Apples are an important source of polyphenolic and most popular fruits worldwide. Due to their phenolic content, consuming apple in a diet tend to low risk and prevention some chronic diseases. The ...main enzyme is responsible for quality loss, which are affecting by phenolic degradation, are polyphenol oxidase (PPO) and peroxidase (POX). PPO and POX are correlated to the rate of browning with substrate content and enzyme activity. The objective of this research was to investigate the polyphenol oxidase (PPO) and peroxidase (POX) activity in different apple cultivars. Apples Gravin Goldach, Bay 4152, Sonnen Glanz, Gala Mitslugla apples were obtained from an orchad of Hohere Bundeslehranstalt und das Bundesamt fur Wein und Obstbau in Klosterneuburg, Vienna, Austria, then Apple from each cultivar was cut and separated in two parts, peel with seed (red flesh) and peel without seed (white flesh), then PPO and POX were determined. The results showed that tThe highest PPO activity is presented by red flesh of Bay 4152 cultivar, whereas the lowest detected in red flesh Gala Mitslugla. PPO activity on apple flesh of red Bay 4152, white Sonnen Glanz, red gravin Goldach and red Gala Mitslugla were 5.01E+04, 4.79+04, 3.17+04 and 1.91E+04 ΔE/S/Kg protein, respectively. PPO activity on apple flesh was not affected by white or red colour. The highest POX activity was found in red flesh of Sonnen Glanz cultivar, whereas the lowest value was presented in white flesh of Gravin Goldach cultivar varied from 1.07E+05 to 7.68E+04 ΔE/S/Kg protein. In all different flesh of apple cultivars showed that the high or low POX activity was not resulted by the red or white flesh coloured. POX is much higher than PPO activity of all cultivars. Result will provide to maintain the phenolic related quality loss and to improve new processing method.
Secondary metabolites play a major role as quality factors in horticultural products by significantly contributing to plant health, optical attributes, sensory attributes and health beneficial ...effects for the consumer. Dihydrochalcones, a rare class of secondary metabolites, which is, however present in particularly high amounts in apple (Malus × domestica. In apple, phloridzin (phloretin 2'-O-glucoside) is prevalent representing more than 90% of the soluble phenolic compounds, but small amounts of 3-hydroxyphloretin and 3-hydroxyphloridzin are also constitutively present. For the systematic investigation, sufficiently comprehensive knowledge of the underlying pathway is yet lacking. Two types of enzymes could catalyze the reaction, polyphenol oxidases (PPOs) and/or cytochrome P450 dependent monooxygenases. To test a possible involvement of the F3'H of apple in the formation of constitutive 3-hydroxydihydrochalcones, cDNA clones of the two types of F3'Hs present in the apple was isolated and heterologously expressed in yeast. Despite showing high F3'H enzyme activity with various flavonoid substrates, hydroxylation of dihydrochalcones was not observed at standard conditions, indicating that F3'H is not part of the dihydrochalcone pathway.
The study was performed on apple trees, 'Golden Delicious' cv., which is a scab-susceptible cultivar. The phenolic content of apple fruit was determined in different parts of the peel. The phenolic ...compounds were analysed in the scab spot, in the tissue around the spot and in the healthy tissue. We determined the concentration of various phenolic compounds and related enzyme activities. Infection with the Venturia inaequalis fungus enhanced the metabolism of phenolic compounds at the scab spot, around the spot and in healthy peel. Compared with the healthy tissue and the tissue around the spot, the scab spot showed higher enzyme activity for all tested enzymes, except for dihydrochalcone 2′-O-glucosyltransferase, which had lower activity in the scab spot. In comparison to the healthy peel, the scab spot showed up to 3.4 times more hydroxycinnamic acids, up to 1.1 times more dihydrochalcones and up to 1.4 times more flavan-3-ols. In contrast, the healthy peel showed up to 1.6 times more flavonols than the scab spot.
