A review of soil NO transformation: associated processes and possible physiological significance on organisms

NO emissions from soils and ecosystems are of outstanding importance for atmospheric chemistry. Here we review the current knowledge on processes involved in the formation and consumption of NO in soils, the importance of NO for the physiological functioning of different organisms, and for inter- and intra-species signaling and competition, e.g. in the rooting zone between microbes and plants. We also show that prokaryotes and eukaryotes are able to produce NO by multiple pathways and that unspecific enzymo-oxidative mechanisms of NO production are likely to occur in soils. Nitric oxide production in soils is not only linked to NO production by nitrifying and denitrifying microorganisms, but also linked to extracellular enzymes from a wide range of microorganisms. Further investigations are needed to clarify molecular mechanisms of NO production and consumption, its controlling factors, and the significance of NO as a regulator for microbial, animal and plant processes. Such process understanding is required to elucidate the importance of soils as sources (and sinks) for atmospheric NO

The apical sensory organ of a gastropod veliger is a receptor for settlement cues

Volume: 198Start Page: 67End Page: 7

Cloning and functional expression of the first eukaryotic Na+–tryptophan symporter, AgNAT6

The nutrient amino acid transporter (NAT) subfamily of the neurotransmitter sodium symporter family (NSS, also known as the solute carrier family 6, SLC6) represents transport mechanisms with putative synergistic roles in the absorption of essential and conditionally essential neutral amino acids. It includes a large paralogous expansion of insect-specific genes, with seven genes from the genome of the malaria mosquito, Anopheles gambiae. One of the An. gambiae NATs, AgNAT8, was cloned, functionally expressed and characterized in X. laevis oocytes as a cation-coupled symporter of aromatic amino acids, preferably l-phenylalanine, l-tyrosine and l-DOPA. To explore an evolutionary trend of NAT-SLC6 phenotypes, we have cloned and characterized AgNAT6, which represents a counterpart of AgNAT8 descending from a recent gene duplication (53.1% pairwise sequence identity). In contrast to AgNAT8, which preferably mediates the absorption of phenol-branched substrates, AgNAT6 mediates the absorption of indole-branched substrates with highest apparent affinity to tryptophan (K0.5Trp=1.3 μmol l–1 vs K0.5Phe=430 μmol l–1) and [2 or 1 Na+ or K+]:[aromatic substrate] stoichiometry. AgNAT6 is highly transcribed in absorptive and secretory regions of the alimentary canal and specific neuronal structures, including the neuropile of ventral ganglia and sensory afferents. The alignment of AgNATs and LeuTAa, a bacterial NAT with a resolved 3D structure, reveals three amino acid differences in the substrate-binding pocket that may be responsible for the indole- vs phenol-branch selectivity of AgNAT6 vs AgNAT8. The identification of transporters with a narrow selectivity for essential amino acids suggests that basal expansions in the SLC6 family involved duplication and retention of NATs, improving the absorption and distribution of under-represented essential amino acids and related metabolites. The identified physiological and expression profiles suggest unique roles of AgNAT6 in the active absorption of indole-branched substrates that are used in the synthesis of the neurotransmitter serotonin as well as the key circadian hormone and potent free-radical scavenger melatonin