Principles and strategies in breeding for higher salt tolerance

Summary Salinity is an environmental component that usually reduces yield. Recent advances in the understanding of salt effects on plants have not revealed a reliable physiological or biochemical marker that can be used to rapidly screen for salt tolerance. The necessity of measuring salt tolerance based upon growth in saline relative to non-saline environments makes salt tolerance measurements and selection for tolerance difficult. Additionally, high variability in soil salinity and environmental interactions makes it questionable whether breeding should be conducted for tolerance or for high yield. Genetic techniques can be used to identify the components of variation attributable to genotype and environment, and the extent of genetic variation in saline and nonsaline environments can be used to estimate the potential for improving salt tolerance. Absolute salt tolerance can be improved best by increasing both absolute yield and relative salt tolerance.     

转基因林木研究进展

生物技术和基因工程为林木商用价值的提高开辟了广阔的前景。综述了最近几年转基因林木耐逆性提高、木质素的分子改造、植物体的繁殖不育以及转基因林木的安全性等研究进展。     

Characterization of a suppressor mutation complementing an acid-sensitive mutation in Streptococcus mutans

We isolated a spontaneous suppressor mutant complementing the acid-sensitive phenotype of Streptococcus mutans strain Tn-1, a mutant previously generated in this laboratory, defective in the activity of the dgk-encoded putative undecaprenol kinase. A relatively simple genetic method was developed to identify the suppressor mutation, based on selection for transformants containing two closely linked markers: a selectable allele of the unknown suppressor gene and an antibiotic resistance gene introduced on a suicide plasmid at random sites into the chromosome via homologous recombination. While we have not actually identified the original suppressor mutation, another mutated gene restoring acid resistance has been isolated, which suggests a possible mechanism of suppression.     

光呼吸途径及其功能

光呼吸是C3植物体内重要的代谢过程,是光合作用研究的热点之一。本文阐述了光呼吸的正常代谢途径及乙醛酸代谢的交替途径,交替途径的功能,及途径中关键酶的生物学特性。就光呼吸在减轻逆境伤害、减缓叶绿素的降解、驱动卡尔文循环、参与三羧酸循环、氮素代谢、蛋白质积累以及PSI和PSⅡ之间的状态转换等生物学功能进行了综述。     

几株饲用益生菌对体外模拟胃肠道环境的抗逆性评估

目的研究几株益生菌胃肠道环境下的抗逆能力。方法体外模拟正常猪的胃肠道环境,配制人工肠液和人工胃液,将实验室几株饲用益生菌在人工胃液和人工肠液中分别作用4、6 h,每2 h测一次活菌量。结果实验菌株对模拟胃液的耐受性都较强;除乳酸菌A外,其他菌株对模拟肠液的耐受性也较强。结论除乳酸菌A外的几株实验菌种作为饲用益生菌在抵御猪胃肠道的不良环境方面有很大优势。     

钙对植物抗逆能力的影响及其生态学意义

随着酸雨的蔓延和化学氮肥用量的增加,土壤酸化日趋严重,钙流失不断加剧,而含钙肥料却因高浓度复合肥比重的增加(磷铵取代含钙磷肥)而不断下降,使钙供应与植物需要的矛盾日渐突出.文中简述了钙对植物抗酸、盐、氨、重金属、渍害、冷害、热害、病害及酸雨等能力的影响,以及维持土壤钙供应的措施,指出植物生长过程中分泌的酸是施肥引起土壤酸化的主要原因.根系分泌酸能力强的田菁改良盐碱土的重要机理之一是促进土壤钙的活化,增强后季作物的抗盐能力.降水中氮素含量的增加,促进了林木的生长,并使其他元素缺乏,易加剧根际酸化,可能是一些工业化地区森林退化的重要机制.基于钙在植物抗逆中的作用,建议在肥料试验设计中增加施钙的空白对照区,以便将钙的效应从其它处理效应中区分出来.磷铵不应作为我国磷肥工业的发展方向.     

Increase in antioxidant enzyme activity,stress tolerance and biocontrol efficacy of Pichia kudriavzevii with the transition from a yeast-like to biofilm morphology

Morphological change, such as from yeast-like to biofilm, has been recently considered to be involved in the mode of action of some antagonistic yeasts used as postharvest biocontrol agents. In the present study, the biocontrol yeast, Pichia kudriavzevii, reversibly shifted from a yeast-like morphology on yeast peptone dextrose (YPD) medium with 2% agar to a biofilm morphology on YPD with 0.3% agar. The tolerance of P. kudriavzevii to heat and oxidative stresses, as well as the biocontrol efficacy against postharvest diseases on pear fruit, increased significantly from the yeast-like form to the biofilm form. The activity of antioxidant enzymes, including catalase and superoxidase dismutase, in the biofilm form was also significantly higher. The elevated activity of antioxidant enzymes was associated with less protein and lipid oxidation in the biofilm form, compared to the yeast-like form, under heat and oxidative stresses. These results suggest that activation of antioxidant system with the morphology shift contributes to the enhancement of abiotic stress tolerance and biocontrol performance of P. kudriavzevii. These findings provide new information on the biology of yeast antagonists that is essential for their potential application and development.     

