A short review on the role of glutathione in the response of yeasts to nutritional, environmental, and oxidative stresses

Glutathione (L-γ-Glutamyl-L-Cysteinylglycine) appears as the major nonprotein thiol compound in yeasts. Recent advances have shown that glutathione (GSH) seems to be involved in the response of yeasts to different nutritional and oxidative stresses. When the yeast Saccharomyces cerevisiae is starved for sulfur or nitrogen nutrients, GSH may be mobilized to ensure cellular maintenance. Glutathione S-transferases may be involved in the detoxification of electrophilic xenobiotics. Vacuolar transport of metal derivatives of GSH ensure resistance to metal stress. Growth of methylotrophic yeasts on methanol results in the formation of an excess formaldehyde that is detoxified by a GSH-dependent formaldehyde dehydrogenase. Growth of yeasts on glycerol results in the accumulation of methylglyoxal detoxified by the glyoxalase pathway. Glutathione per se can react with oxidative agents or is involved in the oxidative stress response through glutathione peroxidase.     

Evaluation of salt tolerance at the seedling stage in rice genotypes by growth performance, ion accumulation, proline and chlorophyll content

Aims

The objectives of this study were to evaluate salt tolerance level of rice genotypes using the well-established screening criteria; the salt injury score, survival percentage and ratio between Na⁺ and K⁺, as well as the contents of proline and chlorophyll, and to identify the relationship between salt tolerance and physiological characters.

Methods

One hundred and six rice genotypes were grown in hydroponic solutions subjected to salt stress and evaluated for salt tolerance ability and the physiological parameters. Multivariate cluster analysis was performed based on salinity tolerance scores (ST scores; score 1 being the most tolerant, score 9 the most sensitive), survival percentage and Na⁺/K⁺ ratio.

Results

ST scores based on salt injury symptoms were negatively correlated with survival percentage and chlorophyll concentration in the stressed seedlings but positively correlated with Na⁺/K⁺ ratio and proline content. Rice genotypes were classified into five salt tolerance groups: tolerant (T), moderately tolerant (MT), moderately sensitive (MS), sensitive (S) and highly sensitive (HS). The means of ST scores were significantly different among the five tolerance groups indicating that the ST score was the most reliable index for identifying salt tolerance. The means of Na⁺/K⁺ ratio and proline content in stressed seedlings were distinctively different between the extreme T and HS groups, but the means among the intermediate groups (MT, MS and S) were not significantly different. Chlorophyll content, on the other hand, was not related to the levels of salt tolerance.

Conclusions

In addition to the commonly used Na⁺/K⁺ ratio, proline content is suggested to be another useful criterion to differentiate salt-tolerant from salt-sensitive rice. This study also identified several Thai improved and local cultivars with the level of salt tolerance and physiological characters comparable to Pokkali, the standard salt-tolerant donor and may be utilized as alternative sources of salt tolerance alleles.     

Role of glutathione in the growth of Bradyrhizobium sp. (peanut microsymbiont) under different environmental stresses and in symbiosis with the host plant

Glutathione (GSH) plays an important role in the defence of microorganisms and plants against different environmental stresses. To determine the role of GSH under different stresses, such as acid pH, saline shock, and oxidative shock, a GSH-deficient mutant (Bradyrhizobium sp. 6144-S7Z) was obtained by disruption of the gshA gene, which encodes the enzyme gamma-glutamylcysteine synthetase. Growth of the mutant strain was significantly reduced in liquid minimal saline medium, and the GSH content was very low, about 4% of the wild-type level. The defect, caused by disruption of the gshA gene in the growth of mutant strain, cannot be reversed by the addition of GSH (up to 100 micromol/L) to the liquid minimal saline medium, and the endogenous GSH level was approximately the same as that observed without the addition of GSH. In contrast, the wild-type strain increased the GSH content under these conditions. However, the growth of the mutant strain in a rich medium (yeast extract--mannitol) increased, suggesting that at least some but not all of the functions of GSH could be provided by peptides and (or) amino acids. The symbiotic properties of the mutant were similar to those found in the wild-type strain, indicating that the mutation does not affect the ability of the mutant to form effective nodules.     

