Plant growth-promoting bacteria as inoculants in agricultural soils

Plant-microbe interactions in the rhizosphere are the determinants of plant health, productivity and soil fertility. Plant growth-promoting bacteria (PGPB) are bacteria that can enhance plant growth and protect plants from disease and abiotic stresses through a wide variety of mechanisms; those that establish close associations with plants, such as the endophytes, could be more successful in plant growth promotion. Several important bacterial characteristics, such as biological nitrogen fixation, phosphate solubilization, ACC deaminase activity, and production of siderophores and phytohormones, can be assessed as plant growth promotion (PGP) traits. Bacterial inoculants can contribute to increase agronomic efficiency by reducing production costs and environmental pollution, once the use of chemical fertilizers can be reduced or eliminated if the inoculants are efficient. For bacterial inoculants to obtain success in improving plant growth and productivity, several processes involved can influence the efficiency of inoculation, as for example the exudation by plant roots, the bacterial colonization in the roots, and soil health. This review presents an overview of the importance of soil-plant-microbe interactions to the development of efficient inoculants, once PGPB are extensively studied microorganisms, representing a very diverse group of easily accessible beneficial bacteria.     

An integrative proteome analysis of different seedling organs in tolerant and sensitive wheat cultivars under drought stress and recovery

Roots, leaves, and intermediate sections between roots and leaves (ISRL) of wheat seedlings show different physiological functions at the protein level. We performed the first integrative proteomic analysis of different tissues of the drought‐tolerant wheat cultivar Hanxuan 10 (HX‐10) and drought‐sensitive cultivar Chinese Spring (CS) during a simulated drought and recovery. Differentially expressed proteins (DEPs) in the roots (122), ISRLs (146), and leaves (163) showed significant changes in expression in response to drought stress and recovery. Numerous DEPs associated with cell defense and detoxifications were significantly regulated in roots and ISRLs, while in leaves, DEPs related to photosynthesis showed significant changes in expression. A significantly larger number of DEPs related to stress defense were upregulated in HX‐10 than in CS. Expression of six HSPs potentially related to drought tolerance was significantly upregulated under drought conditions, and these proteins were involved in a complex protein–protein interaction network. Further phosphorylation analysis showed that the phosphorylation levels of HSP60, HSP90, and HOP were upregulated in HX‐10 under drought stress. We present an overview of metabolic pathways in wheat seedlings based on abscisic acid signaling and important protein expression patterns.     

小麦生长素结合基因 TaABP1-D的定位表达及染色体定位

生长素影响了植物生长发育的诸多过程。生长素结合蛋白 ABP1 (auxin binding protein) 作为一种生长素受体,在质膜上生长素诱导的快速反应中起重要作用。小麦中已经克隆得到了TaABP1-D,但其在细胞中的作用位置以及在染色体定位情况仍不明确。本实验利用洋葱表皮细胞瞬时表达系统对小麦生长素结合基因 TaABP1-D进行亚细胞定位,表明TaABP1-D蛋白为膜蛋白,存在于细胞质和细胞膜中;同时利用中国春缺体-四体材料和信息学方法,将TaABP1-D定位在小麦5D染色体长臂的近着丝粒位置上,距两侧EST标记BE490079和BE405060的遗传距离分别为0.51 cM和0.28 cM。     

太子参连作对根际土壤微生物的影响

采用微生物培养法和末端限制性片断长度多态性(T-RFLP)技术分析连作对太子参根际土壤微生物多样性的影响。结果表明:连作导致太子参根际土壤细菌和好气性自生固氮菌数量极显著下降,相反,真菌、放线菌、厌气性纤维素分解菌数量极显著增加,而硝化细菌数量变化不显著。T-RFLP分析显示:与太子参-水稻-太子参轮作的土壤相比,太子参连作的土壤细菌种(属)略有减少,其中致病菌和病原菌种(属)增多,并出现一些具拮抗功能的链霉菌属(种);真菌种(属)则表现出上升的趋势,但未检索到与植物致病相关的真菌种(属)。     

