Lower Ion Leakage Research Articles

ATP-Citrate Lyase Gene (SoACLA-1), a Novel ACLA Gene in Sugarcane, and Its Overexpression Enhance Drought Tolerance of Transgenic Tobacco

ATP-citrate lyase catalyzes cracking citrate to produce acetyl CoA in the cytoplasm and plays an important role in normal growth and development of plants. In this study, SoACLA-1 gene in sugarcane was cloned and characterized. The amino acid sequence of SoACLA-1 showed high homology with other ACLAs families, and they were clustered together in the phylogenetic tree. On transcript level, SoACLA-1 expressed strongly in root and stalk and responded to polyethylene glycol 6000, drought and ABA stresses. The results indicated that SoACLA-1 possibly involves in stress-responsive metabolic process. PCR analysis was performed to confirm the putative transgenic type in T1 tobacco plants. Overexpression of SoACLA-1 enhanced the tolerance of tobacco plants to drought. The sense transgenic tobacco plants were healthier, had longer roots and higher contents of relative water content and chlorophyll and activities of superoxide dismutase, peroxidase and catalase, but lower ion leakage and contents of malondialdehyde (MDA) and H2O2 than the wild-type and antisense transgenic plants under drought stress. In conclusion, SoACLA-1 plays an important role as a positive factor in drought stress response pathways and can be utilized for transformation to improve crop drought tolerance.

Postharvest dip treatment with a natural lysophospholipid plus soy lecithin extended the shelf life of banana fruit

Lysophosphatidylethanolamine (LPE), a natural phospholipid, has been investigated for retarding senescence and promoting the shelf life of fruit and other plant tissues. LPE is a water insoluble phospholipid. For most experimental purposes, LPE is dispersed in water prior to treatment of fruit using sonication. In this study, the water solubility of LPE was improved by mixing it with soy lecithin prior to mixing with water. A combination of LPE and lecithin was used for a dip treatment of banana fruit. Banana fruit at ripening stage 2 (3/4 green) were dipped in this solution for 30min and then stored at room temperature for 10d. A combination of 200mgL−1 LPE and lecithin gave the best shelf life. In this treatment over 75% of the fruit were marketable 7d after treatment. While only about 20% and 28% of the fruit were marketable in the water (control) and lecithin treated-fruit respectively. Fruit treated with lecithin alone had better shelf life as compared to the control. Furthermore, the LPE+lecithin treatment gave better shelf life as compared to the LPE alone treatment. At 7d after dip, fruit treated with LPE+lecithin had lower ion leakage from peel tissue, higher pulp firmness, and thicker peel as compare to the control and lecithin treatments. A dip treatment with NAA (1-naphthalene acetic acid) was compared with LPE+lecithin for fruit marketability and changes in various fruit properties during ripening. Although NAA improved shelf life and retarded fruit softening as compared to the control, this treatment resulted in abnormal de-greening of fruit peel tissue. Fruit treated with LPE+lecithin had normal yellow color development and had lower ethylene production as compared to NAA and control treatments. The results of this study suggest that a dip treatment with a combination of LPE and lecithin may have potential for improving shelf life of banana fruit.

1-Methylcyclopropene alleviates chilling injury by regulating energy metabolism and fatty acid content in ‘Nanguo’ pears

This study investigated the effects of 1-methylcyclopropene (1-MCP) treatment on chilling injury (CI), energy metabolism, and membrane fatty acid content in harvested ‘Nanguo’ pears during the shelf life after cold storage at 0°C. 1-MCP treated fruit showed slower CI injury development, lower ion leakage and malondialdehyde accumulation, increased adenosine triphosphate content and energy charge during a 25 day shelf life period at 20°C. Activities of enzymes associated with energy metabolism, including H+-adenosine triphosphatase, Ca2+-adenosine triphosphatase, succinic dehydrogenase, and cytochrome C oxidase increased after 1-MCP treatment. The ratio of unsaturated to saturated fatty acids in 1-MCP-treated fruit was higher than that in control fruit. These results suggest that alleviation of CI after 1-MCP treatment might be due to enhanced energy metabolism-related enzyme activities and higher levels of energy and unsaturated to saturated fatty acid ratio.

