Potassium fertilization arrests malate accumulation and alters soluble sugar metabolism in apple fruit

Effects of Potassium-Containing Fertilizers on Sugar and Organic Acid Metabolism in Grape Fruits

To identify suitable potassium fertilizers for grape (Vitis vinifera L.) production and study their mechanism of action, the effects of four potassium-containing fertilizers (complex fertilizer, potassium nitrate, potassium sulfate, and potassium dihydrogen phosphate) on sugar and organic acid metabolism in grape fruits were investigated. Potassium-containing fertilizers increased the activity of sugar and organic acid metabolism-related enzymes at all stages of grape fruit development. During the later stages of fruit development, potassium-containing fertilizers increased the total soluble solid content and the sugar content of the different sugar fractions and decreased the titratable acid content and organic acid content of the different organic acid fractions. At the ripening stage of grape fruit, compared with the control, complex fertilizer, potassium nitrate, potassium sulfate, and potassium dihydrogen phosphate increased the total soluble solid content by 1.5, 1.2, 3.5, and 3.4 percentage points, decreased the titratable acid content by 0.09, 0.06, 0.18, and 0.17 percentage points, respectively, and also increased the total potassium content in grape fruits to a certain degree. Transcriptome analysis of the differentially expressed genes (DEGs) in the berries showed that applying potassium-containing fertilizers enriched the genes in pathways involved in fruit quality, namely, carbon metabolism, carbon fixation in photosynthetic organisms, glycolysis and gluconeogenesis, and fructose and mannose metabolism. Potassium-containing fertilizers affected the expression levels of genes regulating sugar metabolism and potassium ion uptake and transport. Overall, potassium-containing fertilizers can promote sugar accumulation and reduce acid accumulation in grape fruits, and potassium sulfate and potassium dihydrogen phosphate had the best effects among the fertilizers tested.

Potassium Spraying Preharvest and Nanocoating Postharvest Improve the Quality and Extend the Storage Period for Acid Lime (Citrus aurantifolia Swingle) Fruits

Citrus fruits are one of the most abundant crops globally in more than 140 countries throughout the world. Acid lime (Citrus aurantifolia swingle) is one of the citrus fruits which popularly has rich nutritional and therapeutic features. The storage period is the important factor that affects the economic and quality properties of this fruit. This study aims to demonstrate the enhancing effect of preharvest spraying with potassium, in addition to the postharvest dipping of fruits in some edible coatings, on the quality and storability of acid lime fruits. Preharvest spraying with organic and mineral forms of potassium, namely, potassium thiosulfate 1.75 g/L (S) and potassium tartrate 2 g/L (T), were carried out at three different times, in May, June, and July. On the other hand, postharvest treatments were carried out via dipping fruits in different types of biopolymers (carboxymethyl cellulose (E2) and gum arabic (E3)) and carboxymethyl cellulose/gum arabic composite (E4) as well as nanocoating formulation based on both biopolymers and doped zinc oxide nanoparticles (ZnONPs) (E1), which were prepared via acid lime peel waste extract. Herein, the physiochemical and morphological characterizations confirmed that the nanocoating was prepared at the nanoscale and doped with green synthesis ZnONPs, with recorded sizes of around 80 and 20 nm, respectively. Preharvest spraying with potassium tartrate enhanced fruit traits (Spraying with potassium tartrate at pre-harvest and nanocoating dipping at post-harvest (TE1), spraying with potassium tartrate at pre-harvest and carboxy methyl cellulose dipping at post-harvest (TE2), spraying with potassium tartrate at pre-harvest and gum arabic dipping at post-harvest (TE3) and spraying with potassium tartrate at pre-harvest and carboxymethyl cellulose/gum arabic composite dipping at post-harvest (TE4)), followed by potassium thiosulfate (spraying with potassium thiosulfate at pre-harvest and nanocoating dipping at post-harvest (SE1), spraying with potassium thiosulfate at pre-harvest and carboxy methyl cellulose dipping at post-harvest (SE2), spraying with potassium thiosulfate at pre-harvest and gum arabic dipping at post-harvest (SE3) and spraying with potassium thiosulfate at pre-harvest and carboxymethyl cellulose/gum arabic dipping at post-harvest (SE4)), compared to control. For postharvest treatments, E1 improved fruit quality, followed by E2, E4, and E3, respectively. The integration between pre- and postharvest treatments showed a clear superiority of TE2, followed by TE4, SE1, and SE2, respectively.

