Seed Transmission of Pseudoperonospora cubensis

Pseudoperonospora cubensis, an obligate biotrophic oomycete causing devastating foliar disease in species of the Cucurbitaceae family, was never reported in seeds or transmitted by seeds. We now show that P. cubensis occurs in fruits and seeds of downy mildew-infected plants but not in fruits or seeds of healthy plants. About 6.7% of the fruits collected during 2012–2014 have developed downy mildew when homogenized and inoculated onto detached leaves and 0.9% of the seeds collected developed downy mildew when grown to the seedling stage. This is the first report showing that P. cubensis has become seed-transmitted in cucurbits. Species-specific PCR assays showed that P. cubensis occurs in ovaries, fruit seed cavity and seed embryos of cucurbits. We propose that international trade of fruits or seeds of cucurbits might be associated with the recent global change in the population structure of P. cubensis.     

多枝柽柳气体交换特性研究

在美国柽柳（Tamarix L.）被列为臭名昭著的十大我来杂草之一,而在中国,它则作为一种濒危物种生存状况堪忧。对多枝柽柳（Tamarix ramosissima L bd.）气体交换进行研究,探讨其蒸汽压差（VPD）、叶水势、气孔导度（g）和水分利用效率（WUE）之间的联系,结果表明,柽柳之所以能在沙漠生存又能在美国河岸地带疯狂扩展,主要原因可能是：①柽柳属地下水湿生植物,发达的根系能直达地下水。②柽柳适应性生境很广,作为一种阳性树种,柽柳非常耐旱,能够在很低的叶水势（φ）条件下（-4.59Mpa）进行光合作用,而较低的光补偿点和暗呼吸速率又反映出其耐阴湿的特点。③灵敏的气孔适应性调整：其g对VPD的灵敏性随着干湿季其体内的水分状况变化而变化,调整蒸腾速率,从而影响其WUE;gs与φ成显著正相关（P≤0.05）;gs与WUE显著相关（P≤0.05）,但只有当gs处于正在下降的时候,光合作用和蒸腾作用两个交换过程受轻微限制时,可得到水消耗和CO2吸收的最优协调,WUE达到最大值。这些适应性调整可能是柽柳能在美国河岸地带疯狂扩展的主要原因。实验结果表明,柽柳完全能够适应荒漠生长环境,因而导致柽柳在我国处于濒危状况的根本原因不是传统认为的干旱的自然环境,而主要是人为因素造成地下水位下降以及过度砍伐所致。     

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.     

Cytoplasmic filaments and cellular wound healing in amoeba proteus

The flexibility and self-healing properties of animal cell surface membranes are well known. These properties have been best exploited in various micrurgical studies on living cells (2, 3), especially in amoebae (7, 20). During nuclear transplantation in amoebae, the hole in the membrane through which a nucleus passes can have a diameter of 20-30 μm, and yet such holes are quickly sealed, although some cytoplasm usually escapes during the transfer. While enucleating amoebae in previous studies, we found that if a very small portion of a nucleus was pushed through the membrane and exposed to the external medium, the amoeba expelled such a nucleus on its own accord. When this happened, a new membrane appeared to form around the embedded portion of the nucleus and no visible loss of cytoplasm occurred during nuclear extrusion. In the present study, we examined amoebae that were at different stages of expelling partially exposed nuclei, to follow the sequence of events during the apparent new membrane formation. Unexpectedly, we found that a new membrane is not formed around the nucleus from inside but a hole is sealed primarily by a constriction of the existing membrane, and that cytoplasmic filaments are responsible for the prevention of the loss of cytoplasm.     

塔克拉玛干沙漠南缘柽柳和胡杨水势季节变化研究

对塔克拉玛干沙漠南缘的柽柳和胡杨生长周期内的清晨水势和水势日变化的连续野外测定表明,两种植物在整个生长期内均未出现明显的水分亏缺.清晨水势的季节变化幅度不大,正午水势有不同程度的降低;一次性人工灌溉对植物水分状况没有明显影响.采伐利用方式不影响植物的水分状况.地下水是柽柳和胡杨生存与生长的先决条件.维持该区域地下水位的基本稳定是保证该区域柽柳和胡杨恢复重建的重要前提.     

