化感水稻不同组织水浸提液对稗草的化感作用

本研究利用HG1和HG2两个化感水稻品种和稗草为材料,研究了化感水稻品种的叶、叶鞘、根组织的水浸提液对稗草幼苗的化感作用。结果表明：HG1不论是对稗草幼苗的株高还是对稗草幼苗的根都有极强的化感作用,而HG2只对稗草的根有极强的化感作用。在不同组织之间,叶和叶鞘的水浸提液对稗草的抑制作用显著大于根的水浸提液和对照。两个化感水稻对稗草幼苗根的抑制更强于对苗高的抑制。随着稗草密度的增加,稗草受抑程度减少,这可能与单株吸收化感物质的量减少有关。     

干旱胁迫下白桦（Betula plathphylla）实生苗叶片的水分代谢与部分渗透调节物质的变化

在土壤干旱胁迫进程中,白桦实生苗叶片的自然含水量呈下降趋势;相对含水量的总的变化趋势与自然含水量相同;束缚水含量及束缚水/自由水比值显著升高,复水后,三者又重新恢复至正常水平。随着土壤水分逐渐减少,可溶性蛋白质的含量呈现减少趋势,复水后,可溶性蛋白质含量又可恢复至正常水平。白桦实生苗叶片可溶性糖含量增加,复水后可溶性糖含量降至趋于对照水平。     

猪粪与沼气渣对双季稻田甲烷排放的影响

随着环境温度的升高,稻田甲烷排放通量增加。早稻期间甲烷排放通量随着水稻生育期的增加而逐步加快,而晚稻甲烷排放主要集中在水稻生长的前中期,而且排放量很高。一天中甲烷排放具有很强的周期性,在6：00～8：00时,甲烷排放通量进入谷底,14：00时甲烷排放通量达到峰值。稻田甲烷排放通量与土壤5cm处的温度及土壤水溶解甲烷含量具有较高的相关性。猪粪和沼气渣的施用分别提高稻田甲烷排放量22．14％和4．40％。在早稻期间,施用猪粪和沼气渣分别提高土壤水溶解甲烷含量40．3％和11．9％,而晚稻期间仅分别提高23．9％和5．04％。     

江南牡丹草的化学成分研究

江南牡丹草 Leontice kiangnanensis,别名江南玄胡 ,主要分布在浙江西北部和安徽皖南山区。民间草药 ,药用块茎 ,有清热解毒、活血化瘀功效 ;用于治疗跌打损伤、骨折疼痛、头痛、吐血、外伤出血等症 ,疗效显著。其化学成分研究未见报道。我们从江南牡丹草块茎水溶性生物碱中分离得到 1 5个生物碱成分 ,报道了其中 7个已知化合物 ,其它 8个生物碱的结构另文报道。1 　实验部分1 .1 　实验仪器与材料熔点用 X-4型显微熔点仪测定 (温度计未校正 )。红外光谱用 Perkin-Elmer 983型红外光谱仪测定 ,溶剂为 CDCl3和 CDOD,TMS内标。质谱用 V…     

从制胶后的胡芦巴种子中提取甾体长甙元的研究

胡芦巴为一年生草植物,本文以制胶后的胡芦巴种子剩余物为实验原料,研究了甾体皂甙元的最佳提取工艺路线和工艺。在该工艺条件下的重复试验表明,胡芒巴甾体皂甙元的得率在1.15％以上,熔点大于187.5℃,其中薯蓣皂甙元含量达86.5％,结果具有工业化开发价值。     

Evidence of an extractable semiochemical produced by Rhopalosiphum padi acting on Psammotettix alienus

It has previously been shown that the aphid Rhopalosiphum padi (L.) (Homoptera: Aphididae) adversely affects the biology of the leafhopper Psammotettix alienus (Dahlbom) (Homoptera: Cicadellidae) (Alla et al., 2001). In this work, we demonstrate that this effect was due to chemical components produced by the aphid.The increase in the number of aphids in the presence of the leafhopper on wheat caused nymphal mortality, an extended duration of the development and a decrease in nymph production of the leafhopper. Extract of aphids in methanol-water (50/50: v/v), applied on plants significantly increased the mortality in the leafhopper nymphs at both 3AE (3 Aphid Equivalent) and 7AE doses. At the same doses, both the honeydew and water extract of aphids did not have any effect. At the 20AE dose, aphid extracts in methanol-water led to a longer development time and strong mortality in leafhopper nymphs. In female adults of the leafhopper, neither the aphid extracts in methanol-water nor the honeydew showed a conclusive result, but generally, daily nymph production decreased with the increase in the extract doses.These results confirmed the depressive effect of R. padi on P. alienus and showed that this interaction was chemical. The active component(s) is partially extracted in a blend of methanol-water (50/50: v/v). Further studies to identify this component(s) will be undertaken.     

