Anomalous stylet punctures of phloem sieve elements by aphids

A deviating type of potential drop (pd), i.e. the electrically recorded intracellular punctures during the pathway phase of plant penetration by aphids, is described and discussed. This so-called repetitive pd (R-pd) has been observed in 4 aphid species, two on herbs and two on sycamore. Apart from a regular repetition with short intervals, the most characteristic feature of the R-pd is the middle intracellular part, i.e. sub-phase 2, which is extended, making the individual R-pd 2–3 times longer than the normal pd. Differences between the normal and R-pd are described, as well as differences within each pd type between species. The R-pd's seem to reflect repeated punctures of phloem sieve elements. Their biological significance is unknown.     

杜仲休眠枝条中多糖颗粒变化的超微结构研究

在对杜仲（Ｅｕｃｏｍｍｉａ ｕｌｍｏｉｄｅｓ Ｏｌｉｖ．）形成层休眠期枝条的超微结构研究中发现,在筛管分子的筛板附近有一种复合球形体。细胞化学研究证明,这是一种多糖颗粒,但不同于枝条其他薄壁细胞中的多糖颗粒,而与细胞壁中的多糖相似。这种复合球形体只出现于形成层生理休眠期的筛分子中,而在被动休眠期和活动的筛分子中则看不到。     

马尾松人工林土壤各粒径团聚体湿筛后的有机碳分配

选取25a、45a和65a马尾松人工林为研究对象,采用湿筛法对各粒径土壤团聚体分别湿筛。探究了马尾松人工林各粒径团聚体湿筛后的团聚体有机碳分配,以探讨各粒径团聚体湿筛后分配到同一粒级团聚体有机碳含量及其对团聚体水稳性的贡献差异。结果表明：种植年限增加显著降低土壤团聚体水稳性（P<0.05）;各粒径团聚体湿筛后分配的有机碳随粒级减小含量呈先降后增趋势,以保持原粒级团聚体有机碳（12.96-32.01 g/kg）含量最高,其次是<0.25 mm粒级（8.08-23.53 g/kg）。各粒径团聚体湿筛分配到同一粒级的有机碳以保持原粒级的含量最高（P<0.05）;土壤团聚体水稳性与各粒径团聚体湿筛后保持原粒径的有机碳呈显著或极显著正相关（P<0.05或0.01）,分配到越小的粒级正相关性越不显著。此外,团聚体水稳性与各粒径团聚体湿筛分配到同一粒级的有机碳呈正相关,以保持原粒级相关性最高（P<0.01或0.05）;回归方程及相关性系数表明,有机碳与保持原粒径团聚体呈显著呈或极显著正相关（P<0.05或0.01）,与消散到其他粒级的团聚体呈负相关或极显著负相关（P>0.05或<0.01）。本研究得出有机碳含量增加促进更大粒径团聚体形成。反之,促使大粒径团聚体向较小粒径团聚体转化。同一粒级团聚体间,保持原粒级团聚体比易转化形成更大粒级团聚体有更高的有机碳含量和更强的水稳性,这对团聚体的固碳提供了新的认识。     

PHYSIOLOGICAL INVESTIGATIONS ON ALARIA ESCULENTA (LAMINARIALES,PHAEOPHYCEAE). III. EXUDATION BY THE BLADE1,2,3

Comparison of exudation rate of medullary conducting cells in the midrib of Alaria esculenta (L.) Grev. showed lowest rates for the blade meristem and highest rates in the non-growing region, 300–500 mm from the meristem. Holding plants under continuous darkness or severing the wings from the midrib reduced exudation rate by 26 and 37%, respectively. Osmotic pressure of exudate in sink (meristem) and source (non-growing region, up to 500 mm from the meristem) were similar (34.6–36.1 · 10²kpa). Pressure flow mechanism of translocation is evaluated in Alaria.     

