[Show abstract][Hide abstract] ABSTRACT: The second messenger cyclic guanosine 3',5'-monophosphate (cGMP) plays an important role in plant development and responses to stress. Recent studies indicated that cGMP is a secondary signal generated in response to auxin stimulation. cGMP also mediates auxin-induced adventitious root formation in mung bean and gravitropic bending in soybean. Nonetheless, the mechanism of the participation of cGMP in auxin signalling to affect these growth and developmental processes is largely unknown. In this report we provide evidence that indole-3-acetic acid (IAA) induces cGMP accumulation in Arabidopsis roots through modulation of the guanylate cyclase activity. Application of 8-bromo-cGMP (a cell-permeable cGMP derivative) increases auxin-dependent lateral root formation, root hair development, primary root growth, and gene expression. In contrast, inhibitors of endogenous cGMP synthesis block these processes induced by auxin. Data also showed that 8-bromo-cGMP enhances auxin-induced degradation of Aux/IAA protein modulated by the SCF(TIR1) ubiquitin-proteasome pathway. Furthermore, it was found that 8-bromo-cGMP is unable to directly influence the auxin-dependent TIR1-Aux/IAA interaction as evidenced by pull-down and yeast two-hybrid assays. In addition, we provide evidence for cGMP-mediated modulation of auxin signalling through cGMP-dependent protein kinase (PKG). Our results suggest that cGMP acts as a mediator to participate in auxin signalling and may govern this process by PKG activity via its inﬂuence on auxin-regulated gene expression and auxin/IAA degradation.
Journal of Experimental Botany 03/2014; · 5.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Narciclasine (NCS) is an Amaryllidaceae alkaloid isolated from Narcissus tazetta bulbs. Its phytotoxic effects on plant growth were examined in lettuce (Lactuca sativa L.) seedlings. Results showed that high concentrations (0.5-5 μM) of NCS restricted the growth of lettuce roots in a dose-dependent manner. In NCS-treated lettuce seedlings, the following changes were detected: reduction of mitotic cells and cell elongation in the mature region, inhibition of proliferation of meristematic cells, and cell cycle. Moreover, comet assay and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay indicated that higher levels NCS (0.5-5 μM) induced DNA damage in root cells of lettuce. The decrease in meristematic cells and increase in DNA damage signals in lettuce roots in responses to NCS are in a dose-dependent manner. NCS-induced reactive oxygen species accumulation may explain an increase in DNA damage in lettuce roots. Thus, the restraint of root growth is due to cell cycle arrest which is caused by NCS-induced DNA damage. In addition, it was also found that NCS (0.5-5 μM) inhibited the root hair development of lettuce seedlings. Further investigations on the underlying mechanism revealed that both auxin and ethylene signaling pathways are involved in the response of root hairs to NCS.
[Show abstract][Hide abstract] ABSTRACT: KEY MESSAGE : The major insight in this manuscript is that we identified a new flowering regulator, GmSOC1-like, which may participate in the initiation and maintenance of flowering in soybean. Flowering is pivotal for the reproductive behavior of plants, and it is regulated by complex and coordinated genetic networks that are fine-tuned by endogenous cues and environmental signals. To better understand the molecular basis of flowering regulation in soybean, we isolated GmSOC1 and GmSOC1-like, two putative soybean orthologs for the Arabidopsis SUPPRESSOR OF OVEREXPRESSION OF CO1/AGAMOUS-LIKE 20 (SOC1/AGL20). The expression pattern of GmSOC1-like was analyzed by qRT-PCR in Zigongdongdou, a photoperiod-sensitive soybean cultivar. GmSOC1-like was widely expressed at different levels in most organs of the soybean, with the highest expression in the shoot apex during the early stage of floral transition. In addition, its expression showed a circadian rhythm pattern, with the highest expression at midnight under short-day (SD) condition. Intriguingly, GmSOC1-like was induced 4 days earlier than GmSOC1 during flowering transition in SD, suggesting that GmSOC1 and GmSOC1-like expression might be differentially regulated. However, under long-day (LD) condition, the expression of GmSOC1 and GmSOC1-like decreased gradually in the shoot apex of Zigongdongdou, which is in accordance with the fact that Zigongdongdou maintains vegetative growth in LD. In addition, overexpression of GmSOC1-like stimulated the flowering of Lotus corniculatus cv. supperroot plants. In conclusion, the results of this study indicate that GmSOC1-like may act as a flowering inducer in soybean.