A homolog of Class IV HD-Zip transcription factors, EsHdzip1, confers drought resistance in tobacco via enhanced the capacity of water conserving and absorbing

Previous studies have indicated that homeodomain-leucine zipper (HD-Zip) transcription factors play important roles during abiotic stress, but there is no information on the functions of HD-Zip genes in a new model plant Eutrema salsugineum for studying plant abiotic stress tolerance. Here, EsHdzip1 (GenBank No. XM_006390503) belonging to the Class IV subgroup of HD-Zip transcription factor family was isolated from E. salsugineum and characterized for its physiological roles under drought stress conditions. Transgenic tobacco plants overexpressing EsHdzip1 exhibited increased drought resistance with promoted root growth and reduction of water loss. Furthermore, these transgenic plants had lower ion leakage (IL), malondialdehyde (MDA), and reactive oxygen species (ROS) accumulation, but higher content of osmotic solutes (proline and total soluble sugars) and activities of antioxidant enzymes including superoxide dismutase (SOD) and ascorbate peroxidase (APX) relative to wild-type (WT) plants when subjected to drought stress treatments. The content of abscisic acid (ABA) was also observed to be remarkably higher in the transgenic lines than WT plants under drought stress conditions. In addition, the expression levels of three important stress-related genes (NtP5CS, NtERD10C, and NtLEA5) involved in the osmotic adjustment and water maintenance were significantly higher than WT plants under drought stress conditions. Therefore, we have revealed important roles of the EsHdzip1 gene in response to drought stress, suggesting that this gene has a great potential for improving plant drought tolerance by engineering manipulation.

Continuous combined microwave and hot air treatment of apples for fruit fly (Bactrocera tryoni and B. jarvisi) disinfestation

Apples at 24 ± 2 °C were heated in a pilot scale hot air assisted (40 °C) continuous pentagonal microwave system, to evaluate the effectiveness of this treatment on insect mortality (variety Mutsu) and fruit quality (variety Granny Smith). An average temperature of 53.4 ± 1.3 °C at core, bottom and flesh of the apple was recorded at the end of the treatment. One hundred percent mortality of the most tolerant stage of Queensland fruit fly (Bactrocera tryoni, Froggatt) and Jarvis's fruit fly (Bactrocera jarvisi, Tryon), were observed when the Mortality value (M52, equivalent time of isothermal treatment at 52 °C) at the slowest heating point applicable for each experiment was ≥ 50 min and ≥ 37 min, respectively. showed that microwave heat treatment is effective for insect disinfestation without any adverse impact on total soluble solids, flesh or peel firmness of the treated apples. The treated apples recorded a significantly higher pH and lower ion leakage than the untreated apples after 3 or 4 weeks. Therefore, the microwave heat treatment has the potential to be developed as an alternative chemical free quarantine treatment against economically significant insect pests. Hot air assisted microwave heating of fruits and vegetables, is more cost effective compared to vapour heat treatment and ionising radiation for disinfestation of insects. Microwave treatment is environmentally friendly compared to fumigation and chemical treatments. Hot air assisted microwave disinfestation can be performed at farms or centralised pack houses since the capital cost would be comparatively lower than vapour heat or ionising radiation treatments.

TdCBL6, a calcineurin B-like gene from wild emmer wheat (Triticum dicoccoides), is involved in response to salt and low-K+ stresses

