Influence of salinity exposure on wheat root metabolism in the context of tissue tolerance and susceptibility

Salinity is responsible for large yield losses of crops around the world. Wheat is a staple food crop, and its early growth is particularly salt sensitive. Salinity stress causes adverse effects on plant growth and development at both physiological and biochemical levels. To date, numerous studies have focused on plant metabolic responses to salinity in above ground tissues, however surprisingly little is known about the metabolic responses of wheat roots exposed to salt. Within the plant, roots are most vulnerable to salinity as they are directly exposed to salt in the soil. Previous research identified the key role that Gamma Aminobutyric Acid (GABA) metabolism plays in the salt responses of shoots. This project will investigate the regulation of GABA metabolism in salt stressed roots as well as the impact of salt stress on root physiology and respiration. We exposed Scepter wheat variety to 150mM NaCl for 3 days and 6 days through gradual increment of salt and assessed biomass, chlorophyll content, Na+ and K+ levels using flame photometry, and root respiration by Q2 oxygen sensor. Scepter showed significant reduction in fresh weight and dry weight at the whole plant level and organ level after 3 days of treatment with 150 mM NaCl, salt treatment caused a reduction in relative growth rate, chlorophyll content and an increase in root to shoot ratio in salt treated plants compared to the controls. A significant increase of Na+ content was observed in both roots and shoots after 3 days and 6 days of 150 mM NaCl treatment, but K+ levels significantly declined after 3 days of salt treatment in both roots and shoots. The Na+/K+ ratio significantly increased in both shoots and roots after 3 days and 6 days of salt treatment, but roots have higher Na+/K+ ratio compared to shoots. Experiments on oxygen consumption of roots with externally added GABA showed that capacity of roots to use GABA under salt stress to drive respiration increases with salt exposure. The results highlight the implication of salt stress on plants at physiological level and suggest a possible role of GABA in root responses to salinity, further this project will use high throughput mass spectrometry based metabolomics and proteomic approaches to elucidate the metabolic and proteomic changes in roots of wheat varieties which differ in salt tolerance based on the shoot characteristics under salinity.