Alleviated Growth Inhibition Research Articles

Nitric oxide participates in waterlogging tolerance through enhanced adventitious root formation in the euhalophyte Suaeda salsa.

The interactions of NO and other signalling molecules contribute to adventitious root formation in many plant species. To our knowledge, the role of NO in the adventitious root formation of plants subjected to waterlogging are as yet unknown. Populations of Suaeda salsa L., a C3 euhalophytic plant, from inland saline sites develop several adventitious roots in response to waterlogging. The NO donor sodium nitroprusside (SNP) and the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-1-oxyl-3-oxide (cPTIO) were applied to S. salsa seedlings to examine the effects of NO on flooding tolerance and its possible mechanism. SNP alleviated growth inhibition and increased adventitious root formation, endogenous NO levels and adventitious root cell integrity in S. salsa subjected to waterlogging. These SNP-mediated effects were prevented by the extra application of cPTIO. SNP treatment decreased nitrate reductase activity but increased nitric oxide synthase (NOS) activity in adventitious roots. These results suggest that in S. salsa, NO participates in waterlogging tolerance by enhancing adventitious root formation and that NO generation is associated with the NOS-associated pathway.

Exogenous hydrogen sulfide alleviates salt stress in wheat seedlings by decreasing Na+ content

Hydrogen sulfide (H2S) is an important gaseous molecule in a number of plant developmental processes and stress responses. Triticum aestivum L. (LM 15) is a salt-sensitive wheat cultivar that was used here to examine the effect of exogenous H2S on seedling growth, Na+ and K+ concentration, and Na+ transportation under NaCl stress. The results showed that pretreatment with 0.05 mM sodium hydrosulfide (NaHS), a H2S donor, for 12 h significantly alleviated the growth inhibition of wheat seedlings under 100 mM NaCl. In addition, pretreatment with NaHS decreased the Na+ concentration, Na+/K+ ratio, the selective absorption capacity for K+ over Na+ and Na+ efflux ratio, and increased the selective transport capacity for K+ over Na+ under salt stress. Additional experiments with CaCl2 (an inhibitor of nonselective cation channels—NSCCs), TEA+ (an inhibitor of low affinity K+ transporter) or amiloride (an inhibitor of salt overly sensitive 1—SOS1) showed that NSCCs and SOS1 were the major pathways by which H2S reduced Na+ concentration in wheat seedlings. These results showed that exogenous H2S alleviated growth inhibition by maintaining a lower Na+ concentration in wheat seedlings under NaCl stress via the regulation of NSCCs and SOS1 pathways.

Effects of silicon (Si) on growth, quality and ionic homeostasis of aloe under salt stress

Abstract The physiological characteristics of aloe irrigated with brackish water and the relationship with ameliorative effects of silicon (Si) nutrition were studied. Results of cultivation and analysis showed that 2.0 mmol · L− 1 added Si significantly alleviated growth inhibition and quality reduction of aloe under 100 mmol · L− 1 NaCl stress; added Si significantly reduced Na+ content while increased K+ content and K+/Na+ ratio of salt stressed aloe plant, especially absorption and translocation selectivity of aloe root to K+ and Na+ were promoted, and ion homeostasis of aloe plant was kept well. Results of cross-sectional X-ray energy dispersive spectrum microanalysis of aloe root and leaf further confirmed the above findings. One of the mechanisms of silicon was its improvement to activity of plasma membrane H+-ATPase, tonoplast membrane H+-ATPase and H+-pyrophosphates of aloe root under salt stress.

Gallium induces the production of virulence factors inPseudomonas aeruginosa

The novel antimicrobial gallium is a nonredox iron III analogue with bacteriostatic and bactericidal properties, effective for the treatment of Pseudomonas aeruginosa in vitro and in vivo in mouse and rabbit infection models. It interferes with iron metabolism, transport, and presumably its homeostasis. As gallium exerts its antimicrobial effects by competing with iron, we hypothesized that it ultimately will lead cells to an iron deficiency status. As iron deficiency promotes the expression of virulence factors in vitro and promotes the pathogenicity of P. aeruginosa in animal models, it is anticipated that treatment with gallium will also promote the production of virulence factors. To test this hypothesis, the reference strain PA14 and two clinical isolates from patients with cystic fibrosis were exposed to gallium, and their production of pyocyanin, rhamnolipids, elastase, alkaline protease, alginate, pyoverdine, and biofilm was determined. Gallium treatment induced the production of all the virulence factors tested in the three strains except for pyoverdine. In addition, as the Ga-induced virulence factors are quorum sensing controlled, co-administration of Ga and the quorum quencher brominated furanone C-30 was assayed, and it was found that C-30 alleviated growth inhibition from gallium. Hence, adding both C-30 and gallium may be more effective in the treatment of P. aeruginosa infections.

