The extracellular space and blood-eye barrier in an insect retina: An ultrastructural study

Summary (1) The distribution of the extracellular space (ECS) in the outer part of the locust compound eye has been mapped with lanthanum and ruthenium red, applied to the retina. (2) In the photoreceptor zone, about 2.4% of the volume is ECS, in agreement with radiotracer and electrical estimates. Of this ECS, about 70% lies in lacunae between ommatidia, but only 1–2% adjacent to the photosensitive rhabdom. The lacunae are filled with material which binds applied tracers, and are thought to be structural spaces. (3) It has been suggested several times that such a small cation pool is insufficient to sustain more than a few large photoresponses, but this is shown to be incorrect. Enough Na⁺ lies within the rhabdomal ECS and within rapid diffusional access to it, to impose no immediate limitation. (4) The palisade vacuoles surrounding the rhabdom are intracellular, and are typical of light as well as dark-adapted eyes. (5) Tracers fail to penetrate more than about 30 m into the axon zone, in agreement with electrical, dye and radiotracer indications of a blood-eye barrier near this point. Septate and gap junctions between glial membranes proliferate at this level, the lacunae disappear, and the axonal clefts narrow, but no tight junctions were seen. Comparison is made with the barrier around the nerve cord. (6) The secondary pigment cells in the retina may function as osmotic/ionic buffers, in conjunction with the blood-eye barrier.     

Responses of ground vegetation species to clear-cutting in a boreal forest: aboveground biomass and nutrient contents during the first 7 years

Rapid growth of ground vegetation following clear-cutting is important to site productivity because vegetation retains nutrients in the ecosystem and can decrease nutrient leaching prior to stand re-establishment. Aboveground biomass, nutrient contents (N, P, K and Ca) and species composition of ground vegetation were determined 1 year before and for 7 years after clear-cutting of a mixed forest dominated by Norway spruce [Picea abies (L.) H. Karst.] in eastern Finland. The biomass of the feather mosses [Pleurozium schreberi Brid. and Hylocomium splendens (Hedw.) B. S.& G.] and the dwarf shrubs (Vaccinium myrtillus L. and V. vitis-idaea L.), which had dominated the ground vegetation in the mature forest, significantly decreased after clear-cutting. However, with the exception of H. splendens, these species had recovered within 3–5 years. The biomass of Deschampsia flexuosa (L.) Trin. considerably increased soon after clear-cutting, and Epilobium angustifolium L. appeared 3–5 years after cutting. These species contributed to the retention of nutrients not simply because of their biomass but also because of higher nutrient concentrations in their tissues. Total biomass and nutrient contents of the ground vegetation exceeded those of the pre-cutting levels. The proportion of ground vegetation biomass and nutrient contents represented by mosses decreased after cutting, while V. myrtillus, although reduced after cutting, remained a marked nutrient sink. The results suggest that H. splendens is the most sensitive species to cutting, but the biomass of P. schreberi, V. myrtillus and V. vitis-idaea return to initial levels soon after clear-cutting as do the nutrient contents of ground vegetation.     

Differential activation of parts of the serratus anterior muscle during push-up variations on stable and unstable bases of support

No studies have examined the effects of an unstable surface on push-up and push-up plus exercises in terms of the two parts of the serratus anterior muscle. We hypothesized that the lower part of the serratus anterior would have greater activity with an unstable surface, which requires stabilizing the scapular position. The present study was performed to investigate the intramuscular differences between parts of the serratus anterior muscle during push-up and push-up plus exercises. Twelve healthy subjects were included in the study. The upper and lower parts of the serratus anterior and upper and lower parts of the trapezius were investigated by surface EMG during four types of exercise. Repeated one-way ANOVA was used for statistical analyses. Maintaining the push-up plus phase caused significant increases in EMG activity of the upper serratus anterior compared with the push-up ascending phase on both of stable and unstable bases (P < 0.05). The lower serratus anterior showed increased activation on an unstable surface, which required more joint stability than did the stable base. Upper trapezius/upper serratus anterior ratio was significantly lower in the PUP than in the PUA phase with both stable and unstable bases of support (P < 0.05).Further studies are required to investigate the intramuscular variation in activation of the serratus anterior during exercises for rehabilitation.     

Temperature stress and survival ability of Mediterranean sclerophyllous plants

ABSTRACT

The Mediterranean climate with hot and dry summer periods, and low winter temperatures and episodic frosts in northern, altitudinal and continental districts, demands from evergreen broadleaved woody plants an adequate and flexible acclimation to the climatic constraints.

In this brief survey on some responses of Mediterranean sclerophylls to temperature stress, the following is presented and discussed: criteria for cold and heat limits of photosynthetic function; winter depression and summer photoinactivation of photosynthesis; peculiar patterns of tissue freezing of scleromorphous leaves and limits of frost resistance of various plant parts and ontogenetic stages; heat impairment of chloroplasts and thermotolerance of sclerophyllous species; survival capacity and recovery after damage. Risks of damage to plants in relation to stressful temperatures in Mediterranean regions are estimated. Cold stress and drought stress indices, according to Mitrakos (1980), have been applied to characterise different localities in Italy. Additionally, a heat stress index for the Mediterranean region is proposed. Future research topics are suggested.     

