The effect of salicylic acid on barley response to water deficit

The effect of a moderate (PEG −0.75 MPa) and severe (PEG −1.5 MPa) water deficit on SA content in leaves and roots as well as the effect of pre-treatment with SA on reaction to water stress were evaluated in two barley genotypes — the modern cv. Maresi and a wild form of Hordeum spontaneum. Water deficit increased SA content in roots, whereas SA content in leaves did not change. The level of SA in the roots of control plants was about twofold higher in ‘Maresi’ than in H. spontaneum. After 6 hours of a moderate stress the level of SA increased about twofold in H. spontaneum and about two and a half-fold in ‘Maresi’. Under severe stress conditions the level of SA increased about twofold in the both genotypes, but not before 24 hrs of the stress. Plant treatment with SA before stress reduced a damaging action of water deficit on cell membrane in leaves. A protective effect was more noticeable in H. spontaneum than in ‘Maresi’. SA treatment increased ABA content in the leaves of the studied genotypes. An increase of proline level was observed only in H. spontaneum. The obtained results suggest that ABA and proline can contribute to the development of antistress reactions induced by SA.     

Quantifying the biologically possible range of steady-state soil and surface climates with climate model simulations

The terrestrial biosphere shapes the exchange fluxes of energy and mass at the land surface. The diversity of plant form and functioning can potentially result in a wide variety of possible climatic conditions at the land surface and in the soil, which in turn feed back to more or less suitable conditions for terrestrial productivity. Here, I use sensitivity simulations to vegetation form and functioning with a global climate model to quantify this possible range of steady-states (“PROSS”) of the surface energy-and mass balances. The surface energy-and water balances over land are associated with substantial sensitivity to vegetation parameters, with precipitation varying by more than a factor of 2, and evapotranspiration by a factor of 5. This range in biologically possible climatic conditions is associated with drastically different levels of vegetation productivity. Optimum conditions for maximum productivity are close to the simulated climate of present-day conditions. These results suggest the conclusions that (a) climate does not determine vegetation form and function, but merely constrains it, and (b) the emergent climatic conditions at the land surface seem to be close to optimal for the functioning of the terrestrial biosphere.     

Influence of different vegetation types on saturated hydraulic conductivity in alluvial topsoils

In the Parí? creek catchment (southwestern part of Slovakia), the influence of different vegetation types on selected soil properties in alluvial topsoils was studied. Specifically, the effect on saturated hydraulic conductivity considered as indicator of water transport process and the effect on soil bulk density considered as indicator of soil structure were analysed. Due to the mutual influence of plant roots on soil properties, the root biomass was also estimated and its relationship to the studied soil properties was explored. Reed and tall-sedge wetlands and alluvial wet meadows represented the studied vegetation types. Adjacent arable lands (former grasslands) with corn were included for comparison. In total, 64 samples were used for comparative analysis. A standard methodology for measurement of the saturated hydraulic conductivity, the so-called falling head technique was used on 250 cm³ soil cores. Undisturbed soil samples were taken from the depth of 5 cm. Analysis of variance, mutual comparison of mean values and correlation matrix were used for statistical analyses. Measurements showed significantly higher values of saturated hydraulic conductivity for topsoils in wetlands (6.2 m day^?1 on average) compared to mown grasslands (1.47 m day^?1) and arable land (0.79 m day^?1). The results indicated a specific significance of wetlands in relation to water transport processes in alluvial topsoils.     

Biodegradation of the neonicotinoid insecticide thiamethoxam by the nitrogen-fixing and plant-growth-promoting rhizobacterium Ensifer adhaerens strain TMX-23

