Molecular and Biochemical Characterization of Sugar Beet (Beta vulgaris L.) Responses to Different Boron Concentrations: Changes in Antioxidant-Related Gene Expression and Metabolite Profiles

Background: In our previous research, we investigated the effects of different boron concentrations on photosynthetic and oxidative processes. The aim of this study was to examine in greater detail the responses to changes in boron availability, with particular emphasis on the antioxidant defense system and the expression of genes involved in sugar synthesis that play a role in stress responses. Methods: Sugar beet plants grown under controlled conditions were treated with boric acid solutions at six different concentrations (0, 50, 100, 500, 1000, and 2000 µM). We examined the relative expression of genes associated with antioxidant defense and raffinose biosynthesis, and analyzed the concentrations of sugars, vitamin C, and certain organic acids using HPLC, and we also performed FRAP and MDA assays. Results: Based on the gene expression results, the expression of several genes associated with antioxidant defense reached its lowest level at the 500 µM treatment. Glucose concentration increased significantly at the 100 and 500 µM treatment levels, while fructose concentration increased significantly at the 50, 100, and 2000 µM treatment levels. Conclusions: Our results suggest that changes in boron availability influence several interrelated processes of antioxidant defense and primary metabolism during the early developmental stage of sugar beet.