Transgenic down-regulation of the Pt4CL1 gene family encoding 4-coumarate:coenzyme A ligase (4CL) has been reported as a means for reducing lignin content in cell walls and increasing overall growth rates, thereby improving feedstock quality for paper and bioethanol production. Using hybrid poplar (Populus tremula 3 Populus alba), we applied this strategy and examined field-grown transformants for both effects on wood biochemistry and tree productivity. The reductions in lignin contents obtained correlated well with 4CL RNA expression, with a sharp decrease in lignin amount being observed for RNA expression below approximately 50% of the nontransgenic control. Relatively small lignin reductions of approximately 10% were associated with reduced productivity, decreased wood syringyl/guaiacyl lignin monomer ratios, and a small increase in the level of incorporation of H-monomers (p-hydroxyphenyl) into cell walls. Transgenic events with less than approximately 50% 4CL RNA expression were characterized by patches of reddish-brown discolored wood that had approximately twice the extractive content of controls (largely complex polyphenolics). There was no evidence that substantially reduced lignin contents increased growth rates or saccharification potential. Our results suggest that the capacity for lignin reduction is limited; below a threshold, large changes in wood chemistry and plant metabolism were observed that adversely affected productivity and potential ethanol yield. They also underline the importance of field studies to obtain physiologically meaningful results and to support technology development with transgenic trees.Composed of diverse layers of cellulose microfibrils and amorphous hemicelluloses within a matrix of pectins, proteins, and lignin, the secondary cell walls of plants are diverse in their morphology, chemistry, and physiological functions. Lignification is of particular interest, as it exhibits highly predictable temporal and spatial patterning and is the last major step in the structural reinforcement of cell walls before the protoplast is dissolved (Donaldson, 2001

Polyphenolic nonahydroxyterphenoyl-containing C-glycosidic oak ellagitannins are found in wine as a result of the aging of this beverage in oak-made barrels. Once in the slightly acidic wine (pH approximately 3-4), some of these complex natural products such as (-)-vescalagin (1), but not its C-1 epimer (-)-castalagin (2), can capture grape-derived nucleophilic entities such as ethanol, the flavanols catechin (10a) and epicatechin (10b), the anthocyanin oenin (13b), and the thiolic glutathione (16) to furnish condensation products with retention of configuration at the C-1 locus. A computer-aided rationale of this high diastereoselectivity is given. These condensation products can contribute to the modulation of organoleptic properties of the wine, as evidenced by the 23 nm bathochromic shift color absorbance observed with the novel oenin-based anthocyano-ellagitannin (15b). Hydrolysis of 1 under solvolytic conditions furnished another novel compound that we refer to as vescalene (21), in addition to the known (-)-vescalin (18). Of pharmacological importance is the fact that most of these found-in-wine water-soluble ellagitannin derivatives are much more potent than etoposide (VP-16) at inhibiting top2-mediated DNA decatenation in vitro (top2=topoisomerase II)). The known (-)-vescalin (18) and the novel vescalene (21) fully inhibited top2 at 10 microM concentration!

No abstract

This comprehensive review describes the current status and knowledge of biochemical and molecular processes involved in allyl/propenyl phenol, lignan, norlignan and lignin biosynthesis. Recent advances made over the last decade are critically discussed, and placed in context with earlier studies largely dating back to the 1950s. Beginning with the recently established formation of phenylalanine in plants, each downstream biochemical conversion is described from the perspective of the mechanistic details known to this point. Particular emphasis is placed upon proteinaceous control of monolignol-derived radical-radical coupling processes, leading to lignans and lignins, as well as apparently related processes affording the various ellagitannins and phenolic terpenoids. The evidence for non-random macromolecular lignin assembly is discussed in detail, this being in contrast to earlier notions that such processes were random. The latter assumptions have largely resulted from a lack of robust analytical procedures and rigorous quantification, as well as a lack of incisive experimental design. In addition, the often-noted severe effects of modulating lignin compositions and contents on plant vascular tissue properties (i.e. in terms of compromised biophysical properties) are described herein, as well as the severe limitations as regards recent claims of compensatory 'combinatorial chemistry' lignin formation. Much of the latter confusion has also resulted from the serious deficiencies in current lignin analytical protocols and quantification, as well as in the general lack of experimental approaches/design to probe lignin primary structure(s).

Stem byproducts from 10 different grape (Vitis vinifera L.) varieties were evaluated in terms of their total phenolic and total proanthocyanidin contents, flavan-3-ol and proanthocyanidin profiles, and antioxidant capacity measured by ABTS, CUPRAC, FRAP, and ORAC assays, with a view to the recovery of their natural bioactive compounds. Stems from Callet, Syrah, Premsal Blanc, Parellada, and Manto Negro varieties yielded the highest total phenolic and total proanthocyanidin contents and showed the greatest antioxidant capacities, whereas Chardonnay and Merlot stems presented the lowest values. Varieties differed significantly (p<0.05) with regard to both the phenolic composition and antioxidant capacity of their stems. However, no significant differences (p>0.05) were observed when stems from red and white varieties were considered separately. For the 10 grape varieties investigated, this is the first study presenting a detailed description of their stem flavan-3-ol composition determined by HPLC-UV-fluo. All of the analyses confirmed the stem byproducts as a potential polyphenol-rich source, especially promising in the case of the Callet variety.