血管生长异常与流产的关系研究进展

微血管密度异常、血管生长因子(VEGF、PDGF等)及其受体表达异常通过一系列级联反应导致血管异常生长的结果。众多因子均和血管形成有关,在妊娠过程中对胎盘的血管发育有着重要的作用,导致滋养细胞的表型转换障碍、血管结构发育不良、血管生成受阻、血管数目减少,引起胎盘血管重铸障碍,胎儿胎盘单位灌注不足发生流产。研究表明许多自然流产的发生与胎盘组织中血管增生平衡和胎儿血液供应不足有密切关系,从而认为血管生长异常是导致流产的又一重要因素。随着研究的深入进展血管的异常生长与流产的关系是有确定关系的,对于血管生长异常所致的流产,抑制血管各种血管因子的形成、阻止其与受体结合,从而抑制血管的异常生长最终达到克服流产的发展,无异于把幸福带给更多的家庭,不仅是妇产科发展的里程碑,更是人类医学发展史上光辉的一笔。     

Water use by perennial plants in the transition zone between river oasis and desert in NW China

The study aimed at establishing the role of two possible water sources (inundation, ground water) for the water supply to the perennial plant species Alhagi sparsifolia, Calligonum caput-medusae, Populus euphratica and Tamarix ramosissima growing in the transition zone between a river oasis and the open desert at the southern fringe of the Taklamakan desert (Xinjiang province, NW China). The basic hypothesis was that inundations, which normally occur in summer when rivers from a nearby mountain range carry high water, contribute significantly to the plants’ water supply. When, in the first summer, inundations did not occur, four sites, each of which covered by a relatively dense stand of one species, were artificially flooded. Soil and plant water relations as well as meteorological variables were measured during two growing seasons. Water use efficiency of production (WUE_P) was calculated by relating biomass production, which was determined using allometric regressions, to water use.The effects of artificial flooding on the plant water relations were negligible. Water use was relatively high, especially in the A. sparsifolia and the P. euphratica stands and in a dense stand of T. ramosissima (up to approx. 500 kgH₂O m⁻² year⁻¹). Using the total above-ground biomass in the calculation, WUE_P was highest in C. caput-medusae and P. euphratica, and lowest, in A. sparsifolia. From soil and plant water relations, and against the background of the climate and the productivity of the vegetation, it is concluded that all perennial plants in the transition zone between oases and desert in that region must have sufficient access to ground water to ensure long-term survival. Management of ground water such that it remains continuously accessible to the perennial plants is a prerequisite for the conservation and sustainable use of the vegetation in the transition zone.     

Effects of xylem sap flow on carbon dioxide efflux from stems of birch (Betula pendula Roth)

The effect of xylem sap flow in stems of mature Betula pendula Roth on radial CO₂ efflux was studied from April to October 2001. Temperature-controlled respiration cuvettes allowed measurements of CO₂ efflux without interference from temperature gradients between stem surface and sapwood. Variations of sap flow in different stem sectors, and in a given sector at different heights were analysed. Daytime reduction of CO₂ efflux caused by sap flow was expressed as the difference between gross and apparent CO₂ release. Gross CO₂ release was calculated from Arrhenius-equations derived from night-time data records of the same day, which were free from interference by sap flow. In mid-July, daytime reductions of CO₂ efflux reached 1.8–3.9 μmol CO₂ m⁻² g⁻¹ xylem sap transpired. Assuming tree-specific maximum transpiration rates of 30 kg H₂O d⁻¹ this is up to 40% of gross CO₂ release. In relation to photosynthetic CO₂ fixation the endogenous supply of dissolved CO₂ to the leaves acccounted for 0.5–3.7%. This study indicates a negative correlation between sap flow velocity and radial CO₂ efflux from B. pendula stems. Periods of unbalanced CO₂ partial pressures between aqueous and gaseous pathways during increase and decrease of sap flow seem to affect gaseous CO₂ release through lenticels. It is concluded that CO₂ efflux rates are not simply equivalent to respiration rates because of the interference of aqueous CO₂ transport by xylem sap flow in the wood-body of trees.     