[Show abstract][Hide abstract] ABSTRACT: Abundant senescent neutrophils traverse the vascular compartment and may contribute to pathologic conditions. For example, they become procoagulant when undergoing apoptosis and may contribute to thrombosis or inflammation. Our previous studies demonstrated a dominant clearance pathway in which the neutrophils can be phagocytosed by liver macrophages. The aim of this study was to explore an alternate pathway of neutrophil clearance by endothelial cells. Phagocytosis of the neutrophils by endothelial cells was performed using various experimental approaches includingflow cytometry, confocal microscopy and electron microscopy assays in vitro and in vivo. Procoagulant activity of cultured neutrophils was evaluated by coagulation time, factor Xase and prothrombinase assays. Lactadherin functioned as a novel probe for the detection of phosphatidylserine on apoptotic cells, an opsonin (bridge) between apoptotic cell and phagocyte for promoting phagocytosis, and an efficient anticoagulant for inhibition of factor Xase and thrombin formation. When cultured, purified human neutrophils spontaneously entered apoptosis and developed procoagulant activity that was directly related to the degree of phosphatidylserine exposure. Co-culture of aged neutrophils and endothelial cells resulted in phagocytosis of the neutrophils and prolonged coagulation time. Lactadherin diminished the procoagulant activity and increased the rate of neutrophil clearance. In vivo, neutrophils were sequestered by endothelial cells after blockade of Kupffer cells, a process that was dependent upon both phosphatidylserine exposure and P-selectin expression. Thus, the ability of endothelial cells to clear senescent neutrophils may limit the procoagulant and/or inflammatory impact of these cells.
Thrombosis and Haemostasis 04/2013; 109(6). · 6.09 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The reduced coenzyme nicotinamide-adenine dinucleotide phosphate (NADPH) is an important molecule in cellular redox balance. Glucose-6-phosphate dehydrogenase (G6PDH) is a key enzyme in the pentose phosphate pathway, the most important NADPH-generating pathway. In this study, roles of G6PDH in maintaining cell redox balance in rice suspension cells under salt stress were investigated. Results showed that the G6PDH activity decreased in the presence of 80 mM NaCl on day 2. Application of exogenous glucose stimulated the activity of G6PDH and NADPH oxidase under salt stress. Exogenous glucose also increased the ion leakage, thiobarbituric acid reactive substances and hydrogen peroxide (H2O2) contents in the presence of 80 mM NaCl on day 2, implying that the reduction of the G6PDH activity was necessary to avoid serious damage caused by salt stress. The NAPDH/NADP+ ratio increased on day 2 but decreased on day 4 under 80 mM NaCl plus glucose treatment. Diphenyleneiodonium, an NADPH oxidase inhibitor, decreased the H2O2 content under 80 mM NaCl treatment on day 2. These results imply that the H2O2 accumulation induced by glucose treatment under salt stress on day 2 was related to the NADPH oxidase. Western-blot analysis showed that the G6PDH expression was slightly induced by glucose and was obviously blocked by DPI on day 2 under salt stress. In conclusion, G6PDH plays a key role in maintaining the cell redox balance in rice suspension cells under salt stress. The coordination of G6PDH and NADPH oxidase is required in maintaining cell redox balance in salt tolerance.