On the origins of extreme mycorrhizal specificity in the Monotropoideae (Ericaceae): performance trade-offs during seed germination and seedling development

Fungal-induced seed germination is a phenomenon characteristic of mycorrhizal plants that produce dust-like seeds with only minimal nutritional reserves. In such systems, fungi trigger germination and/or subsidize development. We studied mycorrhizal germination in relation to mycorrhizal specificity in the Monotropoideae, a lineage of dust-seeded non-photosynthetic plants that are dependent upon ectomycorrhizal fungi of forest trees. A total of 1695 seed packets, each containing two to five compartments with seeds from different sources, were buried for up to 2 years near known ectomycorrhizal fungi in six different native forest locations. Upon harvest, seedlings were analysed by cultivation-independent molecular methods to identify their mycorrhizal fungi. We report that (i) germination is only induced by the same fungus that associates with mature plants or by closely related congeners; (ii) seedlings associated with the latter fungi develop less than those associated with maternal fungal species in most settings; and (iii) exceptions to this pattern occur in allopatric settings, where novel plant-fungal associations can result in the greatest seedling development. We interpret these results as evidence of performance trade-offs between breadth of host range and rate of development. We propose that in conjunction with host-derived germination cues, performance trade-offs can explain the extreme mycorrhizal specificity observed at maturity. The allopatric exceptions support the idea that performance trade-offs may be based on a coevolutionary arms race and that host range can be broadened most readily when naive fungal hosts are encountered in novel settings.     

Factors influencing seed dormancy and germination in sand,and seedling survival under desiccation,of Psammochloa villosa (Poaceae), inhabiting the moving sand dunes of Ordos,China

Psammochloa villosa (Trin.) Bor. (Poaceae), is distributed primarily in moving sand dunes of the Ordos Plateau, China. Freshly harvested caryopses (seeds) are in non-deep physiological dormancy (non-deep PD). Germination is slow and low and only over a narrow temperature range. A treatment of four weeks cold stratification at 3 to 5 °C in darkness was required to break non-deep PD, allowing germination to reach high percentages at higher temperatures and without light requirement. Rate and percentages of germination were increased by scarifying the caryopsis coat and by artificial removal of different proportions of the endosperm. However, seedling dry weight and increases in root and shoot lengths, were significantly influenced by the proportion of the endosperm that remained on the caryopses. Higher percentages of seedling emergence were obtained from the shallowly buried caryopses, ranging from 0.5–2.0 cm, and the depth of the caryopses in the sand affected the time of germination. The deeper the caryopses were buried, the more that remained ungerminated and in enforced dormancy. The caryopses germinated when the upper sand layer was removed and buried caryopses were at a suitable sand depth for germination, or when the sand was aerated. In natural habitats, germinated seedlings may be wholly exposed to the air by sand erosion and thus be exposed to drought stress. However, young seedlings have the ability to tolerate desiccation and to recover after rehydration. Root length at the `point of no return' is 4 mm.     

Changes in the regulatory form of Rhodospirillum rubrum nitrogenase as influenced by nutritional and environmental factors.

The photosynthetic bacterium Rhodospirillum rubrum regulates the activity of its nitrogenase (N2ase) by interconverting the enzyme into three distinct enzymatic species: N2ase A (a fully active form) and two regulatory forms, N2ase Ractive and N2ase Rinactive. N2ase R is distinguished from N2ase A in vitro by the requirement of its Fe protein for activation by a Mn2+-dependent activating factor. N2ase is converted from the A to the R form in response to certain environmental factors such as carbon starvation, depletion of intracellular adenosine triphosphate, or the addition of NH4+ (or glutamate) to a culture of N-starved cells. The rapid inhibition of R. rubrum N2ase in vivo by NH4+ was shown to result from the conversion of N2ase A to N2ase Rinactive. On depletion of NH4+ from the culture, whole-cell N2ase activity returned; however, the enzyme remained in the R form. Unlike the effect of NH4+, adding glutamate to cells containing N2ase A did not inhibit in vivo activity, but converted the enzyme to the R form (N2ase Ractive). Although glutamate-induced N2ase R formation was much slower than the NH4+-induced reaction, it occurred in the presence of rifampin, indicating that de novo protein synthesis was not involved. This suggested that N2ase R was formed by a modification of N2ase A. Although glutamine synthetase in involved in the conversion of N2ase A to R, the adenylylation state of glutamine synthetase appears not to be involved in regulating this nitrogenase reaction.     

