Magnesium improved fruit quality by regulating photosynthetic nitrogen use efficiency, carbon–nitrogen metabolism, and anthocyanin biosynthesis in ‘Red Fuji’ apple

Abstract

IntroductionBoth nitrogen (N) and magnesium (Mg) play important roles in biochemical and physiological processes in plants. However, the application of excessive N and insufficient Mg may be the factor leading to low nitrogen utilization rate (NUE) and fruit quality degradation in apple production.MethodsIn this study, we analyzed the effects of different application rates of Mg (0, 50, 100, 150, 200 kg/ha) on the photosynthetic nitrogen use efficiency (PNUE), the accumulation and distribution of carbon (C), N metabolism, anthocyanin biosynthesis and fruit quality of the ‘Red Fuji’ apple in 2018 and 2019.ResultsThe results showed that the application of Mg significantly increased the 15NUE and increased the allocation rate of 15N in the leaves whereas the 15N allocation rate in the perennial organs and fruits was decreased. With the increase in Mg supply, the activities of N metabolism enzymes (NiR, GS, and GOGAT) were significantly promoted and the content of intermediate products in N metabolism (NO2−, NH4+, and free amino acid) was significantly decreased. Furthermore, an appropriate rate of Mg significantly promoted the net photosynthetic rate (Pn) and photosynthetic nitrogen use efficiency (PNUE), enhanced the enzyme activities of C metabolism (SS, SPS, S6PDH), and increased the contents of sorbitol and sucrose in leaves. In addition, Mg upregulated the gene expression of sugar transporters (MdSOT1, MdSOT3, MdSUT1, and MdSUT4) in fruit stalk and fruit fresh; 13C isotope tracer technology also showed that Mg significantly increased the 13C allocation in the fruits. Mg also significantly increased the expression of anthocyanin biosynthesis genes (MdCHS and MdF3H) and transcription factors (MdMYB1 and MdbZIP44) and the content of anthocyanin in apple peel.ConclusionThe comprehensive analysis showed that the appropriate application of Mg (150 kg/ha) promoted PNUE, C–N metabolism, and anthocyanin biosynthesis in apple trees.

Natural Grass Cultivation Management Improves Apple Fruit Quality by Regulating Soil Mineral Nitrogen Content and Carbon–Nitrogen Metabolism

“…The method reported by Tian et al [ 2 ] was used to prepare the enzyme solution, which was then dialyzed and used to determine sorbitol dehydrogenase (SDH), sorbitol oxidase (SOX), sucrose synthase decomposition direction (SS-c), acid invertase (AI), and neutral invertase (NI) activities. Subsequently, the methods described by Rufly and Huber [ 42 ] and Yamaki and Asakura [ 43 ] were adopted to determine SDH and SOX, respectively.…”

“…Apples have been cultivated worldwide because of their unique health and economic value [ 1 , 2 ]. Appropriate N application is crucial for the growth and development of apples [ 3 , 4 , 5 , 6 ].…”

“…Substantial research has been conducted to explore effective solutions for improving fruit quality in orchards by coordinating tree C and N metabolism. For example, Tian et al [ 2 ] indicated that the optimal use of Mg could elevate fruit quality by regulating C and N metabolism in leaves (source organs) and fruits (sink organs). Sha et al [ 18 ] observed that the fruit quality could be significantly improved under PBZ (a plant growth regulator) treatment through altering the C and N nutrients in fruits.…”

The power of magnesium: unlocking the potential for increased yield, quality, and stress tolerance of horticultural crops

“…Magnesium is an essential macronutrient vital for various physiological processes in plants, including growth, development, reproduction, and quality enhancement ( Xu J. et al., 2021 ; Li et al, 2023c ; Tian et al., 2023b ). Its importance extends to influencing the taste, texture, shelf life, and nutritional content of fruits and vegetables, thereby driving consumer preferences and market value ( Petrescu et al., 2020 ; Yousaf et al., 2021 ; Zhang S. et al, 2021 ; Mullins and Wolt, 2022 ).…”

“…Magnesium transporters play crucial roles across plants, with significant functions detected in the reproductive parts, ensuring successful pollen development, male fertility, and fruit quality ( Li et al., 2015 ; Xu X. F. et al., 2021 ; Tian et al., 2023b ). Several members of the MGT family, including MGT4, MGT5 , and MGT9 , are vital for pollen development and male fertility.…”