Plums (Prunus domestica L. and Prunus salicina L.) are edible fruits mostly consumed in America, China, and Europe. We have used LC-MS(n) to detect and characterize the phenolic compounds in plum varieties. Forty-one phenolics were detected comprising caffeoylquinic acids, feruloylquinic acid, p-coumaroylquinic acids, methyl caffeoylquinates, methyl p-coumaroylquinate, caffeoylshikimic acids, catechin, epicatechin, rutin, esculin, quercetin, quercetin-3-O-hexosides, dimeric proanthocyanidins, trimeric proanthocyanidins, caffeoyl-glucoside, feruloyl-glucoside, p-coumaroyl-glucoside, vanillic acid-glucosides, 3,4-dihydroxybenzoyl-glucoside, quercetin-3-O-pentosides, quercetin-3-O-rhamnoside, quercetin-pentoside-rhamnosides, and 3-p-methoxycinnamoylquinic acid. This is the first time when 3-p-methoxycinnamoylquinic acid is reported in nature. Chlorogenic acids and proanthocyanidins were the major phenolics present in plums. Furthermore, HPLC with DAD and chemical reaction detection was used to generate quantitative phenolic fingerprints from the fruit flesh of 33 plum varieties. The predominant compound was 3-caffeoylquinic acid in nearly all varieties studied; generally, however, the qualitative and quantitative profiles showed high diversity even among closely related progenies.

The fruits of the European plum Prunus domestica exhibit a great diversity in appearance including skin colors. This study attempts to elucidate the phenylpropanoid and flavonoid profiles of 28 plum varieties belonging to P. domestica and related species as well as hybrids. A total of 49 phenolic compounds extracted from the fruit skin were quantitatively evaluated in an HPLC-DAD-based metabolomic study. The total phenolic contents of the cultivars varied among 0.4-29.9 mg/g fresh weight. The predominant anthocyanins were glycosides of cyanidin and peonidin, and rutin was the principal flavonol, whereas neochlorogenic acid and n-chlorogenic acid were the main hydroxycinnamic acids. Aside from these major phenolic classes, a group of tentatively identified flavones and several acylated flavonoids were also found. Principal component analysis revealed that anthocyanins and hydroxycinnamic acids contributed most to variety separation. The heterogeneity between the different varieties was also assessed using hierarchical cluster analysis of sample phenolics profile. A simple separation of species could not be found confirming the close relationship among them.

The paper shows that N‐induced vigorous shoot growth increases susceptibility of apple trees to Venturia inaequalis. This is due to a weakened defence in infected leaves of the high N cultures showing large lesions with excessive sporulation, whereas infected leaves from the low N cultures exhibited successful defence with only small chlorotic lesions and no sporulation. This might be explained by biosynthesis of phenylpropanoids in the young leaves of the resistant trees. A negative correlation between shoot growth of apple trees and the concentration of phenolic compounds in young leaves was found. Studies on in vitro shoot cultures revealed that the availability of sugars for the phenylpropanoid pathway is a strong regulatory factor. The ratio of sucrose and nitrogen in the medium influenced the total level of secondary products in the in vitro grown plantlets. Moreover, the relative deficiency of sugars was responsible for a metabolic block mainly at the level of glucosyl transferase and concomitant aglycone accumulation.

A stilbene synthase gene along with the selectable marker gene bar for herbicide resistance was transferred via Agrobacterium tumefaciens mediated transformation into apple (Malus domesticaBorkh.) cvs. 'Elstar' and 'Holsteiner Cox'. The stilbene synthase catalyzes the conversion of 1 molecule of p-coumaroyl-CoA and 3 molecules of malonyl-CoA into 3,4',5-trihydroxystilbene, commonly known as resveratrol. This phytoalexin has implications in both phytopathology and human health. Greenhouse-grown transgenic and nontransformed control plants were grafted onto dwarfing rootstock M27. Flowering and fruiting occurred within the following years, offering the opportunity to analyze transgenic apple fruit and fertility of transgenic plants as well as inheritance of the transgenes into the seedling progeny. Molecular analysis revealed that the stilbene synthase is expressed in transgenic plants and in the skin and flesh of transgenic apple fruit. After formation, resveratrol is modified by the addition of a hexose sugar. The resulting component was characterized as piceid. With the aim of characterizing the influence of the novel biosynthetic pathway on the accumulation of other phenolic compounds naturally present in apple fruit, the amounts of flavanols, flavonols, phloretin derivatives and hydroxycinnamic acids in wild type and transgenic fruit were determined by HPLC. In all investigated transformed lines that accumulated piceid, no negative correlation between levels of piceid and the above-mentioned compounds was observed, except for the flavonol contents, which slightly decreased. Inheritance of the transgenes was confirmed in the seedling progeny, which were obtained after pollination of transgenic plants with nontransgenic pollen and vice versa after pollination of nontransgenic plants with pollen obtained from transgenic plants. The fertility of stilbene synthase transgenic plants was demonstrated. To the authors' knowledge this is the first time that data are available on piceid synthesis in transgenic apple fruit and the effects of its accumulation on levels of other phenolic compounds present in the fruit.