Putrescine accumulation in Arabidopsis thaliana transgenic lines enhances tolerance to dehydration and freezing stress

Polyamines have been globally associated to plant responses to abiotic stress. Particularly, putrescine has been related to a better response to cold and dehydration stresses. It is known that this polyamine is involved in cold tolerance, since Arabidopsis thaliana plants mutated in the key enzyme responsible for putrescine synthesis (arginine decarboxilase, ADC; EC 4.1.1.19) are more sensitive than the wild type to this stress. Although it is speculated that the overexpression of ADC genes may confer tolerance, this is hampered by pleiotropic effects arising from the constitutive expression of enzymes from the polyamine metabolism. Here, we present our work using A. thaliana transgenic plants harboring the ADC gene from oat under the control of a stress-inducible promoter (pRD29A) instead of a constitutive promoter. The transgenic lines presented in this work were more resistant to both cold and dehydration stresses, associated with a concomitant increment in endogenous putrescine levels under stress. Furthermore, the increment in putrescine upon cold treatment correlates with the induction of known stress-responsive genes, and suggests that putrescine may be directly or indirectly involved in ABA metabolism and gene expression.Key words: cold acclimation, dehydration, putrescine, polyamines, stress     

Locating QTL for osmotic adjustment and dehydration tolerance in rice

Research was conducted to identify and map quantitative traitloci (QTL) associated with dehydration tolerance and osmoticadjustment of rice. Osmotic adjustment capacity and lethal osmoticpotential were determined for 52 recombinant inbred lines grownin a controlled environment under conditions of a slowly developedstress. The lines were from a cross between an Indica cultivar,Co39, of lowland adaptation and a Japonica cultivar, Moroberekan,a traditional upland cultivar. The QTL analysis was conductedusing single marker analysis (ANOVA) and interval analysis (Mapmaker/QTL).The measurements obtained and the QTL identified were comparedto root traits and leaf rolling scores measured on the samelines. One major locus was associated with osmotic adjustment. Theputative locus for osmotic adjustment may be homoeologous witha single recessive gene previously identified for the same traitin wheat. The putative osmotic adjustment locus and two of thefive QTL associated with dehydration tolerance were close tochromosomal regions associated with root morphology. In thispopulation, osmotic adjustment and dehydration tolerance werenegatively associated with root morphological characters associatedwith drought avoidance. High osmotic adjustment and dehydrationtolerance were associated with Co39 alleles and extensive rootsystems were associated with Moroberekan alleles. To combinehigh osmotic adjustment with extensive root systems, the linkagebetween these traits will need to be broken. Alternatively,if the target environment is a lowland environment with onlybrief water deficit periods, selection for drought tolerancecharacteristics without consideration of the root system maybe most appropriate. Key words: Drought, rice, osmotic adjustment, dehydration tolerance, molecular markers, QTL, breeding     

NaCl胁迫下胡杨(Populus euphratica)和群众杨(P.popularis)抗氧化能力及耐盐性

在盐浓度逐渐提高的胁迫条件下,对抗盐的胡杨(Populus euphratica)和盐敏感的群众杨(P.popularis35~44)1年实生苗木叶片中Na 、Cl-水平、O2-.产生速率以及抗氧化酶:超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)、过氧化氢酶(CAT)和谷胱甘肽还原酶(GR)的动态变化以及抗盐性进行了研究。结果表明,在盐浓度不断提高的胁迫条件下,群众杨叶片中Na 、Cl-浓度持续增加,盐胁迫18d时,群众杨叶中Na 、Cl-含量分别达到对照的17.8和14.6倍,此时O2-.产生速率也达到最高水平。而在盐胁迫期间,群众杨叶片SOD活性没有明显提高,CAT活性维持在对照水平以下,只有APX和GR活性在盐胁迫13~18d,即盐害症状出现前才有所上升,属于典型的盐害反应。胡杨与群众杨明显不同:在盐胁迫初期,胡杨叶片Na 、Cl-含量虽然没有明显的变化,但胡杨叶片中O2-.产生速率在盐胁7d时明显提高,SOD、APX、CAT活性也都先后相应上升,表明胡杨能响应盐胁迫并上调SOD、APX和CAT等保护酶类,降低盐诱导的膜脂过氧化,从而减少了电解质外渗,最终提高了树木的抗盐性。     

