植物角质膜研究进展

植物的角质膜是植物与外界环境的交界面, 有利于植物减少蒸腾、抵抗紫外伤害和防止病虫害等。植物与外部环境相互作用的过程中, 其角质膜会构建自身的防御系统, 如通过自身结构、成分的改变及产生次生代谢产物来减轻外界不利环境因子的胁迫。因此, 植物角质膜与环境之间的密切关系对于植物生长有着重要意义。该文综述了植物角质膜的结构、成分、形成、功能及其与次生代谢和环境的关系, 同时对研究中存在的问题进行了讨论并展望了相关领域的研究前景。     

Biomechanics of Isolated Plant Cuticles

The mechanical properties of isolated cuticles of leaves (Yucca aloifolia, Clusia fluminensis, Nerium oleander, Hedera helix) and one fruit (Lycopersicon esculentum) were investigated by means of a tensile test. Samples of the leaves and the fruit were cut to identical size (12.5 × 50 mm) and the cuticles were enzymatically isolated, cleaned, and air dried. The morphology of the isolated cuticular membranes (CM) was investigated by scanning electron microscopy (SEM) and showed considerable differences. The thickness of the CM was determined by a digital image analysis system and ranged between 2.4 and 13.4 μm. The CM were subjected to a tensile test and the results are presented as stress-strain diagrams. From the latter, Young's moduli were calculated, a measure for the stiffness which allows the direct comparison of different materials. The obtained values ranged between 0.1 and 1.3 CPa. Hydration of CM caused a decrease of Young's moduli of about 35–50%. A possible role of the cuticle as a factor for the stabilization of plant organs is discussed.     

Extracellular Lytic Enzymes of Myxococcus virescens II. Purification of Three Bacteriolytic Enzymes and Determination of their Molecular Weights and Isoelectric Points

The bacteriolytic enzymes produced by Myxococcus virescens and previously concentrated and separated from most of the non-bacteriolytic proteins have been further separated and purified. The bacteriolytic enzyme solution was concentrated by lyo-philization. When applied to a Sephadex G-100 column, three peaks of bacteriolytic activity were eluted. Polyacrylamide gel electrophoresis showed that all the three enzyme fractions were contaminated with at least four non-bacteriolytic proteins. In the first enzyme fraction the bacteriolytic enzymes could be freed from the contaminating proteolytic activity by adsorption on a hydroxylapatite column. The bacteriolytic enzymes could then be adsorbed on a CM-cellulose column. The remaining contaminating proteins passed the column un-adsorbed while the bacteriolytic enzymes could be eluted with a gradient of 0.02–0.10 M ammonium hydrogen carbonate solution. The second enzyme fraction was adsorbed on a CM-cellulose column and then eluted with 0.03–0.15 M NH4 HCO₃. After rechromatography on a new column under the same conditions, all of the contaminating proteins had disappeared. For purification of the third enzyme fraction chro-matography on one single CM-cellulose column was sufficient. The elution of the adsorbed enzymes was performed with a gradient of 0.15–0.30 M NH₄HCO₃. The recovery of activity for each of the ion-exchange chromatography separations was at least 90%. The purity of the enzymes was tested by polyacrylamid gel electrophoresis. Each of the purified enzymes gave only one coloured band which coincided with the enzyme activity assayed in sliced gels. The molecular weights of the enzymes were determined by electrophoresis on acryl-amide gels containing sodiumdodecylsulphate. The molecular weights determined in this way (about 40,000, 30,000 and 20,000, respectively) were about 10,000 daltons higher than those obtained by gel chromatography on Sephadex G-100. This discrepancy seems to depend on interactions between the enzymes and the dextran molecules probably caused by the strongly basic nature of the enzymes or by formation of enzyme-substrate complexes.     