The calcineurin B-like proteins (CBLs), a unique family of calcium sensors in plants, have been shown to be involved in abiotic stresses, such as salt, drought and cold. Although extensive studies and remarkable progress have been made in Arabidopsis (Arabidopsis thaliana) CBLs, very little is known about the role of CBL genes in wheat. In this study, a CBL gene, designated TdCBL6, was cloned and characterized from wild emmer wheat (Triticum dicoccoides), the progenitor of cultivated wheat. Sequence alignment revealed that TdCBL6 shares high sequence homology with rice OsCBL6. Phylogenetic analysis also revealed that TdCBL6 protein has the closest evolutionary relationship with rice OsCBL6 protein. TdCBL6 transcription was induced by NaCl, polyethylene glycol and abscisic acid. Further differential expression analysis revealed that TdCBL6 expression was much higher in the salt-tolerant line than in the salt-sensitive line when they were subjected to salt treatment. Transgenic Arabidopsis ectopic expression of the TdCBL6 gene displayed higher levels of photosynthetic efficiency (Fv/Fm) and lower ion leakage (EL) than wild-type (WT) plants under NaCl stress conditions. Moreover, TdCBL6-overexpressing lines showed low-K+ (LK)-sensitive phenotypes compared with WT plants. Further experiments revealed that ectopic expression of TdCBL6 resulted in reduction of H2O2 content, and affected expression of K+-responsive/H2O2-regulated genes under LK stress. Taken together, we demonstrated that heterologous expression of TdCBL6 in Arabidopsis confers salt tolerance by reducing membrane injury and improving photosynthetic efficiency, and that the TdCBL6 gene may be involved in response to LK stress by regulating the reactive oxygen species-mediated LK signaling pathway.

A cold-induced myo-inositol transporter-like gene confers tolerance to multiple abiotic stresses in transgenic tobacco plants.

A full length cDNA encoding a myo-inositol transporter-like protein, named as MfINT-like, was cloned from Medicago sativa subsp. falcata (herein falcata), a species with greater cold tolerance than alfalfa (M. sativa subsp. sativa). MfINT-like is located on plasma membranes. MfINT-like transcript was induced 2-4 h after exogenous myo-inositol treatment, 24-96 h with cold, and 96 h by salinity. Given that myo-inositol accumulates higher in falcata after 24 h of cold treatment, myo-inositol is proposed to be involved in cold-induced expression of MfINT-like. Higher levels of myo-inositol was observed in leaves of transgenic tobacco plants overexpressing MfINT-like than the wild-type but not in the roots of plants grown on myo-inositol containing medium, suggesting that transgenic plants had higher myo-inositol transport activity than the wild-type. Transgenic plants survived better to freezing temperature, and had lower ion leakage and higher maximal photochemical efficiency of photosystem II (Fv /Fm ) after chilling treatment. In addition, greater plant fresh weight was observed in transgenic plants as compared with the wild-type when plants were grown under drought or salinity stress. The results suggest that MfINT-like mediated transport of myo-inositol is associated with plant tolerance to abiotic stresses.

Improved callus induction, shoot regeneration, and salt stress tolerance in Arabidopsis overexpressing superoxide dismutase from Potentilla atrosanguinea.

Superoxide dismutase (SOD) catalyzes the dismutation of superoxide radicals (O₂( ·-)) to molecular oxygen (O₂) and hydrogen peroxide (H₂O₂). Previously, we have identified and characterized a thermo-tolerant copper-zinc superoxide dismutase from Potentilla atrosanguinea (PaSOD), which retains its activity in the presence of NaCl. In the present study, we show that cotyledonary explants of PaSOD overexpressing transgenic Arabidopsis thaliana exhibit early callus induction and high shoot regenerative capacity than wild-type (WT) explants. Growth kinetic studies showed that transgenic lines have 2.6-3.3-folds higher growth rate of calli compared to WT. Regeneration frequency of calli developed from transgenic cotyledons was found to be 1.5-2.5-folds higher than that of WT explants on Murashige and Skoog medium supplemented with different concentrations of naphthalene acetic acid (NAA) and 6-benzylaminopurine (BAP) within 2 weeks. A positive regulatory effect of PaSOD and H₂O₂ was observed on different stages of callusing and regeneration. However, this effect was more pronounced at the early stages of the regeneration processes in transgenic lines as compared to WT. These results clearly indicate that plant regeneration is regulated by endogenous H₂O₂ and by factors, which enhance its accumulation. Transgenics also exhibited salt stress tolerance with higher SOD activity, chlorophyll content, total soluble sugars, and proline content, while lower ion leakage and less reduction in relative water content, as compared to WT. Thus, it appears that the activation of PaSOD at regeneration stage accompanied by increased H₂O₂ production can be one of the mechanisms controlling in vitro morphogenesis.