[Show abstract][Hide abstract] ABSTRACT: KEY MESSAGE : Two soybean cultivars showed markedly different drought tolerance. G6PDH plays a central role in the process of H ( 2 ) O ( 2 ) regulated GR, DHAR, and MDHAR activities to maintain GSH and Asc levels. Glucose-6-phosphate dehydrogenase (G6PDH) plays a pivotal role in plant resistance to environmental stresses. In this study, we investigated the role of G6PDH in modulating redox homeostasis under drought stress induced by polyethylene glycol 6000 (PEG6000) in two soybean cultivars JINDOU21 (JD-21) and WDD00172 (WDD-172). The G6PDH activity markedly increased and reached a maximum at 96 h in JD-21 and 72 h in WDD-172 during PEG6000 treatments, respectively. Glucosamine (Glucm, a G6PDH inhibitor) obviously inhibited G6PDH activity in both soybeans under PEG6000 treatments. After PEG6000 treatment, JD-21 showed higher tolerance than WDD-172 not only in higher activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione reductase (GR), dehydroascorbate reductase (DHAR), and monodehydroascorbate reductase (MDHAR), but also in higher content of glutathione (GSH) and ascorbate (Asc). And we found that hydrogen peroxide (H(2)O(2)) regulated the cell length in root elongation zone. Diphenylene iodonium (DPI, a plasma membrane NADPH oxidase inhibitor) counteracted the PEG6000-induced H(2)O(2) accumulation and decreased the activities of GR, DHAR, and MDHAR as well as GSH and Asc content. Furthermore, exogenous application of H(2)O(2) increased the GR, DHAR, and MDHAR activities that were decreased by Glucm under drought stress. Western blot analysis showed that the G6PDH expression was stimulated by PEG6000 and buthionine sulfoximine (BSO, glutathione biosynthesis inhibitor), and blocked by Glucm, DPI and N-acetyl-L-cysteine (NAC, GSH precursor) in both cultivars. Taken together, our evidence indicates that G6PDH plays a central role in the process of H(2)O(2) regulated GR, DHAR, and MDHAR activities to maintain GSH and Asc levels.
[Show abstract][Hide abstract] ABSTRACT: Ethylene and light act through specific signal transduction mechanisms to coordinate the development of higher plants. Application of 1-aminocyclopropane-1-carboxylic acid (ACC, an ethylene precursor) suppresses the hypocotyl elongation of Arabidopsis seedlings in dark, but stimulates it in light. However, the mechanisms of opposite effects of ethylene on hypocotyl elongation in light and dark remain unclear. In the present study, we investigated the key factors involved in the opposite effects of ethylene on hypocotyl elongation in Arabidopsis seedlings. The effects of ACC on hypocotyl elongation of IAA-insensitive mutants including tir1-1, axr1-3, and axr1-12 seedlings were reduced in light but not in dark. The DR5 promoter, a synthetic auxin-response promoter, was used to quantify the level of IAA responses. There was a marked increase in DR5-GFP signals in response to ACC treatment in hypocotyls of DR5-GFP seedlings in light, but not in dark. CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) is an important downstream component of light signaling. ETHYLENE-INSENSITIVE3 (EIN3, an ethylene-stabilized transcription factor) directly regulates ETHYLENE-RESPONSE-FACTOR1 (ERF1). The cop1-4 mutant treated with ACC and cop1-4/EIN3ox plants developed long hypocotyls in darkness. Expression of ERF1 in the cop1-4 mutant was induced by ACC treatment in dark, but the expression of ERF1 in the wild type was not affected. Taken together, ethylene-promoting hypocotyl via IAA is mediated by light, and COP1 has a significant impact on the transcription of some genes downstream of EIN3. Thus, COP1 plays a crucial role in the opposite effects of ethylene on hypocotyl elongation.
[Show abstract][Hide abstract] ABSTRACT: The plant hormone auxin plays a central role in the regulation of plant growth and development, as well as in responses to environmental stimuli. Narciclasine (NCS, an Amaryllidaceae alkaloid) isolated from Narcissus tazetta bulbs has a broad range of inhibitory effects on plants. In this study, the role of NCS in responses to auxin in Arabidopsis thaliana roots was investigated. We demonstrated the inhibitory effects of NCS on auxin-inducible lateral root formation, root hair formation, primary root growth, and the expression of primary auxin-inducible genes in Arabidopsis roots using DR5::GUS reporter gene, native auxin promoters (IAA12::GUS, IAA13::GUS), and quantitative reverse transcription PCR analysis. Results also showed that NCS did not affect the expression of cytokinin-inducible ARR5::GUS reporter gene. NCS relieved the auxin-enhanced degradation of the Aux/IAA repressor modulated by the SCFTIR1 ubiquitin-proteasome pathway. In addition, NCS did not alter the auxin-stimulated interaction between IAA7/AXR2 (Aux/IAA proteins) and the F-box protein TIR1 activity of the proteasome. Taken together, these results suggest that NCS acts on the auxin signaling pathway upstream of TIR1, which modulates Aux/IAA protein degradation, and thereby affects the auxin-mediated responses in Arabidopsis roots.
