Soil microorganisms interact with plants in diversified manner ranging from mobilising nutrients and enhancing their growth, to inducing diseases. They also produce allelochemicals directly or indirectly through conversion from other compounds. In order to hamper plant growth, allelochemicals must accumulate and persist at phytotoxic levels in the rhizosphere soil. However, after their entry into environment, persistence, availability and biological activities of allelochemicals are influenced by microorganisms. Transformation of allelochemicals by soil microbes may result into the compounds with modified biological properties. Such bio-transformations affect the overall allelopathic capability of the producer plant in a direct manner. Several reports describe the allelopathic significance of microbial metabolism products. For instance, a bacterium Actinetobacter calcoaceticus, can convert 2(3H)-benzoxazolinone (BOA) to 2,2´-oxo-l,l´-azobenzene (AZOB) which is more inhibitory to some plants. On the contrary, bacterium Pseudomonas putida catabolises juglone in soils beneath walnut trees; otherwise, juglone accumulates at phytotoxic levels. This review article describes the nature of microbially produced allelochemicals, and the ways to mediate microbial degradation of putative allelochemicals. The given information develops an understanding of persistence, fate and phytotoxicity of allelochemicals in the natural environment, and also points out the possible solution of the problems due to microbial interventions in the soil.

A time resolved imaging study of pulsed laser ablated Fe and Al plasma plumes with specific interest in the splitting of plumes into the slow and fast moving components as they expand through the background argon gas at different pressures is reported. The material ablation was achieved using a Q-switched Nd:YAG ͑yttrium aluminum garnet͒ laser operating at 532 nm with a pulse duration of ϳ8 ns full width at half maximum and a fluence of 30 Jcm −2 at the target surface. Typical time resolved images with low magnification show that the splitting occurs at moderate background gas pressures ͑0.5 and 1.0 mbar for Fe, and 0.2 mbar for Al plasma plumes͒. The plume splitting did not occur for higher background gas pressures.

Optical measurements of the cadmium plasma produced by the fundamental, second, and third harmonics of a Nd:YAG laser are reported. The excitation temperature and ionic temperature have been determined from the Boltzmann plot and Saha equation, whereas the number density is estimated from the Stark broadened profile of the spectral lines. The variations in the excitation temperature and number density with the ambient air pressure as well as with the laser irradiance have been studied. Besides, the spatial distributions of the temperature and number density have been investigated.

No abstract

No abstract

No abstract

No abstract

No abstract