels, along with the preservation of certain physicochemical parameters, namely, total soluble solids, pH, fruit firmness, and titratable acidity. Moreover, a 1.5 times higher proline concentration was observed in melatonin-treated peaches when compared to that of nontreated peaches. This rise was linked to the enhanced activity of Δ1-pyrroline-5-carboxylate synthetase and ornithine-δ-aminotransferase along with a decrease in the activity of proline dehydrogenase during 21 d of storage.

Physiological and biochemical characteristics of genetically modified winter wheat

Aim. Analysis of physiological and biochemical characteristics of genetically modified wheat with partially suppressed activity of the proline dehydrogenase gene. Methods. Determination of proline dehydrogenase (PDH) activity, free L-proline (Pro); carbohydrate content (sucrose and fructose). Results. It was established that under conditions of water deficit in genetically modified wheat plants with integrated elements forming the double-stranded RNA suppressor of the pdh gene, there is a partial inhibition of the enzyme activity and an increase in the content of free proline. Changes in carbohydrate metabolism under water deficit stress and in the first hours after rehydration were noted, while the sucrose / fructose ratio in control plants significantly decreases during dehydration and normalizes when water supply is restored, in genetically modified plants this indicator almost does not change under short-term water deficit stress. Conclusions. Partial suppression of the proline dehydrogenase gene leads to an increase in the free proline content, the fluctuations of which contribute to the maintenance of carbohydrate balance.

Obtaining genetically modified winter wheat plants with partial suppression of the prolin dehydrogenase gene

Aim. Production of genetically modified plants of new promising winter wheat genotypes with partial suppression of the proline dehydrogenase gene in in vitro culture and determination of proline content in transgenic and control plants. Methods. Agrobacterium-mediated transformation in culture in vitro, molecular genetic analysis; biochemical determination of proline content; of mathematical statistics. Results. Using the method of Agrobacterium-mediated transformation of callus cultures of new promising genotypes of winter wheat, transgenic plants carrying a double-stranded RNA suppressor of the proline dehydrogenase gene were obtained. The frequency of transformation with the use of the LBA 4404 strain in the studied genotypes was 1.7-2.0 %, and with the use of the AGL0 strain, it was 2.0-2.3 %. It was established that plants with reduced activity of proline dehydrogenase are characterized by a significantly higher content of free L-proline compared to the control. Conclusions. The relatively greater efficiency of using the AGL0 strain for obtaining transgenic plants of winter wheat genotypes with partial suppression of the proline dehydrogenase gene in in vitro culture is shown. The presence of a double-stranded RNA suppressor of the ProDH gene in transgenic plants leads to an increase in the level of free L-proline accumulation.

Regulation of proline metabolism, AsA-GSH cycle, cadmium uptake and subcellular distribution in Brassica napus L. under the effect of nano-silicon

Cadmium (Cd) is known to have detrimental effects on plant growth and human health. Recent studies showed that silicon nanoparticles (SNPs) can decrease Cd toxicity in plants. Therefore, a study was conducted using 50 μM Cd and 1.50 mM SNPs to investigate Cd uptake, subcellular distribution, proline (Pro) metabolism, and the antioxidant defense system in rapeseed seedlings. In this study, results indicated that Cd stress negatively affected rapeseed growth, and high Cd contents accumulated in both shoots and roots. However, SNPs significantly decreased Cd contents in shoots and roots. Moreover, substantial increases were found in root fresh weight by 40.6% and dry weight by 46.6%, as well as shoot fresh weight by 60.1% and dry weight by 113.7% with the addition of SNPs. Furthermore, the addition of SNPs alleviated oxidative injury by maintaining the ascorbate-glutathione (AsA-GSH) cycle and increased Pro biosynthesis which could be due to high activities of Δ1-pyrroline-5-carboxylate synthase (P5CS) and reductase (P5CR) and decreased proline dehydrogenase (ProDH) activity. Furthermore, the addition of SNPs accumulated Cd in the soluble fraction (42%) and cell wall (45%). Results indicate that SNPs effectively reduce Cd toxicity in rapeseed seedlings which may be effective in promoting both rapeseed productivity and human health preservation.