[Show abstract][Hide abstract] ABSTRACT: Narciclasine (NCS) is an Amaryllidaceae alkaloid isolated from Narcissus tazetta bulbs. NCS has inhibitory effects on a broad range of biological activities and thus has various potential practical applications. Here we examine how NCS represses plant root growth.
Results showed that the inhibition of NCS on cell division in Arabidopsis root tips and its effects on cell differentiation are concentration-dependent; at low concentrations (0.5 and 1.0 μM) NCS preferentially targets mitotic cell cycle specific/cyclin complexes, whereas at high concentration (5.0 μM) the NCS-stimulated accumulation of Kip-related proteins (KRP1 and RP2) affects the CDK complexes with a role at both G1/S and G2/M phases.
Our findings suggest that NCS modulates the coordination between cell division and differentiation in Arabidopsis root tips and hence affects the postembryonic development of Arabidopsis seedlings.
[Show abstract][Hide abstract] ABSTRACT: Narciclasine (NCS) is a plant growth inhibitor isolated from the secreted mucilage of Narcissus tazetta bulbs. It is a commonly used anticancer agent in animal systems. In this study, we provide evidence to show that NCS also acts as an agent in inducing programmed cell death (PCD) in tobacco Bright Yellow-2 (TBY-2) cell cultures. NCS treatment induces typical PCD-associated morphological and biochemical changes, namely cell shrinkage, chromatin condensation and nuclear DNA degradation. To investigate possible signaling events, we analyzed the production of reactive oxygen species (ROS) and the function of mitochondria during PCD induced by NCS. A biphasic behavior burst of hydrogen peroxide (H(2)O(2)) was detected in TBY-2 cells treated with NCS, and mitochondrial transmembrane potential (MTP) loss occurred after a slight increase. Pre-incubation with antioxidant catalase (CAT) and N-acetyl-L-cysteine (NAC) not only significantly decreased the H(2)O(2) production but also effectively retarded the decrease of MTP and reduced the percentage of cells undergoing PCD after NCS treatment. In conclusion, our results suggest that NCS induces PCD in plant cells; the oxidative stress (accumulation of H(2)O(2)) and the MTP loss play important roles during NCS-induced PCD.
Physiologia Plantarum 09/2011; 144(1):48-58. · 3.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the present study, the role of phytohormone gibberellins (GAs) on regulating the nitrate reductase (NR) activity was tested in Arabidopsis seedlings. The NR activity in light-grown Col-0 seedlings was reduced by exogenous GA₃ (an active form of GAs), but enhanced by exogenous paclobutrazol (PAC, a gibberellin biosynthesis inhibitor), suggesting that GAs negatively regulate the NR activity in light-grown seedlings. Light is known to influence the NR activity through both photosynthesis and phytochromes. When etiolated seedlings were transferred to white or red light, both exogenously applied GA₃ and PAC were found to function on the NR activity only in the presence of sucrose, implying that GAs are not involved in light signaling-induced but negatively regulate photoproducts-induced NR activity. NR is regulated by light mainly at two levels: transcript level and post-translational level. Our reverse transcription (RT)-PCR assays showed that GAs did not affect the transcript levels of NIA1 and NIA2, two genes that encode NR proteins. But the divalent cations (especially Mg²⁺) were required for GAs negative regulation of NR activity, in view of the importance of divalent cations during the process of post-translational regulation of NR activity, which indicates that GAs very likely regulate the NR activity at the post-translational level. In the following dark-light shift analyses, GAs were found to accelerate dark-induced decrease, but retard light-induced increase of the NR activity. Furthermore, it was observed that application of G₃ or PAC could impair diurnal variation of the NR activity. These results collectively indicate that GAs play a negative role during light regulation of NR activity in nature.
