Contribution of N2 fixing cyanobacteria to rice production: availability of nitrogen from 15N-labelled cyanobacteria and ammonium sulphate to rice

This study investigate the potential contribution of nitrogen fixation by indigenous cyanobacteria to rice production in the rice fields of Valencia (Spain). N₂-fixing cyanobacteria abundance and N₂ fixation decreased with increasing amounts of fertilizers. Grain yield increased with increasing amounts of fertilizers up to 70 kg N ha^-1. No further increase was observed with 140 kg N ha^-1. Soil N was the main source of N for rice, only 8–14% of the total N incorporated by plants derived from ¹⁵N fertilizer. Recovery of applied ¹⁵N-ammonium sulphate by the soil–plant system was lower than 50%. Losses were attributed to ammonia volatilization, since only 0.3–1% of applied N was lost by denitrification. Recovery of ¹⁵N from labeled cyanobacteria by the soil–plant system was higher than that from chemical fertilizers. Cyanobacterial N was available to rice plant even at the tillering stage, 20 days after N application. This revised version was published online in June 2006 with corrections to the Cover Date.     

Gene delivery into mouse retinal ganglion cells by in utero electroporation

Background  

The neural retina is a highly structured tissue of the central nervous system that is formed by seven different cell types that are arranged in layers. Despite much effort, the genetic mechanisms that underlie retinal development are still poorly understood. In recent years, large-scale genomic analyses have identified candidate genes that may play a role in retinal neurogenesis, axon guidance and other key processes during the development of the visual system. Thus, new and rapid techniques are now required to carry out high-throughput analyses of all these candidate genes in mammals. Gene delivery techniques have been described to express exogenous proteins in the retina of newborn mice but these approaches do not efficiently introduce genes into the only retinal cell type that transmits visual information to the brain, the retinal ganglion cells (RGCs).     

Carbonic anhydrase in the carotid body and the carotid sinus nerve

Summary It is well known that carbonic anhydrase plays an important role in the physiological responses of carotidbody chemoreceptors to hypercapnia. Nevertheless the precise location of the enzyme within the carotid body has been a matter of controversy for many years. Using the Hansson method we found histochemical evidence that this enzyme is localized in type I cells. Type II cells and nerve terminals did not show enzymatic activity. These results allow us to define the carotid body as a secondary receptor in the context of the acidic hypothesis of transduction in the carotid body.     

Effects of zinc deficiency on the chick embryo blastoderm

A technique which permits the in vitro study of zinc deficiency in early embryos of Gallus domesticus is described using dithizone as a chelating agent. Zinc deficiency produces specific and constant lesions which are more severe as the embryo is cultivated in more early stages. The most serious alterations affect growth in general and the differentiation of the nervous system and mesoderm.     

Epiphytic cyanobacteria on Chara vulgaris are the main contributors to N(2) fixation in rice fields

The distribution of nitrogenase activity in the rice-soil system and the possible contribution of epiphytic cyanobacteria on rice plants and other macrophytes to this activity were studied in two locations in the rice fields of Valencia, Spain, in two consecutive crop seasons. The largest proportion of photodependent N(2) fixation was associated with the macrophyte Chara vulgaris in both years and at both locations. The nitrogen fixation rate associated with Chara always represented more than 45% of the global nitrogenase activity measured in the rice field. The estimated average N(2) fixation rate associated with Chara was 27.53 kg of N ha(-1) crop(-1). The mean estimated N(2) fixation rates for the other parts of the system for all sampling periods were as follows: soil, 4.07 kg of N ha(-1) crop(-1); submerged parts of rice plants, 3.93 kg of N ha(-1) crop(-1); and roots, 0.28 kg of N ha(-1) crop(-1). Micrographic studies revealed the presence of epiphytic cyanobacteria on the surface of Chara. Three-dimensional reconstructions by confocal scanning laser microscopy revealed no cyanobacterial cells inside the Chara structures. Quantification of epiphytic cyanobacteria by image analysis revealed that cyanobacteria were more abundant in nodes than in internodes (on average, cyanobacteria covered 8.4% +/- 4.4% and 6.2% +/- 5.0% of the surface area in the nodes and internodes, respectively). Epiphytic cyanobacteria were also quantified by using a fluorometer. This made it possible to discriminate which algal groups were the source of chlorophyll a. Chlorophyll a measurements confirmed that cyanobacteria were more abundant in nodes than in internodes (on average, the chlorophyll a concentrations were 17.2 +/- 28.0 and 4.0 +/- 3.8 microg mg [dry weight] of Chara(-1) in the nodes and internodes, respectively). These results indicate that this macrophyte, which is usually considered a weed in the context of rice cultivation, may help maintain soil N fertility in the rice field ecosystem.     

Carbonic anhydrase in the carotid body and the carotid sinus nerve

It is well known that carbonic anhydrase plays an important role in the physiological responses of carotid-body chemoreceptors to hypercapnia. Nevertheless the precise location of the enzyme within the carotid body has been a matter of controversy for many years. Using the Hansson method we found histochemical evidence that this enzyme is localized in type I cells. Type II cells and nerve terminals did not show enzymatic activity. These results allow us to define the carotid body as a secondary receptor in the context of the "acidic hypothesis" of transduction in the carotid body.