Effect of light intensity and ammonium-N on carotenogenesis ofTrentepohlia odorata andDunaliella bardawil

AxenicTrentepohlia odorata was cultured at three different NH₄Cl levels (3.5 × 10^–2, 3.5 × 10^–3, 3.5 × 10^–4 M) and three different light intensities (48, 76, 122 µmol m^–2 s^–1). Chloride had no effect on growth over this range of concentration. High light intensity and high NH₄Cl concentration enhanced the specific growth rate. The carotenoid content increased under a combination of high light intensity and low N concentration. WhenD. bardawil was exposed to the same combination of growth conditions, there was an increase in its carotenoid content. The light saturation and the light inhibition constants (K _s andK _i, respectively) for growth, and the saturation constant (K _m) for NH₄Cl were determined. TheK _s andK _i values were higher inT. odorata (66.7 and> 122 mol m^–2 s^–1, respectively) than inD. bardawil (5.1 and 14.7 µmol m^–2 s^–1, respectively). TheK _m value determined at 122 µmol m^–2 s^–1, however, was lower inT. odorata (0.048 µM) than inD. bardawil (0.062 µM).Author for correspondence     

Influence of light and temperature on photoinhibition of photosynthesis inSpirulina platensis

Photoinhibition of photosynthesis and its recovery in the cyanobacteriumSpirulina platensis was studied to find how photosynthetic rates were influenced by light and temperature. By exposing cell samples from a turbidostat culture to combinations of light and temperature, a connection between light, temperature and photoinhibition was found. The experiments showed that a 10 degree increase from 20 °C to 30 °C considerably reduced the photoinhibition. At 25 °C a photon flux density of 1720 µmol m^–2 s^–1 reduced the photosynthetic rate by 50 % in 1 h, but a similarly high photon flux density had nearly no negative effect at 35 °C. Reactivation in low light from 50% photoinhibition was fast and complete in 60 min at 30 °C, while at 20 °C only about 1/6 of the full capacity was regained in the same time. Addition of the protein synthesis inhibitor streptomycin to cultures undergoing photoinhibition and regeneration indicated the presence also in this organism of a repair mechanism based on protein synthesis.Author for correspondence     

A mechanistic spatio-temporal modeling of COVID-19 data

Understanding the evolution of an epidemic is essential to implement timely and efficient preventive measures. The availability of epidemiological data at a fine spatio-temporal scale is both novel and highly useful in this regard. Indeed, having geocoded data at the case level opens the door to analyze the spread of the disease on an individual basis, allowing the detection of specific outbreaks or, in general, of some interactions between cases that are not observable if aggregated data are used. Point processes are the natural tool to perform such analyses. We analyze a spatio-temporal point pattern of Coronavirus disease 2019 (COVID-19) cases detected in Valencia (Spain) during the first 11 months (February 2020 to January 2021) of the pandemic. In particular, we propose a mechanistic spatio-temporal model for the first-order intensity function of the point process. This model includes separate estimates of the overall temporal and spatial intensities of the model and a spatio-temporal interaction term. For the latter, while similar studies have considered different forms of this term solely based on the physical distances between the events, we have also incorporated mobility data to better capture the characteristics of human populations. The results suggest that there has only been a mild level of spatio-temporal interaction between cases in the study area, which to a large extent corresponds to people living in the same residential location. Extending our proposed model to larger areas could help us gain knowledge on the propagation of COVID-19 across cities with high mobility levels.     

闽南渔场主要游泳动物时空生态位特征及其影响因素

根据2019—2021年在闽南渔场进行的秋季、冬季、春季和夏季四个航次定点底拖网调查资料,利用相对重要性指数、种群聚集强度、生态位宽度、生态位重叠及冗余分析对主要游泳动物时空生态位特征及其影响因素进行研究。结果表明,(1)调查海域共鉴定出游泳动物214种,主要优势种有18种,优势种存在明显的季节更替现象;夏季优势种的丛生指数和平均拥挤度较高,春季较低;(2)在时间维度上,须赤虾(Metapenaeposis barbata De Haan)生态位宽度最大(0.99), 7组种对时间生态位重叠值等于1.00;在空间维度上,带鱼(Trachurus japonicus Temminck&Schlegel)生态位宽度最大(2.57),空间生态位重叠值超过0.6的种类占71.3%;在时空维度上,带鱼生态位宽度最大(2.45),鹿斑仰口鲾(Leiognathus ruconius Hamilton)与赤鼻棱鳀(Thrissa kammalensis Bleeker)时空生态位重叠值最大(0.94);(3)冗余分析表明,底层温度和底层盐度是影响闽南渔场主要游泳动物时空生态位特征的重要环境因...     

