Ion Leakage Levels Research Articles

Assessment of the Cu phytoremediation potential of Chrysanthemum indicum L. and Tagetes erecta L. using analysis of growth and physiological characteristics.

In the current study, the Cu phytoremediation ability of two ornamental plants, Chrysanthemum indicum L. and Tagetes erecta L., was tracked concerning the growth and physiological responses. Plants were subjected to varying concentrations of Cu (0, 100, 200, and 400 mg/kg) under the pot experiment for 8 weeks. The results showed that the measured growth and physiological characteristics declined in T. erecta shoots and roots at all tested treatments compared with the control. However, in C. indicum at 100 mg/kg, shoot biomass, shoot total soluble protein, and leaves number remained equal to that of the control and then reduced by rising Cu concentrations, compared with the control. Also, results indicated that in C. indicum, after 56 days of exposure to Cu, the chlorophyll pigments content markedly increased and reached a maximum level at 100 mg/kg dose and gradually declined with enhancing Cu concentrations, compared with the control. Other measured growth and physiological parameters decreased in both tissues of C. indicum in response to Cu usage in the growth medium. The carotenoid content of T. erecta decreased in all studied Cu levels in comparison to the control, but in C. indicum remained unaffected up to 200 mg/kg Cu in comparison to the control and then enhanced with increasing Cu level. The augmentation of antioxidant enzyme activity in two species, especially in roots, reflected the incident of Cu stress as demonstrated by elevated MDA and ion leakage levels. Data concerning copper accumulation in tissues, TF, and BAF showed T. erecta is a weak Cu accumulator and seems not to be an appropriate candidate for Cu phytoremediation. However, the Cu content in shoots and roots of C. indicum increased significantly with an increment in applied Cu level. Also, C. indicum accumulated higher Cu concentrations in the roots than in shoots and exhibited TF < 1, 0.1 < BAF root < 1, and can be considered as a Cu excluder by the phytostabilization mechanism.

Dynamics of 'Candidatus Liberibacter asiaticus' Growth, Concentrations of Reactive Oxygen Species, and Ion Leakage in Huanglongbing-Positive Sweet Orange.

Citrus Huanglongbing (HLB) caused by 'Candidatus Liberibacter asiaticus' (CLas) is the most devastating citrus disease worldwide. CLas induces systemic and chronic reactive oxygen species (ROS) production, which has been suggested to be a primary cause of cell death in phloem tissues and subsequent HLB symptoms. Mitigating oxidative stress caused by CLas using horticultural approaches has been suggested as a useful strategy to reduce HLB damages. To provide information regarding the application timing to mitigate ROS, we investigated monthly dynamics of CLas concentration, CLas-triggered ROS, and phloem cell death in the bark tissues of asymptomatic and symptomatic branches of HLB-positive Hamlin and Valencia sweet orange trees in the field. Healthy branches in the screenhouse were used as controls. CLas concentration exhibited significant variations over the course of the year, with two distinct peaks observed in Florida citrus groves-late spring/early summer and late fall. Within both Hamlin and Valencia asymptomatic tissues, CLas concentration demonstrated a negative correlation with the deviation between the monthly average mean temperature and the optimal temperature for CLas colonization in plants (25.7°C). However, such a correlation was not evident in symptomatic tissues of Hamlin or Valencia sweet oranges. ROS levels were consistently higher in symptomatic or asymptomatic branches than in healthy branches in most months. ROS concentrations were higher in symptomatic branches than in asymptomatic branches in most months. CLas triggered significant increases in ion leakage in most months for asymptomatic and symptomatic branches compared with healthy controls. In asymptomatic branches of Hamlin, a positive correlation was observed between CLas concentration and ROS concentrations, CLas concentration and ion leakage levels, as well as ROS and ion leakage. Intriguingly, such a relationship was not observed in Valencia asymptomatic branches or in the symptomatic branches of Hamlin and Valencia. This study sheds light on the pathogenicity of CLas by providing useful information on the temporal dynamics of ROS production, phloem cell death, and CLas growth, as well as provides useful information in determining the timing for application of antioxidants and antimicrobial agents to control HLB.