生物炭调控盐胁迫下水稻幼苗耐盐性能

土壤盐渍化降低土壤生产力.探索生物炭对盐胁迫下水稻幼苗耐盐性能的影响,对调控盐渍区水稻生产潜力具有重要意义.本研究通过生物炭介入盐胁迫稻田土壤的盆栽试验,调查了生物炭对盐胁迫下土壤环境和水稻幼苗耐盐性能的影响.盐胁迫设置4个水平,分别为0 g NaCl·kg-1土(S0),1 g NaCl·kg-1土(S1),2 g ...     

Differences in Al tolerance between Plantago algarbiensis and P. almogravensis reflect their ability to respond to oxidative stress

We evaluated the impact of low pH and aluminum (Al) on the leaves and roots of Plantago almogravensis Franco and Plantago algarbiensis Samp., focusing on energy partitioning in photosystem II, H₂O₂ levels, lipid peroxidation, electrolyte leakage (EL), protein oxidation, total soluble protein content and antioxidant enzyme activities. In both species, Al triggered more changes in oxidative metabolism than low pH alone, particularly in the roots. We found that Al increased the levels of H₂O₂ in P. algarbiensis roots, but reduced the levels of H₂O₂ in P. almogravensis leaves and roots. Neither low pH nor Al affected the spatial heterogeneity of chlorophyll fluorescence, the maximum photochemical efficiency of PSII (F_v/F_m), the actual quantum efficiency of PSII (?_PSII) or the quantum yields of regulated (?_NPQ) and nonregulated (?_NO) energy dissipation, and there was no significant change in total soluble protein content and EL. In P. algarbiensis, Al increased the carbonyl content and the activities of superoxide dismutase (SOD) and catalase (CAT) in the roots, and also CAT, ascorbate peroxidase and guaiacol peroxidase activities in the leaves. In P. almogravensis, Al reduced the level of malondialdehyde in the roots as well as SOD activity in the leaves and roots. We found that P. almogravensis plantlets could manage the oxidative stress caused by low pH and Al, whereas the P. algarbiensis antioxidant system was unable to suppress Al toxicity completely, leading to the accumulation of H₂O₂ and consequential protein oxidation in the roots.     

外源ABA对低温胁迫水稻过氧化物酶同工酶的影响

采用聚丙烯酰胺垂直板电泳法,就外源ABA对低温胁迫下水稻幼苗过氧化物酶（POD）同工酶的影响进行了研究。结果表明,低温胁迫下,水稻幼苗长势明显下降,与其相应的过氧化物酶同工酶也发生了变化,外施ABA(10^-5mol/L）提高了水稻幼苗的抗寒能力,其相应的过氧化物酶同工酶却表现为部分酶活性增强,说明：（1）过氧化物同工酶的变化将引起植物对低温的抗性反应;（2）外源ABA引起自由基清除酶（如POD）活力的升高,是植物抗寒性增强的原因之一。     

The relationship between vernalization requirement and frost tolerance in substitution lines of wheat

Two sets of wheat (Triticum aestivum L.) substitution lines for the homoeologous group 5 chromosomes, 5A, 5B and 5D, carrying vernalization genes (Vrn-A1, Vrn-B1, Vrn-D1) were used to study the relationship between vernalization requirement and winter survival, with respect to the induction and maintenance of frost tolerance. Substitution lines carrying dominant Vrn loci substituted from the spring cultivars Zlatka (5A), Chinese Spring (5D) and the alternative cultivar eská Pesívka (5B) into three different winter wheat backgrounds, Vala, Koútka and Zdar, showed lower winter survival by 20, 36, and 41 % for substitutions of 5B, 5A and 5D, respectively, compared to the original winter cultivars. Reciprocal substitution lines between two winter cultivars Mironovskaya 808 and Bezostaya 1 carrying different recessive alleles, vrn-A1, vrn-B1, vrn-D1, did not exhibit a modified induction of frost tolerance, but the duration of good frost tolerance, as well as the ability to survive the whole winter, was changed. In accordance with the model suggesting that genes for vernalization act as a master switch regulating the duration of frost tolerance, substitutions of homoeologous group 5 chromosomes induced, at first, frost tolerance at a level equal to the parental cultivar, and then, relative to the different extent of saturation of vernalization requirement, they gradually lost both frost tolerance and their ability to re-induce significant frost tolerance with a drop in temperature following warm periods in the winter.     