Exogenous melatonin mitigates chilling injury in zucchini fruit by enhancing antioxidant system activity, promoting endogenous proline and GABA accumulation, and preserving cell wall stability

Zucchini fruit are sensitive to chilling injury (CI) during postharvest low temperature storage which makes their cold stored life short. In this work, zucchini fruit were treated with melatonin (200 µmol L−1) and stored at 5 ºC for 15 d. The pre-storage melatonin treatment reduced weight loss (6.51%) and suppressed symptoms of CI (1.5 Score) along with lower malondialdehyde (MDA), relative ion leakage (RIL), superoxide anion and hydrogen peroxide (H2O2) in contrast with control. The treated zucchini exhibited higher L* (51.89) and lower a* (−10.17) and b* (29.15) values of exocarp in comparison with control. Melatonin treated zucchini showed enhanced γ-aminobutyric acid (GABA) concentration due to higher glutamate content and stimulated glutamate decarboxylase (GAD) and suppressed γ-aminobutyric acid transaminase (GABA-T) activities. In addition, melatonin application increased proline accumulation owing to stimulation of Δ-1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine δ-aminotransferase (OAT) enzymes and reduced proline dehydrogenase (ProDH) activity as compared with control. The activity of antioxidative such as ascorbate peroxidase (APX), peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD) enzymes remained higher in melatonin treated zucchini. The fruit treated with melatonin exhibited reduced water soluble pectin (WSPN) along with higher sodium carbonate soluble pectin (SCSP), protopectin (PRPN), chelate soluble pectin (CSPN), cellulose (CLS) and hemicellulose (HLS) in comparison with control. The exogenous melatonin suppressed the activities of polygalacturonase (PG), β-galactosidase (β-Gal), cellulase (CX), and pectin methylesterase (PME) along with higher firmness. In conclusion, exogenous melatonin at 200 µmol L−1 concentration could be used for zucchini fruit CI mitigation under cold storage.

Regulation of Proline Metabolism in Soybean Leaves under Drought Stress at Seedling Phase

Background: Soybean is the most important oil crop globally; however, droughts are expected to seriously affect the growth and development of soybean in the context of climate change. Methods: In this study, polyethylene glycol (PEG) was used to simulate drought to explore the regulation of proline metabolism in soybean leaves under different degrees of drought stress at the seedling stage. Result: The results showed that the activities of ornithine aminotransferase and D1-pyrroline-5-carboxylate synthetase increased while the activities of proline dehydrogenase decreased with an increase in drought stress. During the same number of treatment days, the higher the degree of drought stress, the greater the increase or decrease in enzyme activity. The content of leaf proline increased gradually with an extension in stress time at PEG concentrations of 5% and 10%, first increased and then decreased at PEG concentrations of 15% and 20% and the peak value appeared on the 7th and 9th day, respectively.

N-α-Lauroyl-L-arginine ethyl ester hydrochloride combined with hot water treatment alleviates chilling injury of postharvest cucumber fruit

Postharvest cucumber fruit is prone to chilling injury (CI) under cold stress, leading to severe quality deterioration. In this study, the effects of N-α-Lauroyl-l-arginine ethyl ester hydrochloride (LAE), hot water (HW), and LAE combined with HW treatments on CI in cucumber fruit stored at 4 ± 1 ℃ were investigated. The response surface methodology (RSM) confirmed that the LAE concentration of 1.00 g L−1, HW temperature of 44 ℃, and immersion time of 10 min were the optimal condition for cucumber fruit preservation during cold storage. Further analysis revealed that LAE, HW, and LAE combined with HW treatments, all significantly mitigated chilling injury symptoms in cucumber fruit in comparison with the control, but the application of LAE combined with HW was the most effective method for enhancing cold tolerance in cucumber fruit. Moreover, LAE combined with HW treatment could reduce reactive oxygen species (ROS) accumulation, and enhance superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) activities in cold-stored cucumber fruit. Meanwhile, the activities of arginine decarboxylase (ADC), ornithine decarboxylase (ODC), Δ1-pyrroline-5-carboxylate synthetase (P5CS), ornithine δ-aminotransferase (OAT), and glutamate decarboxylase (GAD) were also increased by LAE combined with HW treatment, while the activities of proline dehydrogenase (PDH) and γ-aminobutyric acid transaminase (GABA-T) were decreased by LAE combined with HW treatment, which contributed to maintaining higher polyamines, proline, and GABA contents. These findings suggested that LAE combined with HW treatment can reduce chilling injury in cucumber fruit via enhancing antioxidant enzymes activities, PA, proline, and GABA contents to maintain ROS homeostasis during cold storage.

Melatonin treatment alleviates chilling injury in mango fruit ‘Keitt’ by modulating proline metabolism under chilling stress

Mangoes often suffer from low temperature-induced chilling injury (CI) during postharvest cold storage. Therefore, advanced techniques are crucial and in high demand to solve the chilling stress of mango fruit for a higher value. This study addresses chilling stress modulation by investigating the effects of melatonin treatment on CI, proline metabolism, and related gene expressions of ‘Keitt’ mango during cold storage after dipped in 0 (control), 0.1 (MT1), and 0.2 mmol L-1 (MT2) melatonin solution for 30 min. The results revealed that melatonin treatment in MT1 significantly reduced CI development and increased proline content in mango fruit during cold storage compared to the control. These changes were along with increases in the activity of critical enzymes as well as the expression of encoding genes involved in proline biosynthesis, such as pyrroline-5-carboxylate synthetase (P5CS), pyrroline-5-carboxylate reductase (P5CR), ornithine D-aminotransferase (OAT), P5CS2, P5CR2, and OAT3. Additionally, proline dehydrogenase (PDH) activity and the expression of the PDH3 gene associated with proline dehydrogenation were lower in MT1-treated mangoes than the controlled group. Thus, melatonin treatment has regulated proline metabolism resulting in the accumulation of proline, subsequently contributing to enhancing the chilling tolerance of ‘Keitt’ mango fruit.

