Does the degree of pectin esterification influence aluminium sorption by the root apoplast?

This study investigates the influence of the degree of pectin esterification (DE) on the sorption of aluminium (Al) by plant roots. Ca-pectates, with varying degrees of esterification, are major constituents of the soil–root interface and of the root apoplast. Ca-pectate networks (Ca–PG and Ca–Al–PG) were formed at three DEs (0%, 26%, 65%) with custom-made cells and used as a model system for the root cell wall. Sorption of Al was conducted for 24 h at a range of oxalic acid concentrations (0–500 μM) at pH 4.50 to examine two different metal resistance mechanisms of plants. In fact, plants release organic acids either to desorb or to complex metals to prevent their sorption by plant roots.Thermal analysis showed that Al sorption did not seem to affect the stability of the pectate gels and the presence of hydrophobic groups (–CH₃) at DE?>?0% seemed to even increase the stability of the gels decreasing thermal decomposition. Results suggest two potential Al tolerance mechanisms: (a) high oxalic acid concentrations (500 μM) were able to desorb almost 100% and 72% at DE 65 and 0%, respectively; (b) high oxalic acid concentrations (500 μM) and thus molar ratios of 5:1 (oxalate/Al) reduced Al sorption by 98% and 86% at DE 65 and 0%, respectively. In conclusion, both mechanisms indicate that high degrees of esterification as 65% are much more efficient in excluding Al from the apoplast and might therefore contribute to Al resistance in plants.     

Lepadiform and scalpelliform barnacles from the Oligocene and Miocene of the Paratethys sea

Abstract: A review on the Oligocene and Miocene stalked barnacles of the Paratethys Sea is presented. The fauna comprises two lepadiform and eight scalpelliform species. Only two species are known from Oligocene deposits, four are documented from Lower Miocene formations, and another four species occur in the Middle Miocene. Only one Oligocene and one Miocene species occur in two different Paratethyan basins in roughly coeval environments, and only a single Middle Miocene species is also known from the adjacent Mediterranean Sea. This low degree of biogeographical similarity is probably a result from the still low number of publications dealing with this group. Stalked barnacles are often indicating bathyal or at least deep sublittoral environments. Especially, the abundance of the benthic deep‐water lepadiform Poecilasma in evaporitic deposits of the Middle Miocene Badenian Salinity Crisis may serve as new evidence for a deeper marine depositional environment. Scalpellum paratethyianum sp. nov. and Lepas sattmanni sp. nov. are described as new species; Arcoscalpellum renevieri (Mayer and Gümbel in Gümbel, 1861) is introduced as new combination.     

Activity of myrosinase from Sinapis alba seeds immobilized into Ca-polygalacturonate as a simplified model of soil-root interface mucigel

Ca-polygalacturonate is a demethoxylated component of pectins which are constitutive of plant root mucigel. In order to define the role of root mucigel in myrosinase immobilization and activity at root level, a myrosinase enzyme which had been isolated from Sinapis alba seeds was immobilized into Ca-polygalacturonate. The activity profile for the immobilized and free enzyme was evaluated using the pH-Stat method as a function of time, temperature, and pH. The Michaelis-Menten kinetic parameters change between the immobilized (V _max ?=?127?±?13 U mg^?1 protein; K _M ?=?6.28?±?0.09?mM) and free (V _max ?=?17?±?1 U mg^?1 protein; K _M ?=?0.96?±?0.01?mM) forms of myrosinase, probably due to conformational changes involving the active site as a consequence of enzyme immobilization. Immobilized enzyme activity evaluated as a function of different substrates gave the highest value with nasturtin, the glucosinolate that is typical of several brassicaceae plant roots containing the glucosinolate-myrosinase defensive system. No feedback regulation mechanism was found in the presence of an excess of enzymatic reaction products (i.e. allyl isothiocyanate or sulphate). The high enzyme immobilization yield into Ca-polygalacturonate and its activity preservation under different conditions suggest that the enzyme released by plants at root level could be entrapped in root mucigel in order to preserve its activity.     

Mechanism and stoichiometry of the redox reaction between iron(III) and caffeic acid

The stoichiometry of the redox reaction of caffeic acid with iron(III) was determined at pH 2.5. A linear increase in the yield of iron(II) was found with increasing iron(III) concentration until reached constant values when iron(III)/caffeic acid molar ratios were higher than 9. The reaction proceeds through two steps each having different rates, and involving intermediates with different redox activities. A mechanism of the redox reaction consistent with our results is proposed.