The Features of Potassium Dynamics in 'Soil-Plant' System of Sour Cherry Orchard

This research aimed to study interannual and seasonal dynamics of different potassium compounds in orchard soil and the potassium status of sour cherry trees affected by the application of nitrogen and potash fertilizers. Afield experiment was started in 2017 at an orchard located in the forest-steppe zone of the Central Russian upland. Urea and potassium sulfate were applied to the soil once a year in early spring with rates from N30K40 to N120K160 kg/ha. The content of exchangeable and water-soluble potassium compounds was determined in soil samples five times throughout the growing season from May to September 2018-2020. The content of non-exchangeable potassium was determined twice, in 2017 and 2020. The interannual and seasonal dynamics of plant-available potash in unfertilized soil depended on the weather patterns and the uptake of potassium by trees. In the unfertilized plots, the first signs of potassium nutrition insufficiency appeared, such as low leaf and fruit potassium status and a decrease in the non-exchangeable potassium reserves in the20-40 cm soil layer. The annual fertilization led to the gradual accumulation of exchangeable potassium in the root zone. The accumulation was accelerated with increasing rates. When the exchangeable potassium level in the topsoil reached 200 mg/kg, the intensification of both the seasonal fluctuations in potash content and the potash leaching into the depths of the soil occurred in all treatments. In the conditions of our experiment, one-time treatments with superfluous potassium rates (over 80 kg/ha) did not provide an enlarged stock of plant-available potash in the soil but caused unreasonable losses of it due to leaching. An increase in fertilizer rates was not essential for normal metabolic processes and did not manifest itself as an increase in potassium content in leaves and fruits or as an increase in yield.

Essential Role of Potassium in Apple and Its Implications for Management of Orchard Fertilization

K (K) is of paramount importance for apple (Malus × domestica Borkh.), not only for tree growth and development but also for the size and quality of fruit yield. The apple plant's demand for K varies, along with the progression of phenological phases, during the growing season. The K demand peaks during ripening of fruits featuring relatively high concentration of K comparable to that of the leaves. The mainstream method of apple tree K fertilization is through application of the fertilizer to the soils to improve K uptake by the roots. The bioavailability of K depends on assorted various factors, including pH, interaction with other nutrients in soil solution, temperature, and humidity. An important role in making the K from soil available for uptake by plants is played by plant growth-promoting microorganisms (PGPM), and the specific role of the PGPM is discussed. Advantages of fertigation (the combination of irrigation and fertilization) as an approach include allowing to balance application rate of K fertilizer against its variable demand by plants during the growing season. Excess K in the soil leads to competitive inhibition of calcium uptake by plants. The K-dependent deficiency of Ca leads to its predominant channeling to the leaves and hence to its decline in fruits. Consequently, the apple fruits affected by the K/Ca imbalance frequently develop physiological disorders in storage. This emphasizes the importance of the balanced K application, especially during the last months of the growing season, depending on the crop load and the actual K demand. The potential use of modern approaches to automated crop load estimation through machine vision for adjustment of K fertilization is underlined.

Noncoding-RNA-Mediated Regulation in Response to Macronutrient Stress in Plants

Macronutrient elements including nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) are required in relatively large and steady amounts for plant growth and development. Deficient or excessive supply of macronutrients from external environments may trigger a series of plant responses at phenotypic and molecular levels during the entire life cycle. Among the intertwined molecular networks underlying plant responses to macronutrient stress, noncoding RNAs (ncRNAs), mainly microRNAs (miRNAs) and long ncRNAs (lncRNAs), may serve as pivotal regulators for the coordination between nutrient supply and plant demand, while the responsive ncRNA-target module and the interactive mechanism vary among elements and species. Towards a comprehensive identification and functional characterization of nutrient-responsive ncRNAs and their downstream molecules, high-throughput sequencing has produced massive omics data for comparative expression profiling as a first step. In this review, we highlight the recent findings of ncRNA-mediated regulation in response to macronutrient stress, with special emphasis on the large-scale sequencing efforts for screening out candidate nutrient-responsive ncRNAs in plants, and discuss potential improvements in theoretical study to provide better guidance for crop breeding practices.