Exogenous serotonin improves drought and salt tolerance in tomato seedlings

Serotonin and melatonin, which are indolamines present in every biological kingdom, show strong bioregulator activity in plant tissues under various stress conditions. Although numerous studies have reported the stress mitigating effects of melatonin, the effect of serotonin on plant stress physiology has rarely been studied in the current literature. In this study, the effects of exogenous serotonin application on tomato seedlings under severe salt and drought stresses were investigated by examining various morphological and physiological plant stress indicators, including tissue length and mass, relative water content (RWC), ion leakage, malonedialdehyde (MDA) and proline content, as well as some oxidative stress related gene activities, ascorbate peroxidase (APX1), superoxide dismutase (FeSOD), catalase (CAT2), glutathione reductase (GR1), delta 1-pyrroline-5-carboxylate synthase (P5CS) and 1-aminocyclopropane-1-carboxylic acid synthase 2 (ACS2). Our results showed that the tissue MDA contents decreased by 29% and 18%, the ion leakage levels decreased by 39% and 34%, whereas the relative water contents increased by 22% and 18%, respectively, under salt and drought stresses upon serotonin application. Serotonin also decreased ACS2 gene expression by 28% and 70%, while increasing FeSOD by 69 and 17%, CAT2 by 145 and 110% and GR1 gene expression by 67 and 22%, respectively, under salt and drought stresses. Also, the transcript level of P5CS increased 48% under serotonin salt coapplication. Our findings showed that similar to its close chemical relative melatonin, serotonin also exhibits stress mitigation effects and boosts the antioxidant capacity of tomato plants under most common abiotic stress conditions.

Ethylene enhances tolerance to chilling stress in tomato fruit partially through the synergistic regulation between antioxidant enzymes and ATP synthases

Gaseous plant hormone ethylene plays a pivotal role during adaptive responses of crop growth and ripening, the mechanisms by which regulates tomato fruit response to chilling stress, however, remain limited. Our results showed that the expression of ACS2, ETR3, EIN2 and ERF2 and the protein content of EIL3 changed rapidly when tomato fruit exposed to 4 °C. Compared with storage at 25 °C, ethylene content and maturity of tomato fruit were inhibited at 4 °C. These results indicated that ethylene signaling might respond to chilling stress. In addition, take advantage of ethephon (ETH) or 1-Methylcyclopropene (1-MCP) treatment, we found that the severity of cold injury in tomato fruit was reduced or intensified, respectively. ETH-treated fruit displayed lower levels of ion leakage, malondialdehyde (MDA), H2O2 and O2.-, but higher activities of antioxidant enzymes including ascorbate peroxidase (APX), peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT), as well as higher expression levels of SlICE1 and SlCBF1 than control (WT) and 1-MCP-treated fruit. Furthermore, ETH treatment attenuated chilling stress by ensuring a higher adenosine triphosphate (ATP) content, which was accompanied with higher activities of energy metabolism enzyme including H+-ATPase, Ca2+-ATPase, succinic dehydrogenase (SDH) and cytochrome C oxidase (CCO) than control and 1-MCP treatment. Correlation analysis showed that ETH treatment increased the correlation of ATP and SOD (r = 0.91), H+-ATP and POD (r = 0.94), H+-ATP and SOD (r = 0.97), while 1-MCP treatment inhibited their correlation. These findings reveal a new regulatory pathway that ethylene enhances tolerance to chilling stress in tomato fruit partially through the synergistic regulation between antioxidant enzymes and ATP synthases.

MsSAMS, a cold stress-responsive gene, provides resistance to environmental stress in T2-generation transgenic plants