秦岭中段不同坡向锐齿栎种子雨、土壤种子库与幼苗更新

以秦岭中段不同坡向(阳坡、半阳坡、半阴坡及阴坡)锐齿栎天然林为对象,对锐齿栎种子雨、种子库的数量、质量动态以及幼苗发育过程进行研究.结果表明: 锐齿栎种子雨一般从8月中旬开始,9月中下旬到10月上旬达到高峰期,11月中上旬结束;不同坡向的种子雨降落历程、发生时间和组成不同;半阳坡种子雨强度最大,为134.13粒·m^-2,其余大小依次为阳坡、半阴坡、阴坡;阳坡种子雨降落时间最早、持续时间最长,高峰期持续时间也最长,阴坡种子雨降落时间最晚、持续时间最短,高峰期持续时间也最短;种子活力及成熟种子占其种子雨的比例大小顺序为半阳坡>阳坡>半阴坡>阴坡.从种子雨降落结束到翌年8月,各坡向土壤种子库总储量大小顺序均为半阳坡>阳坡>半阴坡>阴坡;各坡向的土壤种子库中成熟、未成熟、被啃食种子数量和种子活力均随时间变化呈递减趋势,而霉烂种子数量增加;各坡向土壤种子库中的种子均主要集中在枯落物层,其次为0~2 cm土层,而在2~5 cm土层中只有极少量种子存在.4种坡向中锐齿栎幼苗的密度差异显著,半阳坡幼苗最多,其余依次是阳坡、半阴坡和阴坡.半阳坡更适合锐齿栎种子的萌发和幼苗生长.     

Seasonal variation in the phytomass,chemical composition and nutritional value of Azolla filiculoides Lam. along the water courses in the Nile Delta,Egypt

The present study aims to assess phenological behaviour, phytomass production, chemical composition and nutritional value of Azolla filiculoides in the water courses of the Nile Delta, Egypt. The sampling process was carried out seasonally using twenty‐five plots (each of 1 × 1 m) distributed along 15 irrigation canals and 10 drainage canals in the study area. Sprouting of A. filiculoides had its maximum activity during winter, vegetative growth during spring and summer and withering during autumn. Maximum seasonal phytomass (285.2 g DW m^‐2) was found during spring. The annual mean was significantly higher in drainage canals (278.3 g DW m^‐2) than in irrigation canals (144.4 g DW m^‐2). The concentrations of Ca, Mg and Na in A. filiculoides from drainage canals were significantly higher than in those from irrigation canals. Regarding the type of water courses, there were no significant differences in organic contents and nutritive values between the irrigation and drainage canals. The analysis of growth characteristics indicated that A. filiculoides can grow quite well in drainage canals; its macronutrient (N, Ca, Mg, Na and Fe) contents are high enough to allow it to be used as a bio‐fertilizer. On the other hand, A. filiculoides could be considered as a ‘nutrients and heavy metals remover’ especially in drainage canals for wastewater treatment if the plant is harvested during its maximum phytomass. As feed supplement for animals, this plant could be considered as excellent forage because its high levels of carbohydrate, protein, crude fat, total digestible nutrients and the lower crude fiber contents (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison of seed and seedling functional traits in native Helianthus species and the crop H. annuus (sunflower)