Effects of lanthanum nitrate on growth and chlorophyll fluorescence characteristics of Alternanthera philoxeroides under perchlorate stress

To investigate the effects of exogenous lanthanum (La) on Alternanthera philoxeroides (Mart.) Griseb under perchlorate stress, changes in the growth and physiological parameters were investigated in solution culture experiments under controlled conditions. Different concentrations of La (NO3)(3) were used in our study. It was shown that 0.1 and 0.5 mg/L La3+ alleviated the inhibition effect of perchlorate on A. philoxeroides, including relative growth yield, dry weight of different organs, leaf area and root activity. And La3+ prevented decline in the relative chlorophyll content and chlorophyll fluorescence parameters including F-v/Fm,Fv'/F-m',Phi(PSII) and ETR induced by perchlorate stress. Moreover, 0.5 mg/L La3+ showed an optimal mitigative effect, while excess La3+ (5.0 mg/L) led to synergistic effect on stress. Correlation analysis revealed a significant positive relationship between growth indexes and the chlorophyll fluorescence parameters, root activity and relative chlorophyll content (p<0.05). The results suggested that appropriate concentration of La3+ could effectively alleviate growth inhibition and injury of A. philoxeroides caused by perchlorate stress, and the mitigative effect of La3+ might be achieved by improving root activity, maintaining chlorophyll content and promoting photochemical efficiency of photosystem II of A. philoxeroides under perchlorate stress.

Exogenous salicylic acid enhances wheat drought tolerance by influence on the expression of genes related to ascorbate-glutathione cycle

Treatment with 0.5 mM salicylic acid (SA) significantly alleviated growth inhibition induced by drought in wheat seedlings, manifested by less decreassed fresh mass, dry mass, plant height, root length, and less increased lipid peroxidation. Under drought stress, SA significantly increased the content of ascorbate (ASA) and glutathione (GSH). We determined the full-length cDNA sequences of genes encoding the glutathione-S-transferase 1 (GST1) and 2 (GST2) and we also measured the transcription of eight genes related to ASA-GSH cycle. The results indicated that exogenous SA significantly enhanced the transcription of GST1, GST2, glutathione reductase (GR), and monodehydroascorbate reductase (MDHAR) genes during almost the entire drought period, but only increased those of dehydroascorbate reductase (DHAR) at 12 h, glutathione peroxidase (GPX1) at 48 h, phospholipid hydroperoxide glutathione peroxidase (GPX2) at 12 and 24 h, and glutathione synthetase (GSHS) at 12, 24, and 48 h. This implies that SA alleviates the detrimental effects of drought stress on wheat seedling growth by influencing the ASA-GSH cycle.

Corynebacterium glutamicum harbours a molybdenum cofactor-dependent formate dehydrogenase which alleviates growth inhibition in the presence of formate

Here, we show that Corynebacterium glutamicum ATCC 13032 co-metabolizes formate when it is grown with glucose as the carbon and energy source. CO(2) measurements during bioreactor cultivation and use of (13)C-labelled formate demonstrated that formate is almost completely oxidized to CO(2). The deletion of fdhF (cg0618), annotated as formate dehydrogenase (FDH) and located in a cluster of genes conserved in the family Corynebacteriaceae, prevented formate utilization. Similarly, deletion of fdhD (cg0616) resulted in the inability to metabolize formate and deletion of cg0617 markedly reduced formate utilization. These results illustrated that all three gene products are required for FDH activity. Growth studies with molybdate and tungstate indicated that the FDH from C. glutamicum ATCC 13032 is a molybdenum-dependent enzyme. The presence of 100 mM formate caused a 25 % lowered growth rate during cultivation of C. glutamicum ATCC 13032 wild-type in glucose minimal medium. This inhibitory effect was increased in the strains lacking FDH activity. Our data demonstrate that C. glutamicum ATCC 13032 possesses an FDH with a currently unknown electron acceptor. The presence of the FDH might help the soil bacterium C. glutamicum ATCC 13032 to alleviate growth retardation caused by formate, which is ubiquitously present in the environment.

