New Insights Into the Activity of Apple Dihydrochalcone Phloretin: Disturbance of Auxin Homeostasis as Physiological Basis of Phloretin Phytotoxic Action

Phloretin inhibits the growth of Arabidopsis shoots by inducing chloroplast damage and programmed cell death

Phloretin is a key secondary metabolite produced by apple trees. Known for its strong antioxidant properties, this dihydrochalcone has been extensively studied in animals but less so in plants. Recently, we identified phloretin as a phytotoxic allelochemical that inhibits growth in the model plant Arabidopsis by disrupting auxin metabolism and distribution in the roots. In this study, we found that phloretin significantly hinders the growth of Arabidopsis seedlings' aerial parts after a short-term treatment (10 days) and causes their decay after long-term exposure (28 days). These effects result from ultrastructural damage in the mesophyll cells of the leaves, including chloroplast displacement and swelling, lesions, and alterations in thylakoid and cell wall organization. Interestingly, phloretin-treated plants showed a decrease in malondialdehyde levels and antioxidant enzyme activities, while hydrogen peroxide and proline levels remained unchanged. This suggests that phloretin-induced chlorosis and seedling decay are not due to oxidative stress but rather to severe chloroplast structural damage, leading to inefficient photosynthesis, starch degradation, starvation, and activation of micro- and macroautophagic processes for self-preservation. Ultimately, these processes result in programmed cell death. These new insights into the phytotoxic effects of phloretin on Arabidopsis shoots could pave the way for future research into phloretin as a potential multitarget bioherbicide and enhance our understanding of autoallelopathy in apple trees.

Effects of Phloretin on Seedling Growth and Histochemical Distribution of Phenols, Polysaccharides and Lipids in Capsella bursa-pastoris (L.) Medik

The present study evaluates the phytotoxic effects of phloretin, a prevalent secondary metabolite of apple trees, on the broadleaf weed Capsella bursa-pastoris (L.) Medik. known for its resistant myxospermous seeds that form a long-lasting soil bank. The results indicate a significant, dose-dependent inhibitory effect of phloretin on the growth and morphological parameters of weed seedlings grown in vitro. Although the applied phloretin concentrations (250-1000 µM) were not lethal to the C. bursa-pastoris seedlings after two weeks, the metabolism of the seedlings was impaired, resulting in an accumulation of lipid droplets in the root tips and root hairs. Histochemical analysis shows deposits of phenols in the root epidermal cells, which are probably aggregates of phloretin or its metabolic derivatives. The accumulation of pectin in the cell walls of root border cells in phloretin-treated seedlings indicates an attempt to reduce the uptake of phloretin and reduce its concentration in the cells. Inhibition of shoot growth associated with chlorosis and reduced photosynthetic pigment content is a consequence of seedling exposure to phloretin. This study provides a basis for further evaluation of phloretin as a new bioherbicidal compound and for elucidating the mechanism underlying its phytotoxic activity.

Chalcones-Features, Identification Techniques, Attributes, and Application in Agriculture

This review article is a comprehensive and current overview on chalcones, covering their sources, identification methods, and properties with a particular focus on their applications in the agricultural sector. The widespread use of synthetic pesticides has not only led to increased resistance among weeds and pests, resulting in economic losses, but it has also raised significant health concerns due to the overuse of these chemicals. In line with the European Green Deal 2030 and its Farm to Fork strategy, there is a targeted 50% reduction in the use of chemical pesticides by 2030, emphasizing a shift towards natural alternatives that are more environmentally sustainable and help in the restoration of natural resources. Chalcones and their derivatives, with their herbicidal, fungicidal, bactericidal, and antiviral properties, appear to be ideal candidates. These naturally occurring compounds have been recognized for their beneficial health effects for many years and have applications across multiple areas. This review not only complements the previous literature on the agricultural use of chalcones but also provides updates and introduces methods of detection such as chromatography and MALDI technique.

Fungal Prenyltransferase AnaPT and Its F265 Mutants Catalyze the Dimethylallylation at the Nonaromatic Carbon of Phloretin

Phloretin is widely found in fruit and shows various biological activities. Here, we demonstrate the dimethylallylation, geranylation, and farnesylation, particularly the first dimethylallylation at the nonaromatic carbon of phloretin (1) by the fungal prenyltransferase AnaPT and its mutants. F265 was identified as a key amino acid residue related to dimethylallylation at the nonaromatic carbon of phloretin. Mutants AnaPT_F265D, AnaPT_F265G, AnaPT_F265P, AnaPT_F265C, and AnaPT_F265Y were discovered to generally increase prenylation activity toward 1. AnaPT_F265G catalyzes the O-geranylation selectively at the C-2' hydroxyl group, which involves an intramolecular hydrogen bond with the carbonyl group of 1. Seven products, 1D5, 1D7-1D9, 1G2, 1G4, and 1F2, have not been reported prior to this study. Twelve compounds, 1D3-1D9, 1G1-1G3, and 1F1-1F2, exhibited potential inhibitory effects on α-glucosidase with IC50 values ranging from 11.45 ± 0.87 to 193.80 ± 6.52 μg/mL. Among them, 1G1 with an IC50 value of 11.45 ± 0.87 μg/mL was the most potential α-glucosidase inhibitor, which is about 30 times stronger than the positive control acarbose with an IC50 value of 346.63 ± 15.65 μg/mL.