The dihydrochalcone phloridzin (phloretin 2′-O-glucoside) is the most abundant phenolic compound in apple trees (Malus × domestica) and was also discussed to have an influence on the pathogen defence ...by shifting the dihydrochalcone profile from the glucosides to the more active aglycones. The final step in the biosynthesis of phloridzin is the glycosylation of phloretin at position 2′. Three cDNA clones from apple encoding glycosyltransferases are available which are able to catalyze the reaction in vitro. We investigated the possible role of glycosyltransferase UGT71A15 in phloridzin biosynthesis. The recombinant enzyme showed broad substrate acceptance but highest activities were observed with flavonols. Specific activities and the kinetic data indicated that phloretin is not the preferred native substrate of the UGT71A15. However, an increase of the molar ratio phloridzin:phloretin was found in transgenic lines, indicating a physiological relevance of UGT71A15 in planta, although a decrease of the total amount of dihydrochalcones in the majority of the samples was found. Unexpectedly, the increase of the phloridzin:phloretin ratio was not reflected by an increase of the total glucosyltransferase activities. In contrast, the majority of transgenic plants showed a reduced glucosylating activity with both phloretin and quercetin as a substrate, but the observed activity changes in a given sample were not similar for the two substrates. An increased susceptibility of M. robusta against the fire blight causing bacterium E. amylovora as a result of UGT71A15 overexpression could not be observed. Overexpression of UGT71A15 in transgenic apple trees also did not lead to morphological changes.
Abstract
Enhanced shoot growth and a decrease in flavonoid concentration in apple trees grown under high nitrogen (N) supply was observed in previous studies, along with increasing scab ...susceptibility of cultivar “Golden Delicious” after high N nutrition. Several hypotheses have suggested that there is a trade-off between primary and secondary metabolism because of competition for common substrates, but nothing is known about regulation at the enzyme level. In this study, a set of experiments was performed to elucidate the effect of N nutrition on the activities of key enzymes involved in flavonoid biosynthesis (phenylalanine ammonia-lyase PAL, chalcone synthase/chalcone isomerase CHS/CHI}, flavanone 3-hydroxylase FHT, flavonol synthase FLS, dihydroflavonol 4-reductase DFR) and the accumulation of different groups of phenylpropanoids. The inhibition of flavonoid accumulation by high N nutrition could be confirmed, but the influence of N supply on the flavonoid enzymes CHS/CHI, FHT, DFR, and FLS was not evident. However, PAL activity seems to be downregulated, thus forming a bottleneck resulting in a generally decreased flavonoid accumulation. Furthermore, the response of the scab-resistant cultivar “Rewena” to high N nutrition was not as strong as that of the susceptible cultivar “Golden Delicious”.
Drought events are expected to become more frequent with
climate change. To predict the effect of plant emissions on air quality and
potential feedback effects on climate, the study of biogenic ...volatile
organic compound emissions under stress is of great importance. Trees can
often be subject to a combination of abiotic stresses, for example due to
drought or ozone. Even though there is a large body of knowledge on
individual stress factors, the effects of combined stressors are not much
explored. This study aimed to investigate changes of biogenic volatile
organic compound emissions and physiological parameters in Quercus robur L. during moderate
to severe drought in combination with ozone stress. Results show that
isoprene emissions decreased while monoterpene and sesquiterpene emissions
increased during the progression of drought. We exposed plants with daily
ozone concentrations of 100 ppb for 1 h for 7 d, which resulted
in faster stomatal closure (e.g., a mean value of −31.3 % at an average stem
water potential of −1 MPa), partially mitigating drought stress effects.
Evidence of this was found in enhanced green leaf volatiles in trees without
ozone fumigation, indicating cellular damage. In addition we observed an
enhancement in (C8H8O3)H+ emissions likely corresponding
to methyl-salicylate in trees with ozone treatment. Individual plant stress
factors are not necessarily additive, and atmospheric models should implement
stress feedback loops to study regional-scale effects.