Exogenous proline and trehalose promote recovery of rice seedlings from salt-stress and differentially modulate antioxidant enzymes and expression of related genes

Proline (Pro) and Trehalose (Tre) function as compatible solutes and are upregulated in plants under abiotic stress. They play an osmoprotective role in physiological responses, enabling the plants to better tolerate the adverse effects of abiotic stress. We investigated the effect of exogenous Pro and Tre (10 mM) in seedlings of Thai aromatic rice (cv. KDML105; salt-sensitive) during salt stress and subsequent recovery. Salt stress (S, NaCl) resulted in growth reduction, increase in the Na(+)/K(+) ratio, increase in Pro level and up-regulation of Pro synthesis genes (pyrroline-5-carboxylatesynthetase, P5CS; pyrroline-5-carboxylate reductase, P5CR) as well as accumulation of hydrogen peroxide (H(2)O(2)), increased activity of antioxidative enzymes (superoxide dismutase, SOD; peroxidase, POX; ascorbate peroxidase, APX; catalase, CAT) and transcript up-regulation of genes encoding antioxidant enzymes (Cu/ZnSOD, MnSOD, CytAPX, CatC). Under salt stress, exogenous Pro (PS; Pro+NaCl) reduced the Na(+)/K(+) ratio, further increased endogenous Pro and transcript levels of P5CS and P5CR, but decreased the activity of the four antioxidant enzymes. The transcription of genes encoding several antioxidant enzymes was upregulated. Exogenous Tre (TS; Tre+NaCl) also reduced the Na(+)/K(+) ratio and strongly decreased endogenous Pro. Transcription of P5CS and P5CR was upregulated, the activities of SOD and POX decreased, the activity of APX increased and the transcription of all antioxidant enzyme genes upregulated. Although exogenous osmoprotectants did not alleviate growth inhibition during salt stress, they exhibited a pronounced beneficial effect during recovery period showing higher percentage of growth recovery in PS (162.38%) and TS (98.43%) compared with S (3.68%). During recovery, plants treated with PS showed a much greater reduction in endogenous Pro than NaCl-treated (S) or Tre-treated plants (TS). Increase in CAT activity was most related to significant reduction in H(2)O(2), particularly in the case of PS-treated plants. Advantageous effects of Pro were also associated with increase in APX activity during recovery.

Involvement of the putative Ca2+-permeable mechanosensitive channels, NtMCA1 and NtMCA2, in Ca2+ uptake, Ca2+-dependent cell proliferation and mechanical stress-induced gene expression in tobacco (Nicotiana tabacum) BY-2 cells

To gain insight into the cellular functions of the mid1-complementing activity (MCA) family proteins, encoding putative Ca²⁺-permeable mechanosensitive channels, we isolated two MCA homologs of tobacco (Nicotiana tabacum) BY-2 cells, named NtMCA1 and NtMCA2. NtMCA1 and NtMCA2 partially complemented the lethality and Ca²⁺ uptake defects of yeast mutants lacking mechanosensitive Ca²⁺ channel components. Furthermore, in yeast cells overexpressing NtMCA1 and NtMCA2, the hypo-osmotic shock-induced Ca²⁺ influx was enhanced. Overexpression of NtMCA1 or NtMCA2 in BY-2 cells enhanced Ca²⁺ uptake, and significantly alleviated growth inhibition under Ca²⁺ limitation. NtMCA1-overexpressing BY-2 cells showed higher sensitivity to hypo-osmotic shock than control cells, and induced the expression of the touch-inducible gene, NtERF4. We found that both NtMCA1-GFP and NtMCA2-GFP were localized at the plasma membrane and its interface with the cell wall, Hechtian strands, and at the cell plate and perinuclear vesicles of dividing cells. NtMCA2 transcript levels fluctuated during the cell cycle and were highest at the G1 phase. These results suggest that NtMCA1 and NtMCA2 play roles in Ca²⁺-dependent cell proliferation and mechanical stress-induced gene expression in BY-2 cells, by regulating the Ca²⁺ influx through the plasma membrane.

