Soil salinity is a major constraint on agricultural production as it causes large yield losses in many important crop varieties. Wheat is a major staple crop for human nutrition and most of its commercial varieties are highly salt-sensitive. Salinity stress in wheat is a quantitative trait, affecting plant development at both physiological and biochemical levels. Within wheat plants, shoot tissues are the most sensitive to salinity and accumulate salt over time through the transpiration stream. To build on past studies, we are quantitatively analysing how molecular phenotypes establish in wheat plants over the course of monocot leaf development.

We exposed wheat cv. Wylkatchem to 150 mM NaCl for 8 days through gradual increment of salt and assessed fresh and dry biomass, photosynthetic parameters and chlorophyll content in the 4th leaf. Na+/K+ measurements, proteomic and metabolic analysis were performed after dividing the leaf into sections across the leaf developmental gradient. In monocot leaves, the organization of the growth processes is spatially regulated with dividing cells at the base of the leaf, followed by expanding cells and finally mature cells at the tip.

Wheat leaves showed a significant reduction in physiological parameters such as biomass, chlorophyll content and photosynthesis, under NaCl treatment. A significant decrease in K+ content and an increase in Na+ content and K+/Na+ ratio were observed under the salt treatment, varying from the base to the tip of the leaf. Shotgun proteomic analysis in leaf sections identified the specific spatial arrangements of 1,783 proteins and their salinity response, showing significant reduction in the abundance of protein synthesis machinery and upregulation of protein degradation machinery under salinity stress.

The results highlight the impact of salt stress on plants at the physiological level and in different spatial contexts and suggest a development pattern in the response of protein metabolism in shoots to salinity. Overall, this research will improve fundamental knowledge of the effect of salinity on the establishment of vital cellular functions across the monocot leaf using proteomic techniques. Studying these developmental gradients in breeding populations differing in salinity tolerance molecular mechanisms will aid future development of salt-tolerant wheat varieties to bring significant benefits to global wheat production.