Plant physiology in theory and practice: An analysis of the WBE model for vascular plants

The theoretical model of West, Brown and Enquist (hereafter WBE) proposed the fractal geometry of the transport system as the origin of the allometric scaling laws observed in nature. The WBE model has either been criticized for some restrictive and biologically unrealistic constraints or its reliability debated on the evidence of empirical tests. In this work, we revised the structure of the WBE model for vascular plants, highlighting some critical assumptions and simplifications and discuss them with regard to empirical evidence from plant anatomy and physiology. We conclude that the WBE model had the distinct merit of shedding light on some important features such as conduit tapering. Nonetheless, it is over-simplistic and a revised model would be desirable with an ontogenetic perspective that takes some important phenomena into account, such as the transformation of the inner sapwood into heartwood and the effect of hydraulic constraints in limiting the growth in height.     

Wood day capacitance is related to water content,wood density,and anatomy across 30 temperate tree species

Water released from wood during transpiration (capacitance) can meaningfully affect daily water use and drought response. To provide context for better understanding of capacitance mechanisms, we investigated links between capacitance and wood anatomy. On twigs of 30 temperate angiosperm tree species, we measured day capacitance (between predawn and midday), water content, wood density, and anatomical traits, that is, vessel dimensions, tissue fractions, and vessel–tissue contact fractions (fraction of vessel circumference in contact with other tissues). Across all species, wood density (WD) and predawn lumen volumetric water content (VWC_L-pd) together were the strongest predictors of day capacitance (r²_adj = .44). Vessel–tissue contact fractions explained an additional ~10% of the variation in day capacitance. Regression models were not improved by including tissue lumen fractions. Among diffuse-porous species, VWC_L-pd and vessel–ray contact fraction together were the best predictors of day capacitance, whereas among semi/ring-porous species, VWC_L-pd, WD and vessel–fibre contact fraction were the best predictors. At predawn, wood was less than fully saturated for all species (lumen relative water content = 0.52 ± 0.17). Our findings imply that day capacitance depends on the amount of stored water, tissue connectivity and the bulk wood properties arising from WD (e.g., elasticity), rather than the fraction of any particular tissue.     

Drosophila Cyclin J is a mitotically stable Cdk1 partner without essential functions

Enteric neural crest-derived cells (ENCCs) migrate along the intestine to form a highly organized network of ganglia that comprises the enteric nervous system (ENS). The signals driving the migration and patterning of these cells are largely unknown. Examining the spatiotemporal development of the intestinal neurovasculature in avian embryos, we find endothelial cells (ECs) present in the gut prior to the arrival of migrating ENCCs. These ECs are patterned in concentric rings that are predictive of the positioning of later arriving crest-derived cells, leading us to hypothesize that blood vessels may serve as a substrate to guide ENCC migration. Immunohistochemistry at multiple stages during ENS development reveals that ENCCs are positioned adjacent to vessels as they colonize the gut. A similar close anatomic relationship between vessels and enteric neurons was observed in zebrafish larvae. When EC development is inhibited in cultured avian intestine, ENCC migration is arrested and distal aganglionosis results, suggesting that ENCCs require the presence of vessels to colonize the gut. Neural tube and avian midgut were explanted onto a variety of substrates, including components of the extracellular matrix and various cell types, such as fibroblasts, smooth muscle cells, and endothelial cells. We find that crest-derived cells from both the neural tube and the midgut migrate avidly onto cultured endothelial cells. This EC-induced migration is inhibited by the presence of CSAT antibody, which blocks binding to β1 integrins expressed on the surface of crest-derived cells. These results demonstrate that ECs provide a substrate for the migration of ENCCs via an interaction between β1 integrins on the ENCC surface and extracellular matrix proteins expressed by the intestinal vasculature. These interactions may play an important role in guiding migration and patterning in the developing ENS.     