Physiological Responses of a Centipedegrass Mutant to Chilling Stress

Physiological responses to chilling in γ‐ray‐induced mutant 22‐3 compared with two wild‐type lines (W1 and W2) with yellow‐stemmed stolons from the cultivar Common were analyzed to understand the chilling tolerance mechanism of centipedegrass [Eremochloa ophiuroides (Munro) Hack.]. The mutant 22‐3 showed an elevated chilling tolerance, with lower ion leakage and higher chlorophyll content after chilling treatment than the wild‐type plants. The maximum photochemical efficiency, quantum efficiency of photosystem II photochemistry, photochemical quenching efficiency, and net photosynthetic rate decreased after chilling treatment but were less affected in 22‐3 than in the wild‐type plants. Consistently higher levels of maximum net photosynthetic rate, apparent quantum yield, carboxylation efficiency, and light saturation point and lower levels of the CO2 compensation point and light compensation point were observed in 22‐3 than in the wild‐type plants after chilling treatment. Antioxidant enzyme activities and polyamines (PAs) including putrescine (Put), spermidine (Spd), and spermine (Spm) remained higher in 22‐3 relative to the wild‐type plants during chilling stress. Activities of superoxide dismutase, ascorbate‐peroxidase (APX), catalase (CAT), and glutathione reductase (GR) were highly correlated with Put and Spm, while APX, CAT, and GR were highly correlated with Spd. The results suggest that higher levels of PAs and antioxidants are associated with the elevated chilling tolerance in 22‐3 and improve protection of photosynthesis against chilling‐induced oxidative damage. We propose that manipulation of the biosynthesis of PAs could be valuable in centipedegrass breeding for increased chilling tolerance.

Overexpression of Early Light‐Induced Protein (ELIP) Gene from Medicago sativa ssp. falcata Increases Tolerance to Abiotic Stresses

Medicago sativa subsp. falcata (L.) Arcang. (hereafter falcata) is closely related to alfalfa (Medicago sativa L. ssp. sativa) (hereafter sativa) and shows great tolerance to cold and drought; however, its cold tolerance at molecular or physiological levels has been little investigated. Early light‐induced protein (ELIP) is proposed to play a key role in protection of the photosynthetic apparatus from high light stress. In this work, an open reading frame sequence of MfELIP was cloned from falcata. The MfELIP gene exists in a single copy in the genome of falcata. Its expression at the transcript and protein levels was induced by treatments with cold, dehydration, and abscisic acid (ABA); the MfELIP transcript was induced more by cold than by dehydration or ABA. To assess the role of elevated ELIP gene expression in abiotic stress tolerance, transgenic tobacco (Nicotiana tabacum L.) plants overexpressing MfELIP were generated. Compared with the wild type, transgenic plants exhibited a significantly higher survival rate and lower ion leakage after freezing, lower ion leakage and a higher net photosynthetic rate (A) after chilling, a higher plant fresh weight after osmotic stress, and lower ion leakage and higher maximum photochemical efficiency after high light treatment. The results indicated that transgenic plants had increased tolerance to freezing, chilling, osmotic stress, and high light. We suggest that MfELIP confers tolerance to multiple abiotic stresses.

Transgenic barley lines prove the involvement of TaCBF14 and TaCBF15 in the cold acclimation process and in frost tolerance.

The enhancement of winter hardiness is one of the most important tasks facing breeders of winter cereals. For this reason, the examination of those regulatory genes involved in the cold acclimation processes is of central importance. The aim of the present work was the functional analysis of two wheat CBF transcription factors, namely TaCBF14 and TaCBF15, shown by previous experiments to play a role in the development of frost tolerance. These genes were isolated from winter wheat and then transformed into spring barley, after which the effect of the transgenes on low temperature stress tolerance was examined. Two different types of frost tests were applied; plants were hardened at low temperature before freezing, or plants were subjected to frost without a hardening period. The analysis showed that TaCBF14 and TaCBF15 transgenes improve the frost tolerance to such an extent that the transgenic lines were able to survive freezing temperatures several degrees lower than that which proved lethal for the wild-type spring barley. After freezing, lower ion leakage was measured in transgenic leaves, showing that these plants were less damaged by the frost. Additionally, a higher Fv/Fm parameter was determined, indicating that photosystem II worked more efficiently in the transgenics. Gene expression studies showed that HvCOR14b, HvDHN5, and HvDHN8 genes were up-regulated by TaCBF14 and TaCBF15. Beyond that, transgenic lines exhibited moderate retarded development, slower growth, and minor late flowering compared with the wild type, with enhanced transcript level of the gibberellin catabolic HvGA2ox5 gene.

