Monomeric Composition Of Lignins Research Articles

DIATOMITES AND LIGNINS AS MYCOTOXIN ADSORBENTS

Currently, there is a tendency to deepen the mycotoxin problem, which is associated with the global warming and environmental pollution. The results of a study of the sorption capacity of adsorbents samples based on natural materials diatomites and lignins in relation to mycotoxin T-2 are presented. The chemical composition of diatomites of the Inzensk deposit before and after modification is given and the parameters of the surface-porous structure of the samples are established. The isotherms of adsorption and desorption of nitrogen on the surface of diatomites were studied and for the first time it was shown that they belong to the type IV(a) acording to IUPAC classification. The distribution of pores by size was studied and it was established that a significant proportion of the pore space of diatomites are mesopores with an average width of 7–12 nm. The highest adsorption rates of mycotoxin T-2 were established for a diatomite sample subjected to acid modification. Data on the adsorption of mycotoxin T-2 by samples of lignins isolated from the wood of birch Betula verrucosa, stems of rye Secale sp. and cabbage Brassica oleracea are given. The results of the determination of functional groups, elemental and monomeric composition of lignins are presented. It has been established that the adsorption capacity of drugs depends mainly on the peculiarities of the chemical structure of the studied samples. The highest adsorption rates of mycotoxin T-2 are established for lignin isolated from cabbage stems. Comparison of mycotoxin T-2 adsorption, surface porous structure parameters and chemical structure of various samples leads to the conclusion that for both diatomites and lignins, the chemisorption process plays the most important role.

Impact of jasmonic acid on lignification in the hemp hypocotyl

ABSTRACTPhytohormones are crucial molecules regulating plant development and responses to environmental challenges, including abiotic stresses, microbial and insect attacks. Most notably, phytohormones play important roles in the biosynthesis of lignocellulosics. Jasmonates are involved in secondary growth and secondary metabolism, such as phenylpropanoids and lignin biosyntheses. At the physiological and molecular levels, the actions of phytohormones depend on subtle concentration changes, as well as antagonistic equilibria between two or more of these molecules. In this article, we investigate the consequences of jasmonic acid (JA) spraying on young hemp hypocotyls. First, we show that JA application results in changes in the monomeric composition of lignin. Second, we highlight that, five days after application, JA leads to an increase in salicylic acid (SA) content in hemp hypocotyls. These results are discussed in the light of the known antagonism between JA and SA at both the physiological and molecular levels.

Lignin composition is related to xylem embolism resistance and leaf life span in trees in a tropical semiarid climate.

Wood properties influence the leaf life span (LL) of tree crowns. As lignin is an important component of wood and the water transport system, we investigated its relationship with embolism resistance and the LL of several tree species in a seasonally dry tropical ecosystem. We determined total lignin and the monomer contents of guaiacyl (G) and syringyl (S) and related them to wood traits and xylem vulnerability to embolism (Ψ50 ) for the most common species of the Brazilian semiarid, locally known as Caatinga. Leaf life span was negatively related to Ψ50 and positively related to S:G, which was negatively related to Ψ50 . This means that greater S:G increases LL by reducing Ψ50 . Lignin content was not correlated with any variable. We found two apparently unrelated axes of drought resistance. One axis, associated with lignin monomeric composition, increases LL in the dry season as a result of lower xylem embolism vulnerability. The other, associated with wood density and stem water content, helps leafless trees to withstand drought and allows them to resprout at the end of the dry season. The monomeric composition of lignin (S:G) is therefore an important functional wood attribute affecting several key functional aspects of tropical tree species in a semiarid climate.

Cadmium-induced lignification restricts soybean root growth

The effects of cadmium (Cd), a well-known environmental pollutant with high toxicity to plants, were tested on root growth, cell viability, phenylalanine ammonia-lyase (PAL) soluble plus cell wall-bound peroxidase (POD) activities, hydrogen peroxide (H 2O 2) levels, and the content and monomeric composition of lignin in soybean ( Glycine max) roots. Three-day-old seedlings were cultivated in half-strength Hoagland’s solution (pH 6.0), with or without 25–100 μM CdCl 2 in a growth chamber (25 °C, 12/12-h light/dark photoperiod, irradiance of 280 μmol m −2 s −1) for 24 h. In general, root length and the fresh and dry weights decreased followed by loss of cell viability after Cd treatment. PAL activity, soluble and cell wall-bound POD activities, and H 2O 2 and lignin contents increased significantly after Cd exposure. The lignin monomeric composition of Cd-exposed roots revealed a significant increase of p-hydroxyphenyl (H) and syringyl (S) units. These results suggest that the effects caused by Cd may be due to excessive production of monolignols forming lignin, which solidifies the cell wall and restricts root growth.

Applications of molecular genetics for biosynthesis of novel lignins

For the production of high-quality paper, lignin needs to be removed from cellulose. This process is energy requiring, expensive and toxic. Molecular biology offers tools to generate trees with a modified lignin composition to facilitate the extractability of lignin. We have cloned several genes encoding enzymes in the methylation of the lignin monomers [bi-specific caffeic acid/5-hydroxyferulic acid O-methyltransferase (COMT) and caffeoyl-CoA O-methyltransferase], and encoding enzymes specific for the lignin biosynthesis pathway [cinnamoyl-CoA reductase and cinnamyl alcohol dehydrogenase (CAD)]. The antisense strategy is used to study the effect of a down-regulation of these enzymes on the lignin content and the lignin composition of poplar wood. Our results demonstrate that the monomeric composition of lignin was dramatically affected by down-regulation of COMT. Transgenic poplars with a reduced CAD activity have better pulping properties, due to a higher extractability of the lignin.

The relationship between changes in lignification and the mechanical strength of rose flower peduncles

The resistance to bending of rose flower peduncle is important to the post-harvest quality of rose flowers. The content and composition of lignin was determined in respectively strong and weak peduncles of Rosa × hybrida cv. Mercedes and Nubia. Xylem tissues of the peduncles of the stronger cv. Mercedes were more lignified than in the weaker cv. Nubia. However, phloem lignin content was increased only in the basal parts of the peduncles of cv. Mercedes. Differences in the monomeric composition of lignins were apparent between cultivars. In both the phloem and xylem fractions, lignin in the peduncles of cv. Mercedes was less condensed than in the weaker cultivar Nubia. Furthermore, lignin rich in syringyl monomeric units occurred in the distal parts of the strong peduncles, accounting for the higher S/G ratio observed in the stronger peduncles compared to the weaker ones