• Seed functional traits of native Helianthus species contribute towards ecosystem services but limitations to their use in managed programmes exist. Many perennial Helianthus possess seed dormancy. The ability for germination to occur under different temperature and drought conditions, as well as the capacity of germinated seeds to convert into normal seedlings is rarely considered. Our aim was to identify and quantify these constraints through functional trait analyses.
• In five seed lots of native Helianthus (four perennial and one annual) and five genotypes of sunflower (H. annuus) for comparison, dormancy, thermal and hydro thresholds and times, morphology, mass, oil content and conversion into normal seedlings were quantified. The influence of the seed collection site environment on these traits was also explored.
• Seed dormancy of the perennial species was overcome by scarification followed by germination in 5 mm GA₃. Thermal and hydro‐time analyses revealed slower germination for the native seed lots (>1350 °Ch) in comparison to the sunflower genotypes (<829.9 °Ch). However, native seed lots had a higher capacity to convert into normal seedlings at high temperatures and low water potentials than sunflower genotypes. For the native seed lots, the average monthly temperature of the collection site was negatively correlated with thermal time.
• Variability in seed functional traits of native Helianthus and greater capacity for germinated seeds to convert into normal seedlings suggests they are better equipped to cope with high temperature and drought scenarios than sunflower. Effective dormancy alleviation is required to facilitate the use of native Helianthus species.

     

Arabidopsis thaliana plastidial methionine sulfoxide reductases B,MSRBs, account for most leaf peptide MSR activity and are essential for growth under environmental constraints through a role in the preservation of photosystem antennae

Methionine oxidation to methionine sulfoxide (MetSO) is reversed by two types of methionine sulfoxide reductases (MSRs), A and B, specific to MetSO S‐ and R‐diastereomers, respectively. Two MSRB isoforms, MSRB1 and MSRB2, are present in chloroplasts of Arabidopsis thaliana. To assess their physiological role, we characterized Arabidopsis mutants knockout for the expression of MSRB1, MSRB2 or both genes. Measurements of MSR activity in leaf extracts revealed that the two plastidial MSRB enzymes account for the major part of leaf peptide MSR capacity. Under standard conditions of light and temperature, plants lacking one or both plastidial MSRBs do not exhibit any phenotype, regarding growth and development. In contrast, we observed that the concomitant absence of both proteins results in a reduced growth for plants cultivated under high light or low temperature. In contrast, double mutant lines restored for MSRB2 expression display no phenotype. Under environmental constraints, the MetSO level in leaf proteins is higher in plants lacking both plastidial MSRBs than in Wt plants. The absence of plastidial MSRBs is associated with an increased chlorophyll a/b ratio, a reduced content of Lhca1 and Lhcb1 proteins and an impaired photosynthetic performance. Finally, we show that MSRBs are able to use as substrates, oxidized cpSRP43 and cpSRP54, the two main components involved in the targeting of Lhc proteins to the thylakoids. We propose that plastidial MSRBs fulfil an essential function in maintaining vegetative growth of plants during environmental constraints, through a role in the preservation of photosynthetic antennae.     

Effects of the pericarp on imbibition,seed germination,and seedling establishment in seeds of <Emphasis Type="Italic">Hedysarum scoparium</Emphasis> Fisch. et Mey

Four independent experiments were designed to investigate the effects of the pericarp on seed imbibition, dehydration, germination, seedling establishment, and seed longevity in the field in seeds of Hedysarum scoparium Fisch. et Mey. The results showed that the presence of the pericarp decreased seed imbibition rates in the first 6 h, but the seeds attained significantly higher final water content after 24 h of soaking. The pericarp caused seed dormancy, and removal of the pericarp improved the germination percentage to 90 from 44%. In the pot experiment, where the level of moisture was maintained at field capacity (control), seeds with the pericarp removed had significantly improved seedling establishment. However, no statistical differences were observed in seedling establishment when the experiment was repeated under dry conditions at 40% of the field water capacity. The seedling biomass derived from seeds without the pericarp was much higher in the control but the trend was reversed under dry conditions. For seed longevity, 2 months burial in the field killed almost all seeds without the pericarp, while more than 70% of the seeds with the pericarp intact remained viable. These results indicated that the pericarp was beneficial for seedling establishment and seed longevity in arid environments. The results of this study may have practical application in grassland restoration in dry areas, especially for aerial seeding, which has been extensively used in the northern part of China.     

