Phenotyping the Chilling and Freezing Responses of Young Microspore Stage Wheat Spikes Using Targeted Metabolome and Lipidome Profiling.

Chilling and frost conditions impose major yield restraints to wheat crops in Australia and other temperate climate regions. Unpredictability and variability of field frost events are major impediments for cold tolerance breeding. Metabolome and lipidome profiling were used to compare the cold response in spikes of cold-tolerant Young and sensitive variety Wyalkatchem at the young microspore (YM) stage of pollen development. We aimed to identify metabolite markers that can reliably distinguish cold-tolerant and sensitive wheat varieties for future cold-tolerance phenotyping applications. We scored changes in spike metabolites and lipids for both varieties during cold acclimation after initial and prolonged exposure to combined chilling and freezing cycles (1 and 4 days, respectively) using controlled environment conditions. The two contrasting wheat varieties showed qualitative and quantitative differences in primary metabolites involved in osmoprotection, but differences in lipid accumulation most distinctively separated the cold response of the two wheat lines. These results resemble what we previously observed in flag leaves of the same two wheat varieties. The fact that this response occurs in tissue types with very different functions indicates that chilling and freezing tolerance in these wheat lines is associated with re-modelling of membrane lipid composition to maintain membrane fluidity.