Leaf cell membrane stability‐based mechanisms of zinc nutrition in mitigating salinity stress in rice

• Excess salt affects about 955 million ha of arable land worldwide, and 49% of agricultural land is Zn‐deficient. Soil salinity and zinc deficiency can intensify plant abiotic stress. The mechanisms by which Zn can mitigate salinity effects on plant functions are not well understood.
• We conducted an experiment to determine how Zn and salinity effects on rice plant retention of Zn, K⁺ and the salt ion Na⁺ affect chlorophyll formation, leaf cell membrane stability and grain yield. We examined the mechanisms of Zn nutrition in mitigating salinity stress by examining plant physiology and nutrition. We used native Zn‐deficient soils (control), four salinity (EC ) and Zn treatments – Zn 10 mg·kg^?1 (Zn₁₀), EC 5 dS ·m^?1 (EC ₅), Zn₁₀+EC ₅ and Zn₁₅+EC ₅, a coarse rice (KS ‐282) and a fine rice (Basmati‐515) in the study.
• Our results showed that Zn alone (Zn₁₀) significantly increased rice tolerance to salinity stress by promoting Zn/K⁺ retention, inhibiting plant Na⁺ uptake and enhancing leaf cell membrane stability and chlorophyll formation in both rice cultivars in native alkaline, Zn‐deficient soils (P  <  0.05). Further, under the salinity treatment (EC ₅), Zn inputs (10–15 mg·kg^?1) could also significantly promote rice plant Zn/K⁺ retention and reduce plant Na⁺ uptake, and thus increased leaf cell membrane stability and grain yield. Coarse rice was more salinity‐tolerant than fine rice, having significantly higher Zn/K⁺ nutrient retention.
• The mechanistic basis of Zn nutrition in mitigating salinity impacts was through promoting plant Zn/K⁺ uptake and inhibiting plant Na⁺ uptake, which could result in increased plant physiological vigour, leaf cell membrane stability and rice productivity.

     

5‐Aminolevulinic acid promotes callus growth and paclitaxel production in light‐grown Taxus cuspidata suspension cultures

Cultured plant cells generally produce low levels of secondary metabolites, and elicitors of secondary metabolites usually inhibit callus growth. The aim of this study was to determine the effect of 5‐aminolevulinic acid (ALA), a chlorophyll precursor that promotes plant growth, on callus induction from leaves of Taxus cuspidata, and on callus growth on solid medium. ALA at 0.76, 7.6, and 76 μM had similar effects on callus induction and growth, while ALA at 760 μM had negative effects. Next, the effects of ALA concentrations on callus growth and paclitaxel production in suspension cultures in the dark were evaluated. The results showed that 0.76 and 7.6 μM ALA stimulated growth and paclitaxel production, while 76 μM ALA had negative effects. ALA is thought to promote cellular activity under light conditions. Therefore, the effects of light intensity on callus growth and paclitaxel production in the presence of ALA were evaluated. Our results showed that the best conditions for callus growth and paclitaxel production were 7.6 μM ALA under photosynthetically active radiation of 12 μmol photons m^?2 s^?1. Callus growth and paclitaxel production were inhibited under stronger light (24 μmol photons m^?2 s^?1). Together, these results show that ALA promoted callus growth and the production of paclitaxel by light‐grown cultured T. cuspidata cells.     

Humic acid differentially improves nitrate kinetics under low‐ and high‐affinity systems and alters the expression of plasma membrane H+‐ATPases and nitrate transporters in rice