A functional assessment of the response of grassland vegetation to reduced grazing and abandonment

Question: Predicting the impact of land‐use change on vegetation is vital to understanding how biodiversity and ecosystem function may respond. Is it correct to assume that abandonment is an extreme form of grazing reduction? Location: Borders and central Scotland. Methods: The analysis used data sets from two identical experiments where the impacts of two unfertilized, extensively grazed treatments and one unfertilized abandoned treatment were compared against the species dynamics of a pasture subject to normal, productive grazing management over a 16‐year period. Initial multivariate analysis using Principal Response Curves was used to assess if particular traits were associated with either extensive or abandoned treatments, and was checked using univariate tests of individual traits. RLQ analysis followed by clustering into response groups was used to assess if species behaved in a similar manner between sites. Results: For many traits/attributes the shift in value or proportion was approximately linear across the extensification treatments as grazing was removed. However, certain traits showed step changes and quadratic responses. Leaf dry matter content, an important effect trait, was in the latter group. Most traits/attributes and species behaved similarly at the two sites. However, traits such as regenerative strategy, seed length, longevity and mass and seed bank type behaved differently, indicating that they are not predictable response traits. Conclusion: The results indicate that responses to grazing removal during extensification are largely straightforward and largely independent of species pool. However, there are discrepancies that suggest that simple analyses of the impacts of land‐use changes such as grazing reduction may hide more complex responses.     

A self-fertile trigeneric hybrid,Triticum aestivum ×Agropyron michnoi ×Secale cereale

Trigeneric hybrids between the (Triticum aestivum ×Agropyron michnoi) F₁ (CM, 2n=5x=35; ABDPP) and two winter rye (Secale cereale L., 2n=2x=14; RR) cultivars, Wugong 774 and AR-132, were synthesized. Such trigeneric hybrids could be used to transfer resistance genes for powdery mildew from rye to CM and subsequently to common wheat and to identify (1) the effects of the P genome ofAgropyron on the self-fertility of the hybrids and (2) the differences in genetic background between rye cultivars with marked differences in pollinating habit. The trigeneric hybrids varied widely in morphology and showed a high level of resistance to such diseases as barley yellow dwarf virus (BYDV), stripe rust, leaf rust, stem rust, and powdery mildew. Selfed and many backcross derivatives were obtained from the trigeneric hybrids. The results indicated that rye cvs Wugong 774 and AR132 arose from different gene pools and that the P genome ofAgropyron carries gene(s) responsible for chromosome segregation, leading to functional gamete formation and self-fertility of the hybrids. The F₂ and BC₁ plants could be obtained in two ways — fusion of the unreduced gametes and the assumed apomixis of unreduced female gametes in the trigeneric hybrid plant II-4 — which indicates that this trigeneric hybrid may be a special genetic stock. Chromosome pairing in the trigeneric hybrids and ways of producing wheat/rye and wheat/Agropyron translocations are discussed.     

Assessing species saturation: conceptual and methodological challenges

Is there a maximum number of species that can coexist? Intuitively, we assume an upper limit to the number of species in a given assemblage, or that a lineage can produce, but defining and testing this limit has proven problematic. Herein, we first outline seven general challenges of studies on species saturation, most of which are independent of the actual method used to assess saturation. Among these are the challenge of defining saturation conceptually and operationally, the importance of setting an appropriate referential system, and the need to discriminate among patterns, processes and mechanisms. Second, we list and discuss the methodological approaches that have been used to study species saturation. These approaches vary in time and spatial scales, and in the variables and assumptions needed to assess saturation. We argue that assessing species saturation is possible, but that many studies conducted to date have conceptual and methodological flaws that prevent us from currently attaining a good idea of the occurrence of species saturation.     

长期氮添加对草甸草原生态系统氮库的影响

大气氮沉降增加深刻影响生态系统物种多样性、生产力及其稳定性,研究草原生态系统N库如何响应不断增加的大气氮沉降至关重要.本研究在内蒙古额尔古纳草甸草原开展刈割和不同水平外源氮添加试验,设置6个氮添加水平:0、2、5、10、20和50 g·m-2·a-1,同时设置刈割处理,分为刈割和不刈割2个水平.在连续处理的第7年,采集...     

5例前列腺癌T细胞受体β链CDR3的多样性分析

T淋巴细胞受体(TCRs)在抗原识别免疫应答中作用重要,其多样性与宿主免疫反应及肿瘤预后判断密切相关。目的:采用高通量测序技术研究前列腺癌组织和癌旁组织中T细胞受体(TCR)克隆多样性及其克隆序列。方法:收集5例PC患者的癌组织和癌旁组织,提取DNA后经多重PCR技术对TCRβ链CDR3区进行扩增。用Illumina MiSeq进行测序,经过数据处理和比对分析,比较前列腺癌组织TCR CDR3组库的组成特征。结果:前列腺癌组织具有更高程度的克隆百分比和较高的高度扩增克隆比HEC(HEC:频率样本总读数的0. 5%的TCR克隆),并获得了24对在癌组织样本中差异表达的V-J基因组合、16对在癌旁组织样本中差异表达的V-J基因组合。结论:前列腺癌组织与癌旁组织均存在差异性的V-J基因组合以及高克隆表达的HEC,其中癌组织样品具有更高的HEC。PC发生发展对免疫学研究提供了新的数据,对PC免疫监视、T细胞受体变异标志等研究提供了参考,对以后继续研究打下了基础。