Experiments were conducted in eight ponds of 0.08 ha each for a period of 6 months to evaluate the production performance combinations of Indian major carps and exotic carps at varied stocking densities and species. The four different treatments evaluated were stocking densities of 5000 and 10 000 fingerlings/ha with three Indian major carps (catla, rohu, mrigal) and combination of three Indian major carps with three exotic carp species (silver carp, grass carp and common carp) in replicate ponds. The mean net production levels recorded in different treatments were 1791 kg/ha, 2385 kg/ha, 2532 kg/ha and 3472 kg/ha in 6 months in treatments with three species combinations at 5000/ha, six species at 5000/ha, three species at 10 000/ha and six species at 10 000/ha, respectively. Correspondingly, the mean growth, survival and feed conversion ratios recorded in four treatments were 432 g, 84.7% and 1.49; 567 g, 86.2% and 1.47; 318 g, 82.1% and 1.69; and 444 g, 80.4% and 1.67, respectively.
Senescence is a highly regulated process accompanied by changes in gene expression. While the mRNA levels of most genes decline, the mRNA levels of specific genes (senescence associated genes, SAGs) increase during senescence. Arabidopsis SAG12 (AtSAG12) gene codes for papain-like cysteine protease. The promoter of AtSAG12 is SA-responsive and reported to be useful to delay senescence by expressing cytokinin biosynthesis gene isopentenyltransferase specifically during senescence in several plants including Arabidopsis, lettuce and rice. The physiological role of AtSAG12 is not known; the homozygous atsag12 mutant neither fails to develop senescenceassociated vacuoles nor shows any morphological phenotype. Through BLAST search using AtSAG12 amino acid sequences as query, we identified a few putative homologues from rice genome (OsSAGs; Oryza sativa SAGs). OsSAG12-1 is the closest homologue of AtSAG12 with 64% similar amino acid composition. Expression of OsSAG12-1 is induced during senescence and pathogen-induced cell death. To evaluate the possible role of OsSAG12-1 we generated RNAi transgenic lines in Japonica rice cultivar TP309. The transgenic lines developed early senescence at varying levels and showed enhanced cell death when inoculated with bacterial pathogen Xanthomonas oryzae pv.oryzae. Our results suggest that OsSAG12-1 is a negative regulator of cell death in rice.
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