Journal of plant physiology 08/2011; 168(18):2161-8. · 2.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The roles of ethylene, hydrogen peroxide (H(2)O(2)), and calcium in inducing the capacity of the alternative respiratory pathway (AP) under chilling temperature in Arabidopsis thaliana calli were investigated. Exposure of wild-type (WT) calli, but not the calli of ethylene-insensitive mutants, etr1-3 and ein2-1, to chilling led to a marked increase of the AP capacity and triggered a rapid ethylene emission and H(2)O(2) generation. Increasing ethylene emission by applying 1-aminocyclopropane-1-carboxylic (an ethylene precursor) markedly enhanced the AP capacity in WT calli, but not in etr1-3 and ein2-1 calli, whereas suppressing ethylene emission by applying aminooxyacetic acid (an ethylene biosynthesis inhibitor) abolished the chilling-induced AP capacity in WT calli. Furthermore, exogenous H(2)O(2) treatment increased the AP capacity in WT calli, but not in etr1-3 and ein2-1 calli, while both catalase (H(2)O(2) scavenger) and diphenylene iodonium (DPI, an inhibitor of NADPH oxidase) completely inhibited the chilling-induced H(2)O(2) generation and largely inhibited the chilling-induced AP capacity. Interestingly, the chilling-induced AP capacity was completely inhibited by DPI and EGTA (calcium chelator). Further investigation demonstrated that H(2)O(2) and calcium induced ethylene emission under chilling stress. Ethylene modulated the chilling-induced increase of pyruvate content and the expression of alternative oxidase genes (AOX1a and AOX1c). Taken together, these results indicate that H(2)O(2)-, calcium- and ethylene-dependent pathways are required for chilling-induced increase in AP capacity. However, only ethylene is indispensable for the activation of the AP capacity.
[Show abstract][Hide abstract] ABSTRACT: Plant development displays an exceptional plasticity and adaptability that involves the dynamic, asymmetric distribution of the phytohormone auxin. Polar auxin flow, which requires transport facilitators of the PIN family, largely contributes to the establishment and maintenance of auxin gradients and mediates multiple developmental processes. Here, we report the effects of narciclasine (NCS), an Amaryllidaceae alkaloid isolated from Narcissus tazetta bulbs, on postembryonic development of Arabidopsis roots. Arabidopsis seedlings grown on NCS showed defects in root gravitropism which correlates with a reduction in auxin transport in roots. Expressions of auxin transport genes were affected and the polar localization of PIN2 protein was altered under NCS treatment. Taken together, we propose that NCS modulates auxin transport gene expression and PIN2 localization, and thus affects auxin transport and auxin distribution necessary for postembryonic development of Arabidopsis roots.
Journal of plant physiology 07/2011; 168(11):1149-56. · 2.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Phytochrome interacting factors (PIFs) are members of a subfamily of basic helix-loop-helix transcript factors and have been proposed to act as positive regulators of hypocotyl elongation under normal condition. Here, we show that PIF1, 3, 4, 5 together play a central role in sucrose-induced hypocotyl elongation. When seedlings grown in light were transferred to darkness, exogenously applied sucrose significantly induced hypocotyl elongation in wild type Col-0, but this effect was impaired in all tested pif mutants, especially in the quadruple mutant pif1pif3pif4pif5 (pifq). Subsequent experiments showed that under various light/dark (L/D) cycle conditions sucrose still markedly induced hypocotyl elongation in Col-0, but exhibited little effects in pifq. Phytohormone gibberellins (GAs) have been proven to be required for sucrose-induced hypocotyl elongation, but application of GA(3) (an active form of GAs) was not able to rescue the impairment observed in pifq, suggesting that impairment of sucrose-induced hypocotyl elongation in pifq is not due to the reduced endogenous GAs. Interestingly, through RT-PCR assay, we found that sucrose up-regulated the transcript level of PIF1, 3, 4, 5 in darkness. Furthermore, this effect was dependent on the presence of GAs. Additionally, under continuous light condition, sucrose markedly inhibited the hypocotyl elongation in Col-0 but not in pifq, whereas exogenous GA(3) could recover the repression in Col-0 but only showed slight effect in pifq. These results collectively indicate that PIFs together with GAs control the effect of sucrose on hypocotyl elongation in Arabidopsis seedlings.