The Arabidopsis thaliana/Myzus persicae model system demonstrates that a single gene can influence the interaction between a plant and a sap-feeding insect

We have developed an Arabidopsis thaliana/Myzus persicae model system to allow the dissection of plant/insect interactions at a molecular genetic level. This allows the examination of the role of single plant genes in the interaction between the plant and an aphid. Our initial studies have exploited an Arabidopsis genotype in which the function of the amino acid transporter ANT1 has been abolished. This mutation results in a change in the proportions of several amino acids within the phloem sieve elements (SEs) resulting in an increase in the proportion of essential amino acids. This has been measured using aphid stylectomy to collect SE samples, followed by a novel micellar electrokinetic chromatography method for amino acid analysis. The SE content represents the aphid's diet, and use of electrical penetration graph technology and honeydew clocks have demonstrated that this altered diet results in a change in the feeding rate of the aphid. Balance sheets can be produced to show the amount (nmoles/24 h) of each of 18 amino acids taken up and excreted by aphids feeding on wild type and ant1 mutant plants. The data show that aphids feeding on the ant1 mutant take up larger amounts of amino acids. However, we could not detect any effect on the reproductive rate of the aphids. The results show that, under experimental conditions, this model system can be used to identify plant genes that control the behaviour and fecundity of an insect pest.     

Scaling phloem transport: information transmission

Sieve tubes are primarily responsible for the movement of solutes over long distances, but they also conduct information about the osmotic state of the system. Using a previously developed dimensionless model of phloem transport, the mechanism behind the sieve tube's capacity to rapidly transmit pressure/concentration waves in response to local changes in either membrane solute exchange or the magnitude and axial gradient of apoplastic water potential is demonstrated. These wave fronts can move several orders of magnitude faster than the solution itself when the sieve tube's axial pressure drop is relatively small. Unlike the axial concentration drop, the axial pressure drop at steady state is independent of the apoplastic water potential gradient. As such, the regulation of whole‐sieve tube turgor could play a vital role in controlling membrane solute exchange throughout the translocation pathway, making turgor a reliable source of information for communicating change in system state.     

Seasonal dynamics of phloem and xylem formation in silver fir and Norway spruce as affected by drought

The dynamics of phloem growth ring formation in silver fir (Abies alba Mill.) and Norway spruce (Picea abies Karst.) at different sites in Slovenia during the droughty growing season of 2003 was studied. We also determined the timing of cambial activity, xylem and phloem formation, and counted the number of cells in the completed phloem and xylem growth rings. Light microscopy of cross-sections revealed that cambial activity started on the phloem and xylem side simultaneously at all three plots. However, prior to this, 1–2 layers of phloem derivatives near the cambium were differentiated without previous divisions. The structure of the early phloem was similar in silver fir and Norway spruce. Differences in the number of late phloem cells were found among sites. Phloem growth rings were the widest in Norway spruce growing at the lowland site. In all investigated trees, the cambium produced 5–12 times more xylem cells than phloem ones. In addition, the variability in the number of cells in the 2003 growth ring around the stem circumference of the same tree and among different trees was higher on the xylem side than on the phloem side. Phloem formation is presumably less dependent on environmental factors but is more internally driven than xylem formation.     

难溶于二甲亚砜多糖的甲基化方法研究

本文对难溶于二甲亚砜(DMSO)但易溶于水的多糖——羊栖菜褐藻糖胶的甲基化方法进行了研究。10mg多糖用0．1mL水溶解后,加和3mL DMSO,使多糖转溶于DMSO,然后加人2mL 3A分子筛脱除水分。将DNSO溶液过滤后,滤液中加入50mg NaOH粉末,室温下反应10min。加入0．5mL碘甲烷,室温下反应60min。加1mL水终止反应,加1mol／L HAc中和、透析、冻干。该法简便易行,所得产物的甲基化程度比较高。     

Control of phloem unloading by action potentials in Mimosa

In the sensitive plant, Mimosa pudica , action potentials arise when the leaves are touched and they trigger a sudden decrease in turgor of the pulvinar motor cells, which causes the leaf to close. These potentials may travel through the phloem and they appear to influence pulvinar phloem unloading after stimulation. Mature leaves were exposed to ¹⁴CO₂ and phloem translocation was observed by autoradiography. In unstimulated pulvini, labeled photoassimilates were restricted to the phloem. However, after stimulation, the ¹⁴C-label appeared to be concentrated in the extensor region of the motor cortex. Since stimulation elicits an action potential, it is suggested that it also triggers phloem unloading of sucrose in the pulvini.