Salinity-induced structural and functional changes in 3 cultivars of Alternanthera bettzickiana (Regel) G.Nicholson

Three cultivars of Alternanthera bettzickiana (Regel) G.Nicholson have been evaluated for their tolerance and adaptability potential to salt stress. During the experiment, 5 salt regimes were maintained: 18 (control), 50, 100, 150, and 200 mM NaCl. Salinity adversely affected all growth shoot length and leaves per plant. Root fresh and dry weight decreased with an increase in salinity levels in all 3 cultivars. A. bettzickiana 'Green' was the most tolerant among the cultivars under study, with relatively lower ion leakage through roots, larger vascular region area, and wide metaxylem vessel in roots and stems recorded. Also observed were greater phloem and pith cell area in stems that increased midrib thickness, cortical cell area, vascular bundle area, and metaxylem area in leaves with increase in salinity level. Moreover, the vascular region area in roots, cortical cell area, vascular region thickness, metaxylem area, phloem cell area and pith cell area in stems, leaf thickness, epidermal thickness, cortical cell area, vascular bundle area, and metaxylem area in leaves were recorded in this cultivar with an increase in salinity levels. All cultivars showed increased Na^+ and Cl^- content and decreased K^+ and Ca^{2+} with an increase in the salt level of the medium.

GsSRK, a G-type lectin S-receptor-like serine/threonine protein kinase, is a positive regulator of plant tolerance to salt stress

Receptor-like protein kinases (RLKs) play vital roles in sensing outside signals, yet little is known about RLKs functions and roles in stress signal perception and transduction in plants, especially in wild soybean. Through the microarray analysis, GsSRK was identified as an alkaline (NaHCO3)-responsive gene, and was subsequently isolated from Glycine soja by homologous cloning. GsSRK encodes a 93.22kDa protein with a highly conserved serine/threonine protein kinase catalytic domain, a G-type lectin region, and an S-locus region. Real-time PCR results showed that the expression levels of GsSRK were largely induced by ABA, salt, and drought stresses. Over expression of GsSRK in Arabidopsis promoted seed germination, as well as primary root and rosette leaf growth during the early stages of salt stress. Compared to the wild type Arabidopsis, GsSRK overexpressors exhibited enhanced salt tolerance and higher yields under salt stress, with higher chlorophyll content, lower ion leakage, higher plant height, and more siliques at the adult developmental stage. Our studies suggest that GsSRK plays a crucial role in plant response to salt stress.

Elevated salt tolerance in transgenic tobacco plants expressing cytosolic ascorbate peroxidase genes from rice (Oryza sativa L.).

To identify cell salt tolerant ability generated by cytosolic ascorbate peroxidase (cAPX) from rice(Oryza sativa L.),two encoding genes,OsAPXa and OsAPXb(GenBank accession nos. D45423 and AB053297,respectively) were introduced into tobacco(Nictiana tabacum,N.plum),respectively. Southern blot confirmed that the two genes were integrated into genome of N.tabacum,respectively. Moreover,Northern blot further revealed that foreign genes effectively expressed in vitro. OsAPXa/b transgenic N.tabacum progeny T1,T2 generation were identified and assayed further. Under the carbonate stress,the T2 independent homozygous transgenic lines showed the elevated activity of APX,the lower H2O2,and the lower ion leakage than that in wild type plants. Surprisingly,T2 generation seedlings could survive on MS medium containing either 10mmol·L-1 NaHCO3 or 5mmol·L-1 Na2CO3,just along with the retarded growth of root and yellowish leaf,whereas the wild type plants even could not grow under lower carbonate stress. Our results suggested that transgenic tobacco expressing cytosolic OsAPXs improved cell salt tolerance; both cytosolic OsAPXs played the crucial roles,especially in response to carbonate stress.