Journal of plant physiology 06/2011; 168(15):1771-9. · 2.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 3',5'-cyclic guanosine monophosphate (cGMP) is an important second messenger in plants. In the present study, roles of cGMP in salt resistance in Arabidopsis roots were investigated. Arabidopsis roots were sensitive to 100 mM NaCl treatment, displaying a great increase in electrolyte leakage and Na(+)/K(+) ratio and a decrease in gene expression of the plasma membrane (PM) H(+)-ATPase. However, application of exogenous 8Br-cGMP (an analog of cGMP), H(2)O(2) or CaCl(2) alleviated the NaCl-induced injury by maintaining a lower Na(+)/K(+) ratio and increasing the PM H(+)-ATPase gene expression. In addition, the inhibition of root elongation and seed germination under salt stress was removed by 8Br-cGMP. Further study indicated that 8Br-cGMP-induced higher NADPH levels for PM NADPH oxidase to generate H(2)O(2) by regulating glucose-6-phosphate dehydrogenase (G6PDH) activity. The effect of 8Br-cGMP and H(2)O(2) on ionic homeostasis was abolished when Ca(2+) was eliminated by glycol-bis-(2-amino ethyl ether)-N,N,N',N'-tetraacetic acid (EGTA, a Ca(2+) chelator) in Arabidopsis roots under salt stress. Taken together, cGMP could regulate H(2)O(2) accumulation in salt stress, and Ca(2+) was necessary in the cGMP-mediated signaling pathway. H(2)O(2), as the downstream component of cGMP signaling pathway, stimulated PM H(+)-ATPase gene expression. Thus, ion homeostasis was modulated for salt tolerance.
[Show abstract][Hide abstract] ABSTRACT: Nitric oxide (NO) is a key signal molecule involved in many physiological processes in plants. To study the mechanisms of exogenous NO contribution to alleviate the aluminum (Al) toxicity, roots of rice (Oryza sativa) seedlings pre-treated with sodium nitroprusside (SNP, a NO donor) were used to investigate the effect of Al in this study. Results indicated that NO alleviated the lipid peroxidation induced by Al and promoted the root elongation, whereas butylated hydroxyanisole (BHA), an efficient lipophilic antioxidant, alleviated the lipid peroxidation only. Rice seedling roots pre-treated with SNP followed by Al treatment had lower contents of pectin and hemicellulose, lower Al accumulation in root tips and cell walls, higher degree of methylation of pectin and lower wall Al-binding capacity than the roots with Al treatment only. Therefore, the decreased Al accumulation in the cell walls of rice roots is likely to be the reason for the NO-induced increase of Al tolerance in rice, and it seems that exogenous NO enhanced Al tolerance in rice roots by decreasing the contents of pectin and hemicellulose, increasing the degree of methylation of pectin, and decreasing Al accumulation in root cell walls.
[Show abstract][Hide abstract] ABSTRACT: Low temperature could significantly induce anthocyanin accumulation in the presence of light. Recently, two bZIP transcription factors LONG HYPOCOTYL 5 (HY5) and HOMOLOG OF HY5 (HYH) were identified to play an important role in the process of low temperature-induced anthocyanin accumulation. However, the mechanism by which HY5/HYH regulates anthocyanin accumulation under low temperature still remains unclear. Here, we found that the gibberellins (GAs) could decrease but PAC (endogenous GAs biosynthesis inhibitor) increase the low temperature-induced anthocyanin accumulation, implying that GAs signaling may involve in this process. Furthermore, the transcript levels of GA2ox1, encoding a major member of bioactive GAs-deactivating enzymes, were significantly up-regulated by low temperature in a HY5/HYH-dependent manner. Moreover, hy5hyh mutant was insensitive to PAC in enhancing anthocyanin accumulation under low temperature. From these data we propose that, together with HY5/HYH, GA signaling may play an important role during low temperature-induced anthocyanin accumulation.