菜心和水稻绿叶中不同等电点的乙醇酸氧化酶

The proteins with glycolate oxidase activity from B.parachinensis Bailey and rice( Oryza sativa )green leaves were prepared respectively.From the second protein peak on DEAE\|Cellulose column,two glycolate oxidases,expressed as B.parachinensis Bailey GO Ⅲ(specific activity natove 13 2 U·mg -1 ·min -1 )and rice GOⅢ(specific activity 8 8 U·mg -1 ·min -1 ),could not migrate anywhere in 4%～20% native\|PAGE under a pH8.3 buffer system.GOⅢ's p I was about pH8.3. The protein containing B.parachinensis Bailey GOⅢ showed 67±2,43±2,and 38±2 kD in SDS PAGE,band 43±2 kD was the subunit of B.parachinensis Bailey GOⅢ.From the two proteins above,another group of glycolate oxidases,expressed as B.parachinensis Beiley GOⅠ(specific activity 5 U·mg -1 ·min -1 )and rice GOⅠ(specific activity 1 2 U·mg -1 ·min -1 ),showed only one 43±2 kD band in SDS\|PAGE,and was purified on the Sepharose\|6B column which migrated towards anode in the same native\|PAGE showing the M r about 420 kD,or 460 kD and 260 kD respectively.GOⅠ's p I was smaller than pH8.3.Antibody against B.parachinensis Bailey GOⅠ was prepared and its efficacy was about 1/1600 in ELISA.By native\|PAGE,Western blot and rocket immunoelectrophoresis,the third group of glycolate oxidases,expressed as B.parachinensis Bailey GOⅡ and rice G0Ⅱ,were confirmed in crude protein of green leaves and migrated towards cathode under the same native\|PAGE,so GOⅡ's p I was higher than pH8.3.The M r of B.parachinensis Bailey GOⅡ was about 669 kD determined by native\|PAGE Western blot.Rice GOⅠ,rice GOⅢ and rice GOⅡ showed different quantitation under different physiological conditions.Rice GOⅡ could be induced by glycolate.     

植物角质层生物学特性及水分渗透性研究进展

植物角质层作为植物体与外界环境的第一道保护屏障, 其最主要的功能是防止植物体过度失水。揭示植物角质层的生物学功能及其原理将为现代农业的发展以及仿生材料的开发应用提供科学指导。该文综述了植物角质层的生物学特性及其与水分渗透性关系的研究进展, 并展望了角质层水分渗透研究的应用前景。     

Algal Flocculation with Synthetic Organic Polyelectrolytes

The feasibility of removing algae from water and wastewater by chemical flocculation techniques was investigated. Mixed cultures of algae were obtained from both continuous- and batch-fed laboratory reactors. Representative cationic, anionic, and nonionic synthetic organic polyelectrolytes were used as flocculants. Under the experimental conditions, chemically induced algal flocculation occurred with the addition of cationic polyelectrolyte, but not with anionic or nonionic polymers, although attachment of all polyelectrolyte species to the algal surface is shown. The mechanism of chemically induced algal flocculation is interpreted in terms of bridging phenomena between the discrete algal cells and the linearly extended polymer chains, forming a three-dimensional matrix that is capable of subsiding under quiescent conditions. The degree of flocculation is shown to be a direct function of the extent of polymer coverage of the active sites on the algal surface, although to induce flocculation by this method requires that the algal surface charge must concurrently be reduced to a level at which the extended polymers can bridge the minimal distance of separation imposed by electrostatic repulsion. The influence of pH, algal concentration, and algal growth phase on the requisite cationic flocculant dose is also reported.     

The Determination of Apparent Isoelectric Points of Cell Structures by Staining at Controlled Reactions

The staining reactions at controlled pH-values of various dyes with the nucleus and cytoplasm of Trichonympha collaris under different conditions were investigated. When staining intensity was plotted against pH, it was found that with each dye a different curve was obtained. “Isoelectric points” obtained by superposition of acid and basic dye curves varied for the same material with the dyes employed. It was found that, with the same dye, the curves of staining intensity plotted against pH varied with the buffer system utilized. Moreover, the intensity of staining at any pH was found to vary directly with the concentration of dye and inversely with the concentration of buffer. Various factors modifying staining intensity were studied. In the staining of a protein in buffered solution, it was shown that staining intensity (the index of the concentration of the dye-protein compound) at a given pH-value is dependent upon the interaction of the dye-protein, buffer-protein and dye-buffer systems, and that as the dye or buffer or their concentrations were varied, the resultant “isoelectric points” which were obtained also varied. In view of these facts and of the present lack of knowledge of dyes and dye-protein combinations it would be impossible to determine a true isoelectric point by staining at controlled pH-values without further extensive work on the subject. It follows that no true isoelectric points have hitherto been obtained for nucleus, cytoplasm or other tissue elements by staining at controlled pH.     

Why Some Plant Species Are Rare

Biodiversity, including plant species diversity, is threatened worldwide as a result of anthropogenic pressures such as an increase of pollutants and climate change. Rare species in particular are on the verge of becoming extinct. It is still unclear as to why some plant species are rare and others are not. Are they rare due to: intrinsic reasons, dispersal capacity, the effects of management or abiotic circumstances? Habitat preference of rare plant species may play an important role in determining why some species are rare. Based on an extensive data set of soil parameters we investigated if rarity is due to a narrow habitat preference for abiotic soil parameters. For 23 different abiotic soil parameters, of which the most influential were groundwater-table, soil-pH and nutrient-contents, we estimated species responses for common and rare species. Based on the responses per species we calculated the range of occurrence, the range between the 5 and 95 percentile of the response curve giving the habitat preference. Subsequently, we calculated the average response range for common and rare species. In addition, we designed a new graphic in order to provide a better means for presentation of the results. The habitat preferences of rare species for abiotic soil conditions are significantly narrower than for common species. Twenty of the twenty-three abiotic parameters showed on average significantly narrower habitat preferences for rare species than for common species; none of the abiotic parameters showed on average a narrower habitat preference for common species. The results have major implications for the conservation of rare plant species; accordingly management and nature development should be focussed on the maintenance and creation of a broad range of environmental conditions, so that the requirements of rare species are met. The conservation of (abiotic) gradients within ecosystems is particularly important for preserving rare species.     