Calcium protects roots of Sedum alfredii H. against cadmium-induced oxidative stress

Sedum alfredii is a well-known Cd (cadmium) hyperaccumulator native to China. The impacts of exogenous Ca on Cd-induced oxidative stress and antioxidant systems in roots of S. alfredii were investigated by using cellular and biochemical approaches. Supplementation of the medium with higher Ca levels resulted in alleviated growth inhibition and decreased Cd concentration, as well as increased Ca concentration in roots. Cadmium induced lipid peroxidation and loss of plasma membrane integrity, reactive oxygen species overproduction, as well as ultrastructural changes of root cells were largely reversed by Ca supplementation in the medium. Calcium application significantly altered the Cd effects on antioxidant enzymes and non-enzyme antioxidants (non-protein thiols), and significantly increased glutathione (GSH) biosynthesis. The results suggest that Ca is able to protect the roots of S. alfredii against Cd toxicity by restoration of Cd-displaced Ca, alleviation of the metal induced oxidative stress, as well as promotion of GSH biosynthesis.

Cinnamic acid pretreatment mitigates chilling stress of cucumber leaves through altering antioxidant enzyme activity

To elucidate the physiological mechanism of chilling stress mitigated by cinnamic acid (CA) pretreatment, a cucumber variety (Cucumis sativus cv. Jinchun no. 4) was pretreated with 50 μM CA for 2d and was then cultivated at two temperatures (15/8 and 25/18 °C) for 1d. We investigated whether exogenous CA could protect cucumber plantlets from chilling stress (15/8 °C) and examined whether the protective effect was associated with the regulation of antioxidant enzymes and lipid peroxidation. At 2d, exogenous CA did not influence plant growth, but induced the activities of some antioxidant enzymes, including superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), guaiacol peroxidase (GPX, EC 1.11.1.7), glutathione peroxidase (GSH-Px, EC 1.6.4.2) and ascorbate peroxidase (APX, EC 1.11.1.11) in cucumber leaves, and it also elevated the contents of reduced glutathione (GSH) and ascorbate (AsA). When CA was rinsed and the CA-pretreated seedlings were exposed to different temperatures, the antioxidant activities in leaves at 3d had undergone additional change. Chilling increased the activities of CAT, GSH-PX, APX, GSH and AsA in leaves, but the combination of CA pretreatment and chilling enhanced the antioxidant activities even more. Moreover, chilling inhibited plant growth and increased the contents of malonaldehyde (MDA), superoxide radical (O₂⁻) and hydrogen peroxide (H₂O₂) in cucumber leaves, and the stress resulted in 87.5% of the second leaves being withered. When CA pretreatment was combined with the chilling stress, we observed alleviated growth inhibition and decreased contents of MDA, H₂O₂ and O₂⁻ in comparison to non-pretreated stressed plants, and found that the withered leaves occurred at a rate of 25.0%. We propose that CA pretreatment increases antioxidant enzyme activities in chilling-stressed leaves and decreases lipid peroxidation to some extent, enhancing the tolerance of cucumber leaves to chilling stress.

Modulation of Exogenous Glutathione in Phytochelatins and Photosynthetic Performance Against Cd Stress in the Two Rice Genotypes Differing in Cd Tolerance

