VACUOLAR SODIUM COMPARTMENTATION AND SALT TOLERANCE: DEVELOPMENT OF RICE TRANSGENICS FOR THE Na+ TRANSPORTER GENE NHX1
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Date
2009-07-10
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UNIVERSITY OF AGRICULTURAL SCIENCES GKVK, BENGALURU
Abstract
Salinity is one of the major environmental factors limiting plant growth and its
productivity worldwide. To maintain growth and productivity plants must adapt to stress
conditions and exercise specific tolerance mechanisms. In plants Na+/H+ antiporters
which catalyze the exchange of Na+ for H+ are localized on both plasma and vacuolar
membranes, removing Na+ from cytosol or compartmentalizing it in vacuoles for
maintenance of a low Na+ concentration.
In the present study, analysis of T1 transgenic rice plants overexpressing NHX1 to
select putative transformants was done. To screen putative T1 plants for salt tolerance, a
Stringent Salt Screening Test (SSST) was followed at two levels. At seed level, root and
shoot growth of T1 putative transformants was used as a selection criterion. At plant
level, extent of chlorosis was used at selection criteria. Some of the transgenics showed
significantly higher root and shoot growth and lesser or no chlorotic symptoms compared
to wild type. To confirm the presence of gene in putative T1 transgenic plants, PCR,
Southern analysis and RT-PCR analysis were followed using genomic DNA. The results
showed that all the selected seedlings from the SSST were PCR positives. And four
selected lines were positive for southern and RT-PCR analysis. Physiological studies
such as chlorophyll estimation and membrane permeability tests were also conducted to
assess their levels of tolerance at T1 generation. Some of the T1 transformants showed
lower percent reduction in chlorophyll content and less membrane leakage after NaCl
treatment compared to wild type.
These results clearly demonstrate that transgenic rice plants overexpressing
PgNHX1, a vacuolar antiporter have better salt-tolerance. This could have been mediated
by compartmentation of excess Na+ from cytosol into the vacuole and there by reducing
the toxic effects of Na+ in the cell.
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