Three Small Points: A Cody Complex Problem

Abstract

Three small points which resemble larger Cody Complex projectile points are related to this Complex on the basis of technological and shape attributes. It is concluded that several factors underlie occurrence of tiny Cody points. Resharpening of larger points accounts for one pattern. In addition, diminutive points were produced using two alternative sets of technological procedures. It is suggested that these points were not used in subsistence activities and may reflect ceremonial or symbolic activities practiced by late Paleo-Indian bison hunters.     

Studies on the Ultrastructure and Histochemistry of Plant Cuticles: The Cuticular Membrane of Agave americana L. in situ

The outer epidermal wall of Agave americana leaves was examinedin order to gain more information about the location and chemicalconstitution of the structural components. In middle aged leavesthe wall comprised six layers which were designated epicuticularwax, cuticle proper, exterior and interior cuticular layer,exterior and interior cellin wall. A lamellated structure, consistingof a series of electron translucent lamellae of uniform thicknessalternating with opaque ones of variable thickness, was observedin the thin cuticle proper on the outside of the cuticular membrane,even without heavy metal treatment. The cuticular layers underneathformed the bulk of the cuticular membrane and they also hadtwo components, an amorphous matrix permeated by a reticulumof fibrillae. Cutin, detected with osmium and with iodine/iodine-sulphuricacid–silver proteinate, was a major component of the opaquelamellae of the cuticle proper and the matrix of the cuticularlayer. Carbohydrates were absent from the cuticle proper butwere detected specifically in the fibrillae of the cuticularlayer and in the cellin wall. Pectic material seemed to be presenton both sides of the junction between cuticular membrane andcellin wall, but no discrete zone corresponding to light microscopicalobservations was detected in the electron microscope. Althoughthe lucent lamellae of the cuticle proper were tentatively ascribedto wax there was no structural or ultrahistochemical evidencefor the wax component of the cuticular layer. The various ultrahistochemicalreactions are discussed in relation to the known chemical compositionof the membrane. Agave americana L., epidermis wall, cuticular membrane, cuticle proper, cuticular layer, ultrahistochemistry, wax     

Plant Proteins Are Smaller Because They Are Encoded by Fewer Exons than Animal Proteins

Protein size is an important biochemical feature since longer proteins can harbor more domains and therefore can display more biological functionalities than shorter proteins. We found remarkable differences in protein length, exon structure, and domain count among different phylo-genetic lineages. While eukaryotic proteins have an average size of 472 amino acid residues (aa), average protein sizes in plant genomes are smaller than those of animals and fungi. Proteins unique to plants are ?81 aa shorter than plant proteins conserved among other eukaryotic lineages. The smaller average size of plant proteins could neither be explained by endosymbiosis nor subcellular compartmentation nor exon size, but rather due to exon number. Metazoan proteins are encoded on average by ?10 exons of small size [?176 nucleotides (nt)]. Streptophyta have on average only ?5.7 exons of medium size (?230 nt). Multicellular species code for large proteins by increasing the exon number, while most unicellular organisms employ rather larger exons (>400 nt). Among sub-cellular compartments, membrane proteins are the largest (?520 aa), whereas the smallest proteins correspond to the gene ontology group of ribosome (?240 aa). Plant genes are encoded by half the number of exons and also contain fewer domains than animal proteins on average. Interestingly, endosymbiotic proteins that migrated to the plant nucleus became larger than their cyanobacterial orthologs. We thus conclude that plants have proteins larger than bacteria but smaller than animals or fungi. Compared to the average of eukaryotic species, plants have ?34%more but ?20%smal-ler proteins. This suggests that photosynthetic organisms are unique and deserve therefore special attention with regard to the evolutionary forces acting on their genomes and proteomes.     

Three Potato Centromeres Are Associated with Distinct Haplotypes with or Without Megabase-Sized Satellite Repeat Arrays

We report discoveries of different haplotypes associated with the centromeres of three potato chromosomes, including haplotypes composed of long arrays of satellite repeats and haplotypes lacking the same repeats. These results are in favor of the hypothesis that satellite repeat-based centromeres may originate from neocentromeres that lack repeats.