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1.
Methylviologen compounds are normally used in agronomy as herbicides. They cause an overproduction of reactive oxygen species (ROS) within chloroplasts, subjecting the plant to a severe oxidative stress. Since nitric oxide (NO) is a bioactive ROS scavenger, we analyzed its effect over some toxic processes caused by the methylviologens diquat and paraquat in potato leaves (Solanum tuberosum L. cv. Pampeana). Three NO donors, (i) sodium nitroprusside (SNP), (ii) S-nitroso-N-acetylpenicillamine, and (iii) a mixed solution of ascorbic acid and NaNO2, were able to prevent chlorophyll loss. Residual products from NO generation and decomposition failed to prevent chlorophyll decline and a specific NO scavenger, carboxy-PTIO, arrested NO-mediated chlorophyll protection. Dichlorophenyldimethylurea, an inhibitor of chloroplastic electron transport, mimicked NO-mediated chlorophyll protection. During oxidative stress, cell ion leakage to intercellular compartments occurs as an early step, leading to a special kind of programmed cell death. NO proved to specifically decrease the extent of ion leakage originated by diquat, since the protection originated by 100 microM SNP was completely arrested by carboxy-PTIO. These results suggest that NO can strongly protect plants from methylviologen damage and strengthen the evidence in favor of NO as a potent antioxidant in some situations.  相似文献   

2.
Beligni MV  Lamattina L 《Planta》2000,210(2):215-221
Seed germination, greening of etiolated plants and inhibition of hypocotyl elongation are stimulated by light, which is sensed by various types of photoreceptor. Nitric oxide (NO) has proven to be a bioactive molecule, especially in mammalian cells and, most recently, in plants. Like some phytochrome-dependent processes, many NO-mediated ones are accomplished through increases in cGMP levels. Given these similarities, we proposed that NO could take part in light-mediated events in plants. Here we show that NO promotes seed germination and de-etiolation, and inhibits hypocotyl and internode elongation, processes mediated by light. Two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine induced germination of lettuce (Lactuca sativa L. cv. Grand Rapids) seeds in conditions in which this process is dependent on light (e.g. 26 °C). This was a dose-dependent response and was arrested by addition of an NO scavenger, carboxy-PTIO. In addition, nitrite and nitrate, two NO-decomposition products were ineffective in stimulating germination. Wheat seedlings sprayed with SNP and grown in darkness contained 30–40% more chlorophyll than control seedlings. Nitric-oxide-mediated partial greening was increased by light pulses, wounding and biotic stress. Arabidopsis thaliana (L.) Heynh. (ecotype Columbia) and lettuce seedlings grown in the dark had 20%-shorter hypocotyls in NO treatments than in control ones. On the other hand, internode lengths of potato plants growing under low light intensity and sprayed with 100 μM SNP were also 20% shorter than control ones. These results implicate NO as a stimulator molecule in plant photomorphogenesis, either dependent on or independent of plant photoreceptors. Received: 27 April 1999 / Accepted: 16 June 1999  相似文献   

3.
A greenhouse hydroponic experiment was performed using Cd-sensitive (cv. Dong 17) and Cd-tolerant (Weisuobuzhi) barley seedlings to evaluate how different genotypes responded to cadmium (Cd) toxicity in the presence of sodium nitroprusside (SNP), a nitric oxide (NO) donor. Results showed that 5 μM Cd increased the accumulation of O2•−, H2O2, and malondialdehyde (MDA) but reduced plant height, chlorophyll content, net photosynthetic rate (P n), and biomass, with a much more severe response in the Cd-sensitive genotype. Antioxidant enzyme activities increased significantly under Cd stress in the roots of the tolerant genotype, whereas in leaves of the sensitive genotype, superoxide dismutase (SOD) and ascorbate peroxide (APX), especially cytosol ascorbate peroxidase (cAPX), decreased after 5–15 days Cd exposure. Moreover, Cd induces NO synthesis by stimulating nitrate reductase and nitric oxide synthetase-like enzymes in roots/leaves. A Cd-induced NO transient increase in roots of the Cd-tolerant genotype might partly contribute to its Cd tolerance. Exogenous NO dramatically alleviated Cd toxicity, markedly diminished Cd-induced reactive oxygen species (ROS) and MDA accumulation, ameliorated Cd-induced damage to leaf/root ultrastructure, and increased chlorophyll content and P n. External NO counteracted the pattern of alterations in certain antioxidant enzymes induced by Cd; for example, it significantly elevated the depressed SOD, APX, and catalase (CAT) activities in the Cd-sensitive genotype after 10- and 15-day treatments. Furthermore, NO significantly increased stromal APX and Mn-SOD activities in both genotypes and upregulated Cd-induced decrease in cAPX activity and gene expression of root/leaf cAPX and leaf CAT1 in the Cd-sensitive genotype. These data suggest that under Cd stress, NO, as a potent antioxidant, protects barley seedlings against oxidative damage by directly and indirectly scavenging ROS and helps to maintain stability and integrity of the subcellular structure.  相似文献   

