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A study was performed for phyto-genotoxic assay of chromium (Cr) and arsenic (As) through Allium cepa. Various concentrations (0, 1, 3, 6 and 12 mg L) of Cr and As for 48 and 168 h time points exposed to A. cepa. The phytotoxic effects of metal(loid) were evident through inhibited root length and root protein. Metal(loid) toxicity also lead to genotoxic effects, which included depression of mitotic index and increased frequency of chromosomes aberrations like break, fragments, c-metaphase, multipolar arrangements etc. Genotoxic endpoint as progressive frequency of micronuclei in interphase of root meristem cells in treated plants was also observed. This genotoxic endpoint revealed carcinogenic nature of both aforementioned metal(loid). Along with inhibition in root length and protein content, depression in mitotic index as well as stimulation of various abnormality in mitotic cell division indicated that both metal(loid) are hazardous in nature and causing harmful effect on the environment.

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Plant Genetic Resources (PGR) conserved in gene bank provides genetic variability for efficient utilization in breeding programmes. Pre-breeding is required for broadening the genetic base of the crop through identification of useful traits in un-adapted materials and transfer them into better adapted ones for further breeding. So, pre-breeding is a promising alternative (due to use of un-adapted materials) to link genetic resources and breeding programs. Utilization of PGR in crop improvement programmes including prebreeding have been very limited. Advances in genomics have provided us with high-quality reference genomes, sequencing and re-sequencing platforms with reduced cost, marker and QTL assisted selection, genomic selection and population level genotyping platforms. Further, genome editing tools like, CRISPR/Cas9 and its latest modification base editing technology can be used to generate target specific mutants and are important for establishing gene functions with respect to their phenotypes through developing knockout mutations. These new genomic tools can be used to generate, analyse and manipulate the genetic variability for designing cultivars with the desired traits. The genomic tools has not only accelerated the utilization of PGR but also assisted pre-breeding through rapid selection of trait-specific germplasm, reduced periods in breeding cycle for confirming gene of interest in intermediate material and validation of transfer of gene of interest in the cultivated gene pool. In crops, where limited genetic and genomic resources are available, pre-breeding becomes very challenging. We can say that genomics assisted utilization of PGR and prebreeding has accelerated the pace of introgression of complex traits in different crop cultivars.and yield plateau has already been achieved in these cultivars (Chen et al. 2014a). Under these circumstances, use of Plant Genetic Resources (PGR) in crop improvement programs provides an avenue to solve the problem.

Summary Ammonia excretion was studied in the presence of Mn §247 in liquid culture and soil with amendments of the minerals using two ammonia excreting strains of Azotobacter chroococcum (AC2 and AC50) and a non-excreting strain (AC45) under sterilized as well as unsterilized conditions. Ammonia excretion increased in the presence of 1 • 10-~M Mn * § in liquid culture as well as in soil. But there was a decrease in ammonia excretion with increasing clay content.

Results on the kinetics of 7 alpha-hydroxysteroid dehydrogenase 7 alpha-HSDH showed that this enzyme could oxidize all bile acids having an -OH group at the C-7 position. Lineweaver-Burk plots showed Michaelis constant (Km) values of 0.83 and 0.12 mM for cholic acid and chenodeoxycholic acid, respectively. The effect of enzyme concentration on the reaction velocity showed a constant increase in the enzyme activity with increase in enzyme-protein concentration. 7 alpha-HSDH was activated by Na+, K+, Ca2+, and Mn2+ ions and by reducing agents having a thiol group (dithiothreitol, 2-mercaptoethanol). Co2+, Hg2+, Fe3+, Mg2+, Zn2+, Ba2+, and Cu2+ ions, chelating agents (potassium oxalate, heparin, EDTA) oxidizing agents (sodium perchlorate, sodium periodate, sodium persulphate), and detergents (Tween 20, Tween 40, Tween 80, Triton X-100, sodium lauryl sulphate) were inhibitory to 7 alpha-HSDH activity.