Anthocyanins presumed

Anthocyanins are Che most easily assayed and commonly studied derivatives of aromatic amino acids (Figure 1). Glyphosate drastically reduces accumulation of anthocyanin flavonoids in treated tissues (6, 19) (Figure 3). Levels of rutin and procyanidin, both flavonoids, are reduced in glyphosate-treated buckwheat hypocotyls (6). Glyphosate would presumably similarly affect levels of flavonoids and flavonoid derivatives that are known to be allelochemicals. 

Gong, Z.Z., Yamazaki, M., and Saito, K., A light-inducible My6-like gene that is specifically expressed in red Perilla frutescens and presumably acts as a determining factor of the anthocyanin forma. Mol. Gen. Genet., 262, 65, 1999. 

Finally, several works have also implicated the nutrients P and Fe as possible inductors of changes in phenolic metabolism. However, studies of these relationships have been scarce. With regard to the former nutrient, P deficiency has been observed to raise the level of anthocyanins, but the reason for this rise remains unclear [4]. Meanwhile, low levels of Fe can increase the release of phenolic acids, presumably to help solubilize metals and thereby facilitate their uptake [135]. 

Flavanol oligomers and polymers are also called condensed tannins or proan-thocyanidins. The term tannin refers to their capacity to interact or react with proteins and precipitate them out. When heated under acidic conditions, these molecules release red anthocyanidin pigments, hence the term proanthocyanidins. The term leucoanthocyanidin, also referring to this particular property, is sometimes encountered in the literature. However, this should be restricted to another group of compounds, flavan 3,4-diols, which are intermediates in the biosynthetic pathway leading to flavanols and anthocyanins (Stafford and Lester 1984 Nakajima et al. 2001 Abrahams et al. 2003) but have never been isolated from grapes, presumably due to their instability. 

Again, the wide range of color due to polymeric pigment had greater variation than the anthocyanin content, presumable due to the additional variation in tannin content of the wines. 

Similarly, direct reactions between anthocyanins and a flavanol dimer (namely epicatechin-epicatechin 3-gallate) were investigated in model solutions at pH 2 and pH 3.8 (31). Compounds with mass values corresponding to epicatechin-anthocyanin adducts and to anthocyanin-epicatechin-epicatechin 3-gallate, were detected at pH 2 and pH 3.8, respectively. Given the structure of the flavanol precursor, the former can be interpreted as F-A+ arising from cleavage of the flavanol dimer followed by addition of the anthocyanin AOH form onto the epicatechin carbocation whereas the latter is presumably an A+-F species formed by nucleophilic addition of the flavanol dimer onto the flavylium cation. Anthocyanin dimers (A+-AOH) were detected in model solutions at pH... 

The anthocyanin-ethyl-flavanol adducts thus formed are purple pigments ( nax 5 0 nm), and much more resistant towards acid-catalyzed cleavage than the equivalent colorless ethyl-linked flavanol dimers (29). This presumably results from the displacement of the hydration equilibrium toward the flavylium cation form, due to self association, since similar synthetic pigments have been shown to be greatly stabilized by sandwich-type stacking (28). 

Stafford HA. Regulatory mechanisms in anthocyanin biosynthesis in first internodes of sorghum vulgare effect of presumed inhibitors of protein synthesis. Plant Physiol 1966 41 953-961. 

Amberlite XAD-7 is a nonionic moderately polar acrylic resin that has been used to purify anthocyanins. Lacking ionic groups, it presumably separates compounds... 

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