The SAMS (S-adenosylmethionine synthetase) gene is known to play an important role in the mechanism of cold resistance, as overexpression of this gene results in phenotypic changes in T1-generation transgenic plants. Accordingly, this study was conducted to test the expression of the MsSAMS gene in T2-generation transgenic plants and to investigate the resistance of these plants and the function of the transgene in response to various environmental stresses. For the morphological analysis of T2-generation transgenic plants overexpressing the MsSAMS gene, observations using scanning electron microscopy (SEM) were performed. T2-generation transgenic plants were obtained by planting a total of 5 lines, and their characteristics were tested by comparisons with those of the control. SEM revealed that the thickest leaves were produced by the T6 transgenic line-161.24 ± 8.05µm. The number of stomata ranged from 20.00 ± 2.65 to 34.00 ± 1.00 in the T2-generation transgenic plants, but the control had more stomata. Resistance to various factors, such as low temperature, drought, and oxidative stress, in the T2-generation transgenic plants was also confirmed. Under cold-stress conditions, the T6 transgenic line presented the lowest value (22.73%) of ion leakage, and under drought-stress conditions, compared with the control, the transgenic lines presented lower ion leakage after being treated with various concentrations of mannitol. Even under oxidative-stress conditions, the T2-generation transgenic plants presented ion leakage levels that were 32.91 ± 4.24 to 48.33 ± 3.54% lower than those of the control after treatment with various concentrations of methyl viologen. Regarding SAMS enzyme activity, as the duration of cold treatment increased, the activity in the transgenic plants tended to decrease and then increase. During 48h of cold treatment, the control showed a decrease in SAM content, while the T2-generation transgenic plants presented an increase in SAM content, from 13.58 ± 1.04 to 22.75 ± 1.95mg protein/g FW. The results suggest that the MsSAMS gene may be important to the mechanisms of resistance to oxidative and drought stresses in addition to its previously known association with cold resistance. Based on these results, it was suggested that the MsSAMS gene, whose expression is induced by cold stress, can serve as a marker of various responses to environmental stresses, because resistance to cold damage and various environmental stresses are stably inherited in the T2 generation.

Overexpression of SgDREB2C from Stylosanthes guianensis Leads to Increased Drought Tolerance in Transgenic Arabidopsis.

Stylosanthes guianensis is an excellent forage legume in subtropical and tropical regions with drought tolerance, but little is known about its drought tolerance mechanism. Dehydration responsive element binding proteins (DREBs) are responsive to abiotic stresses. A SgDREB2C was cloned from S. guianensis, while SgDREB2C protein was localized at nucleus. SgDREB2C transcript was induced by dehydration treatment. Transgenic Arabidopsis overexpressing SgDREB2C showed enhanced osmotic and drought tolerance with higher levels of relative germination rate, seedlings survival rate and Fv/Fm and lower levels of ion leakage compared with WT after osmotic and drought stress treatments. In addition, higher levels of superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities and stress responsive gene (COR15A, COR47) transcripts were observed in transgenic Arabidopsis than in WT under drought stress. These results suggest that SgDREB2C regulated drought tolerance, which was associated with increased SOD and APX activities and stress-responsive gene expression under drought stress.

New function of Hypoxia-responsive unknown protein in enhanced resistance to biotic stress

ABSTRACT Submergence and waterlogging lead to significant reductions in crop productivity and trigger dramatic changes in gene expression of plant biotic/abiotic stress response. Several of the host factors are involved in low-oxygen stress that is induced by endogenous reactive oxygen species (ROS) accumulation. Hypoxia-response unknown protein (HUP) has been found as a host factor of hypoxia screening but HUPs function largely is unknown. In this study, we found the Arabidopsis HUP26 gene which was conserved in different plant species and responded to various oxidative stress. HUP26 promoter analysis showed GUS activity in root and leaf tissues was significantly responsive to oxidative stress. HUP26-GFP is predominantly located in the cytoplasmic region. HUP26 overexpression results in altered enhanced pathogenesis-related gene 1 gene expression and reduced ion leakage levels compared with hup26 knockout and WT plants after inoculation with Pst DC3000. HUP26 overexpression transgenic plants showed improved resistance to Pst DC3000, but hup26 knockout plants exhibited increased susceptibility. Collectively, these results indicate that HUP26 plays important role in responses to various oxidative stress and confers biotic stress resistance. Engineering of HUP26 gene expression may represent a strategy to enhance biotic stress resistance of crops.

A novel aquaporin gene MaSIP2-1 confers tolerance to drought and cold stresses in transgenic banana

Plant aquaporins (AQPs) are subdivided into eight groups: PIPs, NIPs, GIPs, HIPs, XIPs, LIPs, TIPs, and SIPs. However, the genetic function and physiological mechanisms of the SIP group in abiotic stress response in plants remains unknown. In this study, we cloned and characterized a banana SIP group AQP gene, designated MaSIP2-1. MaSIP2-1 showed upregulation after osmotic, salt, and cold treatments. Overexpression of MaSIP2-1 in bananas resulted in smaller leaf area and lower plant height than wild-type (WT) plants under normal growth conditions. Lines over-expressing MaSIP2-1 showed increased tolerance to drought and cold stresses, demonstrating that transgenic lines had higher content of chlorophyll, proline, soluble sugar, and abscisic acid (ABA), but lower levels of ion leakage (IL), malondialdehyde (MDA), H2O2, and gibberellins (GAs), than WT after drought, cold, and recovery conditions. Moreover, transgenic lines had higher expression of ABA biosynthetic and responsive genes than WT under drought and cold conditions. Taken together, our results show that MaSIP2-1 plays a positive role in dwarfing and tolerance to drought and cold stresses through improved osmotic adjustment, less membrane injury, and changes in ABA and GA levels. Therefore, MaSIP2-1 has the potential for utilization to improve abiotic stress tolerance in crop breeding.

