Plants interact with microbial polysaccharides

Plants are resistant to almost all of the microorganisms with which they come in contact. In response to invasion by a fungus, bacterium, or a virus, many plants produce low molecular weight compounds, phytoalexins, which inhibit the growth of microorganisms. Phytoalexins are produced whether or not the invading microorganism is a pathogen. The production of phytoalexins appears to be a widespread mechanism by which plants attempt to defend themselves against pests. Molecules of microbial origin which trigger phytoalexin accumulation in plants are called elicitors. Structural polysaccharides from the mycelial walls of several fungi elicit phytoalexin accumlation in plants. Approximately 10 ng of the polysaccharide elicits the accumulation in plants of more than sufficient amounts of phytoalexin to stop the growth of microorganisms in vitro. The best characterized elicitors have been demonstrated to be β-1,3-glucans with branches to the 6 position of some of the glucosyl residues. Oligosaccharides, produced by partial acid hydrolysis of the mycelial wall glucans, are exceptionally active elicitors. The smallest oligosaccharide which is still an effective elicitor is composed of about 8 sugar residues. Bacteria also elicit phytoalexin accumulation in plants, but the Rhizobium symbionts of legumes presumably have a mechanism which allows them to avoid either eliciting phytoalexin accumulation or the effects of the phytoalexins if they are accumulated. The lectins of legumes bind to the lipopolysaccharides of their symbiont, but not of their non-symbiont, Rhizobium. It is not known whether the lectin-lipopolysaccharide interaction is involved with the establishment of symbiosis. However, evidence will be presented that suggests that lectins are, in fact, enzymes capable of modifying the structurs of the lipopolysaccharides of their symbiont, but not of their non-symbiont, Rhizobium. It will also be shown that the lipopolysaccharides isolated from different Rhizobium species and from different strains of individual Rhizobium species have different sugar compositions. Thus, the different strains of a single Rhizobium species are as different from one another as the different species of Salmonella and other gram-negative bacteria. This conclusion is substantiated by experiments demonstrating that antibodies to the lipopolysaccharide from a single Rhizobium strain can differentiate that strain from other strains of the same species as well as from other Rhizobium species. The role in symbiosis of the strain-specific O-antigens is unknown.     

Dipeptides as Nitrogen Sources for Drosera rotundifolia in Aseptic Culture

The growth of Drosera rotundifolia was studied in aseptic cultures with 17 dipeptides as the only nitrogen source. About half of the dipeptides were well or partly utilized. Compounds containing glycine, alanine, glutamic or aspartic acid are clearly more favourable than dipeptides containing proline. Arginyl-aspartic acid (1.25 mM) promoted growth more than inorganic nitrogen (1.25 mM of NH₄NO₃). Glycyl-alanine gave about the same growth response as NH₄NO₃. The inocules died rapidly in medium containing leucyl-tyrosine and dipeptides containing methionine and valine were also toxic. There was usually a clear correlation between the growth-retarding or growth-stimulating effect of the dipeptides and the effects of their amino acid components.     

C4 photosynthesis in Spartina townsendii at low and high temperatures

The metabolism of ¹⁴CO₂ in the cool temperate saltmarsh grass Spartina townsendii was investigated in plants grown in their natural habitats at two temperatures. Both in the spring at 10°C and in the late summer at 25°C radioactivity was initially incorporated into the organic acids malate and aspartate and then transferred to 3-phosphoglycerate in the manner characteristic of the C₄ pathway of photosynthesis. Metabolism was not disrupted at the lower temperature as in some C₄ plants. Radioactivity was transferred more slowly from malate into alanine, glycine and serine at 10°C, but sugars were labelled equally at both temperatures.     

The population biology of the Orange Tip butterfly Anthocharis cardamines in Britain

ABSTRACT.

• 1 The population biology of Anthocharis cardamines (L.) is described and shown to vary with locality. Southern and Western populations emerge earlier than Northern ones, but Western and Northern populations occupy similar, wetter habitats and are associated primarily with Cardamine pratensis (L.). Southern populations are recorded mostly from Alliaria petiolata (Bieb.).
• 2 Studies on egg and larval survival indicate that host plant-induced death and parasitization by a tachinid are important mortality factors. However, a key-factor analysis on one population indicates that the major determinant of population size may be the number of eggs laid by ovipositing females, itself dependent upon weather during the oviposition period. Populations in different localities do show similar trends in abundance, corroborating the effect of weather.
• 3 Human effects on distribution and abundance are discussed, and some conservation strategies suggested.