Effects of Fruit Load on Sugar/Acid Quality and Puffiness of Delayed-Harvest Citrus

Delayed harvesting technology is believed to improve the citrus fruit flavor, but improper tree fruit load under delayed harvest might cause puffiness and reduce fruit quality. In order to find out an optimum tree fruit load level to obtain better flavor quality as well as reduce puffiness in delayed-harvest citrus under protected cultivation, experiments were conducted in the present study between 2019 and 2020 to determine the effect of different fruit loads and fruit-bearing per single branch on the soluble sugars and organic acids metabolism in the peel and flesh, the anatomical structure of the matured fruit peel, and fruit texture-related indexes. The results suggested significant negative correlations between leaf N level and flesh sucrose and glucose contents, and between branch P level and flesh citric acid contents; no significant correlation between NPK levels and flesh texture; relatively lower leaf N and branch P under relatively higher load can increase flesh sucrose and glucose accumulation and slow down citric acid degradation to the greater extent, thus optimizing the sugar/acid ratio of fruits during delayed harvest. The lignification of parenchyma cells closely around peel secretory cavities due to ascorbic acid deficiency might be the primary cause for puffiness under low-load treatments.

Gradual Application of Potassium Fertilizer Elevated the Sugar Conversion Mechanism and Yield of Waxy and Sweet Fresh-Eaten Maize in the Semiarid Cold Region

Fresh-eaten maize (Zea mays L.) is favored by consumers for its unique flavor, good health, and medical effects. Heilongjiang province is a semiarid cold region with the annual output of 3.35 billion ears, and the demand for fresh eaten maize is increasing in the region. Therefore, improving its yield and quality is urgently needed in this area. In this study, two of thirty varieties (waxy maize Jin-262 and sweet maize Jingke-183) were used and five proportions of potassium (K2O, 120 kg/ha) were applied at sowing, jointing, and large trumpet stages to identify the high yield and quality of fresh-eaten maize under a semiarid cold ecological condition in Daqing, Heilongjiang province, China, during 2017-2018. The results from the screening of eighteen maize varieties showed that waxy maize Jin-262 and sweet maize Jingke-183 had higher starch content and soluble sucrose contents than those of other varieties. While the potassium proportions application during the sowing (20%), jointing (40%), and large trumpet stages (40%) had further significantly increased the starch content, soluble sugar content, sucrose content, and sucrose metabolic enzymes activities of Jin-262 and Jingke-183, however, the yields of Jin-262 and Jingke-183 had increased by applying potassium fertilizer during the sowing stages (50%) and jointing stages (50%). Considering the overall higher maize quality, we recommended the waxy maize Jin-262 and sweet maize Jingke-183 varieties along with application of 20% (sowing), 40% (jointing), and 40% (large trumpet stages) of 120 kg/ha potassium fertilizer for the improvement of grain quality of maize planting in the semiarid cold region. Otherwise, reasonable gradual potassium fertilization might be a wiser option.

Advances in Mineral Nutrition Transport and Signal Transduction in Rosaceae Fruit Quality and Postharvest Storage

Mineral nutrition, taken up from the soil or foliar sprayed, plays fundamental roles in plant growth and development. Among of at least 14 mineral elements, the macronutrients nitrogen (N), potassium (K), phosphorus (P), and calcium (Ca) and the micronutrient iron (Fe) are essential to Rosaceae fruit yield and quality. Deficiencies in minerals strongly affect metabolism with subsequent impacts on the growth and development of fruit trees. This ultimately affects the yield, nutritional value, and quality of fruit. Especially, the main reason of the postharvest storage loss caused by physiological disorders is the improper proportion of mineral nutrient elements. In recent years, many important mineral transport proteins and their regulatory components are increasingly revealed, which make drastic progress in understanding the molecular mechanisms for mineral nutrition (N, P, K, Ca, and Fe) in various aspects including plant growth, fruit development, quality, nutrition, and postharvest storage. Importantly, many studies have found that mineral nutrition, such as N, P, and Fe, not only affects fruit quality directly but also influences the absorption and the content of other nutrient elements. In this review, we provide insights of the mineral nutrients into their function, transport, signal transduction associated with Rosaceae fruit quality, and postharvest storage at physiological and molecular levels. These studies will contribute to provide theoretical basis to improve fertilizer efficient utilization and fruit industry sustainable development.

