Sugarcane (Saccharum spp.) has a large complex polyploid genome. Assay of molecular variation in the expressed component of its genome has relevance to the analysis of genetic diversity, variety identification and introgression of agronomically useful genes present in different members of the Saccharum complex. The present study was designed to evaluate single-strand conformational polymorphism (SSCP) as a potential tool to detect genetic variation in the expressed sequence tag (EST) derived microsatellites. Twenty primer pairs obtained from EST libraries and one designed from soluble acid invertase gene sequence were used to characterise 21 clones belonging to four different Saccharum species and 22 sugarcane varieties/genotypes. All the markers, including the two, which were reported monomorphic even at the interspecific level in an automated fragment analysis system in a previous study, could be successfully converted into polymorphic ones using SSCP analysis. A broad range of variation could be revealed by this technique. The Saccharum spp. clones could be grouped into distinct clusters, confirming the species relationships postulated earlier using morphological, biochemical and molecular methods. The polymorphic markers could also differentiate all the 22 sugarcane varieties from each other. This is a first report that demonstrates the usefulness of SSCP technique, in obtaining polymorphic microsatellite markers developed from EST sequences for various genetic and breeding applications, in this polyploid species.
Flue-cured tobacco is an important commercial crop, which is highly sensitive to the wet conditions. An experiment was conducted with different periods of waterlogging (0, 24, 48, 72 and 96 h) at flower bud initiation stage to study its effect on gas exchange parameters, activity of antioxidative enzymes, yield and quality of fluecured tobacco. The gas exchange parameters viz., photosynthetic rate, stomatal conductance and transpiration rate and soluble proteins decreased with increase in waterlogging period. The activities of peroxidase, polyphenol oxidase and catalase as well as superoxide dismutase showed variation under waterlogging condition which protects the cells from reactive oxygen species generated under waterlogging. With increase in period of waterlogging yield was reduced by 23, 43, 76 and 82 % due to waterlogging for a period of 24, 48, 72 and 96 h, respectively. Quality constituents viz., nicotine and reducing sugars decreased with increase in the period of waterlogging at all leaf positions on the plant. The results showed that tobacco plants tried to counteract the adverse effects of waterlogging by enhancing the activity of superoxide dismutase.
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