Humic acids (HAs) have a major effect on nutrient uptake, metabolism, growth and development in plants. Here, we evaluated the effect of HA pretreatment applied with a nutrient solution on the uptake kinetics of nitrate nitrogen (N‐NO₃^?) and the metabolism of nitrogen (N) in rice under conditions of high and low NO₃^? supply. In addition, the kinetic parameters of NO₃^? uptake, N metabolites, and nitrate transporters (NRTs) and the plasma membrane (PM) H⁺‐ATPase gene expression were examined. The plants were grown in a growth chamber with modified Hoagland and Arnon solution until 21 days after germination (DAG), and they were then transferred to a solution without N for 48 h and then to another solution without N and with and without the addition of HAs for another 48 h. After this period of N deprivation, the plants received new nutrient solutions containing 0.2 and 2.0 mM N‐NO₃^?. Treatment of rice plants with HA promoted the induction of the genes OsNRT2.1‐2.2/OsNAR2.1 and some isoforms PM H⁺‐ATPase in roots. The application of HAs differentially modified the parameters of the uptake kinetics of NO₃^? under both concentrations. When grown with 0.2 mM NO₃^?, the plants pretreated with HA had lower K_m and C_min values as well as a higher V_max/K_m ratio. When grown with 2 mM NO₃^?, the plants pretreated with HA had a higher V_max value, a greater root and shoot mass, and a lower root/shoot ratio. The N fractions were also altered by pretreatment with HA, and a greater accumulation of NO₃^? and N‐amino was observed in the roots and shoots, respectively, of plants pretreated with HA. The results suggest that pretreatment with HA modifies root morphology and gene expression of PM H⁺‐ATPases and NO₃^? transporters, resulting in a greater efficiency of NO₃^? acquisition by high‐ and low‐affinity systems.     

Ethylenediamine‐N,N′‐disuccinic acid mitigates salt‐stress damages in strawberry by interfering with effects on the plant ionome

This study evaluated the hypothesis that the organic chelant ethylenediamine‐N,N′‐disuccinic acid (EDDS) mitigates plant damage under salinity, and that this is accomplished by EDDS‐induced effects on cation uptake. Damaging effects of salinity on plants often involve inhibited uptake of nutritional cations, such as K and Ca, and excessive accumulation of Na. Therefore, mechanisms that improve uptake of K and Ca, or reduce Na uptake, have a potential for ameliorating salinity damages. Organic chelants increase heavy‐metal cation availability at the site of uptake and increase their uptake by the roots or in planta transport. Although organic chelants are routinely used in agriculture to enhance uptake of heavy‐metal cations into plants, and for soil bioremediation, their effect on uptake of cation‐macronutrients is not known, and neither is their impact on plant function under salinity. In this study, we evaluated the response of strawberry plants to EDDS application (0, 1, 3 and 5 mmol kg soil^?1), under six levels of NaCl (0, 3, 6, 9, 12 and 15 mmol L^?1). EDDS application under salinity improved vegetative development, as well as reproductive growth and chlorophyll content, with statistically significant interaction between chelant dosage and level of salinity. The mitigation of salinity damage by EDDS occurred at high salinity treatments (from 9 mM NaCl). Application rates of 1–3 mmol EDDS kg^?1 were optimal for mitigating salinity effects on reproductive development, but in accordance with the extent of chelant‐induced accumulation of the macronutrients K, Ca and P in the leaves, higher application rates (3–5 mmol EDDS kg^?1) were required for optimal improvement of vegetative development. These results suggest that EDDS improves plant function under mild salinities by interfering with salinity effects on the plant ionome.     

Increased synthesis of α‐tocopherol,paramylon and tyrosine by Euglena gracilis under conditions of high biomass production

Aims: To analyse the production of different metabolites by dark‐grown Euglena gracilis under conditions found to render high cell growth. Methods and Results: The combination of glutamate (5 g l^?1), malate (2 g l^?1) and ethanol (10 ml l^?1) (GM + EtOH); glutamate (7·15 g l^?1) and ethanol (10 ml l^?1); or malate (8·16 g l^?1), glucose (10·6 g l^?1) and NH₄Cl (1·8 g l^?1) as carbon and nitrogen sources, promoted an increase of 5·6, 3·7 and 2·6‐fold, respectively, in biomass concentration in comparison with glutamate and malate (GM). In turn, the production of α‐tocopherol after 120 h identified by LC‐MS was 3·7 ± 0·2, 2·4 ± 0·1 and 2 ± 0·1 mg [g dry weight (DW)]^?1, respectively, while in the control medium (GM) it was 0·72 ± 0·1 mg (g DW)^?1. For paramylon synthesis, the addition of EtOH or glucose induced a higher production. Amino acids were assayed by RP‐HPLC; Tyr a tocopherol precursor and Ala an amino acid with antioxidant activity were the amino acids synthesized at higher concentration. Conclusions: Dark‐grown E. gracilis Z is a suitable source for the generation of the biotechnologically relevant metabolites tyrosine, α‐tocopherol and paramylon. Significance and Impact of the Study: By combining different carbon and nitrogen sources and inducing a tolerable stress to the cell by adding ethanol, it was possible to increase the production of biomass, paramylon, α‐tocopherol and some amino acids. The concentrations of α‐tocopherol achieved in this study are higher than others reported previously for Euglena, plant and algal systems. This work helps to understand the effect of different carbon sources on the synthesis of bio‐molecules by E. gracilis and can be used as a basis for future works to improve the production of different metabolites of biotechnological importance by this organism.     

