Nitrogen Levels Regulate Sugar Metabolism and Transport in the Shoot Tips of Crabapple Plants

Abstract

To comprehensively understand the responses of carbohydrate metabolism and transport to different levels of nitrogen supply in growing shoot tips of crabapple (Malus hupehensis Rehd), enzyme activities and related genes involved in the sugar metabolism pathway were investigated. The nitrogen and chlorophyll content of plants increased with increasing nitrogen supply. High nitrogen application increased the net photosynthesis rate and the growth rate of shoot tips but decreased the synthesis capability of sucrose and sorbitol in mature leaves. However, the shoot tips of plants under high-nitrogen treatment had higher contents of sucrose and sorbitol than did those under low-nitrogen treatment, while the activity of sucrose phosphate synthase and aldose-6-phosphate was increased and the transporters MdSOT and MdSUT were up-regulated. Moreover, the activities of enzymes involved in sucrose and hexose metabolism (including sucrose synthase, fructokinase, and hexokinase) were enhanced in the shoot tips of plants under high-nitrogen conditions, and the expression levels of MdSUSY3 and MdHK1 were significantly up-regulated. These findings indicate that a high nitrogen supply increases the metabolic capacity of assimilatory substances in shoot tips, accelerates the efficiency of sugar utilization and eventually leads to a rapid increase in the growth of shoot tips. Our results highlight that high nitrogen increases the capacity of sugar unloading and metabolic utilization in growing shoot tissues.

Differential Metabolic Responses of Lettuce Grown in Soil, Substrate and Hydroponic Cultivation Systems under NH4+/NO3− Application

“…The application of NH 4 + /NO 3 − ratios have been considered to be of paramount importance to reduce the environmental effect and improved the N use efficiency [ 67 ]. Plant primary and secondary metabolic contents have been reduced when applying only a single form of N or when applying it in excess without mixing the NH 4 + /NO 3 − ratios due to internal competition for plants [ 68 ]. In the present study, sugar-related compounds (sucrose, fructose, lactulose, and maltose) in lettuce identified and analyzed via GC-MS and UPLC VION LC-MS/MS.…”

Low-Altitude Boundary of Abies faxoniana Is More Susceptible to Long-Term Open-Top Chamber Warming in the Eastern Tibetan Plateau

“…We think that on the one hand, the decreases in F6P and G6P contents can be attributed to the lower efficiency of hexose phosphorylation by hexokinase rather than the reduction in glucose supply. On the other hand, under warming conditions, A. faxoniana growing at high altitudes possibly consumes less energy than that growing at low altitude ( Zhao et al, 2020 ; Zhang et al, 2021 ). Therefore, A. faxoniana at low altitude need to obtain more energy to cope with warming, whereas it is most likely to adopt an energy conservation strategy at high altitude.…”

Transcriptome and Metabolome Analysis Reveals the Effect of Nitrogen–Potassium on Anthocyanin Biosynthesis in “Fuji” Apple

“…In contrast, K promoted the translocation of photosynthate to the fruit, as demonstrated by a significant increase in 13 C partitioning in the fruit due to the important role of K in photosynthate transport . Sorbitol is an important form of carbohydrate transport in apple and many other fruit tree species of the Rosaceae family . We determined the expression of MdSUTs and MdSOTs in leaves and fruits and found that high N suppressed the expression of MdSUT1 , MdSUT2 , MdSUT3 , and MdSOT1 , and K effectively alleviated this suppression.…”