杉木人工林土壤微生物群落结构特征

采用氯仿熏蒸法、稀释平板法和磷脂脂肪酸(phospholipid fatty acid,PLFA)方法,分析了常绿阔叶林转变成杉木人工林后土壤微生物种群数量和群落结构的变化特征.结果表明:常绿阔叶林转变为杉木人工林后,林地土壤的微生物生物量碳、可培养细菌和放线菌数降低.杉木人工林地总PLFAs、细菌PLFAs、真菌PLFAs比常绿阔叶林分别降低了49.4％、52.4％和46.6％,革兰氏阳性和阴性细菌PLFAs远低于常绿阔叶林.杉木人工林根际土壤微生物生物量碳、可培养细菌和放线菌数显著高于杉木人工林林地土壤,根际土壤中总PLFAs、细菌PLFAs、革兰氏阳性和阴性细菌PLFAs的含量也高于林地土壤,但真菌PLFAs和细菌PLFAs之比却低于林地土壤.对土壤微生物群落结构进行主成分分析发现,第1主成分和第2主成分共解释了土壤微生物群落结构变异的78.2％.表明常绿阔叶林与杉木人工林土壤的微生物群落结构间存在差异.     

Structural heterogeneity of wheat arabinoxylans revealed by Raman spectroscopy

A set of arabinoxylan samples differing in their arabinose composition and various samples of arabino-xylo-oligosaccharide samples were analysed by Raman spectroscopy. Specific signatures for arabinose substitution were found in several spectral regions, that is, 400-600, 800-950 and 1030-1100 cm(-1). A linear relationship was observed between the peak ratio 855/895 cm(-1) of the second derivative spectra and the A/X ratio determined by chemical analysis. Moreover, spectral changes were observed in the 400-600 cm(-1) region assigned to the coupled vibrations mode in the skeleton: while the intensity of the band at 570 cm(-1) increased with the degree of substitution, that at 494 cm(-1) decreased. Similarly, a linear relationship was observed between the peak intensity ratio 570/494 cm(-1) calculated on the second derivative spectra and the composition data. Analysis of Raman spectra of arabino-xylo-oligosaccharides allowed to identify specific spectral features of disubstitution.     

Morgane, a new LTR retrotransposon group, and its subfamilies in wheats

Transposable elements are the main components of grass genomes, especially in Triticeae species. In a previous analysis, we identified a very short element, Morgane_CR626934-1; here we describe more precisely this unusual element. Morgane_CR626934-1 shows high sequence identity (until 98%) with ESTs belonging to other possible small elements, expressed under abiotic and biotic stress conditions. No putative functional polyprotein could be identified in all of these different Morgane-like sequences. Moreover, elements from the Morgane_CR626934-1 subfamily are found only in wheats and Agropyrum genomes and among these species, only Ae. tauschii and T. aestivum present a high copy number of these elements. They are highly conserved in wheat genomes (95.5%). Based on the uncommon characteristics of the described Morgane-like elements, we proposed to classify them in a new group within the Class I LTR retrotransposon, the Morgane group. Electronic Supplementary Material Supplementary material is available for this article at     

Influence of inorganic nitrogen and pH on the elongation of maize seminal roots

BACKGROUND AND AIMS: Root absorption and assimilation of inorganic nitrogen usually alters rhizosphere pH, but the immediate influence of such pH changes on root elongation as well as that of exogenous inorganic nitrogen itself has been uncertain. METHODS: A differential extensiometer that monitored on a real-time, continuous basis root elongation in an intact 3-d-old maize plant was developed. Treatments included root media at pH 6.5 or 5.6 that lacked nitrogen and ones at pH 6.5 that contained 100 mmol m(-3) NH(4)(+) or NO(3)(-). KEY RESULTS: Acidifying the root medium from pH 6.5 to 5.6 nearly doubled the elasticity of the seminal root, but slightly decreased its elongation. Plasticity of the root apex was not detectable in all treatments. The presence of ammonium or nitrate in the medium stimulated elongation by 29 % or 14 %, respectively. Addition of an osmoticum to the medium had no effect on root elongation in the absence of inorganic nitrogen, but diminished the stimulation of elongation in the presence of ammonium and nitrate. This indicates that these ions or their by-products serve partially as osmolytes. CONCLUSIONS: In nutrient solution, root elongation of a maize seedling--even one with ample nitrogen reserves--depended most strongly on exogenous inorganic nitrogen, and less so, if at all, on either the pH of the bulk nutrient solution or the mechanical properties of cell walls.