Date of Award
Master of Science (MS)
Plant and Environmental Science
To meet the increasing food demand, conventional agriculture practices emphasizes on quantitative yield and often involves intensification of nitrogen fertilizers. However, owing to the high mobility in the soil, nitrogen leaching imposes serious consequences on environment and subsequently on human health. Although the quantitative yield is predominantly determined by primary metabolism, the secondary metabolism in the plant not only function as response molecules against biotic and abiotic stress but also determines the qualitative composition of the crop. Nitrogen deficiency limits growth more than photosynthesis, leading to accumulation of the carbon based secondary precursors. Nitrogen deficiency or excess is also associated with increase in the reactive oxygen species (ROS) further driving the biosynthesis of secondary metabolism and utilization of the carbon precursors. Furthermore, the leaves are documented to accumulate a higher proportion of phenolics and exhibit translocation across the plants based on the environmental trigger and developmental stage.
Polyphenols constitute one such class of carbon based secondary metabolites biosynthesized throughout the plant’s life and have key role as signaling molecules, free radical scavengers etc. Although, the presence of an aromatic carbon ring structure is the characteristic of phenolics, there exist vast structural diversity based on the addition and modification to the core ring structure and location of one or more hydroxyl groups. These distinctions both within and between the different classes of phenolics further dictates their biological activity and efficiency. However, variation in the quantitative and qualitative metabolic pool of phenolics in the plant could not only be driven by the stress stimuli but also by the extent of the stress. Thus, the present study investigated the content, composition and localization of foliar phenolics from two cultivars of Fragaria ananassa (cv. Camarosa and cv. Albion) exposed to four different nitrogen (N) fertilization treatments (control, 8mM N, 16mM N and 30mM N). Using a non-targeted metabolomics approach, present study not only exhibited a non-linear response in the content between foliar phenolic classes but also emphasizes the compositional variation and preferential localization of the biosynthesized phenolics.
The tentatively identified metabolites encompassed different groups of non-anthocyanic phenolics namely, hydrolysable tannins (simple galloyl glucoses, ellagic acid derivatives and ellagitannins), hydroxycinnamate derivatives, flavones, flavonols, flavan-3-ols and oligomeric proanthocyanidins. For both the cultivars, the content of different phenolic classes showed the general trend of increase with decrease in N concentration, however, the magnitude of response varied between both the cultivars and the different classes. Primary metabolites viz. sugars, organic acids and the key amino acid glutamine, did not exhibit a significant response to the applied N treatments, across both the cultivars. Total hydrolysable tannin (HTs) decreased by 70% as N concentration increased from 8mM N to 16mM N in cv. Camarosa and no variation across the treatments in cv. Albion. However the total phenylpropanoids decreased (P
From the study, we concluded that along with the increase in carbon based secondary compounds under nitrogen deficiency; the variation within the class of phenolics is linked to the biosynthetic origin and physiological role of the phenolic class.
Narvekar, Ashwini Sushil, "Changes in the Content, Composition and Localization of Foliar Phenolic Compounds of Strawberries as Influenced by Nitrogen Regimen" (2018). All Theses. 3256.