INPLANTA TRANSFORMATION AND MOLECULAR AND PHYSIOLOGICAL CHARACTERIZATION OF EARLY GENERATION TRANSGENIC TOMATO PLANTS (Solanum lycopersicum L.) OVEREXPRESSING PgNHX1 GENE
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Date
18-11-11
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University of Agricultural Sciences GKVK, Bangalore
Abstract
Tomato is a widely distributed annual vegetable crop adapted to a large variety of climates. However, in spite of its broad adaptation, production is concentrated in a few warm and rather dry areas. In these areas with an optimal climate for tomato, salinity is a serious constraint for maintaining high productivity. Salinity has a negative effect on tomato yield as it decreases fruit weight and marketable yield. Although, there are comparatively salt tolerant relatives of tomato, it has proved difficult to enrich elite lines with genes from wild species that confer tolerance because of the complexity of the trait. One possible mechanism by which plants could survive salt stress is to compartmentalize sodium ions away from the cytosol and this is performed by sequestration of Na+ ions into the vacuole through the action of Na+/H+ antiporter. So the overexpression of this gene would provide higher salt tolerance in transgenic plants.
In the present study, a reproducible protocol for floral dip transformation of tomato has been used. The frequency of transformation was eleven percent. Transgenic tomato lines overexpressing Na+/H+ antiporter (PgNHX1) gene was developed. The transgenic nature of these plants was confirmed by PCR with gene specific primer (PgNHX1), marker gene (hptII) and reporter gene (GUS) primers and transcript level of the gene was analyzed using reverse transcription analysis (RT-PCR) and ten lines recorded as high expression level. The enhanced levels of proline, high retention of chlorophyll a, chlorophyll b, total chlorophyll, total soluble sugar and relative water content in roots, young leaves and old leaves in transgenic plants as compared to non-transformed control was observed. In addition, cell viability and total soluble solids in fruits conferred better tolerance of transgenic lines for NaCl induced salinity stress (250mM NaCl). High germination percentage and better seedling vigour was observed in presence of 100mM NaCl with 20mg/L hygromycin. Though, these plants accumulated high Na+ and less K+ ions, but showd high K+/Na+ ratio as compared to control plants. They were able to grow, flower and set fruits in the presence of 200mM of NaCl in T1 and 250mM in T2 generation.