Effect of Silicon Application on Wheat Under Boron Stress

In this study, effects of different silicon (Si) concentrations (0.75, 5, 10 mM) on wheat under boron(B) stress, investigated by means of some stress indicators such as tissue length, malondialdehyde (MDA), ion leakage, relative water content (RWC) and total chlorophyll content. Stress mitigating effects of silicon were observed mainly as reductions on membrane damage with reduced MDA concentrations and decreased ion leakage levels. Although necrosis was present on shoot tissues due to the boron stress, no significant change observed on shoot and root length with the application of Si. On the contrary, relative water content (RWC) has changed positively with the implementation of Si under boron stress. Furthermore Si has enhanced RWC level in Si+B co-applicated sets to the level of control plants. Total chlorophyll content increased with the existance of 0.75 and 5 mM Si, while 10 mM Si had no effect on the chorophyll content under boron stress. Overall, silicon was found to have a potential to alleviate boron stress in wheat production.

An eukaryotic elongation factor 2 from Medicago falcata (MfEF2) confers cold tolerance

BackgroundAn eukaryotic translation elongation factor-2 (eEF-2) plays an important role in protein synthesis, however, investigation on its role in abiotic stress responses is limited. A cold responsive eEF2 named as MfEF2 was isolated from yellow-flowered alfalfa [Medicago sativa subsp. falcata (L.) Arcang, thereafter M. falcata], a forage legume with great cold tolerance, and transgenic tobacco (Nicotiana tabacum L.) plants overexpressing MfEF2 were analyzed in cold tolerance and proteomic profiling was conducted under low temperature in this study.ResultsMfEF2 transcript was induced and peaked at 24 h and remained at the high level during cold treatment up to 96 h. Overexpression of MfEF2 in trasngenic tobacco plants resulted in enhanced cold tolerance. Compared to the wild type, transgenic plants showed higher survival rate after freezing treatment, higher levels of net photosynthetic rate (A), maximum photochemical efciency of photosystem (PS) II (Fv/Fm) and nonphotochemical quenching (NPQ) and lower levels of ion leakage and reactive oxygen species (ROS) production after chilling treatment. iTRAQ-based quantitative proteomic analysis identified 336 differentially expressed proteins (DEPs) from leaves of one transgenic line versus the wild type after chilling treatment for 48 h. GO and KEGG enrichment were conducted for analysis of the major biological process, cellular component, molecular function, and pathways of the DEPs involving in. It is interesting that many down-regulated DEPs were grouped into “photosynthesis” and “photosynthesis-antenna”, such as subunits of PSI and PSII as well as light harvesting chlorophyll protein complex (LHC), while many up-regulated DEPs were grouped into “spliceosome”.ConclusionsThe results suggest that MfEF2 confers cold tolerance through regulating hundreds of proteins synthesis under low temperature conditions. The elevated cold tolerance in MfEF2 transgenic plants was associated with downregulation of the subunits of PSI and PSII as well as LHC, which leads to reduced capacity for capturing sunlight and ROS production for protection of plants, and upregulation of proteins involving in splicesome, which promotes alternative splicing of pre-mRNA under low temperature.

Overexpression of maize MYB-IF35 increases chilling tolerance in Arabidopsis

Chilling stress is a critical environmental factor that limits plant growth, yield and distribution. Maize (Zea mays L.) is an important food and forage crop, and industrial raw material, in China. Low temperatures can decrease maize production, especially in early spring. The R2R3-MYB transcription factor ZmMYB-IF35 was isolated from maize cDNA. The open reading frame of ZmMYB-IF35 is 1038 bp, encoding 345 amino acids with a molecular mass of 37.9 kDa. ZmMYB-IF35 localized in the nucleus. Low temperatures induced the expression of ZmMYB-IF35 in maize, and the relative expression level reached its maximum after 4 h of chilling stress. The overexpression of ZmMYB-IF35 under the control of the CaMV35S promoter in Arabidopsis conferred tolerance to chilling stress compared with the wild-type plants by maintaining the maximal photochemical efficiency of photosystem II. Furthermore, under chilling stress, the ZmMYB-IF35 transgenic plants showed greater antioxidant enzyme activity levels, lower reactive oxygen species contents and lower ion leakage levels than those of wild-type plants. Thus, the overexpression of ZmMYB-IF35 may enhance resistance to chilling and oxidative stresses in transgenic Arabidopsis and alleviates PSII photoinhibition.