Spatial and temporal evolution of quantitative magnetic resonance imaging parameters of peach and apple fruit - relationship with biophysical and metabolic traits

Fruits are complex organs that are spatially regulated during development. Limited phenotyping capacity at cell and tissue levels is one of the main obstacles to our understanding of the coordinated regulation of the processes involved in fruit growth and quality. In this study, the spatial evolution of biophysical and metabolic traits of peach and apple fruit was investigated during fruit development. In parallel, the multi-exponential relaxation times and apparent microporosity were assessed by quantitative magnetic resonance imaging (MRI). The aim was to identify the possible relationships between MRI parameters and variations in the structure and composition of fruit tissues during development so that transverse relaxation could be proposed as a biomarker for the assessment of the structural and functional evolution of fruit tissues during growth. The study provides species-specific data on developmental and spatial variations in density, cell number and size distribution, insoluble and soluble compound accumulation and osmotic and water potential in the fruit mesocarp. Magnetic resonance imaging was able to capture tissue evolution and the development of pericarp heterogeneity by accessing information on cell expansion, water status and distribution at cell level, and microporosity. Changes in vacuole-related transverse relaxation rates were mostly explained by cell/vacuole size. The impact of cell solute composition, microporosity and membrane permeability on relaxation times is also discussed. The results demonstrate the usefulness of MRI as a tool to phenotype fruits and to access important physiological data during development, including information on spatial variability.

miR-19a mitigates hypoxia/reoxygenation-induced injury by depressing CCL20 and inactivating MAPK pathway in human embryonic cardiomyocytes

OBJECTIVE

Myocardial infarction (MI) is a prevalent cardiovascular puzzle and a mainspring of disease-induced mortality. We performed this investigation to detect the role of putative important miRNAs or genes in MI.

RESULTS

CCL20 may be a potential therapeutic target, which was directly targeted and negatively regulated by miR-19a. CCL20 expression was significantly increased in MI tissue samples, but miR-19a was expressed at lower levels in MI. H/R treatment inhibited cell viability and induced an increase of apoptotic rate compared with Sham group. However, miR-19a mimic relieved the H/R-stimulated injury to cardiomyocytes. Protective effect of miR-19a against H/R in cardiomyocytes was reversed by CCL20 enhancement, and MAPK pathway was inactivated during this progression.

CONCLUSIONS

miR-19a eliminates the H/R-induced injury in cardiomyocytes through directly targeting CCL20 and attenuating the activity of MAPK signaling pathway. These observations highlighted the therapeutic roles of miR-19a and CCL20 for MI treatment.

Correction of Potassium Fertigation Rate of Apple Tree (Malus domestica Borkh.) in Central Russia during the Growing Season

The proper use of potassium fertilizer can stimulate a significant yield increase. However, the application of excessively high rates of potassium can reduce the availability of soil calcium for apple trees. The potassium fertigation rate must meet the apple tree's requirements so that the applied fertilizers can be absorbed by the roots as much as possible. Crop load in apple orchards sometimes varies significantly in different years. The potassium content in apple fruits is relatively high, and the maximum requirement for this nutrient occurs when fruits grow and ripen. Different crop loads at that time mean the various demands of trees and need for changing application rates for this nutrient. The investigation was carried out in the experimental orchard of I.V. Michurin Federal Scientific Centre (Michurinsk, Russia) in 2016 and 2017 (52.885131, 40.465613). We studied seasonal changes of potassium and calcium contents in soil, fruits, and leaves and their relationship with yield during the research. We paid much attention to the potassium rate shift on its content in leaves and fruits and cultivars "Lobo" and "Zhigulevskoye" yield. If the potassium application rate changes according to the actual crop load, it stimulates the yield growth or (if the crop load was relatively low) the reduction of the rate did not lower the productivity. Moreover, we studied the relationship between potassium and calcium nutrition. The decrease in potassium fertigation rate increased the availability of soil calcium. It was the reason for fruit calcium concentration enlargement and mitigation of the K/Ca ratio. We also specified some parameters for soil-leaf diagnosis for potassium nutrition during the growing season.