Overexpression of a PLDα1 gene from Setaria italica enhances the sensitivity of Arabidopsis to abscisic acid and improves its drought tolerance

Phospholipase D (PLD) plays an important role in various physiological processes in plants, including drought tolerance. Here, we report the cloning and characterization of the full-length cDNA of PLDalpha1 from foxtail millet, which is a cereal crop with high water use efficiency. The expression pattern of the SiPLDalpha1 gene in foxtail millet revealed that it is up-regulated under dehydration, ABA and NaCl treatments. Heterologous overexpression of SiPLDalpha1 in Arabidopsis can significantly enhance their sensitivity to ABA, NaCl and mannitol during post-germination growth. Under water deprivation, overexpression of SiPLDalpha1 in Arabidopsis resulted in significantly enhanced tolerance to drought stress, displaying higher biomass and RWC, lower ion leakage and higher survival percentages than the wild type. Further analysis indicated that transgenic plants showed increased transcription of the stress-related genes, RD29A, RD29B, RAB18 and RD22, and the ABA-related genes, ABI1 and NCED3 under dehydration conditions. These results demonstrate that SiPLDalpha1 is involved in plant stress signal transduction, especially in the ABA signaling pathway. Moreover, no obvious adverse effects on growth and development in the 35S::SiPLDalpha1 transgenic plants implied that SiPLDalpha1 is a good candidate gene for improving crop drought tolerance.

Interaction Between Polyamine and Nitric Oxide Signaling in Adaptive Responses to Drought in Cucumber

The effect of polyamines (PAs) on nitric oxide (NO) generation was investigated in cucumber (Cucumis sativus cv. Dar) primary leaves using bio-imaging with an NO-selective fluorophor, DAF-2DA. Seedlings pretreated with PAs and subjected to water deficit showed early (after 5 h) and transient NO production. The amplitude of the response depended on the form of the applied polyamine. Spermine (1.0 mM) and spermidine (1.0 mM) induced higher NO-dependent fluorescence compared with putrescine (1.0 mM) and the control. The NO production was blocked by tungstate, an inhibitor of nitrate reductase, and partially by an inhibitor of nitric oxide synthase (NOS-like) enzymes. NO donor administration preceding drought had no effect on endogenous PA levels but was positively correlated with an alleviation of water deficit-induced membrane permeability and lipid peroxidation. Application of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a membrane-permeable NO scavenger, markedly reversed the NO donor effects. Similarly, pretreating seedlings with PAs resulted in lower ion leakage from the membrane and modified lipid peroxidation. The results indicate that NO may act downstream of PAs in cucumber seedlings under water stress.

Gamma‐ray radiation induced dwarf mutants of turf‐type bermudagrass

AbstractTo generate new breed lines of bermudagrass and reduce management costs of turfgrass, gamma‐ray irradiation was used for induction of dwarf mutants from a native bermudagrass (Cynodon dactylon) germplasm. Three dwarf‐type mutant lines (7‐9, 10‐5 and 10‐12) were isolated from 3000 irradiated stolons. The data from 3‐year greenhouse tests and 2‐year field tests indicated that the dwarf mutant lines had lower canopy height, shorter internodes and shorter leaves. The line 7‐9 had a similar turf coverage rate to the wild‐type control, while the lines 10‐5 and 10‐12 had a slower turf coverage rate than the wild‐type control. Under drought stress, all three dwarf mutant lines maintained higher relative water content and lower ion leakage than the wild type in the greenhouse tests. The field tests showed that the dwarf mutant lines had lower leaf firing during a progressive drying of soil. Our results indicated that bermudagrass mutants induced by gamma radiation exhibited dwarf characteristics and improved drought resistance, which was probably associated with unbalance of plant hormones in vivo.

