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.

Application of glutamic acid improved As tolerance in aromatic rice at early growth stage.

To alleviate the arsenic (As) toxicity in aromatic rice, a hydroponic experiment of two As concentrations (0 and 100 µM sodium arsenite: A0, A1), three glutamic acid (Glu) concentrations (0, 100, and 500 µM l-glutamic acid: G0, G1, and G2) with Xiangyaxiangzhan and Meixiangzhan 2 was conducted. Results showed that the root As content were increased under A1G2 but reduced under A1G1 for Xiangyaxiangzhan as compared with A1G0. A decrement of As was transported from root to shoot caused by up-regulated OsABCC1 relative expression in Meixiangzhan 2. Likewise, As stress enhanced the H2O2 and malondialdehyde content, resulting in the impaired cell wall observed by transmission electron microscopy. However, compared with A1G0, the superoxide dismutase activity, ascorbic acid, glutathione, proline, and soluble sugar content were increased under A1G1. Additionally, arsenate reductase, monodehydroascorbate reductase activity, Glu, proline, and soluble sugar content were found positively associated with the As accumulation. Further, the metabolome analysis indicated that the pathway of amino acid and arginine biosynthesis were notably enriched after Glu application. Generally, 100 µM Glu application was the better treatment to enhance As tolerance in aromatic rice through up-regulating amino acid biosynthesis with increasing antioxidants and osmolytes to scavenge excessive reactive oxygen species.

Effect of Exogenous Melatonin Application on the Grain Yield and Antioxidant Capacity in Aromatic Rice under Combined Lead-Cadmium Stress.

This study aimed to determine the mechanism of exogenous melatonin application in alleviating the combined Pb and Cd (Pb-Cd) toxicity on aromatic rice (Oryza sativa L.). In this study, a pot experiment was conducted; two aromatic rice varieties, Yuxiangyouzhan and Xiangyaxiangzhan, were selected, and sprays using 50, 100, 200, and 400 µmol L-1 melatonin (denoted as S50, S100, S200, and S400) and irrigation using 100, 300, and 500 µmol L-1 melatonin (denoted as R100, R300, and R500) were also selected. The results showed that, under the S50, S100, and S200 treatments, the Pb content of aromatic rice grain decreased, and the grain yield increased significantly. Moreover, the application of exogenous melatonin significantly reduced the accumulation of H2O2 in rice leaves at maturity under Cd-Pb stress and reduced the MDA content in Xiangyaxiangzhan leaves. In addition, the microbial community structure changed significantly under S50 and R300 treatments. Some pathways, such as the synthesis of various amino acids and alanine, aspartate, and glutamate metabolism, were regulated by S50 treatment. Overall, melatonin application improved aromatic rice grain yield while reducing heavy metal accumulation by regulating the antioxidant capacity and metabolites in aromatic rice plants and altering the physicochemical properties and microbial community structures of the soil.

Transcriptome Analysis Revealed the Mechanisms Involved in Ultrasonic Seed Treatment-Induced Aluminum Tolerance in Peanut.

Ultrasonic (US) treatment is an efficient method to induce crop tolerance against heavy metal toxicity; however, US-induced aluminum (Al) tolerance in peanuts was rarely studied. This study was comprised of two treatments, namely, CK, without ultrasonic treatment, and US, an ultrasonic seed treatment, for 15 min. Both treated and non-treated treatments were applied with Al in the form of AlCl3.18H2O at 5 mmol L-1 in Hoagland solution at one leaf stage. Results depicted that plant height, main root length, and number of lateral roots increased significantly under US treatment. Transcriptome analysis revealed that plant hormone signal transduction and transcription factors (TFs) were significantly enriched in the differentially expressed genes (DEGs) in US treatment, and the plant hormones were measured, including salicylic acid (SA) and abscisic acid (ABA) contents, were substantially increased, while indole acetic acid (IAA) and jasmonic acid (JA) contents were decreased significantly in US treatment. The TFs were verified using quantitative real-time (qRT)-PCR, and it was found that multiple TFs genes were significantly upregulated in US treatment, and ALMT9 and FRDL1 genes were also significantly upregulated in US treatment. Overall, the US treatment induced the regulation of hormone content and regulated gene expression by regulating TFs to improve Al tolerance in peanuts. This study provided a theoretical rationale for US treatment to improve Al tolerance in peanuts.

Ultrasonic seed treatment improved cadmium (Cd) tolerance in Brassica napus L.

Cadmium (Cd) affects crop growth and productivity by disrupting normal plant metabolism. To determinate whether ultrasonic (US) seed treatment can alleviate Cd stress in rape (Brassica napus L.), the seeds of two oilseed rape cultivars i.e., 'Youyanzao18' and 'Zaoshu104' were exposed to ultrasonic waves for 1 min at 20 KHz frequency. Seeds without US treatment were taken as control (CK). Results revealed that the germination rate of both cultivars was significantly (P < 0.05) higher in US treatment than CK only at 0 and 10 mg Cd L-1. The shoot and root length of both cultivars were significantly higher in US treatment than CK at all Cd treatments except the root length of Youyanzao18 at 50 mg Cd L-1. The fresh weight Youyanzao18 was significantly (P < 0.05) higher in US than CK except for Youyanzao18 at 25 mg Cd L-1. Moreover, the superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) activities and the proline, glutathione (GSH), and soluble protein contents in Youyanzao18 were relatively higher in the US treatment than CK. The malondialdehyde (MDA) contents were prominently reduced in US treatment than CK. The pods per plant, seeds per pod and rapeseed yield were increased by 15.9, 11.4, and 16.4% in Youyanzao18 and 10.3, 9.5, and 11.5% in Zaoshu104, respectively in US treatment, compared to CK. Moreover, the contents of Cd in root, stem, leaf, rape pod shell, and rapeseeds were comparatively less in US treatment than CK whereas the Cd concentrations in different plant parts of both rape cultivars were recorded as: leaf ˃ root ˃ stem ˃ rape pod shell ˃ rapeseed. In sum, the US treatment improved the morphological growth and rapeseed yield whereas reduced the Cd accumulation in different plant parts of rapeseed under Cd contaminated soil.

Mesenchymal stem cells enhanced cardiac nerve sprouting via nerve growth factor in a rat model of myocardial infarction.

BACKGROUND: Transplantation of mesenchymal stem cells (MSCs) alters the ventricular electrophysiologic properties after myocardial infarction (MI) in rats. However, it is unclear whether MSCs transplantation enhances the secretion of nerve growth factor (NGF) and affects cardiac sympathetic remodeling. METHODS: MI was induced in 35 male Sprague-Dawley rats. Two weeks later, the animals were randomized to MSCs or phosphate buffer solution (PBS) injections into the infarcted myocardium. Six weeks thereafter, the expressions of NGF, growth associated protein 43 (GAP43) and tyrosine hydroxylase (TH) were measured and the density of GAP43 and TH positive nerves was calculated in the borderzone. NGF levels were detected in different culture conditions with neonatal rat ventricular myocytes (NRVMs, 2 × 10(5)/well) and MSCs (2 × 10(5)/well). RESULTS: Compared with PBS, mRNA expression and protein levels of NGF, GAP43 and TH increased in the border zone after MSCs injection. Immunohistochemistry showed more GAP43- and TH-positive nerves in the MSCs than in the PBS group. Compared to monocultured MSCs, mono-cultured NRVMs secreted more NGF in vitro. CONCLUSIONS: The expression of NGF increased after MSCs transplantation, which may affect sympathetic remodeling and the electrophysiological properties after MI. Paracrine factors secreted by MSC-CM may be involved in this process.