Evaluation of the xylan breakdown potential of eight mesophilic endoxylanases

In biomass degradation using simultaneous saccharification and fermentation (SSF), there is a need for efficient biomass degrading enzymes that can work at lower temperatures suitable for yeast fermentation. As xylan is an important lignocellulosic biomass constituent, this study aimed at investigating the possible differences in xylan breakdown potential of endoxylanases using eight different endoxylanases at conditions relevant for SSF. Both solubilising and degrading capacities of the endoxylanases were investigated using water-insoluble and water-soluble oat spelt xylan as model substrates for biomass xylan. Results showed that selecting for combinations of endoxylanases that are efficient at solubilising xylan on the one hand and degrading it to large extent on the other hand, coupled to high specific activities, seems the best option for complete xylan breakdown in lignocellulosic biomass conversion using SSF.     

燕麦种质资源形态学性状的遗传多样性

【目的】燕麦种质资源遗传多样性研究不仅有助于种质资源的收集和评价,而且对燕麦生产和育种具有重要指导意义。【方法】研究对260份燕麦种质资源的20个形态学性状多样性、变异及聚类进行分析,评价其形态学性状的遗传变异水平,明确燕麦种质资源的性状特点与遗传多样性,以期为燕麦种质创新和品种改良提供依据。【结果】260份燕麦种质资源形态学性状间存在广泛的遗传多样性,质量性状的遗传多样性指数以粒色最大(1.53),芒色最小(0.76);12个数量性状呈正态分布,数量性状的遗传多样性指数以千粒重最大(2.03),有效分蘖数最小(1.22),变异系数最大的是有效分蘖数(89.02%),最小的是株高(11.19%)。根据燕麦品种(系)间各性状的遗传差异,聚类分析将供试的260份燕麦种质资源分为6类,其中种质群Ⅰ包括42份材料,可作为种用型育种目标的亲本材料;种质群Ⅱ包括31份材料,可作为选育高产饲草品种的亲本材料;种质群Ⅳ包括41份材料,可作为选育大粒专用型品种的育种材料;种质群Ⅴ包括46份材料,可作为燕麦矮化的亲本材料;而种质群Ⅲ包括46份材料,种质群Ⅵ包括54份材料,这两类种质群材料的综合性状表现不突...     

不同时期喷施NaHS对盐碱胁迫下裸燕麦H2S产生和活性氧代谢的影响

为了解气体信号硫化氢（H₂S）对盐碱胁迫下裸燕麦（Avena nuda）活性氧（ROS）代谢的调节效应,筛选和确定H₂S最佳的施用时期和适宜浓度。采用盆栽土培试验,研究了在裸燕麦不同时期（幼苗期、拔节期、抽穗期、开花期和灌浆期）喷施0、25、50、100、200、400 μmol·L^-1 H₂S供体硫氢化钠（NaHS）对3.0 g·kg^-1盐碱混合 （NaCl∶Na₂SO₄∶NaHCO₃∶Na₂CO₃摩尔比为12∶8∶9∶1）胁迫下裸燕麦叶片H₂S含量、H₂S生成关键酶L-半胱氨酸脱巯基酶（LCD）活性和ROS代谢相关物质含量和酶活性的影响。结果表明：喷施时期和NaHS浓度及其交互作用对盐碱胁迫下裸燕麦叶片中H₂S、超氧阴离子（）、过氧化氢（H₂O₂）、丙二醛（MDA）、抗坏血酸（AsA）和谷胱甘肽（GSH）含量及LCD、超氧化物歧化酶（SOD）、过氧化氢酶（CAT）、过氧化物酶（POD）、抗坏血酸过氧化物酶（APX）和谷胱甘肽还原酶（GR）活性存在显著影响。与喷施0 μmol?L^-1 NaHS相比,喷施一定浓度NaHS能够提高H₂S、AsA、GSH含量和LCD、SOD、CAT、POD、APX和GR活性,减少、H₂O₂和MDA积累,但以上各指标最佳的喷施时期和NaHS浓度存在差异。隶属函数综合分析显示,在幼苗期和拔节期喷施25~200 μmol?L^-1 NaHS的综合评价值（D）最高,表明在幼苗—拔节期喷施25~200 μmol?L^-1 NaHS能更好提高ROS清除能力,从而缓解盐碱胁迫诱导ROS对裸燕麦的氧化伤害。     

Gravity sensing in oat coleoptiles: scatter in growth orientation under different g-conditions

Dark-grown oat seedlings depart from the expected vertical orientation, suggesting that the coleoptile is less responsive to the lateral component of a gravitational stimulus than would be expected. This phenomenon was studied by investigating the gravitropic curvatures of oat (Avena sativa L. cv. Seger) coleoptiles at 10g and over a range of longitudinally applied centripetal accelerations up to 19·4g. In most experiments, the plants were grown and observed at a particular g-level throughout the experiment. Time-lapse video recordings permitted studies of the scatter, measured as the variability of the plants' angle from the vertical (or root mean square value, RMS). The coleoptiles' heights at the end of the experiments were not significantly altered under the centrifugation. Scatter increased with plant age and decreased with increasing g. It decreased in an almost linear fashion as a function of the logarithm of the g-acceleration. In a series of experiments, the g-level was changed from 10g to a higher test g-acceleration. The scatter was then reduced within half an hour after the g-transition. It is pointed out that the experiments confirm that the scatter is g-related but that it was not predicted quantitatively by present theories of the oat coleoptile's gravitropic response kinematics.     