Modestobacter excelsi sp. nov., a novel actinobacterium isolated from a high altitude Atacama Desert soil

A polyphasic study was undertaken to establish the taxonomic status of three Modestobacter strains isolated from a high altitude Atacama Desert soil. The isolates, strains 1G6^T, 1G14 and 1G50, showed chemotaxonomic and morphological properties characteristic of members of the genus Modestobacter. The peptidoglycan contained meso-diaminopimelic acid, the whole cell sugars were glucose and ribose (diagnostic sugars) and arabinose, the predominant menaquinone was MK-9(H₄), polar lipid patterns contained diphosphatidylglycerol, glycophosphatidylinositol, phosphatidylethanolamine (diagnostic component), phosphatidylglycerol and phosphatidylinositol while whole cellular fatty acid profiles consisted of complex mixtures of saturated, unsaturated iso- and anteiso-components. The isolates were shown to have different BOX-PCR fingerprint and physiological profiles. They formed a distinct phyletic line in Modestobacter 16S rRNA gene trees, were most closely related to the type strain of Modestobacter italicus (99.9 % similarity) but were distinguished from this and other closely related Modestobacter type strains using a combination of phenotypic properties. Average nucleotide identity and digital DNA:DNA hybridization similarities between the draft genome sequences of isolate 1G6^T and M. italicus BC 501^T were 90.9 % and 42.3 %, respectively, indicating that they belong to different species. Based on these phenotypic and genotypic data it is proposed that the isolates be assigned to a novel species in the genus Modestobacter, namely as Modestobacter excelsi with isolate 1G6^T (=DSM 107535^T =PCM 3004^T) as the type strain. Analysis of the whole genome sequence of M. excelsi 1G6^T (genome size of 5.26 Mb) showed the presence of genes and gene clusters that encode for properties that are in tune with its adaptation to extreme environmental conditions that prevail in the Atacama Desert biome.     

Stress tolerance in a yeast sterol auxotroph: role of ergosterol, heat shock proteins and trehalose

The role of ergosterol in yeast stress tolerance, together with heat shock proteins (hsps) and trehalose, was examined in a sterol auxotrophic mutant of Saccharomyces cerevisiae. Ergosterol levels paralleled viability data, with cells containing higher levels of the sterol exhibiting greater tolerances to heat and ethanol. Although the mutant synthesised hsps and accumulated trehalose upon heat shock to the same levels as the wild-type cells, these parameters did not relate to stress tolerance. These results indicate that the role of ergosterol in stress tolerance is independent of hsps or trehalose.     

Adaptive response of yeasts to furfural and 5-hydroxymethylfurfural and new chemical evidence for HMF conversion to 2,5-bis-hydroxymethylfuran

Renewable lignocellulosic materials are attractive low-cost feedstocks for bioethanol production. Furfural and 5-hydroxymethylfurfural (HMF) are among the most potent inhibitory compounds generated from acid hydrolysis of lignocelluloses to simple sugars for fermentation. In Saccharomyces cerevisiae ATCC 211239 and NRRL Y-12632 and Pichia stipitis NRRL Y-7124, furfural and HMF inhibition were determined to be dose-dependent at concentrations from 10 to 120 mM. The yeast strains were more sensitive to inhibition by furfural than HMF at the same concentration, while combined treatment of furfural and HMF synergistically suppressed cell growth. A metabolite transformed from HMF by strain NRRL Y-12632 was isolated from the culture supernatant, and conclusively identified as 2,5-bis-hydroxymethylfuran, a previously postulated HMF alcohol, with a composition of C₆H₈O₃ and a molecular weight of 128. It is proposed that, in the presence of HMF, the yeast reduces the aldehyde group on the furan ring of HMF into an alcohol, in a similar manner as for furfural. The accumulation of this biotransformed metabolite may be less toxic to yeast cultures than HMF, as evidenced by the rapid yeast fermentation and growth rates associated with HMF conversion. The ability of yeasts to adapt to and transform furfural and HMF offers the potential for in situ detoxification of these inhibitors and suggests a genetic basis for further development of highly tolerant strains for biofuel production.     

Relationship between gibberellins, height, and stress tolerance in barley (Hordeum vulgare L.) seedlings

The relationship between gibberellin (GA) levels, height, and stress tolerance was investigated using barley (Hordeum vulgare L.) seedlings, which were exposed to heat stress (50 °C for 3 h) and a free radical generator (Paraquat). Barley cv. Perth seedlings were treated with GA-inhibitors, either a triazole or one of two acylcyclohexanediones. They were tested along with four mutants that were either responsive (MC96 and dwf1) or non-responsive (MC90 and Dwf2) to applied growth-active GAs. Analyses of seedlings, whether mutants, or treated with GA-inhibitors, gave a negative correlation between height and tolerance. We also observed that the shorter seedlings with the least amount of growth active GAs were the most tolerant to stress. The overall results of this study suggest that reduced GA levels or sensitivity to GA, with a concomitant reduction in height are important for induction of stress tolerance.     