A rice jacalin‐related mannose‐binding lectin gene,OsJRL, enhances Escherichia coli viability under high salinity stress and improves salinity tolerance of rice

• Salinity, which is one of the most common abiotic stresses, may severely affect plant productivity and quality. Although plant lectins are thought to play important roles in plant defense signaling during pathogen attack, little is known about the contribution of plant lectins to stress resistance.
• We cloned and functionally characterized a rice jacalin‐related mannose‐binding lectin gene, OsJRL, from rice ‘Nipponbare’. We analyzed the expression patterns of OsJRL under various stress conditions in rice. Furthermore, we overexpressed OsJRL in Escherichia coli and rice.
• The cDNA of OsJRL contained a 438 bp open reading frame, which encodes a polypeptide of 145 amino acids. OsJRL was localized in the nucleus and cytoplasm. Real time PCR analyses revealed that OsJRL expression showed tissue specificity in rice and was upregulated under diverse stresses, namely salt, drought, cold, heat and abscisic acid treatments. Overexpression of OsJRL in E. coli enhanced cell viability and dramatically improved tolerance of high salinity. Overexpression of OsJRL in rice also enhanced salinity tolerance and increased the expression levels of a number of stress‐related genes, including three LEA (late embryogenesis abundant proteins) genes (OsLEA19a, OsLEA23 and OsLEA24), three Na⁺ transporter genes (OsHKT1;3, OsHKT1;4 and OsHKT1;5) and two DREB genes (OsDREB1A and OsDREB2B).
• Based on these results, we suggest that OsJRL plays an important role in cell protection and stress signal transduction.

     

Serum miR‐92a‐1 is a novel diagnostic biomarker for colorectal cancer

Colorectal cancer (CRC) is one of the most common cancers worldwide, with high mortality. Abnormally expressed microRNAs (miRNAs) are considered novel biomarkers in cancer diagnosis. The aim of this study was to investigate the diagnostic value of miR‐92a‐1 in patients with CRC. Serum samples were collected from 148 patients pathologically diagnosed with CRC and 68 gender‐ and age‐matched healthy volunteers. Quantitative real‐time polymerase chain reaction (qRT‐PCR) was used to measure serum miR‐92a‐1 level. Relationship between miR‐92a‐1 and clinicopathological features of CRC cases was analysed via chi‐square test. Receiver operating characteristic (ROC) curve was plotted to estimate the diagnostic value of miR‐92a‐1 in CRC. Serum miR‐92a‐1 was significantly up‐regulated in CRC patients compared with healthy individuals (P < .001). Moreover, miR‐92a‐1 expression was correlated with TNM stage (P = .02), histological stage (P = .003), lymph node metastasis (P = .003) and distant metastasis (P < .001). ROC analysis showed that the area under the ROC curve (AUC) was 0.914, suggesting high diagnostic accuracy of miR‐92a‐1 in ROC. The optimal cut‐off value was 1.485, with a sensitivity of 81.8% and a specificity of 95.6%. MiR‐92a‐1 is increased in CRC patients and correlated with aggressive clinical characteristics. Serum miR‐92a‐1 may be a potential diagnostic biomarker for CRC.     

Metabolism in 1,3‐propanediol fed‐batch fermentation by a D‐lactate deficient mutant of Klebsiella pneumoniae