Polyamines and antioxidant defense system are associated with cold tolerance in centipedegrass

Physiological responses to low temperature were analyzed in a chilling-tolerant centipedegrass (<i>Eremochloa ophiuroides</i>) accession, Shao Guan (SG), in comparison to the commercial cultivar, Common. Lower levels of ion leakage and higher chlorophyll (Chl) concentration were observed in SG than in Common during chilling stress. The maximum photochemical efficiency, the actual photosystem II (PSII) efficiency, photochemical quenching efficiency, and net photosynthetic rate were decreased during chilling stress in both genotypes, with higher levels of these parameters shown by SG than Common. In addition, higher activities of superoxide dismutase (SOD), catalase (CAT), ascorbate-peroxidase (APX) and glutathione reductase (GR), and higher concentrations of ascorbic acid (AsA) and glutathione (GSH) were observed in SG than in Common. Moreover, higher concentrations of putrescine (Put), spermidine (Spd), and spermine (Spm) were observed in SG than in Common. Correlation analysis indicated that SOD, CAT, APX and GR activities, and AsA and GSH concentrations showed high correlation to Put, while APX, GR, and AsA concentrations were correlated to Spd. Exogenous Put or Spd increased antioxidant enzyme activities and chilling tolerance. The results suggested that polyamine-regulated antioxidants are important for chilling tolerance in centipedegrass and protect plants against chilling induced oxidative damage.

Differential Responses of Polyamines and Antioxidants to Drought in a Centipedegrass Mutant in Comparison to Its Wild Type Plants.

Centipedegrass (Eremochloa ophiuroides [Munro] Hack.) is an important warm-season turfgrass species with low turf maintenance requirements. However, our knowledge on physiological adaptation of centipedegrass to drought stress is limited. Physiological responses to drought in a gamma-ray-induced mutant 22-1 as compared with two wild type (WT) lines were analyzed for understanding of drought tolerance mechanism of centipedegrass. The mutant showed an elevated drought tolerance with higher levels of relative water content, net photosynthetic rate (A) and stomatal conductance (gs) and lower levels of ion leakage and malondialdehyde (MDA) under drought stress as compared with WT plants. A showed significant correlation with gs and MDA. Higher levels of antioxidant enzymes activities, non-enzyme antioxidants, and polyamines including putrescine (Put), spermidine (Spd), and spermine (Spm) were maintained in 22-1 than in WT plants. Superoxide dismutase (SOD), catalase (CAT), ascorbate-peroxidase (APX), and glutathione reductase (GR) activities and ascorbic acid (AsA) content were significantly correlated with both Put and Spd levels, and reduced glutathione level was correlated with Put during drought stress. Exogenous application of Put, Spd, and Spm increased drought tolerance and activities of SOD, CAT, APX, and GR in WT plants. The results suggest that higher levels of polyamines and antioxidant defense system are associated with the elevated drought tolerance in 22-1, which may improve protection on photosynthesis against drought induced oxidative damage.

Overexpression of sugarcane gene SoSnRK2.1 confers drought tolerance in transgenic tobacco.

