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A Possible Role of Triosephosphate/Phosphate Translocator of Chloroplast Envelope Membrane in the Responses of Tomato Plants to Salinity

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Author(s): Magda Mahmoud El-Araby | Abla Hassan Nassar | Hanan Farid Shaaban

Journal: International Journal of Botany
ISSN 1811-9700

Volume: 2;
Issue: 2;
Start page: 177;
Date: 2006;
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Keywords: Salinity | tomato plants | photosynthesis | chlorophylls | carotenes | triosephosphate translocator (TPT)

ABSTRACT
Triose phosphate/phosphate translocon (TPT) is a transporter of the inner chloroplast envelope membrane, responsible of exporting carbon fixed in photosynthesis as triosephosphate to the cytosol in a counter antiport with inorganic phosphate. Thus, TPT functional rate exerts strong control on the rate of CO2 assimilation, as a result of positive control on sucrose biosynthesis in the cytosol and negative control on the rate of starch accumulation in the leaf, which generally mimics metabolic trends of plants with stress disorders. Consequently, possible responses of TPT to varying levels of NaCl (50, 100 and 150 mM) salinity were investigated in the present work in 28-day-old Castle rock tomato seedlings. First, the sensitivity of Castle rock tomato seedlings to varying levels of salinity was evaluated. Responses of seedlings were addressed as progressive highly significant reduction of growth parameters with lapse of time from 7 to 28 days from sowing. Significant reductions in the leaf area per plant, as well as in their fresh and dry weights were recorded, with a concomitantly significant drop in chlorophylls, particularly chlorophyll a and enhanced levels of α- and β- carotenes. Thus, an excessively salinity-induced stress on photosynthetic machinery with increase in NaCl concentration could be assumed. Chloroplasts were isolated from leaves of 28-day-old seedlings of the control and salinity treatments, using Percoll gradient. Chloroplast envelope was separated from chloroplasts by ultracentrifugation, using sucrose gradient. On the bases of SDS-PAGE protein banding patterns of the pure envelope membrane, TPT was assumed as a 30.1 kDa protein. The intensity of this protein showed a statistically strong negative correlation with increase of salinity level from 50 to 150 mM. Thus, it could be suggested that TPT attenuation under the impact of salinity might be implicated within metabolic adaptations of plants to stressful conditions.

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