Greenhouse hydroponic experiments were conducted using Cd-sensitive (Xiushui63) and tolerant (Bing97252) rice genotypes to evaluate genotypic differences in response of photosynthesis and phytochelatins to Cd toxicity in the presence of exogenous glutathione (GSH). Plant height, chlorophyll content, net photosynthetic rate (Pn), and biomass decreased in 5 and 50μM Cd treatments, and Cd-sensitive genotype showed more severe reduction than the tolerant one. Cadmium stress caused decrease in maximal photochemical efficiency of PSII (Fv/Fm) and effective PSII quantum yield [Y(II)] and increase in quantum yield of regulated energy dissipation [Y(NPQ)], with changes in Cd-sensitive genotype being more evident. Cadmium-induced phytochelatins (PCs), GSH, and cysteine accumulation was observed in roots of both genotypes, with markedly higher level in PCs and GSH on day5 in Bing97252 compared with that measured in Xiushui63. Exogenous GSH significantly alleviated growth inhibition in Xiushui63 under 5μM Cd and in both genotypes in 50μM Cd. External GSH significantly increased chlorophyll content, Pn, Fv/Fm, and Y(II) of plants exposed to Cd, but decreased Y(NPQ) and the coefficient of non-photochemical quenching (qN). GSH addition significantly increased root GSH content in plants under Cd exposure (except day5 of 50μM Cd) and induced up-regulation in PCs of 5μM-Cd-treated Bing97252 throughout the 15-day and Xiushui63 of 5-day exposure. The results suggest that genotypic difference in the tolerance to Cd stress was positively linked to the capacity in elevation of GSH and PCs, and that alleviation of Cd toxicity by GSH is related to significant improvement in chlorophyll content, photosynthetic performance, and root GSH levels.

Applying Spermidine for Differential Responses of Antioxidant Enzymes in Cucumber Subjected to Short-term Salinity

To examine whether spermidine (SPD) modifies plant antioxidant enzyme expression in response to short-term salt stress, cucumber (Cucumis sativus) seedlings were treated with NaCl in the presence or absence of SPD for 3 days. Compared with untreated control plants, free radical production and malondialdehyde content in leaves and roots increased significantly and plant growth was suppressed under 50 mm NaCl stress. Exogenous SPD sprayed on leaves at a concentration of 1 mm alleviated salinity-mediated growth reduction. Salt stress caused a consistent increase in soluble protein content, as well as peroxidase (POD) and superoxide dismutase (SOD) activities in cucumber seedlings. By native polyacrylamide gel electrophoresis, five POD isozymes were detected in cucumber seedling leaves, and seven in roots. We detected five SOD isozymes in leaves and four in roots, and two catalase (CAT) isozymes in leaves and two in roots. Our results indicate that salt stress induced the expression of POD and SOD isozymes in cucumber seedlings, but inhibited the expression of CAT isozymes in roots. Application of exogenous SPD further increased POD and SOD expression and activity, and led to the differential regulation of CAT in leaves and roots. These data show that antioxidant enzymes, especially POD and SOD, appear to protect cucumber seedlings against stress-related damage, and they appear to function as the molecular mechanisms underlying the response of cucumber seedlings to salinity. Moreover, SPD has potential to scavenge directly free radical and to alleviate growth inhibition and promote the activity and expression of antioxidant system enzymes in cucumber seedlings under short-term salt stress.

Salt affects plant Cd-stress responses by modulating growth and Cd accumulation

Cadmium contamination is a serious environmental problem for modern agriculture and human health. Salinity affects plant growth and development, and interactions between salt and cadmium have been reported. However, the molecular mechanisms of salinity-cadmium interactions are not fully understood. Here, we show that a low concentration of salt alleviates Cd-induced growth inhibition and increases Cd accumulation in Arabidopsis thaliana. Supplementation with low concentrations of salt reduced the reactive oxygen species level in Cd-stressed roots by increasing the contents of proline and glutathione and down-regulating the expression of RCD1, thereby protecting the plasma membrane integrity of roots under cadmium stress. Salt supplementation substantially reduces the Cd-induced elevation of IAA oxidase activity, thereby maintaining auxin levels in Cd-stressed plants, as indicated by DR5::GUS expression. Salt supply increased Cd absorption in roots and increased Cd accumulation in leaves, implying that salt enhances both Cd uptake in roots and the root-to-shoot translocation of Cd. The elevated Cd accumulation in plants in response to salt was found to be correlated with the elevated levels of phytochelatin the expression of heavy metal transporters AtHMA1-4, especially AtHMA4. Salt alleviated growth inhibition caused by Cd and increased Cd accumulation also was observed in Cd accumulator Solanum nigrum.