干旱胁迫下红砂幼苗非结构性碳水化合物动态变化特征

该试验以荒漠区主要建群种红砂幼苗为研究对象,设置适宜水分(CK)、轻度干旱(MD)、中度干旱(SD)和重度干旱(VSD)4个胁迫处理(即田间持水量的80%、60%、40%和20%),采用盆栽控水试验,分别测定干旱胁迫15、30、45和60 d时红砂幼苗的叶、茎、粗根和细根中非结构碳水化合物(NSC)及其组分的含量,分析不同胁迫强度下不同干旱持续时间红砂幼苗NSC的动态变化及各组分差异,以揭示红砂NSC对干旱胁迫的响应机制。结果表明:(1)干旱胁迫强度和胁迫持续时间对红砂幼苗不同器官NSC及其组分均有显著影响,其中胁迫持续时间对NSC动态变化的影响尤为显著。(2)干旱胁迫初期,红砂叶中的NSC含量呈下降趋势,而茎中的NSC含量呈上升趋势,粗根和细根中NSC含量在各胁迫处理下基本保持稳定。(3)干旱胁迫后期,红砂叶和茎中的可溶性糖、淀粉和NSC含量逐渐增加,而粗根和细根中的淀粉和NSC含量呈下降趋势(中度干旱除外),且这一时期重度干旱处理下各器官可溶性糖和NSC的含量明显高于CK。研究发现,重度干旱胁迫能显著诱导提高红砂幼苗不同器官中的NSC含量,并通过分解根中淀粉和增加叶片中可溶性糖含量的方式来调节细胞渗透势平衡,以维持细胞活力,进而保持红砂在干旱胁迫后期的存活。     

Light (Blt), a Mutation That Causes Melanocyte Death,Affects Stria Vascularis Function in the Mouse Inner Ear

The Light mutation (B^lt) is a dominant allele of the b-locus on mouse chromosome 4 which causes progressive dilution of coat colour. Melanocytes within the hair follicles of mutant mice develop normally but later degenerate, due to the accumulation of a toxic product, so that the hair becomes lighter with age. Previous studies on W-locus spotting mutants, from which melanocytes are absent, have shown that melanocytes in the stria vascularis of the inner ear are essential for the development and/or maintenance of the endocochlear potential (EP) which is normally around 100 mV. In this study, physiological recordings from the ears of Light mutants were correlated with strial ultrastructure. EPs recorded from all b/b controls and young homozygous and heterozygous mutants (20–22 days old) were normal (77 to 113 mV), but were reduced (19 to 59 mV) in about 30% of ears from older mutants (B^lt/B^lt and B^lt/b). Strial function therefore appears to develop normally but later degenerates in some mutants. This suggests that strial melanocytes are affected by the Light allele and that the continued presence of melanocytes is necessary for strial function. There was no obvious association between the recorded EP value and the ultrastructural appearance of the stria. No structural abnormalities of the stria were noted in control or mutant mice aged 20 days to 4 months including those which had a reduced EP. Strial atrophy was common in old controls and mutants (1–2 years), and appeared to be an age-related process rather than an effect of the Light mutation. Similarly, pigment build-up was common in all strial cells of old mice. However, the accumulations of lipofuscin-like pigment were much larger and more abundant in aged brown non-agouti mice than those observed in old agouti mice, which suggests that this age-related process also has a genetic component.     

Ultrastructural changes associated with June Yellows in strawberry and with leaf yellowing symptoms of viral and genetic origin in Fragaria, Rubus and Ribes

Light and electron microscopy was used to study the ultrastructural effects of June Yellows (JY) in leaves of strawberry. Four cultivars of strawberry, affected to different extents by JY, were compared with healthy (JY-free) cv. Cambridge Favourite and with strawberry infected with strawberry crinkle rhabdovirus, Fragaria vesca infected with strawberry mottle virus (SMotV), raspberry and black currant showing virus-induced yellowing and with strawberry and raspberry showing chaemeric yellow sectors in the leaves. Except for isometric virus-like particles detected in SMotV-infected F. vesca, no virus-like particles or structures of other pathogenic agents were found in any of the tissues examined. Leaf cells of JY-affected strawberry showed severe disruption of chloroplasts and plasmalemma, whorls of membranous vesicles and decreased vacuole size. The extent and severity of these abnormalities increased with increased severity of JY symptoms but, even in leaves with mild JY symptoms, chloroplast abnormalities were obvious. In the most severely affected leaves, the cells lacked discrete vacuoles and extensive hypertrophy was seen in other organelles such as nuclei and mitochondria. Few, if any, ultrastructural abnormalities were observed in virus-infected strawberry or F. vesca, or in chaemeric leaves of strawberry and raspberry. By contrast, in raspberry and black currant with yellowed leaves caused by virus infection, the cells showed enlarged chloroplasts, decreased vacuole size and vesicle formation. However, chloroplast enlargement and disruption in this material seemed due to increased size of starch grains which were largely absent from swollen chloroplasts of JY-affected strawberry. The ultrastructural abnormalities observed in JY-affected strawberry are, therefore, not inconsistent with the possibility that a pathogenic agent may be involved in the condition.     