高温胁迫下2个超级杂交稻组合耐受性比较

在抽穗开花期对2个超级杂交稻组合'Y两优1号'和'两优培九'进行了高温胁迫处理,比较研究了这2个超级杂交稻组合对高温胁迫的耐受性.实验结果显示,经高温胁迫后,'Y两优1号'和'两优培九'头季稻的花药开裂系数和花粉可染率均显著下降(P<0.05),结实率则分别下降6.07%和54.48%,千粒重分别下降9.03%和9.98%,'两优培九'的各指标降幅均大于'Y两优1号'.经高温胁迫后,'Y两优1号'和'两优培九'头季稻剑叶中的叶绿素含量较各自的对照分别下降1.18%和3.20%,POD和CAT活性均呈先升高后下降再升高的趋势,MDA含量则呈先下降后升高再下降的趋势,'Y两优1号'的POD和CAT活性总体上高于'两优培九'、MDA含量总体上低于'两优培九'.高温胁迫导致'Y两优1号'和'两优培九'再生稻的活芽率、平均芽长以及单茎腋芽数均显著下降,且后者再生稻各指标的降幅大于前者;高温胁迫对'Y两优1号'和'两优培九' 再生稻的再生率和每穗总粒数的影响不明显,但均使再生稻的结实率和千粒重降低,且'两优培九'再生稻的结实率和千粒重与对照差异显著(P<0.05).高温胁迫对'Y两优1号'和'两优培九'头季稻的热害指数分别为0.19和0.56,对再生稻的热害指数分别为0.04和0.13,差异显著(P<0.05).研究结果表明,在抽穗开花期,'Y两优1号'对高温胁迫的耐受性高于'两优培九',且头季稻耐高温有利于再生芽的生长.     

Proteomics of rice in response to heat stress and advances in genetic engineering for heat tolerance in rice

Rice is the most important food crop worldwide. Global warming inevitably affects the grain yields of rice. Recent proteomics studies in rice have provided evidence for better understanding the mechanisms of thermal adaptation. Heat stress response in rice is complicated, involving up- or down-regulation of numerous proteins related to different metabolic pathways. The heat-responsive proteins mainly include protection proteins, proteins involved in protein biosynthesis, protein degradation, energy and carbohydrate metabolism, and redox homeostasis. In addition, increased thermotolerance in transgenic rice was obtained by overexpression of rice genes and genes from other plants. On the other hand, heterologous expression of some rice proteins led to enhanced thermotolerance in bacteria and other easily transformed plants. In this paper, we review the proteomic characterization of rice in response to high temperature and achievements of genetic engineering for heat tolerance in rice.     

Tissue-specific regulation of rice molybdenum cofactor sulfurase gene in response to salt stress and ABA

Molybdenum-containing aldehyde oxidase is a key enzyme for catalyzing the final step of abscisic acid (ABA) biosynthesis in plants. Sulfuration of the molybdenum cofactor (MoCo) is an essential step for activating aldehyde oxidase. The molybdenum cofactor sulfurase (MCSU) that transfers the sulfur ligand to aldehyde oxidase-bound MoCo is thus considered an important factor in regulating the ABA levels in plant tissues. In this study, we identified the rice MCSU cDNA (OsMCSU), which is the first MCSU gene cloned in monocot species. According to the functional domain analysis of the predicted amino acid sequence, the OsMCSU protein contains a Nifs domain at its N-terminus and a MOSC domain at the C-terminus. Expression of the OsMCSU gene was up-regulated by salt stress in root tissues of rice seedlings, but this effect was not observed in leaf tissues. In roots, regulations of OsMCSU expressions could be mediated by both ABA-dependent and ABA-independent signaling pathways under salt stress condition.     