Exogenous Salicylic Acid Alleviates Growth Inhibition and Oxidative Stress Induced by Hypoxia Stress in Malus robusta Rehd

Salicylic acid (SA) as a signal molecule mediates many biotic and environmental stress-induced physiologic responses in plants. In this study we investigated the role of SA in regulating growth and oxidative stress in Malus robusta Rehd under both normoxic and hypoxic conditions. Hypoxia stress inhibited plant growth and dramatically reduced biomass. Addition of SA significantly alleviated the plant growth inhibition. The amounts of superoxide radicals (O2 −) and hydrogen peroxide (H2O2) significantly increased in leaves of the plants exposed to hypoxia stress and resulted in oxidative stress, which was indicated by accumulated concentration of malondialdehyde (MDA) and electrolyte leakage. Addition of SA significantly decreased the level of O2 −, electrolyte leakage, and lipid peroxidation and enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) under hypoxia stress. As important antioxidants, ascorbate (AsA) and glutathione (GSH) contents in the plant leaves were slightly increased by SA treatment compared to hypoxia stress treatment alone. It was concluded that SA could alleviate the detrimental effects of hypoxia stress on plant growth and of oxidative stress by enhancing the antioxidant defense system in leaves of M. robusta Rehd.

Salicylic acid alleviates growth inhibition and oxidative stress caused by zucchini yellow mosaic virus infection in Cucurbita pepo leaves

The effects of zucchini yellow mosaic virus (ZYMV) infection and pretreatments with salicylic acid (SA) on biomass accumulation of pumpkin (Cucurbita pepo cv. Eskandarani) were investigated. The response of photosynthesis, transpiration and the activities of antioxidant enzymes in leaves was also considered. Significant reductions in growth parameters (i.e. leaf area, biomass and shoot height), photosynthesis and chlorophyll a and b content were detected in ZYMV-infected leaves in comparison to healthy controls. Antioxidant enzyme activities were increased up to 3-fold for peroxidase (POD), 2-fold for ascorbate peroxidase (APX) and catalase (CAT) activities and 1.3-fold for SOD activity by virus infection. ZYMV infection also caused increases in H2O2 and malondialdehyde (MDA) contents. These results suggest that ZYMV infection causes oxidative stress in pumpkin leaves leading to the development of epidemiological symptoms. Interestingly, spraying pumpkin leaves with SA led to recovery from the undesirable effects of ZYMV infection. Leaves treated with 100 μM SA three days before inoculation had the appearance of healthy leaves. No distinct disease symptoms were observed on the leaves treated with 100 μM SA followed by inoculation with ZYMV. In non-infected plants, SA application increased activities of POD and superoxide dismutase (SOD) and inhibited APX and CAT activities. In contrast, SA treatment followed by ZYMV inoculation stimulated SOD activity and inhibited activities of POD, APX and CAT. In addition, MDA displayed an inverse relation, indicating inhibition of lipid peroxidation in cells under SA treatment. It is suggested that the role of SA in inducing plant defense mechanisms against ZYMV infection might have occurred through the SA-antioxidant system. Such interference might occur through inhibition or activation of some antioxidant enzymes, reduction of lipid peroxidation and induction of H2O2 accumulation following SA application.

Sulfur Alleviates Growth Inhibition and Oxidative Stress Caused by Cadmium Toxicity in Rice

ABSTRACT A hydroponic experiment was conducted to investigate the effect of sulfur (S) on growth inhibition and oxidative stress caused by Cd2+ toxicity, using two rice cultivars with different grain Cd2+ content. Treatments consisted of factorial arrangement of three S levels (0.2, 0.4, and 0.8 mmol), two cadmium (Cd) levels (0 and 1 μ mol), and two rice cultivars (‘Bing 97252,’ a cultivar with low grain Cd2+ content, and ‘Xiushui 63,’ a cultivar with high grain Cd2+ content). The results showed that Cd2+ addition in the medium generally increased Cd2+ and malondialdehyde (MDA) content in both roots and shoots; the increases were more pronounced in ‘Xuishui 63’ than in ‘Bing 97252.’ Dramatic reductions in growth parameters, including plant height, root and shoot weight, tillers per plant, chlorophyll content, and net photosynthetic rate were found in the plants exposed to Cd stress relative to the plants without Cd2+ treatment. ‘Xiushui 63’ showed more sensitivity than ‘Bing 97252’ under Cd2+ exposure. In comparison with the lower S level (0.2 mmol), the higher S levels (0.4 and 0.6 mmol) helped alleviate Cd toxicity, characterized by a significant increase in growth parameters, and a decrease in Cd2+ and MDA content in both roots and shoots. In addition, superoxide dismutase (SOD) activity in the plants varied among tissues, cultivars, and Cd treatments. High Cd2+ and MDA content was consistently accompanied by higher SOD activity, and higher S levels caused a marked increase in glutathione content and a reduction in SOD activity, indicating a positive effect of S in alleviating oxidative stress.