Correlation between hordatine accumulation, environmental factors and genetic diversity in wild barley (Hordeum spontaneum C. Koch) accessions from the Near East Fertile Crescent

Wild barley shows a large morphological and phenotypic variation, which is associated with ecogeographical factors and correlates with genotypic differences. Diversity of defense related genes and their expression in wild barley has been recognized and has led to attempts to exploit genes from H. spontaneum in breeding programs. The aim of this study was to determine the variation in the accumulation of hordatines, which are Hordeum-specific preformed secondary metabolites with strong and broad antimicrobial activity in vitro, in 50 accessions of H. spontaneum from different habitats in Israel. Differences in the accumulation of hordatines in the seedling stage were significant between different H. spontaneum genotypes from different regional locations and micro-sites. Variation in the hordatine accumulation within genotypes was between 9% and 45%, between genotypes from the same location between 13% and 38%, and between genotypes from different locations up to 121%. Principal component analysis showed that water related factors explain 39%, temperature related factors explain 33% and edaphic factors account for 11% of the observed variation between the populations of H. spontaneum. Genetic analysis of the tested accessions with LP-PCR primers that are specific for genes involved in the biosynthetic pathway of hordatines showed tight correlations between hordatine abundance and genetic diversity of these markers. Multiple regression analyses indicated associations between genetic diversity of genes directly involved in hordatine biosynthesis, ecogeographical factors and the accumulation of hordatines.     

Micropropagation and preparation of synthetic seed in M.26 apple rootstock I: Attempts towards saving labor in the production of adventitious shoot tips suitable for encapsulation

In order to achieve a time and hand-labor saving procedure for the use of direct organogenesis in the production of shoot tips suitable for encapsulation, a set of experiments aimed at the gradual reduction in the accuracy of selection, hand and machine excision of the explants (leaves and whole shoot clusters) was attempted. Vegetative performance of the regenerated shoots was evaluated and encapsulation and subsequent regrowth of adventitious shoot tips was performed. The research provided useful information to devise a mechanical protocol for the production of synthetic seed through encapsulation of differentiating propagules (tissue fragments with shoot primordia) in woody species. This revised version was published online in June 2006 with corrections to the Cover Date.     

城市化背景下广佛都市圈农林生态系统服务价值

从广佛都市圈1990、1995、2000、2005和2010年5期土地利用矢量数据中提取出耕地、林地、园地和水域4类农林业用地.基于Costanza等生态系统服务价值计算方法,在对谢高地等提出的“中国陆地生态系统单位面积生态服务价值”进行区域修正及功能性和经济性调整的基础上,估算了1990—2010年间广佛都市圈农林生态系统的生态服务价值.结果表明: 1990—2010年间,随着经济的不断发展以及人们生活水平的不断提高,居民对农林生态系统服务的支付意愿和支付能力逐年增强,使得广佛都市圈农林生态系统服务价值总体上呈波动上升趋势,1990、1995、2000、2005和2010年的服务价值分别为413.74×10⁸、612.83×10⁸、582.88×10⁸、773.44×10⁸和698.67×10⁸元,20年间提高了284.93×10⁸元,平均年增幅为2.7%.研究期间,总服务价值增加最多的为水域,达 166.74×10⁸元,其次为林地和园地,分别增加了103.01×10⁸和47.74×10⁸元.耕地的服务价值则降低了32.56×10⁸元,降幅达23.1%.在空间分布上,广佛都市圈各年的农林生态系统服务价值均表现为从东北和西南部向中部减少的趋势.各类型农林生态系统服务价值所占比例在年际间变化不大,总体表现为:涵养水源>废物处理>生物多样性保护>气候调节>土壤形成与保护>气体调节>娱乐休闲与文化>原材料提供>食物生产.