The mechanism of enhanced lignin regulating foliar Cd absorption and yield in rice (Oryza sativa L.).

The impact of atmospheric deposition of cadmium (Cd) in cereal crops has become a global concern. Enhanced lignin content was expected to benefit the plant performance against Cd exposure. To date, however, the underlying mechanisms of lignin regulating foliar Cd absorption in rice (Oryza sativa L.) and its effect on grain yield remains unclear. In present study, the effect and mechanism of rice in response to leaf Cd exposure were investigated using 113Cd stable isotope and a lignin-increased rice mutant. The highest Cd uptake efficiency and uptake amount was observed in wild type (WT) plant grown in the maturity period, which were 3-fold higher than in mutant plant. Compared to WT, the mutant exhibited 14.75% and 25.43% higher contents in G- and S-unit of lignin monomers. Lignin biosynthesis and polymerization related genes (OsPAL/OsCOMT/Os4CL3/OsLAC5/OsLAC15) were significantly up-regulated in mutants. In addition, the enzyme activities involved in the above process were also significantly increased by 1.24-1.49-fold. The increased Cd retention in cell wall and decreased gene expression levels of OsNRAMP5, OsHMA3 and OsIRT1 in mutant indicated that lignin effectively inhibited Cd transportion in plant tissues. Moreover, the antioxidant capacity and photosynthesis efficiency in mutant plant were obviously improved, leading to higher Cd tolerance and increased grain yield. Our results revealed the molecular and physiological mechanisms of enhanced lignin regulating foliar Cd absorption and yield in rice, and provided the valuable rice genotype to ensure food safety.

Host responses and metabolic profiles of wood components in Dutch elm hybrids with a contrasting tolerance to Dutch elm disease.

BACKGROUND AND AIMS: Changes occurring in the macromolecular traits of cell wall components in elm wood following attack by Ophiostoma novo-ulmi, the causative agent of Dutch elm disease (DED), are poorly understood. The purpose of this study was to compare host responses and the metabolic profiles of wood components for two Dutch elm (Ulmus) hybrids, 'Groeneveld' (a susceptible clone) and 'Dodoens' (a tolerant clone), that have contrasting survival strategies upon infection with the current prevalent strain of DED. METHODS: Ten-year-old plants of the hybrid elms were inoculated with O. novo-ulmi ssp. americana × novo-ulmi. Measurements were made of the content of main cell wall components and extractives, lignin monomer composition, macromolecular traits of cellulose and neutral saccharide composition. KEY RESULTS: Upon infection, medium molecular weight macromolecules of cellulose were degraded in both the susceptible and tolerant elm hybrids, resulting in the occurrence of secondary cell wall ruptures and cracks in the vessels, but rarely in the fibres. The (13)C nuclear magnetic resonance spectra revealed that loss of crystalline and non-crystalline cellulose regions occurred in parallel. The rate of cellulose degradation was influenced by the syringyl:guaiacyl ratio in lignin. Both hybrids commonly responded to the medium molecular weight cellulose degradation with the biosynthesis of high molecular weight macromolecules of cellulose, resulting in a significant increase in values for the degree of polymerization and polydispersity. Other responses of the hybrids included an increase in lignin content, a decrease in relative proportions of d-glucose, and an increase in proportions of d-xylose. Differential responses between the hybrids were found in the syringyl:guaiacyl ratio in lignin. CONCLUSIONS: In susceptible 'Groeneveld' plants, syringyl-rich lignin provided a far greater degree of protection from cellulose degradation than in 'Dodoens', but only guaiacyl-rich lignin in 'Dodoens' plants was involved in successful defence against the fungus. This finding was confirmed by the associations of vanillin and vanillic acid with the DED-tolerant 'Dodoens' plants in a multivariate analysis of wood traits.

Effects of thermal treatment on chemical, mechanical and colour traits in Norway spruce wood.

In several different branches of the wood industry heat treatment is a growing application as it changes the chemical, mechanical, physical and biological properties of wood. Investigations using wet chemical analyses, Fourier transform infrared spectroscopy, size exclusion chromatography, and CIELab colour system have been conducted to study the changes in Norway spruce wood subjected to temperature up to 270°C over a 30 min time period. The results showed that mass loss (ML), total crystallinity index (TCI) of cellulose, total colour difference (ΔE*), and the content of lignin and extractives increased with the temperature, whereas degree of polymerization (DP) of cellulose, modulus of rupture (MOR), modulus of elasticity (MOE), lightness difference (ΔL*), and the content of holocellulose, cellulose and hemicelluloses all decreased with the thermal treatment. Relationships between temperature and the examined wood traits were all fitted by exponential curves. Power law relationships were found to fit the trends for DP of cellulose with ΔE*, ΔL*, and TCI of cellulose. Also found were power law regressions for the content of hemicelluloses with MOE, MOR, ΔL*, and ML. Temperatures ranging from 20 to 187°C formed a compact cluster, clearly separated from the higher examined temperatures in the multivariate wood trait space.