Zinc alleviates growth inhibition and oxidative stress caused by cadmium in rice

AbstractA hydroponic experiment with two rice cultivars differing in cadmium (Cd) tolerance was conducted to investigate the alleviating effect of zinc (Zn) on growth inhibition and oxidative stress caused by Cd. Treatments consisted of all combinations of two Zn concentrations (0.2 and 1 μM), three Cd concentrations (0, 1, and 5 μM), and two rice cultivars (Bing 97252, Cd‐tolerant; Xiushui 63, Cd‐sensitive). Cd toxicity caused a dramatic reduction in plant height and biomass, chlorophyll concentration and photosynthetic rate, and an increase in Cd concentration in both roots and shoots, malondialdehyde (MDA) concentration, and superoxide dismutase (SOD) and peroxidase (POD) activities in shoots. The response of all these parameters was much larger for Xiushui 63 than for Bing 97252. Addition of Zn to the medium solution alleviated Cd toxicity, which was reflected in a significant increase in plant height, biomass, chlorophyll concentration, and photosynthetic rate, and a marked decrease in MDA concentration and activity of anti‐oxidative enzymes. However, it was noted that Zn increased shoot Cd concentration at higher Cd supply, probably due to the enhancement of Cd translocation from roots to shoots. Therefore, further studies are necessary to determine the effect of Zn supply on Cd translocation from vegetative organs to grains or grain Cd accumulation before Zn fertilizer is applied to Cd‐contaminated soils to alleviate Cd toxicity in rice.

The metabolic imbalance underlying lesion formation in Arabidopsis thaliana overexpressing farnesyl diphosphate synthase (isoform�1S) leads to oxidative stress and is triggered by the developmental decline of endogenous HMGR activity

Overexpression of Arabidopsis thaliana farnesyl diphosphate synthase isoform 1S (FPS1S) in transgenic A. thaliana (L.) Heynh. leads to necrotic lesion formation in leaves in planta and to premature senescence in detached leaves [A. Masferrer et al. (2002) Plant J 30:123-132]. Here we report that leaves of plants overexpressing FPS1S with symptoms of necrosis show increased H2O2 formation and induction of both the pathogenesis-related 1 (PR-1) and the alternative oxidase 1a (AOX1a) genes. These findings indicate that plants overexpressing FPS1S should be considered as lesion-mimic mutants and lead us to propose that H2O2 is the main inducing agent of necrosis in these plants. The onset of necrosis appears in a developmentally regulated manner that correlates with the developmental decline of endogenous 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) activity. Accordingly, constitutive overexpression of HMGR in plants overexpressing FPS1S prevents both necrosis and premature senescence. These observations demonstrate that both phenotypes are due to an insufficient supply of mevalonic acid and support the notion that the metabolic imbalance associated with FPS1S overexpression is, in fact, triggered by the developmental decline of HMGR activity. We also show that overexpression of FPS1S alleviates growth inhibition caused by overexpression of the catalytic domain of isoform HMGR1S. Overall, our results reinforce the view that the levels of specific intermediates of the mevalonic acid pathway must be strictly controlled, particularly those located at branch-point positions, in order to avoid deleterious effects on plant growth and development.

Caspase-3 inhibits growth in Saccharomyces cerevisiae without causing cell death

Caspase-3, a member of the caspase family of cell death proteases, cleaves cytoplasmic and nuclear substrates and promotes apoptotic cell death in mammalian cells. Although yeast homologs of apoptotic genes have not been identified, some components of apoptotic pathways retain function in yeast. Here we show that the expression of caspase-3 delays cell growth in Saccharomyces cerevesiae without causing cell death. Mutation of the caspase-3 QACRG active site abolished effects on yeast growth. Co-expression of caspase inhibitors alleviated growth inhibition in yeast as did the tripeptide caspase inhibitor ZVAD-fmk. These results suggest that substrates for caspase-3 are present in S. cerevesiae and may participate in the normal cell growth and division processes.