Nitrous oxide emissions from multiple combined applications of fertiliser and cattle slurry to grassland

Identifying forage species that are productive in saline environments is an important research priority in many areas of the world affected by salinity. The salt and waterlogging tolerances of 19 species of Melilotus were evaluated in a series of glasshouse experiments. Measurements taken on each species included: dry matter (DM) production, root growth and development, shoot ion (Na⁺, K⁺ and Cl⁻) concentrations, root porosity, and in vitro estimates of nutritive value. Research on several species was restricted because of their potential as weed risks. Of the remaining species, M. siculus (syn. M. messanensis), an annual species, showed high relative salt and waterlogging tolerances, good DM production under non-stressed and stressed (saline and hypoxic) conditions, a high level of root porosity under stagnant conditions, low tissue ion (Na⁺, Cl⁻) concentrations, and a reasonable dry matter digestibility content (range 66–69%) under highly saline conditions. M. sulcatus ssp. segetalis and M. indicus were also identified as species with good DM production and tolerance to salinity and waterlogging stresses. Further weed risk assessments and field trials on these species are required before they can be promoted for use as pasture forages on saline areas.     

Cold activity and tolerance of the entomopathogenic fungus Tolypocladium spp. to UV-B irradiation and heat

Studies on the stress resistance of insect-pathogenic fungi are very important to better understand the survival of these organisms in the environment. In this study, we examined the cold activity (8 ± 1 °C for 7 days), UV-B tolerance (Quaite-weighted UV-B irradiance at 847.90 mW m⁻² for 1, 2, 3, and 4 h), and wet-heat tolerance (45 °C for 1, 2, 3, and 4 h) of two isolates of Tolypocladiumcylindrosporum (ARSEF 3392 and 5558), one isolate of Tolypocladium geodes (ARSEF 3275), and two isolates of Tolypocladium inflatum (ARSEF 4772 and 4877) based on their germination, compared with Metarhizium robertsii (ARSEF 2575). After 3 h of UV-B exposure, T. cylindrosporum germinated at a greater rate than the other Tolypocladium species and had similar viability to that of the M. robertsii. Most Tolypocladium isolates, however, were less UV-B tolerant than M. robertsii. The T.cylindrosporum isolates were also the most thermotolerant, with similar tolerance to the M. robertsii. The isolates of T. inflatum and T. geodes, which had similar heat tolerance, were the least heat tolerant compared with the isolates of T. cylindrosporum and M. robertsii. After 4 h of heat exposure, the germination of T. inflatum and T. geodes isolates was not significantly different. For cold activity, both T.cylindrosporum isolates germinated to ca. 100% in only 3 days. Approximately 50% of the two T. inflatum isolates germinated, and less than 5% of T. geodes germinated after 3 days. All fungal isolates, however, completely germinated by the seventh day, except M.robertsii. The isolates of T. cylindrosporum, therefore, were the most heat and UV-B tolerant, and had the highest cold activity compared to the other species. The tolerance of M. robertsii to UV-B radiation and heat was similar to that of T.cylindrosporum.     

大肠杆菌海藻糖合成酶基因对提高烟草抗逆性能的研究

编码大肠杆菌海藻糖合成酶的otsA基因由农杆菌介导引入野生型烟草植株并在花椰菜花叶病毒启动子序列 (CaMV35S)控制下获得表达。蒸发光散射高效液相层析法测定海藻糖实验表明 ,转基因烟草能够合成海藻糖 ,合成量达 1 4μg g叶片湿重 ;转基因烟草表现为耐盐性生长、干燥失重缓慢等抗逆表型。说明海藻糖合成酶otsA基因的引入 ,改变了烟草的糖代谢途径 ,同时也提高了植物的耐盐碱、耐干旱特性。     

Isolation by genetic and physiological characteristics of a fuel-ethanol fermentative Saccharomyces cerevisiae strain with potential for genetic manipulation

Fuel ethanol fermentation process is a complex environment with an intensive succession of yeast strains. The population stability depends on the use of a well-adapted strain that can fit to a particular industrial plant. This stability helps to keep high level of ethanol yield and it is absolutely required when intending to use recombinant strains. Yeast strains have been previously isolated from different distilleries in Northeast Brazil and clustered in genetic strains by PCR-fingerprinting. In this report we present the isolation and selection of a novel Saccharomyces cerevisiae strain by its high dominance in the yeast population. The new strain, JP1 strain, presented practically the same fermentative capacity and stress tolerance like the most used commercial strains, with advantages of being highly adapted to different industrial units in Northeast Brazil that used sugar cane juice as substrate. Moreover, it presented higher transformation efficiency that pointed out its potential for genetic manipulations. The importance of this strain selection programme for ethanol production is discussed.