Rice flooding negatively impacts root branching and arbuscular mycorrhizal colonization,but not fungal viability

Rice is mostly cultivated in wetlands, where arbuscular mycorrhization (AM) is reported to decrease. The mechanisms regulating such events are largely unknown. Rice uninoculated and inoculated with Rhizophagus irregularis were grown in dry and flooded conditions, allowing also for the transfer of plants from one water regime to the other. Roots were sampled at different times, from 7 to 35 d post‐inoculation (dpi). The morphological and molecular parameters (root branching, aerenchyma formation, mycorrhizal colonization, AM marker gene expression) were evaluated. Root branching was more pronounced in dry conditions, and such phenotype was enhanced by the fungus. In wetlands, the colonization level was comparable till 21 dpi, when the mycorrhization then decreased, paralleled by an increase in aerenchyma. Expression of the fungal transporters was comparable under the two conditions. The root apparatus, when shifted from one water regime to the other, rapidly adapted to the new condition, revealing a marked plasticity. The reversibility of the AM rice symbiosis was also mirrored by expression changes of plant marker genes. The results demonstrate that the water regime is the driving force that regulates AM colonization under flooding conditions, by directly influencing root architecture and anatomy, but without impacting the basic AM functionality.     

Redescription of Tethya norvegica Bowerbank (Porifera, Demospongiae), with remarks on the genus Tethya in the North East Atlantic

Tethya norvegica Bowerbank, 1872, a northern species generally synonymized with T. aurantium . has been studied from Scotland, The Faroes, Norway, Iceland, Spitzbergen and Bear Island. The species is redescribed and its North East Atlantic distribution delimited Tethya norvegica is compared, on the basis of morphometric and electrophoretic features, with T. aurantium and F.citrina . Morphological, morphometric and electrophoretic data suggest that I norvegica is a distinct biological species.