Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2017
Publication Date: 7/12/2017
Citation: Das, A., Kim, D., Kdadka, P., Rakwal, R., Rohila, J.S. 2017. Unravling Key metabolomic alterations of embryos derived from water-imbibed seeds of two wheat cultivars contrasting with contrasting dormancy status. Frontiers in Plant Science. doi.org10.3389fpls.2017.01203. Interpretive Summary: Pre-harvest sprouting (PHS) is pre-mature germination of seeds that occurs in many field crops due to periods of rainfall and excess humidity during crop maturation and before harvesting. This event adversely affects the grain quality, seedling vigor, seed viability and results in poor grain yield and inferior quality of flour, which may cause millions of dollar loss to farmers worldwide. Metabolites are one of the key factors in plant cells that affect the expression of myriad of genes, and proteins controlling cellular processes that leads to untimely germination of wheat seeds before harvest. Through metabolomic profiling we can get a snap shot of metabolites in two contrasting genotypes that have been treated simultaneously for high moisture conditions. The selected metabolites with a role in PHS-tolerance/susceptibility could be used as molecular markers and can be utilized in breeding programs for developing PHS-tolerant breeding lines. In this study, we compared metabolomic snap shot of two contrasting winter wheat varieties [Baegjoong (PHS-susceptible) and Sukang (PHS-tolerant)]. The study revealed that in response to high moisture conditions, abundance of several key metabolites, such as carbohydrates, amino acids, lipids, oxalate, plant hormones, and their precursors, were found altered when compared in the embryos of PHS-susceptible and PHS-tolerant genotypes. Metabolites that were specifically abundant in the PHS-tolerant Sukang provide clues into the cellular mechanisms that promote tolerance to pre-mature germination of wheat seeds.
Technical Abstract: Untimely rains in wheat fields during harvest season can cause pre-harvest sprouting (PHS) which deteriorates yield and quality of the crop. Metabolic homeostasis of embryo and endosperm plays a role in seed dormancy, and determines the status of the maturing grains either as dormant (PHS-tolerant) or non-dormant (PHS-susceptible). Under the current investigation, physiologically matured freshly harvested wheat seeds of a PHS-tolerant (cv. Sukang, dormant) and a PHS-susceptible (cv. Baegjoong, non-dormant) variety were water-imbibed and the isolated embryos were subjected to high-throughput, global non-targeted metabolomic profiling. A careful comparison of identified metabolites between Sukang and Baegjoong embryos at 0 and 48 h of water-imbibition revealed that several key metabolic pathways (such as - lipid, fatty acid, oxalate, hormones, raffinose family of oligosaccharides (RFOs) and amino acids) and phytochemicals were differentially regulated between dormant and non-dormant varieties. Most of the membrane lipids were highly reduced in Baegjoong compared to Sukang, which indicates that cell membrane instability in response to water treatment could also be a key factor in non-dormant wheat varieties for their untimely germination. This study also identifies several key marker metabolites (e.g. RFOs: glucose, fructose, maltose and verbascose), which were highly expressed in Baegjoong after water-imbibition, and can be useful for developing a sensitive early detection system for PHS-damage in wheat. Further, our data show that the key secondary metabolites and phytochemicals (vitexin, chrysoeriol, ferulate, salidroside and genistic acid), which have antioxidant properties, were comparatively low at basal level in Baegjoong, a PHS-susceptible, and non-dormant variety.