4.
During January 1989, phytoplankton biomass and species composition were studied in a north / south transect at the Weddell / Scotia Confluence (47°W), between 57° and 61°30′S. Results showed a diatom bloom in the Scotia Sea (chlorophyll a 1.9 μg l−1, particulate organic carbon 239 μg l−1), dominated by Fragilariopsis cylindrus, Dactyliosolen antarcticus and Chaetoceros dichaeta. Low chlorophyll a / phaeopigments ratios (about 1.4) and silicate concentrations (15 μmol l−1) suggested that this was an advanced bloom phase, probably linked to high grazing pressure. Minimum chlorophyll a values of 0.1–0.2 μg l−1 and particulate organic carbon 46 μg l−1 were found at the Weddell / Scotia Front and in a subsurface layer of the Weddell Sea Water. In the southern part of the transect (61°30′S), in the Weddell Sea, a second surface maximum was found (chlorophyll a 0.9 μg l−1, particulate organic carbon 120 μg l−1), but with a different species composition, with Cryptomonas sp. dominant. Our results show a succession within the diatom community in the Weddell / Scotia Confluence Waters when comparing the three EPOS legs. In the Weddell Sea from spring to summer, nanoflagellates, with only a minor contribution from diatoms, persist over a long period with little change in the community structure. We suggest that the frontal system, together with the receding ice edge and the grazing pressure of either krill or protozooplankton, are mainly responsible for the phytoplankton distribution patterns found. Received: 3 July 1996 / Accepted: 3 November 1996  相似文献   

5.
The interaction between Phytophthora infestans (Mont.) de Bary and Solanum was examined cytologically using a diverse set of wild Solanum species and potato (S. tuberosum L.) cultivars with various levels of resistance to late blight. In wild Solanum species, in potato cultivars carrying known resistance (R) genes and in nonhosts the major defense reaction appeared to be the hypersensitive response (HR). In fully resistant Solanum species and nonhosts, the HR was fast and occurred within 22 h. This resulted in the death of one to three cells. In partially resistant clones, the HR was induced between 16 and 46 h, and resulted in HR lesions consisting of five or more dead cells, from which hyphae were occasionally able to escape to establish a biotrophic interaction. These results demonstrate the quantitative nature of the resistance to P. infestans. The effectiveness of the HR in restricting growth of the pathogen differed considerably between clones and correlated with resistance levels. Other responses associated with the defense reaction were deposition of callose and extracellular globules containing phenolic compounds. These globules were deposited near cells showing the HR, and may function in cell wall strengthening. Received: 22 April 1999 / Accepted: 4 November 1999  相似文献   

6.
 Efficacy of silver thiosulfate (STS) in reducing ethylene-induced culture abnormalities during minimal growth conservation of microplants was studied in seven potato (Solanum tuberosum L.) genotypes. Different concentrations of STS (0, 1.5, 3.0, 4.5, 6.0, 7.5 and 9.0 μg ml–1) were tested in minimal growth medium based on MS medium supplemented with 20 g l–1 mannitol and 40 g l–1 sucrose. STS improved the microplant growth and reduced the culture abnormalities during prolonged maintenance of potato shoot cultures in vitro. The beneficial effect of STS was most prominent for number of green leaves per microplant and leaf senescence. After 16 months of storage, desirable microplant growth was observed in cultures conserved in medium containing 6.0–9.0 μg ml–1 STS. The profile of the peroxidase isozymes of conserved cultures did not show any apparent genetic variation due to the presence of STS in the conservation medium. Received: 2 September 1998 / Revision received: 20 November 1998 / Accepted: 12 December 1998  相似文献   

7.
 Routine cryopreservation of shoot tips from sweet potato [Ipomoea batatas (L.) Lam] has been hampered by their survival variability after cryogenic exposure. We examined the effects of light conditions on stock plants, sucrose preculture and cryoprotectant loading on survival after vitrification using PVS2 solution. The survival of vitrified sweet potato shoot tips cooled to approximately –208  °C was increased by preculturing with 0.3 M sucrose for 24 h at 22  °C. Survival was also enhanced by excising shoot tips immediately after the 8-h dark photoperiod. The best survival after cryogenic exposure was obtained using 2 M glycerol +0.4 M sucrose for 1 h at 22  °C followed by dehydration with PVS2 for 16 min at 22  °C. Rapid cooling was used and achieved by the immersion of foil strips into partially solidified nitrogen. Successfully vitrified and warmed shoot tips directly developed shoots on a medium containing 1 μM NAA, 0.5 μM BA and 0.1 μM kinetin with only minimum callus formation. Shoot formation occurred in all surviving shoot tips. This procedure shows promise for cryopreserving sweet potato shoot tips. Received: 2 March 1999 / Revision received: 21 September 1999 / Accepted: 29 September 1999  相似文献   

