Molecular Plant Breeding 2024, Vol.15, No.6, 328-339 http://genbreedpublisher.com/index.php/mpb 335 and fruit quality by foliar spraying with different concentrations of sodium selenite (10, 40, 70, 100 mg/L). Results indicated that a 40 mg/L selenium treatment showed the best performance, significantly increasing leaf area, chlorophyll content, and photosynthesis efficiency, as well as improving fruit weight, soluble sugar content, and vitamin C levels (Lin et al., 2024). It also optimized the sugar-to-acid ratio, enhancing the fruit's flavor. Furthermore, selenium treatment regulated sugar and acid metabolism by inhibiting citric acid production and promoting the activity of sugar metabolism-related enzymes (Figure 4). Additionally, low to medium selenium concentrations significantly enhanced the activities of antioxidant enzymes (such as SOD, POD, and CAT) and reduced MDA levels, effectively alleviating oxidative stress (Lin et al., 2024). These findings suggest that foliar application of appropriate selenium concentrations is not only an effective strategy to enhance strawberry fruit quality but also provides scientific support for selenium’s agricultural applications and nutritional fortification, contributing to the advancement of sustainable agriculture. Figure 4 Changes of sugar metabolism-involved enzyme activities and gene expression during fruit development. (A), Sucrose synthase synthesis activity; (B), Sucrose synthase cleavage activity; (C), Activity of sucrose phosphate synthase; (D), Neutral invertase activity; (E), Acid invertase activity; (F), Sucrose synthase gene expression; (G), Sucrose phosphate synthase gene expression; (H), Neutral invertase gene expression; (I), Acid invertase gene expression. BG, W, PR, and FR indicate fruit at the big green, white, partial red, and full red stages, respectively. Columns with error bars represent the mean values of three biological replicates ± standard deviation. The LSD multiple comparisons test was used to compare the differences between control and treatment. The lower-case letters indicate a significant difference at the P≤ 0.05 level (Adopted from Lin et al., 2024) Image caption: The figure illustrates the effects of different concentrations of sodium selenite (Na2SeO3) on key enzyme activities involved in sugar metabolism (A-E) and their related gene expressions (F-I) in strawberry fruits. The results show that selenium treatment significantly enhanced the activity of sucrose phosphate synthase (SPS) and acid invertase (AI), promoting bidirectional regulation of sugar metabolism, while the activities of sucrose synthase (SS) and neutral invertase (NI) showed no significant changes. Gene expression analysis revealed that the SPS-related gene (FaSPS) was significantly upregulated in the 40 mg/L and 70 mg/L treatment groups, whereas the expression of the AI-related gene (FaAI) was slightly inhibited. Overall, selenium primarily promoted sugar synthesis and degradation by enhancing the activity of key enzymes in sugar metabolism rather than significantly altering gene expression. This highlights selenium’s critical role in regulating sugar metabolism, increasing sugar content, and optimizing flavor quality in strawberry fruits (Adapted from Lin et al., 2024) 7 Challenges and Future Research Directions 7.1 Insufficient research on selenium dosage and safety The application of Se in enhancing the stress resistance and quality of strawberries has shown promising results, yet significant research gaps remain in determining the optimal dosage and safety of selenium application. Studies indicate that low concentrations of selenium effectively alleviate stress and improve plant quality, while excessive
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