Nitrogen nutrition is a key modulator of the sugar and organic acid content in citrus fruit

Abstract

‘Huangguogan’ (Citrus reticulata × C. sinensis) is a new cultivar of mandarin citrus in China, and the research on fertilization of ‘Huangguogan’ is very limited. In this study, the effect of N fertilization on ‘Huangguogan’ fruit quality was determined at ripening. Sugars (sucrose, fructose, and glucose), organic acids (pyruvic, oxalic, citric acid, etc.), and vitamin components were measured at six stages of fruit development, and eight enzymes related to the glycolytic and Krebs cycle were assessed. The 1.81 kg N y-1 treatment group showed the highest total soluble solids concentration and total soluble solids/titratable acidity ratio but the lowest titratable acidity (acid content) at ripening, while the N1 treatment (0 kg N y-1) showed the opposite trend. Sucrose and citric acid accumulated to the largest extent during fruit development. Sucrose and ascorbic acid content increased (8.46 to 50.97 mg g-1 and 8.16 to 27.39 mg g-1, respectively), while citric acid content decreased (90.81 to 0.02 mg g-1). Aconitase was the key enzyme responsible for the observed changes in citric acid. The N concentrations in ripening fruit ranged from 2.25% to 4.15%. Curve estimation and principal component analysis revealed that fruit N was positively correlated with the sugars and vitamin components and negatively correlated with the organic acids. The accumulation of these metabolites seemed closely related to the dynamic changes in fruit N concentration at the five N levels tested. In conclusion, we suggest that the 1.81 kg N y-1 treatment represents the most suitable N fertilizer treatment for ‘Huangguogan’ citrus fruit.

A Novel Banana Mutant “RF 1” (Musa spp. ABB, Pisang Awak Subgroup) for Improved Agronomic Traits and Enhanced Cold Tolerance and Disease Resistance

“…Sugar is the ultimate precursor for most quality-relevant components in the fruit of bananas, such as acids, pigments, tannins, and aroma volatiles (Hall et al, 2011 ). A high acid content often reduces fruit quality, though a moderate concentration of acid can improve the palatability of fruits (Liao et al, 2019 ). Therefore, the quality of a fruit and its taste are usually influenced by the sugar and acid contents or, more simply, by its sugar-to-acid ratio (Qiao et al, 2018 ).…”

Biofertilizers as Strategies to Improve Photosynthetic Apparatus, Growth, and Drought Stress Tolerance in the Date Palm

“…However, a high amount of N and P in the rhizosphere soil of plants amended with compost and inoculated with AMF and PGPR could be due to a direct absorption via compost or by the fact that AMF and PGPR efficiently and directly take up from the soil to the plant nutrients such as N and P (Grobelak et al, 2015;Liu et al, 2018). In order to tolerate drought stress, plant adaptation is associated with high concentration of solutes such as soluble sugars and protein to regulate the osmotic potential of cells which, in turn, induce an improvement in water absorption under unfavorable condition (Zhang et al, 2010;Liao et al, 2019). Our data indicated that the concentrations of soluble sugars and protein in leaves increased during drought stress in treated plants as compared to microbes-free controls.…”

Arbuscular Mycorrhizal Fungi Mitigates Salt Stress Toxicity in Stevia rebaudiana Bertoni Through the Modulation of Physiological and Biochemical Responses

“…In order to tolerate salt stress, plant synthesizes a high concentration of compatible carbohydrates like protein and soluble sugars, which are able to increase intracellular osmotic (Liao et al 2019). They play a crucial role in enzyme and membrane protection from adverse effect of stress (Hare et al 1998).…”