Xylem water flow in tropical vines as measured by a steady state heating method

Summary A method for determining the mass flow rate of xylem water in thin stems under natural field conditions is presented. Diurnal courses of xylem water flow and stomatal conductance of the vines Entadopsis polystachya, Cyclanthera multifoliolata, and Serjania brachycarpa were examined in a tropical deciduous forest on the west coast of Mexico. E. polystachya (leaf area 23.6 m²) had a maximum water flow rate of 6.50 kg h^-1 or 1.44 kg cm^-2 _{stem basal area} h^-1; daily water use was 2.00 kg m^-2 _{leaf area} day^-1. S. brachycarpa (leaf area 4.5 m²) and C. multifoliolata (leaf area 3.6 m²) had a maximum water flow rate of 0.72 and 0.19 kg h^-1 or 0.63 and 0.92 kg cm^-2 _{stem basal area} h^-1. Daily water use was 1.26 and 0.39 kg m^-2 _{leaf area} day^-1, respectively. The daily courses of xylem water flow were strongly influenced by the orientation of the leaf area to irradiance and its intensity. While leaves of E. polystachya had a constant high stomatal conductance during the day, S. brachycarpa had a maximum stomatal opening in the morning followed by continuous closure during the rest of the day. In contrast to the woody species, the herbaceous C. multifoliolata exhibited a strong midday depression of stomatal conductance and wilting of its leaves. The leaf biomass accounted for 8% (Entadopsis), 16% (Serjania), and 23% (Cyclanthera) of above-ground biomass. The relation of sapwood area to leaf area supplied (Huber value) was 0.19 (Entadopsis), 0.18 (Serjania), and 0.06 (Cyclanthera) cm² m^-2     

Expression of phenylalanine ammonia-lyase gene during tracheary-element differentiation from cultured mesophyll cells ofZinnia elegans L.

Expression of the phenylalanine ammonialyase (PAL) gene during tracheary-element differentiation was studied in mesophyll cell-suspension cultures ofZinnia elegans. Dose-response curves of benzyladenine (BA) and α-naphthaleneacetic acid (NAA) were obtained for the cultures in order to achieve the highest percentage of differentiation. The optimal concentrations of BA and NAA were 0.1 mg·l^-1 and 0.06 mg·l^-1, respectively, which normally stimulated about 40% differentiation by 96 h of culture. The effects of the same ratio but different amounts of BA and NAA on tracheary-element formation have been tested and the results indicate that the absolute amounts of BA and NAA rather than the ratio of them were important for tracheary-element formation in theZinnia cultures. The cells when cultured in the presence of 0.001 mg·l^-1 of BA and 0.06 mg·l^-1 of NAA expanded and divided but did not differentiate. The level of PAL activity, synthesis of PAL protein and the level of PAL mRNA peaked during 72 to 96 h when lignin was actively deposited. This indicated that the PAL gene was temporally and preferentially expressed in association with the lignification during tracheary-element differentiation and thus it can be regarded as a molecular marker for the process. We thank Bejing Agricultural University, the Lundgren Research fund (University of Cambridge) and an ORS award for financial support.     

Wound-induced and naturally occurring regenerative differentiation of xylem in Zea mays L.

The regenerative differentiation of xylem, both around a wound in the stem and at the root junction was studied in seedlings of maize. The regeneration of vessels around a wound was very small, being limited to the very young internodes and sharply declining basipetally. There were more regenerative vessel elements and they differentiated faster above the wound than below it. The regenerative vessel elements around the wound were characterized by helical or annular pattern of secondary wall thickenings. Wounding also resulted in the development of additional vascular anastomoses in the leaf immediately above the wound, and in differentiation of discontinuous vessels in adjacent bundles. Regenerative vessel elements were very common where the adventitious roots connected with the stem internodes, and exhibited pitted or reticulated secondary wall thickenings.