Lime pretreatment of sugar beet pulp and evaluation of synergy between ArfA, ManA and XynA from Clostridium cellulovorans on the pretreated substrate

Sugar beet pulp (SBP) is a waste product from the sugar beet industry and could be used as a potential biomass feedstock for second generation biofuel technology. Pretreatment of SBP with ‘slake lime’ (calcium hydroxide) was investigated using a 23 factorial design and the factors examined included lime loading, temperature and time. The pretreatment was evaluated for its ability to enhance enzymatic degradation using a combination of three hemicellulases, namely ArfA (an arabinofuranosidase), ManA (an endo-mannanase) and XynA (an endo-xylanase) from C. cellulovorans to determine the conditions under which optimal activity was facilitated. Optimal pretreatment conditions were found to be 0.4 g lime/g SBP, with 36 h digestion at 40 °C. The synergistic interactions between ArfA, ManA and XynA from C. cellulovorans were subsequently investigated on the pretreated SBP. The highest degree of synergy was observed at a protein ratio of 75% ArfA to 25% ManA, with a specific activity of 2.9 U/g protein. However, the highest activity was observed at 4.2 U/g protein at 100% ArfA. This study demonstrated that lime treatment enhanced enzymatic hydrolysis of SBP. The ArfA was the most effective hemicellulase for release of sugars from pretreated SBP, but the synergy with the ManA indicated that low levels of mannan in SBP were probably masking the access of the ArfA to its substrate. XynA displayed no synergy with the other two hemicellulases, indicating that the xylan in the SBP was not hampering the access of ArfA or ManA to their substrates and was not closely associated with the mannan and arabinan in the SBP

Non-destructive assessment of developing hydraulic connections in the graft union of tomato

Hydraulic architecture prescribes water flow in plants and is, therefore, fundamental to many areas of plant physiology. It is usually analysed destructively, or on excised material. A method is explored here based on displacement transducers for the continuous, nondestructive assessment of functional hydraulic connections within the intact plant. The graft union was chosen as a test system. The technique involves repeated application of water at some point in the system, while simultaneously observing patterns of swelling (increase in water status) at other points. Such patterns will reflect the hydraulic resistance of the intervening pathways. It is demonstrated that the major hydraulic connections within the graft union of tomato become functional over a period of about 48 h from the fifth day after grafting. This is consistent with histological observations on the appearance of wound-xylem bridges at this time. This approach could be useful for non-destructive monitoring of changes in hydraulic connections in various other intact systems, for example, during abscission, drought-induced embolism, or attack by vascular-wilt pathogens