Continuous cropping of potato changed the metabolic pathway of root exudates to drive rhizosphere microflora

For potato production, continuous cropping (CC) could lead to autotoxicity buildup and microflora imbalance in the field soil, which may result in failure of crops and reduction in yield. In this study, non-targeted metabolomics (via liquid chromatography with tandem mass spectrometry (LC-MS/MS)) combined with metagenomic profiling (via high-throughput amplicon sequencing) were used to evaluate correlations between metabolomics of potato root exudates and communities of bacteria and fungi around potato plants to illustrate the impacts of CC. Potato plants were grown in soil collected from fields with various CC years (0, 1, 4, and 7 years). Metabolomic analysis showed that the contents and types of potential autotoxins in potato root exudates increased significantly in CC4 and CC7 plants (i.e., grown in soils with 4 and 7 years of CC). The differentially expressed metabolites were mainly produced via alpha-linolenic acid metabolism in plant groups CC0 and CC1 (i.e., no CC or 1 year CC). The metabolomics of the groups CC4 and CC7 became dominated by styrene degradation, biosynthesis of siderophore group non-ribosomal peptides, phenylpropanoid biosynthesis, and biosynthesis of various plant secondary metabolites. Continuous cropping beyond 4 years significantly changed the bacterial and fungal communities in the soil around the potato crops, with significant reduction of beneficial bacteria and accumulation of harmful fungi. Correlations between DEMs and microflora biomarkers were established with strong significances. These results suggested that continuous cropping of potato crops changed their metabolism as reflected in the plant root exudates and drove rhizosphere microflora to directions less favorable to plant growth, and it needs to be well managed to assure potato yield.

Crystal structure of phloridzin and its distribution changes in flowering and fruiting stage of Malus rockii

The exact structure of phloridzin was further confirmed as phloretin 6'-O-glucopyranoside by a single-crystal X-ray diffraction experiment. The distribution changes of phloridzin in flowering, fruitlet, and fruit ripening phases of Malus rockii were quantified by an HPLC with an external standard. The concentrations of phloridzin in leaves, twigs, and bark and xylem of twigs increased at first and then decreased, and reached the highest value in the fruitlet period. The highest concentration of phloridzin was found in leaves, with the percentage contents of 10.92-14.43 %. What is more, the decreased value of the concentration of phloridzin in leaves from fruit ripening period was almost equivalent to the increased value of the concentration of phloretin. This interesting physiological phenomenon should be able to provide the readers, especially plant physiologists, with a new perspective for the development and utilization of phloridzin.

Distribution and Stability of Polyphenols in Juices Made from Traditional Apple Cultivars Grown in Bosnia and Herzegovina

The present research was undertaken to investigate polyphenolic profiles of peel, pulp and juices made from two standard commercial and five traditional apple cultivars from Bosnia and Herzegovina. The main goal of the study was to monitor the distribution and changes of polyphenolic profiles through different phases of apples' processing into cloudy and clear juices, with regard to L-ascorbic acid pretreatment. Quantitative determination of phenolic compounds was carried out by using high-performance liquid chromatography with diode-array detection. The obtained results showed that traditional cultivars, namely 'Paradija' and 'Prijedorska zelenika', displayed significantly higher content of these compounds compared to commercial ones. Flavan 3-ols and flavonol glycosides were mostly found in peels of all cultivars (21.2-44.1 and 5.40-33.3%, respectively), while phenolic acids along with flavan 3-ols were predominant in the pulp (8.20-30.8 and 5.10-13.9%, respectively). Apples' processing into juices caused decrease (more than 90%) in the content of all polyphenols and the distribution of these compounds from fruits to final products had a negative trend, particularly evident in clear juices. The most drastic loss occurred in the flavonol glycosides and dihydrochalcones content, while chlorogenic acid displayed quite stable distribution from apples to final products due to its good solubility. Apple mash pretreatment with L-ascorbic acid had a positive impact on the preservation and retention of polyphenols.

A New Strategy Based on LC-Q TRAP-MS for Determining the Distribution of Polyphenols in Different Apple Varieties

Apples are a rich source of polyphenols in the human diet. However, the distribution of polyphenols in different apple varieties and tissues is still largely unclear. In this study, a new liquid chromatography-tandem mass spectrometry (LC-MS/MS) strategy was developed to reveal the spatial distribution of polyphenols in different apple tissues and varieties. A method based on multiple reaction monitoring (MRM)-enhanced product ion (EPI) was established in the information-dependent acquisition (IDA) mode for pseudo-target screening of major apple polyphenols. A total of 39 apple polyphenolic metabolites were finally identified. Qualitative and quantitative results showed that the variety and content of polyphenols in apple peels were higher than those of other tissues. In apple roots, stems, and leaves, the highest polyphenol variety and content were found in wild species, followed by cultivars and elite varieties. Dihydrochalcone substances, one kind of major apple polyphenols, were more abundant in apple roots, stems, and leaves. This strategy can be applied as a model for other agricultural products, in addition to revealing the distribution of polyphenols in different tissues of apples, which provides a theoretical basis for the utilization of polyphenol resources and variety selection.