Thiamethoxam (THIA), a second generation neonicotinoid insecticide in the thianicotinyl subclass, is used worldwide. Environmental studies revealed that microbial degradation is the major mode of removal of this pesticide from soil. However, microbial transformation of THIA is poorly understood. In the present study, we isolated a bacterium able to degrade THIA from rhizosphere soil. The bacterium was identified as Ensifer adhaerens by its morphology and 16S ribosomal DNA sequence analysis. High-performance liquid chromatography and mass spectrometry analysis suggested that the major metabolic pathway of THIA in E. adhaerens TMX-23 involves the transformation of its N-nitroimino group (=N–NO₂) to N-nitrosoimino (=N–NO) and urea (=O) metabolites. E. adhaerens TMX-23 is a nitrogen-fixing bacterium harboring two types of nifH genes in its genome, one of which is 98 % identical to the nifH gene in the cyanobacterium Calothrix sp. MCC-3A. E. adhaerens TMX-23 released various plant-growth-promoting substances including indole-3-acetic acid, exopolysaccharides, ammonia, HCN, and siderophores. Inoculation of E. adhaerens TMX-23 onto soybean seeds (Glycine max L.) with NaCl at 50, 100, or 154 mmol/L increased the seed germination rate by 14, 21, and 30 %, respectively. THIA at 10 mg/L had beneficial effects on E. adhaerens TMX-23, enhancing growth of the bacterium and its production of salicylic acid, an important plant phytohormone associated with plant defense responses against abiotic stress. The nitrogen-fixing and plant-growth-promoting rhizobacterium E. adhaerens TMX-23, which is able to degrade THIA, has the potential for bioaugmentation as well as to promote growth of field crops in THIA-contaminated soil.     

Intermediate herbivory intensity of an aboveground pest promotes soil labile resources and microbial biomass via modifying rice growth

Background and Aims

The importance of aboveground herbivores for modifying belowground ecosystems has prompted numerous studies; however, studies can be biased by context dependent conditions which lead to extremely inconsistent results. So far, the impacts of herbivory intensity by important rice pests on rice paddy soil ecosystems are lacking. The aim of this study was to test the hypothesis that intermediate herbivory intensity of the brown planthopper (Nilaparvata lugens Stål) could promote soil labile resources and microbial biomass, while high intensity would show a reverse pattern, by mediating rice plant growth. This study will also help the development of integrative pest management.

Methods

Four hopper infestation density treatments (0, 4, 8 and 12 nymphs per rice plant) and two infestation duration treatments (9 and 15 days after N. lugens infestation, DAI 9 and DAI 15) were established in a glasshouse experiment. Soil and plant were sampled destructively from four replicates and analysed for soil labile resources availability, soil microbial biomass and plant performance, respectively.

Results

The infestation density significantly affected both shoot and root mass of rice (P?<?0.05), soil dissolved organic carbon (DOC) and nitrogen (DON), and microbial biomass carbon (MBC) and nitrogen (MBN), and the effects were further enhanced by prolonged infestation duration. Compared to the control (CK) without N. lugens, plant dry mass, DOC, DON, MBC and MBN increased under low (LD) and moderate hopper densities (MD) but decreased under high density (HD) on DAI 9. Moreover, the LD treatment exerted the most promotional effects on DAI 15. Rice root to shoot ratio generally increased in treatments subjected to herbivory. The labile resources and microbial biomass showed close relationships with both shoot and root mass across treatments, in particular with root mass on DAI 15. Such a trend indicated that the shift of photosynthate allocation to belowground contributed to changes of soil resource availability and microbial biomass.

Conclusions

Intermediate herbivory intensity showed positive effects on rice seedling performance and, further, promoted soil labile resource availability and microbial biomass. The importance of extrapolating temporal and spatial scale, i.e. from the short-term greenhouse experiment to an entire rice growing season in the field, was highlighted.     