Antioxidant Responses of Radiation-induced Dwarf Mutants of Bermudagrass to Drought Stress

Improving the drought tolerance of widely used bermudagrass [Cynodon dactylon (L.) Pers. var. dactylon] is important for water conservation and producing quality turf with limited irrigation. Mutants of bermudagrass were generated using gamma-ray irradiation with an aim toward developing dwarf and drought-resistant bermudagrass. The objectives of this study were to compare morphological characteristics between radiation-induced mutants and the wild-type of bermudagrass and to determine antioxidant responses associated with changes in drought resistance in the bermudagrass mutants. Three mutant lines (7-9, 10-5, and 10-12) that exhibit slow growth and good turf quality were chosen for this study. Plants were exposed to drought stress by withholding irrigation in a greenhouse. Mutant lines had lower canopy height, shorter internodes, and shorter leaves than the wild type under well-watered conditions. Under drought stress, all three dwarf mutant lines maintained higher relative water content and lower ion leakage and malondialdehyde content than the wild type. Antioxidant enzyme activities decreased in response to the drought stress in the mutant lines and the wild type, whereas nonenzymatic antioxidants increased under drought stress. Compared with the wild type, higher enzyme activities and antioxidant contents were maintained in mutant lines under drought stress. Our results indicated that bermudagrass mutants induced by gamma radiation exhibited dwarf characteristics and improved drought resistance, which was associated with maintenance of higher levels of antioxidant enzyme activities and nonenzymatic antioxidant contents.

Nitric oxide protects against oxidative stress under heat stress in the calluses from two ecotypes of reed

Calluses from two ecotypes of reed (Phragmites communis Trin.) plant (dune reed [DR] and swamp reed [SR]), which show different sensitivity to heat stress, were used to study plant acclimations to heat stress. SR callus suffered more oxidative damage than DR callus, and DR callus maintained higher relative growth rate and cell viability and lower ion leakage than SR callus under heat stress. Application of two nitric oxide donors, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP), dramatically alleviated heat stress induced ion leakage increase, growth suppression and cell viability decrease in both calluses under heat stress. H2O2 and MDA contents were decreased and the activities of superoxide dismutase, catalase, ascorbate peroxidase and peroxidase increased in both calluses in the presence of NO donors under heat stress. The potassium salt of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a specific NO scavenger, arrested NO donors mediated protective effects. Moreover, measurement of the rate of NO release showed that NO production increased significantly in DR callus while kept stable in SR callus under heat stress. Pretreatment with cPTIO had no effect on SR callus under heat stress while it significantly enhanced oxidative stress in DR callus compared with that of heat stress alone. These results suggest that NO can effectively protect both calluses from oxidative stress induced by heat stress and that NO might act as a signal in activating active oxygen scavenging enzymes under heat stress and thus confer DR callus thermotolerance.

Antisense suppression of phospholipase D alpha retards abscisic acid- and ethylene-promoted senescence of postharvest Arabidopsis leaves.

Membrane disruption has been proposed to be a key event in plant senescence, and phospholipase D (PLD; EC 3.1.4.4) has been thought to play an important role in membrane deterioration. We recently cloned and biochemically characterized three different PLDs from Arabidopsis. In this study, we investigated the role of the most prevalent phospholipid-hydrolyzing enzyme, PLD alpha, in membrane degradation and senescence in Arabidopsis. The expression of PLD alpha was suppressed by introducing a PLD alpha antisense cDNA fragment into Arabidopsis. When incubated with abscisic acid and ethylene, leaves detached from the PLD alpha-deficient transgenic plants showed a slower rate of senescence than did those from wild-type and transgenic control plants. The retardation of senescence was demonstrated by delayed leaf yellowing, lower ion leakage, greater photosynthetic activity, and higher content of chlorophyll and phospholipids in the PLD alpha antisense leaves than in those of the wild type. Treatment of detached leaves with abscisic acid and ethylene stimulated PLD alpha expression, as indicated by increases in PLD alpha mRNA, protein, and activity. In the absence of abscisic acid and ethylene, however, detached leaves from the PLD alpha-deficient and wild-type plants showed a similar rate of senescence. In addition, the suppression of PLD alpha did not alter natural plant growth and development. These data suggest that PLD alpha is an important mediator in phytohormone-promoted senescence in detached leaves but is not a direct promoter of natural senescence. The physiological relevance of these findings is discussed.