Flavonoids are important secondary metabolites in strawberry as they fulfill a wide variety of physiological functions. In addition, they are beneficial for human health. Previous studies have shown ...for selected enzymes from the flavonoid pathway that flavonoid biosynthesis shows two peaks during fruit development. We provide optimized protocols for the determination of the activities of the key flavonoid enzymes: phenylalanine ammonia lyase, chalcone synthase/chalcone isomerase, flavanone 3-hydroxylase, dihydroflavonol 4-reductase, flavonol synthase, flavonoid 3-O-glucosyltransferase, and flavonoid 7-O-glucosyltransferase. Using these protocols we were able to demonstrate two distinct activity peaks during fruit ripening at early and late developmental stages for all enzymes with the exception of flavonol synthase. The first activity peak corresponds to the formation of flavanols, while the second peak is clearly related to anthocyanin and flavonol accumulation. The results indicate that flavonoid 3-O-glucosyltransferase activity is not essential for redirection from flavanol to anthocyanin formation in strawberry. Keywords: Strawberry (Fragaria × ananassa); fruit ripening; fruit color; flavonoid concentrations; flavonoid enzymes; anthocyanins; flavan 3-ols (catechin, epicatechin, and derived proanthocyanidins); flavonols
A flavonoid 8-hydroxylase was demonstrated for the first time with enzyme preparations of
Chrysanthemum segetum. The enzyme is localized in the microsomal fraction and uses NADPH and FAD as ...cofactors. The flavonoid 8-hydroxylase seems to represent a novel type of hydroxylating enzyme in the flavonoid pathway.
Yellow flavonols contribute to flower pigmentation in Asteraceae. In contrast to common flavonols, they show additional hydroxyl groups in position 6 and/or 8 of the aromatic A-ring in addition to the basic 5,7-hydroxylation pattern. An enzyme introducing a hydroxyl group in position 8 of flavonols and flavones was demonstrated for the first time with enzyme preparations from petals of
Chrysanthemum segetum. Flavanones, dihydroflavonols and glucosylated flavonols and flavones were not accepted as substrates. The enzyme was localized in the microsomal fraction and uses NADPH and FAD as cofactors. Experiments with carbon monoxide/blue light and with antibodies specific for cytochrome P450 reductase did not indicate the involvement of a classical cytochrome P450 dependent monooxygenase in the reaction. Thus, the flavonoid 8-hydroxylase represents a novel type of hydroxylating enzyme in the flavonoid pathway. Apart from flavonoid 8-hydroxylase activity, the presence of all enzymes involved in the formation of flavonoid 7-
O-glucosides in
C. segetum was demonstrated. The pathway leading to 8-hydroxyflavonoids in
C. segetum has been derived from enzyme activities and substrate specificities observed.
The application of prohexadione-Ca on apple and pear trees leads to enhanced resistance against fire blight, and scab in case of apple, which is accompanied by the accumulation of unusual ...3-deoxyflavonoids and other phenolic compounds in the leaves. An alternative pathway leading to the different 3-deoxyflavoids is hypothesised. A resistance effect of 3-deoxyanthocyanidins against certain fungi is known in Sorghum species. The enormous economic damage caused by fire blight leads to increased interest in the resistance mechanism. The identification of the responsible compound(s) is ongoing. The effect of prohexadione-Ca is studied at the biochemical and molecular biological levels. Standard assays were optimised for the enzymes involved in flavonoid metabolism. The respective genes were cloned from apple and pear. Studies were performed with heterologously-expressed dihydroflavonol 4-reductase (DFR) and flavanone 3-hydroxylase (FHT) enzymes. It was shown that prohexadione-Ca has an inhibitory effect on apple and pear FHT in vitro. This supports the assumption that the formation of common flavonoids is blocked by prohexadione-Ca and that the accumulating flavanones serve as precursors of the resulting 3-deoxyflavonoids. The key step in the formation of 3-deoxyflavonoids is the enzymatic reduction of flavanones to flavan 4-ols. It has been shown that the DFR enzymes of apple and pear are able to perform this reaction. Further work will investigate if this approach is also suitable for the control of other plant diseases.
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