ABA synthesis in protoplasts of different origin in response to osmotic stress

All the protoplasts analysed in this study whatever the original plant material were able to accumulate ABA under osmotic stress. The time course of ABA accumulation strongly differed according to the plant material. In both rose petal or Amaranthus leaf protoplasts, the increase in ABA level was significant but transient. Protoplasts prepared from Amaranthus cell suspensions behaved differently, showing a late and durable accumulation of ABA. Similar patterns of changes in ABA accumulation were observed in the original plant material under osmotic stress. A pretreatment of plant material by fluridone induced a strong inhibition of ABA accumulation whatever the origin of protoplasts was. This result suggests that ABA could be synthesised via the carotenoid pathway in the absence of the cell wall.     

Selenium spares ascorbate and alpha-tocopherol in cultured liver cell lines under oxidant stress.

The selenoenzyme thioredoxin reductase (TR) can recycle ascorbic acid, which in turn can recycle alpha-tocopherol. Therefore, we evaluated the role of selenium in ascorbic acid recycling and in protection against oxidant-induced loss of alpha-tocopherol in cultured liver cells. Treatment of HepG2 or H4IIE cultured liver cells for 48 h with sodium selenite (0-116 nmol/l) tripled the activity of the selenoenzyme TR, measured as aurothioglucose-sensitive dehydroascorbic acid (DHA) reduction. However, selenium did not increase the ability of H4IIE cells to take up and reduce 2 mM DHA, despite a 25% increase in ascorbate-dependent ferricyanide reduction (which reflects cellular ascorbate recycling). Nonetheless, selenium supplements both spared ascorbate in overnight cultures of H4IIE cells, and prevented loss of cellular alpha-tocopherol in response to an oxidant stress induced by either ferricyanide or diazobenzene sulfonate. Whereas TR contributes little to ascorbate recycling in H4IIE cells, selenium spares ascorbate in culture and alpha-tocopherol in response to an oxidant stress.     

Morphological and molecular screening of rice germplasm lines for low soil P tolerance

Phosphorus (P) is an essential macronutrient to all crops including rice and it plays a key role in various plant activities and development. Low availability of P in the soils negatively, influences rice crop growth and causes significant yield loss. In the present study, we characterized a set of 56 germplasm lines for their tolerance to low soil P by screening them at low soil P and optimum soil P levels along with low soil P tolerant and sensitive check varieties. These lines were genotyped for the presence/absence of tolerant allele with respect to the major low soil P tolerance QTL, Pup1, using a set of locus specific PCR-based markers, viz., K46-1, K46-2, K52 and K46CG-1. High genetic variability was observed for various traits associated with low soil P tolerance. The yield parameters from normal and low soil P conditions were used to calculate stress tolerance indices and classify the genotypes according to their tolerance level. Out of the total germplasm lines screened, 15 lines were found to be tolerant to low soil P condition based on the yield reduction in comparison to the tolerant check, but most of them harbored the complete or partial Pup1 locus. Interestingly, two tolerant germplasm lines, IC216831 and IC216903 were observed to be completely devoid of Pup1 and hence they can be explored for new loci underlying low soil P tolerance.

     

Response of rice to Al stress and identification of quantitative trait Loci for Al tolerance

Rice (Oryza sativa L.) shows the highest tolerance to Al toxicity among small-grain cereal crops, however, the mechanisms and genetics responsible for its high Al tolerance are not yet well understood. We investigated the response of rice to Al stress using the japonica variety Koshihikari in comparison to the indica variety Kasalath. Koshihikari showed higher tolerance at various Al concentrations than Kasalath. The Al content in root apexes was less in Koshihikari than in Kasalath, suggesting that exclusion mechanisms rather than internal detoxification are acting in Koshihikari. Al-induced secretion of citrate was observed in both Koshihikari and Kasalath, however, it is unlikely to be the mechanism for Al tolerance because there was no significant difference in the amount of citrate secreted between Koshihikari and Kasalath. Quantitative trait loci (QTLs) for Al tolerance were mapped in a population of 183 backcross inbred lines (BILs) derived from a cross of Koshihikari and Kasalath. Three putative QTLs controlling Al tolerance were detected on chromosomes 1, 2 and 6. Kasalath QTL alleles on chromosome 1 and 2 reduced Al tolerance but increased tolerance on chromosome 6. The three QTLs explained about 27% of the phenotypic variation in Al tolerance. The existence of QTLs for Al tolerance was confirmed in substitution lines for corresponding chromosomal segments.