3) Ms. Dakshayani Lokesh

Saline soil limits crop productivity and can negatively affect seed germination in drylands. Therefore, understanding the molecular mechanisms underlying salt-inhibition of germination is crucial for improving germination in saline environments. Halophytes are highly tolerant to extreme salinity, yet seeds of many halophytes will not germinate under saline conditions. Our previous research revealed that salt-treated seeds of the model halophyte Eutrema salsugineum (Brassicaceae) enter a previously uncharacterized state, which we coined “dormant-like”. This state is distinguished by retarded germination-associated metabolism and increased expression of germination repressors. Seeds sense the osmotic component of salt exposure and will germinate immediately upon transfer to non-saline medium confirming that they do not enter secondary dormancy. We therefore surmised that salt-inhibition of E. salsugineum seed germination could be model for examining the long-term survival of imbibed seeds.
Remarkably, we found that salt-inhibited, imbibed E. salsugineum seeds remain viable for at least 9 months. During this period, seed protein and oil reserves are gradually mobilized. The levels of the constituent sugars of pectin and cellulose as well as nucleotide levels subsequently rise, indicating the possible mobilization of cell wall sugars and nucleic acids for energy production. However, there is an eventual decrease in the levels of TCA cycle intermediates. After 7 months of salt treatment, seedling establishment is impaired. These findings led us to hypothesize that salt-inhibited E. salsugineum seeds possess a reduced metabolic rate. To test this hypothesis, we fed [U-13C] glucose to salt- and non-salt-treated seeds and demonstrated reduced glycolytic carbon flux in salt-treated seeds. This low metabolic rate was further reflected in reduced respiration of salt-treated seeds. We now postulated that boosting the metabolic rate of the TCA cycle by feeding citrate to long-term salt-inhibited seeds could improve seedling establishment. Seedlings germinated from citrate-fed, 6-month salt-treated seeds exhibited enhanced carbon flux through the TCA cycle, which was associated with improved seedling establishment. Our findings suggest that a reduced metabolic rate allows conservation of seed storage reserves while maintaining a low level of energy production. This adaptation would ensure long-term survival of seeds in the imbibed, dormant-like state until rainfall provides more favorable conditions for seedling establishment.