Foliar methyl jasmonate (MeJA) application increased 2-acetyl-1-Pyrroline (2-AP) content and modulated antioxidant attributes and yield formation in fragrant rice

Endogenous methyl jasmonate (MeJA) mediates abiotic and biotic stresses in plants. Exogenous MeJA application can stimulate and defend plant gene expression and induce plant chemical defense. The effects of foliar MeJA application on yield and 2-acetyl-1-pyrroline (2-AP) biosynthesis of fragrant rice are scarcely investigated. The pot experiment was conducted by spraying different concentrations of MeJA (0, 1, and 2 μM; denoted as CK, MeJA-1, and MeJA-2) at the initial heading stage of two fragrant rice cultivars, Meixiangzhan and Yuxiangyouzhan. The results showed that foliar MeJA application significantly increased the grain 2-AP content by 32.1% and 49.7%, respectively, following MeJA-1 and MeJA-2 treatments, and the two cultivars showed the highest 2-AP content upon MeJA-2 treatment. However, the grain yield was increased in MeJA-1 as compared with MeJA-2 treatment for all rice cultivars and no significant differences were observed in yield and yield-related traits compared with CK. The aroma was improved by foliar MeJA application which was strongly associated with the regulation of the precursors and enzymes involved in 2-AP biosynthesis. In particular, the contents of proline, pyrroline-5-carboxylic acid, and pyrroline at maturity, as well as the activities of proline dehydrogenase, ornithine aminotransferase, and pyrroline-5-carboxylic acid synthetase, were positively correlated with grain 2-AP content. On the other hand, foliar MeJA application improved the contents of soluble protein, chlorophyll a and b, and carotenoid, and increased the activity of antioxidant enzymes. Moreover, peroxidase activity and leaf chlorophyll contents were significantly positively correlated to 2-AP content following foliar MeJA application. Therefore, our results implied that foliar MeJA application increased aroma and influenced yield by regulating the physio-biochemistry characters and resistance, and suggested that the optimal concentration of MeJA for the best positive effect on the yield and aroma was 1 μM. However, further study is required to evaluate the metabolic level and molecular basis of the regulatory mechanism of foliar MeJA application on 2-AP in fragrant rice.

Increasing basal nitrogen fertilizer rate improves grain yield, quality and 2-acetyl-1-pyrroline in rice under wheat straw returning.

Straw returning plays an essential role in crop yields and the sustainable development of agriculture. However, the effects and mechanisms of nitrogen (N) fertilizer management on grain yield, quality and aroma substance 2-acetyl-1-pyrroline (2-AP) content under wheat straw returning are still unclear. In this field experiment, two japonica rice cultivars were used as materials, wheat straw non-returning (NS) and wheat straw full returning (WS) were designed coupled with two N application ratios, namely basal fertilizer: tiller fertilizer: panicle fertilizer =5:1:4 (local farmers' fertilizer practice, LFP) and 7:1:2 (increasing basal fertilizer rate, IBF) under the total N application rate of 270kg ha-1. The effects of the four treatment combinations (NS-LFP, NS-IBF, WS-LFP, WS-IBF) on yield, cooking and eating quality, and 2-AP content in rice were investigated. The two-year (2020, 2021) results showed that: 1) WS-IBF significantly increased the number of panicles and grains per panicle, leading to the increase in grain yield by 6.67%-12.21%, when compared with NS-LFP, NS-IBF and WS-LFP. 2) WS-IBF enhanced the taste value, peak viscosity, breakdown value, the ratio of amylopectin to amylose, and the ratio of glutelin to prolamin while reducing the setback value and amylose content of rice flour. 3) Compared with NS, WS increased the activities of proline dehydrogenase and ornithine transaminase, the synthetic precursors of 2-AP, and finally increased 2-AP content in rice grains. WS-IBF slightly decreased 2-AP content, but there was no significant difference with WS-LFP. The above results indicated that adjusting the N regime and increasing basal N fertilizer rate under wheat straw returning is conducive to improving grain yield, cooking and eating quality, and 2-AP content in rice.