Overexpression of SoSnRK2.1 improved drought tolerance and growth of tobacco plants. Sucrose non-fermenting1-related protein kinase 2 (SnRK2) is a key enzyme in regulating ABA signal transduction in plants, and it plays a significant role in response to multiple abiotic stresses. In this research, SoSnRK2.1 gene was cloned from sugarcane variety GT21 and characterized under various stresses. The cloned SoSnRK2.1 gene has a complete open reading frame of 1002bp, encoding a peptide of 333 amino acids. The amino acid sequence of SoSnRK2.1 has high homology with those of Zea mays and Oryza sativa, which belongs to SnRK2s families. The expression of SoSnRK2.1 under stresses of drought, PEG, and ABA indicated that this gene is involved in stress responses in sugarcane. To investigate the gene function, fusional SoSnRK2.1-GFP-pBI121 under control of CaMV 35S was transformed into tobacco plants. Growth and morphology of transgenic plants demonstrated that overexpression of SoSnRK2.1 enhanced drought tolerance in tobacco. Transgenic tobacco plants had lower levels of ion leakage (IL), and contents of maleic dialdehyde (MDA) and H2O2, with higher activities of three antioxidant enzymes, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and chlorophyll and relative water content (RWC) than those in wide type (WT) tobacco. SoSnRK2.1 was stably transmitted to the next generation via sexual reproduction. Though the data presented here are from a heterologous system, it is highly likely that SoSnRK2.1 is involved in the abiotic stress response in sugarcane and may be playing an important role in regulation of its growth.

Transgenic poplar expressing codA exhibits enhanced growth and abiotic stress tolerance

Glycine betaine (GB), a compatible solute, effectively stabilizes the structure and function of macromolecules and enhances abiotic stress tolerance in plants. We generated transgenic poplar plants (Populus alba×Populus glandulosa) expressing a bacterial choline oxidase (codA) gene under the control of the oxidative stress-inducible SWPA2 promoter (referred to as SC plants). Among the 13 SC plants generated, three lines (SC4, SC14 and SC21) were established based on codA transcript levels, tolerance to methyl viologen-mediated oxidative stress and Southern blot analysis. Growth was better in SC plants than in non-transgenic (NT) plants, which was related to elevated transcript levels of auxin-response genes. SC plants accumulated higher levels of GB under oxidative stress compared to the NT plants. In addition, SC plants exhibited increased tolerance to drought and salt stress, which was associated with increased efficiency of photosystem II activity. Finally, SC plants maintained lower levels of ion leakage and reactive oxygen species under cold stress compared to the NT plants. These observations suggest that SC plants might be useful for reforestation on global marginal lands, including desertification and reclaimed areas.

Antioxidant responses of peanut (Arachis hypogaea L.) seedlings to prolonged salt-induced stress

In this study, the effects of long-term NaCl treatment were investigated in two cultivars of peanut designated as drought-resistant and drought-sensitive. Growth parameters, changes in the concentrations of MDA, H2O2 and proline, and the activities of antioxidant enzymes were determined under salinity stress. Growth parameters indicated the superiority of cv. Florispan to cv. Gazipa?a under milder salinity stress treatment. However, comparative analysis of the two cultivars showed that MDA, H2O2, ion leakage levels and photosystem II activities were not significantly different, except for the proline activity, which increased only in Florispan leaf tissues under 100 mM salt treatment. Among the processes that govern the tolerance in peanut tissues, proline level and the activity of glutathione reductase (GR) appeared to be only components that play an important part in salt stress protection.

Overexpression of tomato GDP-L-galactose phosphorylase gene in tobacco improves tolerance to chilling stress.

The overexpression of tomato GDP- l -galactose phosphorylase gene enhanced tolerance to chilling stress and reduced photoinhibition of photosystems I and II in transgenic tobacco. Chilling stress is a crucial factor that limits the geographical distribution and yield of chilling-sensitive plants. Ascorbate (AsA) protects plants by scavenging reactive oxygen species and reduces photoinhibition by promoting the conversion of violaxanthin to zeaxanthin in the xanthophyll cycle to dissipate excess excitation energy. Possible mechanisms of AsA for plant photoprotection under chilling stress were investigated by isolating the tomato GDP-L-galactose phosphorylase gene (SlGGP) and producing transgenic tobacco plants with overexpression of SlGGP. The transgenic plants subjected to chilling stress accumulated less H(2)O(2), demonstrated lower levels of ion leakage and malondialdehyde, and acquired higher net photosynthetic rate, higher maximum photochemical efficiency of PSII, and higher D1 protein content compared with the wild-type (WT) plants. The transgenic plants subjected to chilling stress also showed higher GDP-L-galactose phosphorylase activity, increased AsA content as well as ascorbate peroxidase and oxidizable P700 activities than WT plants. Thus, SlGGP overexpression is crucial in promoting AsA synthesis and alleviating photoinhibition of two photosystems.