CHARACTERIZATION AND BIOLOGICAL IMPLICATIONS OF SCYTONEMIN,A CYANOBACTERIAL SHEATH PIGMENT1

Scytonemin, the yellow-brown pigment of cyanobacterial (blue-green algal) extracellular sheaths, was found in species thriving in habitats exposed to intense solar radiation. Scytonemin occurred predominantly in sheaths of the outermost parts or top layers of cyanobacterial mats, crusts, or colonies. Scytonemin appears to be a single compound identified in more than 30 species of cyanobacteria from cultures and natural populations. It is lipid soluble and has a prominent absorption maximum in the near-ultraviolet region of the spectrum (384 nm in acetone; ca. 370 nm in vivo) with a long tail extending to the infrared region. Microspectrophotometric measurements of the transmittance of pigmented sheaths and the quenching of ultraviolet excitation of phycocyanin fluorescence demonstrate that the pigment was effective in shielding the cells from incoming near-ultraviolet-blue radiation, but not from green or red light. High light intensity (between 99 and 250 μmol photon · m^?2· S^?1, depending on species) promoted the synthesis of scytonemin in cultures of cyanobacteria. In cultures, high light intensity caused reduction in the specific content of Chl a and phycobilins, increase in the ratio of total carotenoids to Chl a, and scytonemin increase. UV-A (320–400 nm) radiation was very effective in eliciting scytonemin synthesis. Scytonemin production was physiological and not due to a mere photochemical conversion. These results strongly suggest that scytonemin production constitutes an adaptive strategy of photoprotection against short-wavelength solar irradiance.     

有机磷农药对土壤动物群落结构的影响研究

本文研究了有机磷农药废水灌溉对土壤动物群落结构的影响,并探讨了影响机理,结果表明,土壤动物种类和数量随着农药影响程度的增加而减少,在农药污染影响严重的１、２区,计有土壤动物２１类和２２类,动物平均密度为２８５７１个／ｍ＾２和５１２６９个／ｍ＾２,受中度和轻蔗污染影响的３、４区分别有３５类和４７类,平均密度为５９２８５个／ｍ＾２,１５６５８７个／ｍ＾２。污染区土壤动物种类的减少主要由于常见类群和稀有     

Comparison of two cacao (Theobroma cacao L.) clones for the effect of pollination intensity on fruit set and seed content

We compared the influence of pollination intensity (PI) on fruit set and seed number per pod in two cacao (Theobroma cacao L.) clones, IFC5 (Forastero Lower-Amazon Amelonado), which is self-compatible and known to produce a high number of seeds per pod under open pollination, and SCA6 (Forastero Upper-Amazon), which is self-incompatible and known to produce a low number of seeds per pod under open pollination. With both clones, PI had a positive effect on fruit set, with the maximum rate requiring more than 150 pollen grains per pod. One-half of the maximum rate of fruit set was reached with 39 pollen grains per pod for SCA6, and 78 for IFC5. With SCA6, a significant positive effect of PI on seed number per pod was also observed, with maximum seed number requiring more than 200 pollen grains per pod. In contrast, seed numbers with IFC5 were approximately equal over the PI range 100–800 pollen grains per pod. Patterns of seed number per pod were compared after: (1) open insect pollination, (2) low-intensity hand pollination and (3) high-intensity hand pollination. The patterns obtained with IFC5 under open pollination showed a peak of 40–50 seeds per pod, whereas the distribution patterns were more even with SCA6. The pattern of seed number under open pollination was similar to that obtained with high-intensity hand pollination for IFC5, and with low-intensity hand pollination for SCA6. We concluded that the high number of seeds per pod observed with IFC5 under natural insect pollination may be explained by a high number of compatible self-pollen grains on the stigma and by a severe drop of low-pollinated flowers eliminating potential lowfilled fruits. With SCA6, however, the number of compatible pollen grains deposited on the stigma was probably low under open pollination, and the flowers required lower pollen quantities to set fruit, which resulted in a high frequency of low seed numbers per fruit. This difference in the capacity to set low-seeded fruits might be considered as an adaptive trait related to the mode of reproduction.