     

机械损伤对9种水生植物叶片的影响

水生植物叶片的功能性状特征与陆生植物有所不同,同时叶脉类型也显著影响叶片的功能性状。本研究选取9种具有不同叶脉类型的水生植物,通过对叶脉进行直接损伤,分析叶片性状（形态、色素含量和叶绿素荧光指标）在叶脉受损后的变化程度与叶脉类型的关系。结果显示：具有平行脉的3种水生植物对叶脉损伤具有较强的耐受性;具羽状脉的4种植物主脉受损后显著抑制叶片生长,而侧脉受损的影响在不同物种间有所不同,具有物种特异性。本研究可为大型湖泊水生植物修复的水生物种筛选提供参考。     

植物蛋白质S-亚硝基化修饰的检测与分析

S-亚硝基化是一种重要的蛋白质翻译后修饰方式, 是指一氧化氮(NO)基团共价连接至靶蛋白特定半胱氨酸残基的自由巯基, 从而形成S-亚硝基硫醇(SNO)的过程。S-亚硝基化修饰广泛存在于各有机体中, 通过改变蛋白质生化活性、稳定性、亚细胞定位以及蛋白质-蛋白质相互作用等机制而调控不同的生物学过程或信号通路。在蛋白质S-亚硝基化检测分析方法中, 最为广泛使用的是生物素转化法(biotin switch assay), 其基本原理是首先封闭未被修饰的自由巯基, 进而将被修饰的SNO基团特异地还原为自由巯基并使用生物素将其特异标记。被生物素标记的半胱氨酸残基(即被修饰位点)可进一步通过蛋白质免疫印迹和/或质谱等方法进行检测分析。该文详细描述了植物蛋白质样品的体内和体外生物素转化法的实验流程, 并对实验过程中的注意事项进行了讨论。     

Light and dark assimilation of nitrate in plants

Abstract. Heterotrophic assimilation of nitrate in roots and leaves in darkness is closely linked with the oxidative pentose phosphate pathway. The supply of glucose-6-phosphate to roots and chloroplasts in leaves in darkness is essential for assimilation of nitrite into amino acids. When green leaves are exposed to light, the key enzyme, glucoses-phosphate dehydrogenase, is inhibited by reduction with thioredoxin. Hence the dark nitrate assimilatory pathway is inhibited under photoautotrophic conditions and replaced by regulatory reactions functioning in light. On account of direct photo-synthetic reduction of nitrite in chloroplasts and availability of excess NADH for nitrate reduclase, the rate of nitrate assimilation is extremely rapid in light. Under dark anaerobic conditions also nitrate is equally rapidly reduced to nitrite on account of abolition of competition for NADH between nitrate reductase and mitochondrial oxidation.     

海南植物增补（三）

本文继续报道海南岛新记录的植物,计24个新记录种,4个新记录属。1个新记录科,其中指叶瓶蕨在我国是首次发现。本文引用的标本,全部收藏在中国科学院华南植物研究所标本室(SCBI)。     

Vegetation zonation in dune slacks on the Leba Bar,Polish Baltic Sea coast

Vegetation zones in dune slacks on the Leba Bar on the Polish Baltic Sea coast are described. Plant colonization starts on moist sand in eastern ends of slacks, in the wake of receding mobile dunes. Communities on deflation ribs, dominated by psammophytic grasses, sedges and lichens, are structurally simple. Communities in troughs, dominated by species of fresh habitats, become structurally more complex in a western direction and they culminate with the Pinus silvestris forest. The main lines of vegetation variation correlate with groundwa-ter depth, micro topography, soil profile build-up and substrate acidification.     

Crucial factors determining the spatio-temporal distribution patterns of threeAthalia sawflies feeding on common cruciferous plants

Three Athalia sawflies, A. japonica, A. rosae and A. infumata, feeding on cruciferous plants, coexist in Japan. However, it is not known what ecological strategies they use and what environmental factors are crucial to such strategies. I attempted to explain these questions by examining the relationship between the spatio-temporal distribution patterns of three Athalia sawflies and their habitats in three districts (Lowland, Intermediate and Mountain). The three sawflies have different spatio-temporal distribution patterns, though they usually used common cruciferous plants. A. japonica was abundant in spring and autumn but disappeared during summer in all the districts. In the Lowland, populations of A. rosae and A. infumata, like that of A. japonica, crashed in summer. However A. rosae occurred mainly in summer in the Intermediate and Mountain. Although A. infumata occurred in the same seasons as A. rosae in all districts, population levels of A. infumata were always lower than those of A. rosae. The crucial factors controlling their population patterns were the availability of host plants and temperature. Population crashes of A. rosae and A. infumata were due to food depletion, and those of A. japonica were due to heat stress. On the other hand, their population patterns may be interpreted as phenological synchronization with their original host plants, though they all existed on common cruciferous plants. The three sawflies may have evolved different strategies to escape from unfavorable habitat conditions. Such strategies are speculated to be summer diapause in A. japonica, long distance migration in A. rosae, and local dispersal in A. infumata.