Modeling the synergy between HSV-2 and HIV and potential impact of HSV-2 therapy

Mounting evidence indicates that genital HSV-2 infection may increase susceptibility to HIV infection and that co-infection may increase infectiousness. Accordingly, antiviral treatment of people with HSV-2 may mitigate the incidence of HIV in populations where both pathogens occur. To better understand the epidemiological synergy between HIV and HSV-2, we formulate a deterministic compartmental model that describes the transmission dynamics of these pathogens. Unlike earlier models, ours incorporates gender and heterogeneous mixing between activity groups. We derive explicit expressions for the reproduction numbers of HSV-2 and HIV, as well as the invasion reproduction numbers via next generation matrices. A qualitative analysis of the system includes the local and global behavior of the model. Simulations reinforce these analytical results and demonstrate epidemiological synergy between HSV-2 and HIV. In particular, numerical results show that HSV-2 favors the invasion of HIV, may dramatically increase the peak as well as reducing the time-to-peak of HIV prevalence, and almost certainly has exacerbated HIV epidemics. The potential population-level impact of HSV-2 on HIV is demonstrated by calculating the fraction of HIV infections attributable to HSV-2 and the difference between HIV prevalence in the presence and absence of HSV-2. The potential impact of treating people with HSV-2 on HIV control is demonstrated by comparing HIV prevalence with and without HSV-2 therapy. Most importantly, we illustrate that the aforementioned aspects of the population dynamics can be significantly influenced by the sexual structure of the population.     

Duration of sucrose preculture is critical for shoot regrowth of in vitro-grown apple shoot-tips cryopreserved by encapsulation-dehydration

A simple and efficient cryopreservation protocol using encapsulation-dehydration was established for in vitro-grown shoot-tips of apple ‘Gala’ (Malus × domestica Borkh.). Shoot-tips, of 2.0 mm in length and with 5–6 leaf primordia, excised from 4-week-old shoot stock cultures, without cold-hardening, were encapsulated into beads, each being about 5 mm in diameter and containing a single shoot-tip. The beads were precultured on MS medium containing 0.5 M sucrose for 7 days. The precultured beads were dehydrated by air-drying to reduce the water content of the beads to about 22–20 % in 5–7 h, followed by a direct immersion in liquid nitrogen for 1 h. Frozen shoot-tips were re-warmed in a water bath at 38 °C for 2 min and post-cultured on a recovery medium for shoot regrowth. This protocol was successfully applied to four Malus species and one hybrid, among which M. micromalus and M. robusta are wild species native to China. The highest and lowest shoot regeneration rates were found in ‘Gala’ (75 %) and ‘Wangshanhong’ (36 %), with a mean shoot regrowth rate of 61 % attained for the seven Malus genotypes tested. Histological studies revealed that shoots could be regenerated in cryopreserved shoot-tips only when many cells in the leaf primordia and most of the cells in the apical dome survived following cryopreservation. Morphologies of the regenerated plantlets were identical to those from the in vitro stock cultures. Therefore, the encapsulation-dehydration procedure developed in the present study should provide a technical support for setting-up Malus cryo-banking in China.     

Proposal of Ensifer psoraleae sp. nov., Ensifer sesbaniae sp. nov., Ensifer morelense comb. nov. and Ensifer americanum comb. nov

In a survey of rhizobia associated with the native legumes in Yunnan Province, China, seven and nine strains isolated from the root nodules of Psoralea corylifolia, Sesbania cannabina and Medicago lupulina were respectively classified into the novel genomic species groups I and II in the genus Ensifer (former Sinorhizobium) based on the sequence analyses of the 16S rRNA gene. Analyses of concatenated housekeeping genes (atpD, recA and glnII) further revealed that they were distinct lineages in the genus, and group I was most similar to Ensifer terangae and Ensifer garamanticus (both with 94.2% similarity), while group II was most similar to Ensifer adhaerens (94.0%). These groups could be distinguished from closely related species by DNA–DNA relatedness, MALID-TOF MS, cellular fatty acid profiles and a series of phenotypic characters. Therefore, two novel species were proposed: Ensifer psoraleae sp. nov. (seven strains, type strain CCBAU 65732^T = LMG 26835^T = HAMBI 3286^T) and Ensifer sesbaniae sp. nov. (nine strains, type strain CCBAU 65729^T = LMG 26833^T = HAMBI 3287^T). They had a DNA G + C mol% (T_m) of 58.9 and 60.4, respectively. Both of the type strains formed effective nodules on common bean (Phaseolus vulgaris) and their hosts of origin. In addition, the previously described species Sinorhizobium morelense and Sinorhizobium americanum were renamed as Ensifer morelense comb. nov. and Ensifer americanum comb. nov. according to the accumulated data from different studies.