Klebsiella pneumoniae HR526, a new isolated 1,3‐propanediol (1,3‐PD) producer, exhibited great productivity. However, the accumulation of lactate in the late‐exponential phase remained an obstacle of 1,3‐PD industrial scale production. Hereby, mutants lacking D ‐lactate pathway were constructed by knocking out the ldhA gene encoding fermentative D ‐lactate dehydrogenase (LDH) of HR526. The mutant K. pneumoniae LDH526 with the lowest LDH activity was studied in aerobic fed‐batch fermentation. In experiments using pure glycerol as feedstock, the 1,3‐PD concentrations, conversion, and productivity increased from 95.39 g L^?1, 0.48 and 1.98 g L^?1 h^?1 to 102. 06 g L^?1, 0.52 mol mol^?1 and 2.13 g L^?1 h^?1, respectively. The diol (1,3‐PD and 2,3‐butanediol) conversion increased from 0.55 mol mol^?1 to a maximum of 0.65 mol mol^?1. Lactate would not accumulate until 1,3‐PD exceeded 84 g L^?1, and the final lactate concentration decreased dramatically from more than 40 g L^?1 to <3 g L^?1. Enzymic measurements showed LDH activity decreased by 89–98% during fed‐batch fermentation, and other related enzyme activities were not affected. NADH/NAD⁺ enhanced more than 50% in the late‐exponential phase as the D ‐lactate pathway was cut off, which might be the main reason for the change of final metabolites concentrations. The ability to utilize crude glycerol from biodiesel process and great genetic stability demonstrated that K. pnemoniae LDH526 was valuable for 1,3‐PD industrial production. Biotechnol. Bioeng. 2009; 104: 965–972. © 2009 Wiley Periodicals, Inc.     

Vitamin E and Hippophea rhamnoides L. extract reduce nicotine‐induced oxidative stress in rat heart

The effects of vitamin E and Hippophea rhamnoides L. extract (HRe‐1) on nicotine‐induced oxidative stress in rat heart were investigated. There were eight rats per group and supplementation period was 3 weeks. The groups were: nicotine [0.5 mg kg^?1day^?1, intraperitoneal (i.p.)]; nicotine plus vitamin E [75 mg kg^?1day^?1, intragastric (i.g.)]; nicotine plus HRe‐1 (250 mg kg^?1day^?1, i.g.); and the control group (receiving only vehicles). Nicotine increased the malondialdehyde level, which was prevented by both vitamin E and HRe‐1. Glutathione peroxidase (GPx) activity in nicotine plus vitamin E supplemented group was higher than the others. Glutathione S‐transferase (GST) activity in nicotine plus HRe‐1 supplemented group was increased compared with the control group. Catalase activity was higher in nicotine group compared with others. GPx activity in nicotine plus vitamin E supplemented group was elevated compared with the others. Total and non‐enzymatic superoxide scavenger activities in nicotine plus vitamin E supplemented group were lower than nicotine plus HRe‐1 supplemented group. Superoxide dismutase (SOD) activity was higher in nicotine plus HRe‐1 supplemented group compared with others. Glutathione reductase activity and nitric oxide level were not affected. Increased SOD and GST activities might have taken part in the prevention of nicotine‐induced oxidative stress in HRe‐1 supplemented group in rat heart. Flavonols such as quercetin, and isorahmnetin, tocopherols such as α‐tocopherol and β‐tocopherol and carotenoids such as α‐carotene and β‐carotene, reported to be present in H. rhamnoides L. extracts may be responsible for the antioxidant effects of this plant extract. Copyright © 2010 John Wiley & Sons, Ltd.     

Metabolomic profiling of wild‐type and mutant soybean root nodules using laser‐ablation electrospray ionization mass spectrometry reveals altered metabolism

The establishment of the nitrogen‐fixing symbiosis between soybean and Bradyrhizobium japonicum is a complex process. To document the changes in plant metabolism as a result of symbiosis, we utilized laser ablation electrospray ionization‐mass spectrometry (LAESI‐MS) for in situ metabolic profiling of wild‐type nodules, nodules infected with a B. japonicum nifH mutant unable to fix nitrogen, nodules doubly infected by both strains, and nodules formed on plants mutated in the stearoyl‐acyl carrier protein desaturase (sacpd‐c) gene, which were previously shown to have an altered nodule ultrastructure. The results showed that the relative abundance of fatty acids, purines, and lipids was significantly changed in response to the symbiosis. The nifH mutant nodules had elevated levels of jasmonic acid, correlating with signs of nitrogen deprivation. Nodules resulting from the mixed inoculant displayed similar, overlapping metabolic distributions within the sectors of effective (fix⁺) and ineffective (nifH mutant, fix^?) endosymbionts. These data are inconsistent with the notion that plant sanctioning is cell autonomous. Nodules lacking sacpd‐c displayed an elevation of soyasaponins and organic acids in the central necrotic regions. The present study demonstrates the utility of LAESI‐MS for high‐throughput screening of plant phenotypes. Overall, nodules disrupted in the symbiosis were elevated in metabolites related to plant defense.