A comparison of the influence of sterols on the specific activity of the H+-ATPases in isolated plasma membrane vesicles from oat, rye and rice shoots

Plasma membrane vesicles were extracted from the shoots of 10-day-old oat, rye and rice plants and incubated with either cholesterol, stigmasterol or a mixture of sitosterol ⁺ campesterol (60:40). After ascertaining that the sterol composition of the vesicles had been altered by this treatment, the specific hydrolytic activity of the membrane-bound H⁺-ATPase (EC 3. 6. 1. 35) was measured. The results indicated that, although all sterols were taken up, cholesterol was best integrated into the plasma membrane of the species tested. After treatment, ATPase activity was altered in oat and rice, but not in rye. The results are discussed in the context of sterol/lipid and sterol/protein interactions in the plasma membrane.     

Metabolism of diclofop-methyl in cell cultures of Avena sativa and Avena fatua

The metabolism of the herbicide, diclofop-methyl (methyl-2-[4-(2', 4'-dichlorophenoxy) phenoxy]propanoate), in cell suspension cultures of Avena sativa L. (cv. Garry) and in callus of Avena fatua L. (transferred to liquid) was determined as a function of time (8 h to about 3 weeks) and was compared to previous metabolism data from intact plants. A. fatua metabolized ¹⁴C-labeled diclofop-methyl more rapidly than A. sativa, but the metabolites formed were similar if not identical. Within 2 days, approximately 50% of the total ¹⁴C recovered was in A. fatua cells whereas less than 15% was in A. sativa cells. In older cultures of A. fatua, the amounts of ¹⁴C in the cells and in the medium were about 45% each; 10 to 12% was in the non-extractable cell residue. The ¹⁴C recovered from A. sativa cells increased to a maximum of about 35% at 7 days and then slowly decreased to about 18% by 21 days, whereas the ¹⁴C in the medium of A. sativa decreased to about 60% at 7 days and then increased to over 75% by 21 days. The nonextractable ¹⁴C residue was 5% or less even after 21 days. Major metabolites in methanolic extracts of cells of both A. sativa and A. fatua were diclofop (2-[4-(2', 4'-dichlorophenoxy)phenoxy] propanoate), diclofop hydroxylated at an undetermined position on the 2,4-dichlorophenyl ring (ring OH-diclofop), and conjugates of diclofop and ring-OH diclofop.     

Influence of cereal leaf epicuticular wax on Diuraphis noxia probing behavior and nymphoposition

The effect of cereal leaf surface wax on Diuraphis noxia (Mordvilko), the Russian wheat aphid, probing behavior and nymphoposition was evaluated. Ultrastructure of leaf epicuticular wax from wheat (Triticum aestivum L.) c.v. Arapahoe and Halt was different from barley (Hordeum vulgare L.) c.v. Morex, and oat (Avena sativa L.) c.v. Border. Both wheat cultivars had similar rod-shaped epicuticular wax, while barley and oat plants had flakes. The chemical composition comparison of gas chromatograms also indicated that the extract of the two wheat cultivars had similar pattern of peaks, while the barley and oat leaves had similar peaks. Cereal variety significantly affected aphid probing behavior (P < 0.05), but wax removal using ethyl ether swab did not (P < 0.05). Aphids initiated significantly more probes on Border oat leaves than on Morex barley irrespective of wax removal, although total probing duration per aphid was not significantly different among the four cereals examined. Accumulative salivation duration per aphid on oat leaves with wax was significantly longer than other cereal leaves with wax, while accumulative ingestion duration per aphid on Arapahoe wheat and Morex barley was significantly longer than on oat. Nymphoposition of D. noxia on cereal leaves maintained on the benzimidazole-agar medium showed that aphids produced a greater number of nymphs on Morex barley and less on Border oat leaves, although wax removal did not affect aphid nymphoposition. Removal of leaf epicuticular waxes from the 4 cereal genotypes using ethyl ether swab indicated that the influence of wax on plant resistance to D. noxia probing and reproduction was limited. Morex barley was the most favorable, while Border oat was the least favorable cereal host of D. noxia.     

Oat leaf phosphoglucose isomerase: competitive inhibition by erythrose-4-phosphate

Phosphoglucose isomerase was partially purified from oat leaves and shown to be strongly inhibited by erythrose-4-P. Estimated Ki values were between 0.4 and 4.0 M. The inhibition was of the competitive type with respect to either of the substrates glucose-6-P and fructose-6-P. Several other plant phosphoglucose isomerases were found to be similarly sensitive to erythrose-4-P.