Identification of a Lifespan Extending Mutation in the Schizosaccharomyces pombe Cyclin Gene clg1 + by Direct Selection of Long-Lived Mutants

Model organisms such as budding yeast, worms and flies have proven instrumental in the discovery of genetic determinants of aging, and the fission yeast Schizosaccharomyces pombe is a promising new system for these studies. We devised an approach to directly select for long-lived S. pombe mutants from a random DNA insertion library. Each insertion mutation bears a unique sequence tag called a bar code that allows one to determine the proportion of an individual mutant in a culture containing thousands of different mutants. Aging these mutants in culture allowed identification of a long-lived mutant bearing an insertion mutation in the cyclin gene clg1 ⁺. Clg1p, like Pas1p, physically associates with the cyclin-dependent kinase Pef1p. We identified a third Pef1p cyclin, Psl1p, and found that only loss of Clg1p or Pef1p extended lifespan. Genetic and co-immunoprecipitation results indicate that Pef1p controls lifespan through the downstream protein kinase Cek1p. While Pef1p is conserved as Pho85p in Saccharomyces cerevisiae, and as cdk5 in humans, genome-wide searches for lifespan regulators in S. cerevisiae have never identified Pho85p. Thus, the S. pombe system can be used to identify novel, evolutionarily conserved lifespan extending mutations, and our results suggest a potential role for mammalian cdk5 as a lifespan regulator.     

Antibody-directed fibrinolysis. An antibody specific for both fibrin and tissue plasminogen activator

An investigation was made to determine whether it is possible to attract tissue plasminogen activator (tPA) to the site of a thrombus by means of an antibody with affinites for both tPA and fibrin. A bispecific antibody conjugate was constructed by cross-linking two monoclonal antibodies: one specific for tPA, the other specific for fibrin. The bispecific antibody enhanced fibrinolysis by capturing tPA at the site of a fibrin deposit. In an in vitro quantitative fibrinolysis assay, the relative fibrinolytic potency of tPA bound to the bispecific antibody was 13 times greater than that of tPA and 200 times greater than that of urokinase. When fibrin was treated with the bispecific antibody before being mixed with tPA, the relative fibrinolytic potency of tPA was enhanced 14-fold. This capture also occurred when the concentration of tPA present in the assay was less than the concentration of tPA present in normal human plasma. In a human plasma clot assay, samples containing both the bispecific antibody and tPA exhibited significantly more lysis than did samples containing tPA alone. In spite of the increased clot lysis effected by the presence of bispecific antibody, there was no significant increase in fibrinogen or alpha 2-antiplasmin degradation at equal tPA concentrations. The ability of the bispecific antibody to concentrate exogenous tPA in vivo was then examined in the rabbit jugular vein model. Systemic infusion of a small amount of tPA (10,000 units) produced no significant increment in thrombolysis over the level of spontaneous lysis (14 +/- 8%). However, the simultaneous infusion of 10,000 units of tPA and 2 mg of bispecific antibody resulted in 42 +/- 14% (p less than 0.01) lysis. These results suggest that a molecule capable of binding both fibrin and tPA with high affinity could enhance thrombolysis in the circulation by capturing endogenous tPA.     

A proto-telomere is elongated by telomerase in a shelterin-dependent manner in quiescent fission yeast cells

Telomere elongation is coupled with genome replication, raising the question of the repair of short telomeres in post-mitotic cells. We investigated the fate of a telomere-repeat capped end that mimics a single short telomere in quiescent fission yeast cells. We show that telomerase is able to elongate this single short telomere during quiescence despite the binding of Ku to the proto-telomere. While Taz1 and Rap1 repress telomerase in vegetative cells, both shelterin proteins are required for efficient telomere extension in quiescent cells, underscoring a distinct mode of telomerase control. We further show that Rad3^ATR and Tel1^ATM are redundantly required for telomere elongation in quiescence through the phosphorylation of Ccq1 and that Rif1 and its associated-PP1 phosphatases negatively regulate telomerase activity by opposing Ccq1 phosphorylation. The distinct mode of telomerase regulation in quiescent fission yeast cells may be relevant to that in human stem and progenitor cells.     

A note on the excitation of nerve pathways

LetS denote the intensity of a stimulus, ν the frequency of discharge of a fiber, and ν _T the integral frequency of discharge of a nerve pathway. The relation between ν _T andS can be derived when the relation between ν andS, as well as the distribution function of the fiber thresholds are given. It is investigated under what conditions the functions ν _T (S) and ν(s) will be both of the same exponential form, and it is shown that this can happen only ifS exceeds the highest threshold of the pathway.