Chronic mild salinity affects source leaves physiology and productivity parameters of rice plants (Oryza sativa L., cv. Taipei 309)

Aim

In rice, the top two leaves are the major carbohydrate source during grain filling. Physiological performance of these leaves under salinity may allow estimate stress-induced yield loss.

Methods

Greenhouse grown rice plants (cv. Taipei 309) were subjected to 10 and 20 mM NaCl stress levels from germination till maturity. Plant development was measured at the flowering stage and yield parameters were quantified after complete ripening of panicles.

Results

Gas exchange in the main source leaves were not significantly affected by any of the stress levels. However, growth parameters as well as total metabolizable carbohydrates content, chlorophyll content (CCI), maximal efficiency of PSII photochemistry in dark-adapted state (F _v/F _m) and lipid peroxidation were significantly affected. Rice yield, measured as total panicle production, declined to 78 and 21 % of controls in 10 and 20 mM NaCl stress, respectively. Stress-induced yield loss was positively related with the decline in CCI, F _v/F _m and K⁺/Na⁺ ratio as well as with the increase in lipid peroxidation and total soluble carbohydrate contents.

Conclusions

Though the stress levels used in this work are below what is considered the minimal critical threshold of toxicity for rice, they induce significant negative effects on plant development and yield, when present along the whole plant life cycle.     

How do pollinator visitation rate and seed set relate to species’ floral traits and community context?

Differences among plant species in visitation rate and seed set within a community may be explained both by the species’ floral traits and the community context. Additionally, the importance of species’ floral traits vs. community context on visitation rate and seed set may vary among communities. In communities where the pollinator-to-flower ratio is low, floral traits may be more important than community context, as pollinators may have the opportunity to be choosier when visiting plant species. In this study we investigated whether species’ floral traits (flower shape, size and number, and flowering duration) and community context (conspecific and heterospecific flower density, and pollinator abundance) could explain among-species variation in visitation rate and seed set. For this, we used data on 47 plant species from two Norwegian plant communities differing in pollinator-to-flower ratio. Differences among species in visitation rate and seed set within a community could be explained by similar variables as those explaining visitation rate and seed set within species. As expected, we found floral traits to be more important than community context in the community with a lower pollinator-to-flower ratio; whereas in the community with a higher pollinator-to-flower ratio, community context played a bigger role. Our study gives significant insights into the relative importance of floral traits on species’ visitation rate and seed set, and contributes to our understanding of the role of the community context on the fitness of plant species.     

Mapping Dominican transnationalism: narrow and broad transnational practices

This article maps the structure for understanding the Dominican transnational field. By transnational field we refer to a web of linkages that affects the lives of Dominicans in their places of residence in every social field. We find that social boundaries of the nation do not coincide with political ones and the degree of participation in transnational exchanges varies. We suggest that the structure of the transnational social field is better understood by establishing and defining broad and narrow transnational social practices.     

Isolation and Characterization of Mercury Resistant Bacillus sp. from Soils with an Extensive History as Substrates for Mercury Extraction in Mexico

Metal phytoextraction assisted by bacteria plays an important role in bioremediation systems. In this work, mercury-resistant bacterial strains were isolated from soils with high levels of mercury (San Joaquin, Queretaro State, Mexico) and identified as Bacillus sp. based on the 16S rDNA gene sequence analysis. The bacterial strains were found to exhibit different multiple mercury-resistance and carbon source utilization characteristics. The mercury reduction ability was tested through a volatilization assay. The bacterial isolates were also evaluated for their ability to promote growth and mercury uptake in tomato plants. In a roll towel assay, the maximum vigor index of tomato plants was obtained with the inoculation of Bacillus sp. A2, A12, B11, B15 and C1, while in a pot assay, the maximum vigor index was obtained with the inoculation of Bacillus sp. A6, A7 and B20, compared with un-inoculated controls in the presence of HgCl₂. Maximum Hg accumulation in the roots and shoots of tomato plants was obtained only with Bacillus sp. A7 in the roll towel assay, whereas in the pot assay, maximum accumulation was obtained with Bacillus sp. A12 compared with un-inoculated controls. Our results show that mercury accumulation in tissue is enhanced by these plant growth promoting bacterial strains, which recommends their possible use as microbe-assisted phytoremediation systems in mercury-polluted soils.     

Effect of different C/N ratios on carotenoid and lipid production by Rhodotorula glutinis

Due to the increasing demand for sustainable biofuels, microbial oils as feedstock for the transesterification into biodiesel have gained scientific and commercial interest. Also, microbial carotenoids have a considerable market potential as natural colorants. The carbon to nitrogen (C/N) ratio of the respective cultivation media is one of the most important parameters that influence the production of microbial lipids and carotenoids. Thus, in the present experiment, the influence of different C/N ratios, initial glucose loadings, and ammonium concentrations of the cultivation medium on microbial cell growth and lipid and carotenoid production by the oleaginous red yeast Rhodotorula glutinis has been assessed. As a general trend, both lipid and carotenoid production increased at high C/N ratios. It was shown that not only the final C/N ratio but also the respectively applied initial carbon and nitrogen contents influenced the observed parameters. The lipid yield was not affected by different ammonium contents, while the carotenoid production significantly decreased both at low and high levels of ammonium supply. A glucose-based increase from C/N 70 to 120 did not lead to an increased lipid production, while carotenoid synthesis was positively affected. Generally, it can be asserted that lipid and carotenoid synthesis are stimulated at higher C/N ratios.