Showing papers on "Sesbania rostrata published in 2006"

Microbial Biomass Turnover in Indian Subtropical Soils under Different Sugarcane Intercropping Systems

Abstract: Changes in soil organic C (C org ), total N (N t ), available nutrients, soil microbial biomass C (C mic ) and N (N mic ), and mineralizable C and N in the sugarcane (Saccharum officinarum L.) rhizosphere were evaluated under intensive sugarcane cropping systems with intercrops including wheat (Triticum aestivum L.), maize (Zea mays L.), rajmash (Phaseolus vulgaris L.), green gram [Vigna radiata (L.) R. Wilczek var. radiata], cowpea [Vign aunguiculata (L.) Walp.], lentil (Lens culinaris Medik.), mustard (Brassica rapa L.), potato (Solanum tuberosum L.), and sesbania (Sesbania rostrata Bremek. & Oberm.) in subtropical soils of India. Organic C increased significantly when maize (25%), wheat (24%), mustard (19%), potato (17%), and rajmash (13%) were intercropped with sugarcane, while legume intercrops substantially increased N t and available N. Increase in microbial respiration was greater where maize (42%), wheat (37%), or mustard (31%) were intercropped compared with pulse crops. Soil microbial biomass C accounted for 2.7 to 3.3% of C org content and N mic accounted for 2.6 to 3.7% of N t under different intercropping conditions. A higher CO 2 evolution rate and wider C mic /N mic ratics were recorded with cereal and mustard intercrops, whereas higher N mineralization was recorded with pulse intercrops. Results indicate that intercropping with pulse crops and incorporation of their labile C substrate improved N mineralization. The build up of the C pool and C mic in the case of cereals, mustard, and potato intercropping should promote long-term stability.

Signaling and Gene Expression for Water-Tolerant Legume Nodulation

Abstract: In the symbiotic interaction with rhizobia, legumes develop nodules in which nitrogen fixation takes place. Upon submersion, most temperate legumes are incapable of nodulation, but tropical legumes that grow in waterlogged soils have acquired water stress tolerance for growth and nodulation. One well-studied model plant, the tropical, semi-aquatic Sesbania rostrata, develops stem-located adventitious root primordia that grow out into adventitious roots upon submergence and develop into stem nodules after inoculation with the microsymbiont, Azorhizobium caulinodans. Sesbania rostrata also has a nodulated underground root system. On well-aerated roots, nodules form via root hair curling infection in the zone, just above the root tip, where root hairs develop; on hydroponic roots, an alternative process is used, recruiting a cortical intercellular invasion program at the lateral root bases that skips the epidermal responses. This intercellular cortical invasion entails infection pocket formation, a process t...

Isolation and differential expression of β-1,3-glucanase messenger RNAs, SrGLU3 and SrGLU4, following inoculation of Sesbania rostrata.

Abstract: We report here the isolation and characterisation of two new β-1,3-glucanase cDNAs, SrGLU3 and SrGLU4, from a tropical legume Sesbania rostrata Bremek. & Oberm., which form N2-fixing nodules on the stem after infection by Azorhizobium caulinodans. SrGLU3 was characterised as being grouped in a branch with tobacco class I β-1,3-glucanases, where the isoforms were reported to be induced by either pathogen infection or ethylene treatment. SrGLU4 was characterised as separate from other classes, and we propose this new branch as a new class (Class VI). The SrGLU3 gene was constitutively expressed in normal stem nodules induced by the wild type strain of A. caulinodans (ORS571), and also even in immature stem nodules induced by a mutant (ORS571-C1), which could not form mature stem-nodules. In contrast, the transcript accumulation of SrGLU4 was hardly detectable in immature nodules inoculated by the ORS571-C1 mutant. We suggest that S. rostrata makes use of SrGLU4 to discriminate between symbionts and non-symbionts (mutants) in developing nodules. We propose the SrGLU4 gene as a new nodulin during nodulation.