[Show abstract][Hide abstract] ABSTRACT: Alternative respiratory pathway (AP) plays an important role in plant thermogenesis, fruit ripening and responses to environmental stresses. AP may participate in the adaptation to salt stress since salt stress increased the activity of the AP. Recently, new evidence revealed that ethylene and hydrogen peroxide (H(2)O(2)) are involved in the salt-induced increase of the AP, which plays an important role in salt tolerance in Arabidopsis callus, and ethylene may be acting downstream of H(2)O(2). Recent observations also indicated both ethylene and nitric oxide (NO) act as signaling molecules in responses to salt stress, and ethylene may be a part of the downstream signal molecular in NO action. In this addendum, a hypothetical model for NO function in regulation of H(2)O(2)- and ethylene-mediated induction of AP under salt stress is presented.
[Show abstract][Hide abstract] ABSTRACT: Nitric oxide (NO) acts as a key molecule in many physiological processes in plants. In this study, the roles of NO in mitochondrial respiration were investigated in the calli from wild-type Arabidopsis and NO associated 1 mutant (Atnoa1) which has a reduced endogenous NO level. Long-term exposure of wild-type Arabidopsis callus to sodium nitroprusside (SNP) increased mitochondrial respiration in both cytochrome and alternative pathways. In Atnoa1 callus, the capacity of both the cytochrome pathway and the alternative pathway was lower than that in wild-type callus. Further study indicated that NO enhanced the transcript abundance of genes encoding mitochondrial respiration-chain proteins as well as the protein expression of the NADH-ubiquinone reductase 75 kDa subunit and the alternative oxidase 1/2 in wild-type and Atnoa1 calli. 2-Phenyl-4,4,5,5-tetremethy-limidazolinone-1-oxyl-3-oxide (PTIO), a NO scavenger, inhibited the effects of NO in both calli. Co-incubation of callus with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a guanylate cyclase inhibitor, also abolished NO effects. The membrane-permeable cGMP analog 8Br-cGMP mimicked NO effects. Moreover, the alternative pathway showed a higher sensitivity to the cellular cGMP changes than the cytochrome pathway did in gene transcription, protein expression and O(2) consumption. Taken together, NO could enhance mitochondrial respiration in both cytochrome and alternative pathways in a cGMP-dependent manner in Arabidopsis.
[Show abstract][Hide abstract] ABSTRACT: Glucose-6-phosphate dehydrogenase (G6PDH) is important for the activation of plant resistance to environmental stresses, and ion homeostasis is the physiological foundation for living cells. In this study, we investigated G6PDH roles in modulating ion homeostasis under salt stress in Carex moorcroftii callus. G6PDH activity increased to its maximum in 100 mM NaCl treatment and decreased with further increased NaCl concentrations. K+/Na+ ratio in 100 mM NaCl treatment did not exhibit significant difference compared with the control; however, in 300 mM NaCl treatment, it decreased. Low-concentration NaCl (100 mM) stimulated plasma membrane (PM) H+-ATPase and NADPH oxidase activities as well as Na+/H+ antiporter protein expression, whereas high-concentration NaCl (300 mM) decreased their activity and expression. When G6PDH activity and expression were reduced by glycerol treatments, PM H+-ATPase and NADPH oxidase activities, Na+/H+ antiporter protein level and K+/Na+ ratio dramatically decreased. Simultaneously, NaCl-induced hydrogen peroxide (H₂O₂) accumulation was abolished. Exogenous application of H₂O₂ increased G6PDH, PM H+-ATPase and NADPH oxidase activities, Na+/H+ antiporter protein expression and K+/Na+ ratio in the control and glycerol treatments. Diphenylene iodonium (DPI), the NADPH oxidase inhibitor, which counteracted NaCl-induced H₂O₂ accumulation, decreased G6PDH, PM H+-ATPase and NADPH oxidase activities, Na+/H+ antiporter protein level and K+/Na+ ratio. Western blot result showed that G6PDH expression was stimulated by NaCl and H₂O₂, and blocked by DPI. Taken together, G6PDH is involved in H₂O₂ accumulation under salt stress. H₂O₂, as a signal, upregulated PM H+-ATPase activity and Na+/H+ antiporter protein level, which subsequently resulted in the enhanced K+/Na+ ratio. G6PDH played a central role in the process.
Physiologia Plantarum 11/2010; 141(3):239-50. · 3.66 Impact Factor