Zhongqi Liu

Effect of lignocellulosic composition and structure on the bioethanol production from different poplar lines.

Branches from three transgenic poplar lines and their wild type line 107 were used to study the effect of lignocellulosic composition and structure on the production of glucose and ethanol. Experimental results showed that the transgenic line 18-1 had the high cellulose content and amorphous fibril structure. After poplar meals were pretreated with 10% NaOH and a mixture of hydrogen peroxide and acetic acid, their lateral order index decreased significantly. The highest glucose yield in enzymatic hydrolysis and ethanol yield from the substrate of 18-1 was much higher than that from feedstock of 107 by 192.7% and 108.7%, respectively. Scanning electron microscopy images confirmed that lignocellulose from the 18-1 could be destroyed by chemicals more easily than those from other lines. These results demonstrated that changing lignocellulose structure could be more effective on improving the digestibility and enzymatic hydrolysis of poplar biomass than increasing the cellulose content in biomass.

Effects of growing seasons and genotypes on the accumulation of cadmium and mineral nutrients in rice grown in cadmium contaminated soil.

Heavy metals naturally occur in soil but their concentrations may be changed by seasonal rainfall under double-rice cropping system. The field trials at three sites, which represent low, medium and high cadmium (Cd) content in soil, revealed significant genotypic and environmental variations in grain Cd concentrations. Most cultivars in late rice at three sites produced grains with Cd content over the maximum permissible concentration (MPC) 0.20mgkg-1. However, grain Cd content in early rice was over MPC only at high Cd site. When planted at same site, late rice showed remarkably higher content of Cd as well as K, Mg, Fe and Mn than that in early rice in both grains and rachises. Content of Ni, Pb and Cr was generally in the safe range and it was determined by the interactions between genotypes and environmental factors. Element concentrations in rachises were about 2-10 times higher than those in grains, depending on element species, cultivars, locations and seasons. Low-Cd-accumulation cultivars generally displayed both lower Cd content in rachis and lower Cd transportation ratio from rachises to grains than those of high-Cd-accumulation cultivars. There was a significant and positive correlation between Cd and Mn concentrations in grains. The most important factor that causes great variation in Cd accumulation in rachises and grains between early and later rice is water contents and levels in paddy soils mainly caused by different rainfall amount. Inhibiting Cd accumulation in rachises and Cd transportation from rachises to grains could efficiently decrease Cd content in rice grains produced in contaminated soil.

Modeling uptake of cadmium from solution outside of root to cell wall of shoot in rice seedling

It has long been recognized that the plasma membranes (PMs) play significant roles in the transport of ions across PMs, but kinetics of cadmium (Cd) transport between root and shoot via internal membrane system is not clear. Our experimental results showed that Cd2+ flux across the root PMs was well fitted by the Michaelis–Menten kinetics and the high-Cd-accumulation (HCA) variety displayed much higher maximum flux rate (Fmax) than the low-Cd-accumulation (LCA) variety. After Cd2+ was internalized, its flux into shoot PMs was linearly correlated with Cd2+ concentration in soluble fraction (FIII) of root cells. The efflux of Cd2+ across shoot PMs into cell wall was linearly correlated with Cd2+ concentration in shoot FIII. Only little amount of Cd2+ in cytosol was transported into organelles. The HCA variety displayed higher Cd2+ concentrations in FIII of root and shoot cells as well as higher Cd2+ flux rate by trans-cellular pathway than the LCA variety. However, efflux rate across shoot PMs to cell wall in the LCA variety was higher than that in the HCA variety. The low influx across PMs of root cells and high efflux across PMs of shoot cells probably are the special detoxification defense mechanisms of the LCA variety.