Effect of Shading on Development, Yield and Quality of Bastard Balm Herb (Melittis melissophyllum L.)

Recent Advances of Polyphenol Oxidases in Plants

Polyphenol oxidase (PPO) is present in most higher plants, but also in animals and fungi. PPO in plants had been summarized several years ago. However, recent advances in studies of PPO in plants are lacking. This review concludes new researches on PPO distribution, structure, molecular weights, optimal temperature, pH, and substrates. And, the transformation of PPO from latent to active state was also discussed. This state shift is a vital reason for elevating PPO activity, but the activation mechanism in plants has not been elucidated. PPO has an important role in plant stress resistance and physiological metabolism. However, the enzymatic browning reaction induced by PPO is a major problem in the production, processing, and storage of fruits and vegetables. Meanwhile, we summarized various new methods that had been invented to decrease enzymatic browning by inhibiting PPO activity. In addition, our manuscript included information on several important biological functions and the transcriptional regulation of PPO in plants. Furthermore, we also prospect some future research areas of PPO and hope they will be useful for future research in plants.

Developmental and chemical characteristics of Melittis melissophyllum L. in limited access of sunlight

Introduction: Bastard balm grows in forests, in central and southeastern part of Europe. The herb of this species is rich in phenolics, mainly flavonoids, phenolic acids and coumarins. The plant is used in traditional European medicine, in digestive problems and for aromatizing tobacco and alcohol products.

Objective: The purpose of this study was to determine the influence of shading on bastard balm development and the accumulation of phenolics in its herb, with special respect to coumarin as a quality marker of this raw material.

Methods: The plants were cultivated in full sunlight, in 30% and 50% shade provided by shading nets. The herb was harvested from plants in the third year of vegetation, at four subsequent developmental stages and then subjected to chemical evaluation. In the raw material, the total contents of flavonoids, phenolic acids and coumarins was determined. The content of coumarin was analyzed using HPLC-DAD.

Results: Plants grown in 30% shade produced the highest number of flowers and seeds. They produced the highest mass of herb at the beginning of the seed-setting stage. The plants grown in full sunlight revealed the highest content of flavonoids and phenolic acids, especially during flowering and at the beginning of the seed-setting stage. The mass of herb obtained by plants cultivated at deep (50%) shade was the lowest, however, the content of coumarin in these plants was the highest.

Conclusion: The influence of shade on bastard balm was expressed by the herb mass and coumarin content increment. The plants thrived best in 30% shade, both in terms of flowering abundance and the mass of herb, whereas those from 50% shade were the richest in coumarin.

Chemical Diversity of Bastard Balm (Melittis melisophyllum L.) as Affected by Plant Development

The phytochemical diversity of Melittis melissophyllum was investigated in terms of seasonal changes and age of plants including plant organs diversity. The content of phenolics, namely: coumarin; 3,4-dihydroxycoumarin; o-coumaric acid 2-O-glucoside; verbascoside; apiin; luteolin-7-O-glucoside; and o-coumaric; p-coumaric; chlorogenic; caffeic; ferulic; cichoric acids, was determined using HPLC-DAD. Among these, luteolin-7-O-glucoside, verbascoside, chlorogenic acid, and coumarin were the dominants. The highest content of flavonoids and phenolic acids was observed in 2-year-old plants, while coumarin in 4-year-old plants (272.06 mg 100 g-1 DW). When considering seasonal changes, the highest content of luteolin-7-O-glucoside was observed at the full flowering, whereas verbascoside and chlorogenic acid were observed at the seed-setting stage. Among plant organs, the content of coumarin and phenolic acids was the highest in leaves, whereas verbascoside and luteolin-7-O-glucoside were observed in flowers. The composition of essential oil was determined using GC-MS/GC-FID. In the essential oil from leaves, the dominant was 1-octen-3-ol, whilst from flowers, the dominant was α-pinene.