Antisense-mediated suppression of tomato thylakoidal ascorbate peroxidase influences anti-oxidant network during chilling stress

Photosynthesis is a well-established source of reactive oxygen species (ROS) in plants particularly under chilling stress. Ascorbate peroxidase (APXs) plays an important role in the anti-oxidant system by utilizing AsA as specific electron donor to reduce H(2)O(2) to water. In order to investigate the possible mechanisms of ascorbate peroxidsae (APX) in photoprotection under chilling stress, a tomato (Lycopersicon esculentum Mill.) thylakoidal ascorbate peroxidase gene (LetAPX) was isolated and antisense transgenic tomato plants were produced. Under chilling stress, transgenic plants accumulated more H(2)O(2), and showed higher levels of ion leakage and malondialdehyde (MDA), lower net photosynthetic rate (Pn), lower maximal photochemical efficiency of PSII (Fv/Fm) and less content of D1 protein compared with wild type (WT) plants. On the other hand, after chilling stress, transgenic plants showed higher reduced ascorbate (AsA) and activities of catalase (CAT) and superoxide dismutase (SOD) than those in WT plants, and the expression of several known stress-responsive and antioxidative genes was also higher at the end of chilling treatment. These results suggested that the suppression of LetAPX gene induced compensatory anti-oxidant mechanisms in tomato, and inactivation of tAPX may have a regulatory role in facilitating redox signaling pathways under chilling stress. Furthermore, transient increases in ROS levels also have a vital role in stress signaling and thereby in the survival of plants under chilling conditions.

Evidence that Cell Death is Associated with Zebra Chip Disease in Potato Tubers

Zebra chip (ZC) is an established and highly destructive disease of potato (Solanum tuberosum L.) that occurs in several southwestern states of the United States, Mexico, Central America, and New Zealand. The causal agent for this disease has not been identified. However, the bacterium “Candidatus Liberibacter solanacearum” and the potato psyllid, Bactericera cockerelli (Sulc), its insect vector, are associated with the disease. Tubers from ZC-affected potato plants exhibit dramatic browning of vascular tissue concomitant with “necrotic flecking” both of which can affect the entire tuber. Upon frying, these tubers develop a characteristic striped pattern of discoloration rendering them unmarketable. These characteristic ZC symptoms in the tubers have been suggested to be associated with general cell death, though no evidence to confirm this hypothesis has been shown. In order to determine if cell death is associated with ZC disease, a series of experiments were undertaken. Cell death was initially quantified by comparing cellular ion leakage from ZC-affected and ZC-free tubers. Levels of ion leakage were found to be significantly higher in ZC-affected tubers compared to ZC-free tubers. To examine further the association of cell death with ZC disease, ZC-affected and ZC-free tubers were compared using classical histochemical staining methods in conjunction with optical microscopy, which revealed layers of dead cells surrounding numerous, small, irregularly-shaped lesions throughout the parenchymatic medullary region, vascular ring and cortex of ZC-affected tubers. This cell death was confirmed using high-resolution, field-emission scanning electron microscopy (FE-SEM) of fresh-cut tuber tissue.

Tobacco seeds simultaneously over-expressing Cu/Zn-superoxide dismutase and ascorbate peroxidase display enhanced seed longevity and germination rates under stress conditions.

Reactive oxygen species (ROS) are produced during seed desiccation, germination, and ageing, leading to cellular damage and seed deterioration and, therefore, decreased seed longevity. The effects of simultaneous over-expression of two antioxidant enzymes on seed longevity and seed germination under stressful conditions were investigated. Transgenic tobacco simultaneously over-expressing the Cu/Zn-superoxide dismutase (CuZnSOD) and ascorbate peroxidase (APX) genes in plastids showed normal growth and seed development. Furthermore, the transgenic seeds displayed increased CuZnSOD and APX enzymatic activities during seed development and maintained antioxidant enzymatic activity after two years of dried storage at room temperature. The two-year stored non-transgenic seeds (aged NT seeds) had higher levels of ion leakage than the two-year stored transgenic seeds (aged CA seeds), indicating membrane damage caused by ROS was more severe in the aged NT seeds than the aged CA seeds. The aged CA seeds decreased germination rates as compared to newly harvested transgenic and non-transgenic seeds. The aged CA seeds, however, significantly increased germination rates under various abiotic stress conditions as compared to aged NT seeds. These data strongly suggest that simultaneous over-expression of the CuZnSOD and APX genes in plastids improves seed longevity and germination under various environmental stress conditions by attenuating the effects of oxidative stress produced by elongated storage conditions and harsh environmental stresses.