8.
Eighteen metals were estimated in the scalp hair samples from cancer patients (n = 111) and normal donors (n = 113). Nitric acid–perchloric acid wet digestion procedure was used for the quantification of the selected metals by flame atomic absorption spectrophotometry. In the scalp hair of cancer patients, highest average levels were found for Ca (861 μg/g), followed by Na (672 μg/g), Zn (411 μg/g), Mg (348 μg/g), Fe (154 μg/g), Sr (129 μg/g), and K (116 μg/g), whereas in comparison, the dominant metals in the scalp hair of normal donors were Ca (568 μg/g), Zn (177 μg/g), Mg (154 μg/g), Fe (110 μg/g), and Na (103 μg/g). The concentrations of Ca, Cd, Co, Cr, Fe, K, Mg, Mn, Na, Ni, Pb, Sb, Sr, and Zn were notably higher in the hair of cancer patients as compared with normal donors, which may lead to a number of physiological disorders. Strong positive correlations were found in Mn–Pb (0.83), Cd–Cr (0.82), Cd–Li (0.57), Fe–Pb (0.56), and Fe–Mn (0.55) in the hair of cancer patients whereas Na–Cd, Li–Cr, Li–Co, Co–Cd, Li–Cd, Na–Co, Na–Li, Ca–Mg and Na–Cr exhibited strong relationships (r > 0.50) in the hair of normal donors. Principal Component Analysis (PCA) of the data revealed seven PCs, both for cancer patients and normal donors, but with significantly different loadings. Cluster Analysis (CA) was also used to support the PCA results. The study evidenced significantly different pattern of metal distribution in the hair of cancer patients in comparison with normal donors. The role of trace metals in carcinogenesis was also discussed.  相似文献   

9.
In this article, the effects of increased light intensities on antioxidant metabolism during ex vitro establishment of Ulmus minor micropropagated plants are investigated. Three month old in vitro plants were acclimatized to ex vitro conditions in a climate chamber with two different light intensities, 200 μmol m−2 s−1 (high light, HL) and 100 μmol m−2 s−1 (low light, LL) during 40 days. Immediately after ex vitro transfer, the increase of both malondialdehyde (MDA) and electrolyte leakage in persistent leaves is indicative of oxidative stress. As the acclimatization continues, an upregulation of the superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) enzyme activities were also observed. Simultaneously, MDA content and membrane permeability stabilized, suggesting that the antioxidant enzymes decrease the deleterious effects of reactive oxygen species (ROS) generation. Unexpectedly, newly formed leaves presented a different pattern of antioxidative profile, with high levels of MDA and membrane leakage and low antioxidant enzyme activity. Despite these differences, both leaf types looked healthy (e.g. greenish, with no necrotic spots) during the whole acclimatization period. The results indicate that micropropagated U. minor plantlets develop an antioxidant enzyme system after ex vitro transfer and that, in general, LL treatment leads to lower oxidative stress. Moreover, new leaves tolerate higher levels of ROS without the need to activate the antioxidative pathway, which suggests that the environment at which leaves are exposed during its formation determinate their ability to tolerate ROS.  相似文献   

10.
During the course of cancer radiation treatment, normal skin invariably suffers from the cytotoxic effects of γ-radiation and reactive oxygen species (ROS), which are generated from the interaction between radiation and the water molecules in cells. The present study was designed to investigate the radioprotective role of α-lipoic acid (LA), an antioxidant on murine skin fibroblasts exposed to a single dose of 2, 4, 6, or 8Gy γ-radiation. Irradiation of fibroblasts significantly increased ROS, nitric oxide, and lipid peroxidation (P < 0.001); all of these factors substantially decreased with 100 μM LA treatment. Hydroxyl radical (OH) production from 8Gy irradiated fibroblasts was measured directly by electron spin resonance using spin-trapping techniques. LA was found to inhibit OH production at 100-μM concentrations. Dose-dependent depletion of antioxidants, such as catalase and glutathione reductase, was observed in irradiated fibroblasts (P < 0.001), along with increased superoxide dismutase (P < 0.001). LA treatment restored antioxidant levels. Concentration of the pro-inflammatory cytokine IL-1β was significantly reduced in irradiated fibroblasts when treated with LA. MTT and lactate dehydrogenase assays demonstrated that LA treatment reduced cell injury and protected cells against irradiation-induced cytotoxicity. Thus, we conclude that results are encouraging and need further experiments to demonstrate a possible benefit in cancer patients and the reduction of harmful effects of radiation therapy.  相似文献   

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