Enzymic and Structural Studies on Drosophila Alcohol Dehydrogenase and Other Short-Chain Dehydrogenases/Reductases

Enzymic and structural studies on Drosophila alcohol dehydrogenases and other short-chain dehydrogenases/reductases (SDRs) are presented. Like alcohol dehydrogenases from other Drosophila species, the enzyme from D. simulans is more active on secondary than on primary alcohols, although ethanol is its only known physiological substrate. Several secondary alcohols were used to determine the kinetic parameters k_cat and K_m. The results of these experiments indicate that the substrate-binding region of the enzyme allows optimal binding of a short ethyl side-chain in a small binding pocket, and of a propyl or butyl side-chain in large binding pocket, with stereospecificity for R(−) alcohols. At a high concentration of R(−) alcohols substrate activation occurs. The k_cat and K_m values determined under these conditions are about two-fold, and two orders of magnitude, respectively, higher than those at low substrate concentrations. Sequence alignment of several SDRs of known, and unknown three-dimensional structures, indicate the presence of several conserved residues in addition to those involved in the catalyzed reactions. Structural roles of these conserved residues could be derived from observations made on superpositioned structures of several SDRs with known structures. Several residues are conserved in tetrameric SDRs, but not in dimeric ones. Two halohydrin-halide-lyases show significant homology with SDRs in the catalytic domains of these enzymes, but they do not have the structural features required for binding NAD⁺. Probably these lyases descend from an SDR, which has lost the capability to bind NAD⁺, but the enzyme reaction mechanisms may still be similar. Received: 23 May 2000 / Accepted: 4 January 2001     

Mobilization of sparingly soluble inorganic phosphates by the external mycelium of an abuscular mycorrhizal fungus

Red clover (Trifolium pratense L.) and Glomus versiforme (Karsten) Berch growing in rhizoboxes were employed in two glasshouse experiments to study the mobilization of sparingly soluble phosphates by arbuscular mycorrhizal fungal (AMF) mycelium. In one experiment, four inorganic sources of phosphate, CaHPO₄.2H₂O (Ca₂-P), Ca₈H₂(PO₄)₆.5H₂O (Ca₈-P), Ca₁₀(PO₄)₆.F₂ (Ca₁₀-P) and AlPO₄.nH₂O (Al-P), were chemically synthesized, labelled with ³²P in an atomic pile and applied to the hyphal compartments of the rhizoboxes. Shoot yield, ³²P and total P uptake were measured in clover growing in the root compartments. A similar experiment was conducted simultaneously using the same phosphate sources unlabelled and clover mycorrhizal infection and soil pH were determined. Although AMF inoculation increased the P uptake and biomass of clover shoots, the contribution of AMF to shoot P uptake and biomass varied with phosphate source, and was greatest with Ca₂-P and least with Ca₁₀-P. ³²P measurements indicated that external hyphae could mobilize Ca₂-P, Ca₈-P and Al-P, but not Ca₁₀-P. This indicates that AMF not only mobilize the same types of phosphates that plants mobilize under stress conditions of low P, but give increased contact with phosphates in the soil compared with non-mycorrhizal root systems.     

Molecular and biochemical responses of perennial forage crops to oxygen deprivation at low temperature

Anaerobic conditions developing under ice cover affect winter survival and spring regrowth of economically important perennial crops. Our objective was to assess interspecific differences in the resistance to anaerobic conditions at low temperature, and to relate those differences to plant metabolism. Four perennial forage species, alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), timothy (Phleum pratense L.) and orchardgrass (Dactylis glomerata L.), were subjected to a progressively developing anoxic stress by enclosing potted plants in gas‐tight bags in late autumn and exposing them to simulated winter conditions in an unheated greenhouse. Near‐anaerobic conditions were reached after 60 d of enclosure for orchardgrass, alfalfa and red clover, and after 80 d for timothy. The sensitivity of the species to anaerobic conditions, based on plant regrowth, was: red clover and orchardgrass > alfalfa > timothy. The concentration of ethanol increased in response to oxygen deprivation, and reached the highest value in the sensitive red clover, whereas its concentration was the lowest in timothy. The expression of the alcohol dehydrogenase (ADH) gene was markedly lower in timothy than in the other three species for which the expression was equivalent. We conclude that the greater resistance of timothy to anaerobic conditions at low temperature is associated with a slower glycolytic metabolism.     

The importance of ethanolic fermentation for primary root growth of germinating rice under anoxia

The relationship between primary root growth and ethanolic fermentationwas investigated in five cultivars of germinating rice (Oryza sativa L.) seeds subjected to 48 h-anoxic stress. The anoxic stressinhibited the growth of all rice cultivars, however, there were significantdifferences in the growth among the cultivars. The stress increased alcoholdehydrogenase activities and ethanol concentrations in the roots of all ricecultivars but there were differences between cultivars in the activity and theconcentration. The ethanol concentrations in the roots were closely correlatedwith the root growth of the corresponding cultivars. These results suggest thatability to induce ethanolic fermentation may play an important role in theprimary root growth of germinating rice in anoxic condition.