Changes and response mechanism of sugar and organic acids in fruits under water deficit stress

The content and the ratio of soluble sugars and organic acids in fruits are significant indicators for fruit quality. They are affected by multiple environmental factors, in which water-deficient is the most concern. Previous studies found that the content of soluble sugars and organic acids in fruit displayed great differences under varied water stress. It is important to clarify the mechanism of such difference and to provide researchers with systematic knowledge about the response to drought stress and the mechanism of sugar and acid changes in fruits, so that they can better carry out the study of fruit quality under drought stress. Therefore, the researchers studied dozens of research articles about the content of soluble sugar and organic acid, the activity of related metabolic enzymes, and the expression of related metabolic genes in fruits under water stress, and the stress response of plants to water stress. We found that after plants perceived and transmitted the signal of water deficit, the expression of genes related to the metabolism of soluble sugars and organic acids changed. It was then affected the synthesis of metabolic enzymes and changed their metabolic rate, ultimately leading to changes in soluble sugar and organic acid content. Based on the literature review, we described the pathway diagrams of sugar metabolism, organic acid metabolism, mainly malic acid, tartaric acid, and citric acid metabolism, and of the response to drought stress. From many aspects including plants' perception of water stress signal, signal conversion and transmission, induced gene expression, the changes in soluble sugar and the enzyme activities of organic acids, as well as the final sugar and acid content in fruits, this thesis summarized previous studies on the influence of water stress on soluble sugars and the metabolism of organic acids in fruits.

Yield, Physiology, Fruit Quality and Water Footprint in Persian Lime (Citrus latifolia Tan.) in Response to Soil Moisture Tension in Two Phenological Stages in Campeche, México

Sixteen irrigation treatments were applied on Persian lime, based on the combination of four soil moisture tensions (SMTs) used to define the start of irrigation: −10, −35, −60, and −85 kPa during the phenological stages (PSs) of flowering (FL) and fruiting (FR). Variables evaluated were, among others: leaf water potential (Ψ), leaf stomatal conductance (gs), fruit weight (FW), fruit juice content (FJC), total soluble solids in juice (TSS), fruit yield (FY), and water footprint (WF). Greater values on the Ψ and gs variables were observed in plants subjected to SMTs of −10 and −35 kPa (p < 0.05). The SMT of −85 kPa during FR produced a low FW value, while the lower SMTs in this PS increased it (p < 0.05). FY was greater in the treatments including −10 kPa or −35 kPa during either of the two PSs, with the exception of those with −85 kPa in one of the stages (p < 0.05). Lower FJC values were obtained at a SMT of −85 kPa in FR, and higher TSS values were observed in the two driest treatments (p < 0.05). The smallest WF values were observed in the −60 kPa FL and −60 kPa FR treatment (p ≤ 0.05). Irrigation management based on the SMT significantly affected almost all the response variables evaluated. It is recommended to irrigate the crop at a SMT of −35 kPa in FL and −60 kPa in FR, the treatment in which the greatest FW, FY, and FJC values and the lowest TSS and WF values were obtained (p < 0.05) and in which only 93 L of water was used by the trees to produce one kilogram of fruit (16% of the amount used in the treatment with the largest WF). The use of blue water is limited by its scarcity and high opportunity cost, an aspect that can be mitigated if blue water is used efficiently in Persian lime production systems, based on the results of this study.

Foliar Application of Nano, Chelated, and Conventional Iron Forms Enhanced Growth, Nutritional Status, Fruiting Aspects, and Fruit Quality of Washington Navel Orange Trees (Citrus sinensis L. Osbeck)

Iron (Fe) is required for most metabolic processes, including DNA synthesis, respiration, photosynthesis, and chlorophyll biosynthesis; however, Fe deficiency is common in arid regions, necessitating additional research to determine the most efficient form of absorbance. Nano-fertilizers have characteristics that are not found in their traditional equivalents. This research was implemented on Washington navel orange trees (Citrus sinensis L. Osbeck) to investigate the effect of three iron forms-nano (Fe-NPs), sulfate (FeSO₄), and chelated (Fe-chelated)-as a foliar spray on the growth, fruiting aspects, and nutritional status of these trees compared to control. The highest values of the tested parameters were reported when the highest Fe-NPs level and the highest Fe-chelated (EDTA) rate were used. Results obtained here showed that the spraying of the Washington navel orange trees grown under similar environmental conditions and horticulture practices adopted in the current experiment with Fe-NPs (nanoform) and/or Fe-chelated (EDTA) at 0.1% is a beneficial application for enhancing vegetative growth, flower set, tree nutritional status, and fruit production and quality. Application of Fe-NPs and Fe-chelated (EDTA, 0.1%) increased yield by 32.0% and 25% and total soluble solids (TSS) by 18.5% and 17.0%, respectively, compared with control. Spraying Washington navel orange trees with nano and chelated iron could be considered a significant way to improve vegetative growth, fruit production, quality, and nutritional status while also being environmentally preferred in the arid regions.

Deficit irrigation and maturation stage influence quality and flavonoid composition of 'Valencia' orange fruit

BACKGROUND

Effects of continuous deficit irrigation (DI) and partial rootzone drying (PRD) treatments (50% ETc) in comparison with full irrigation (CI, 100% ETc) were investigated during 'Valencia' orange fruit maturation. Ultra-high-performance liquid chromatography/high-resolution mass spectrometry was used to quantify hesperidin, narirutin, tangeritin, nobiletin, didymin and neoeriocitrin in the fruit juice and peel.

RESULTS

No significant effect of irrigation was found on yield, juice soluble solids or acidity. Juice color was not influenced by irrigation or harvest date, whereas peel color increased during maturation and was more pronounced in CI and PRD fruits. Juice acidity reached a peak in May, while soluble solids increased linearly throughout maturation. Hesperidin was the major flavanone detected during maturation, with concentrations 200-fold higher in the fruit peel than in the juice. In the peel, narirutin, didymin and neoeriocitrin decreased while hesperidin, nobiletin and tangeritin increased with maturation. Narirutin synthesis in the orange fruit was insensitive to irrigation strategy. In fruit peels, PRD and DI induced the decline of hesperidin, nobiletin and tangeritin only in June, whereas in the juice, deficit irrigation treatments induced an increase in hesperidin and didymin.

CONCLUSION

These results suggest that deficit irrigation, in particular the conditions imposed with PRD, may cause a significant accumulation shift of total flavonoids from the fruit peel into the juice, with a positive impact on juice quality and nutritional value. Fruit compositional changes during maturation also suggest that late harvest can improve fruit palatability and nutritional quality under the cultural and environmental conditions of this study. © 2016 Society of Chemical Industry.