TRANSPARENT TESTA1 interacts with R2R3-MYB factors and affects early and late steps of flavonoid biosynthesis in the endothelium of Arabidopsis thaliana seeds

Wild type seed coats of Arabidopsis thaliana are brown due to the accumulation of proanthocyanidin pigments (PAs). The pigmentation requires activation of phenylpropanoid biosynthesis genes and mutations in some of these genes cause a yellow appearance of seeds, termed transparent testa (tt) phenotype. The TT1 gene encodes a WIP‐type zinc finger protein and is expressed in the seed coat endothelium where most of the PAs accumulate in wild type plants. In this study we show that TT1 is not only required for correct expression of PA‐specific genes in the seed coat, but also affects CHS, encoding the first enzyme of flavonoid biosynthesis. Many steps of this pathway are controlled by complexes of MYB and BHLH proteins with the WD40 factor TTG1. We demonstrate that TT1 can interact with the R2R3 MYB protein TT2 and that ectopic expression of TT2 can partially restore the lack in PA production in tt1. Reduced seed coat pigmentation was obtained using a TT1 variant lacking nuclear localisation signals. Based on our results we propose that the TT2/TT8/TTG1 regulon may also comprise early genes like CHS and discuss steps to further unravel the regulatory network controlling flavonoid accumulation in endothelium cells during A. thaliana seed development.     

Scales of spatiotemporal variability in macroinvertebrate abundance and diversity in monsoonal streams: detecting environmental change

1. We quantified spatial and temporal variability in benthic macroinvertebrate species richness, diversity and abundance in six unpolluted streams in monsoonal Hong Kong at different scales using a nested sampling design. The spatial scales were regions, stream sites and stream sections within sites; temporal scales were years (1997–99), seasons (dry versus wet seasons) and days within seasons. 2. Spatiotemporal variability in total abundance and species richness was greater during the wet season, especially at small scales, and tended to obscure site‐ and region‐scale differences, which were more conspicuous during the dry season. Total abundance and richness were greater in the dry season, reflecting the effects of spate‐induced disturbance during the wet season. Species diversity showed little variation at the seasonal scale, but variability at the site scale was apparent during both seasons. 3. Despite marked variations in monsoonal rainfall, inter‐year differences in macroinvertebrate richness and abundance at the site scale during the wet season were minor. Inter‐year differences were only evident during the dry season when streams were at base flow and biotic interactions may structure assemblages. 4. Small‐scale patchiness within riffles was the dominant spatial scale of variation in macroinvertebrate richness, total abundance and densities of common species, although site or region was important for some species. The proportion of total variance contributed by small‐scale spatial variability increased during the dry season, whereas temporal variability associated with days was greater during the wet season. 5. The observed patterns of spatiotemporal variation have implications for detection of environmental change or biomonitoring using macroinvertebrate indicators in streams in monsoonal regions. Sampling should be confined to the dry season or, in cases where more resources are available, make use of data from both dry and wet seasons. Sampling in more than one dry season is required to avoid the potentially confounding effects of inter‐year variation, although variability at that scale was relatively small.     

海南岛青冈属(壳斗科)一新种

描述海南岛昌化岭青冈一新种。     

Antiviral polysaccharides isolated from Hong Kong brown seaweed <Emphasis Type="Italic">Hydroclathrus clathratus</Emphasis>

Two relatively pure polysaccharides H3-a1 and H3-b1 had been isolated from the brown seaweed Hydroclathrus clathratus. They were characterized by HPLC, ultraviolet scanning, gas chromatography, infrared spectroscopy and elemental analysis, and shown to be two different sulfated polysaccharides with different monosaccharide content, but both with high relative molecular mass. They contained some proteins and uronic acid respectively. The sulfate content and bioactivity of these polysaccharides varied during purification. The fractions derived from the hot water extract also exhibited low anticoagulant effect. This is the first time that the antiherpetic and anticoagulant activities were evaluated for the polysaccharides from the Hong Kong brown seaweed Hydroclathrus clathratus.     

基于红外相机数据评估华南地区豹猫的种群密度和活动节律

可靠的种群密度数据对野生动物的保护和管理十分重要。豹猫(Prionailurus bengalensis)是中国分布最广且常见的猫科动物, 但野生种群密度估算的研究并不多。本研究于2020年6月至2021年5月在香港新界嘉道理农场暨植物园开展红外相机调查, 利用空间标记-重捕法估算当地豹猫的种群密度并用核密度估计方法分析其活动节律。本次调查以网格方式布置红外相机, 在约1.5 km²的研究范围之内设置了19个相机位点, 每个位点安装2台相机以获取豹猫身体两侧花纹来进行个体识别。连续12个月调查共捕获113次有效的豹猫拍摄事件, 当中仅61次事件的照片足够清晰以进行个体识别。基于种群封闭的要求, 我们以2个月为单位将12个月的数据分为6个采样期去分析豹猫种群密度, 结果显示仅两个采样期的估算值最为准确, 分别为0.64 ± 0.31 (0.26-1.55)只/km²和0.87 ± 0.48 (0.31-2.40)只/km², 是已知全球豹猫密度最高的地点之一。结果还发现, 雨季研究地点的豹猫并无明显的日活动节律, 在旱季则偏夜行-晨昏行性多一些, 但也有一定的日间活动; 雨季和旱季的日活动节律无显著差异。本研究是首次以个体识别配以空间标记-重捕模型对中国大陆地区豹猫种群密度调查的研究; 我们也提出一些关于红外相机架设方法的建议, 以提高照片个体识别的准确度并增加重捕次数, 最后提高密度估算的准确度。本研究也进一步证明豹猫适应性极强, 在活动节律上表现出极高的可塑性, 在严格保护下可以恢复健康的种群。     

Transparent exopolymer particle production and aggregation by a marine planktonic diatom (Thalassiosira weissflogii) at different growth rates

Transparent exopolymer particles (TEP) play an important role in the ocean carbon cycle as they are sticky and affect particle aggregation and the biological carbon pump. We investigated the effect of growth rate on TEP production in nitrogen limited semi‐continuous cultures of the diatom Thalassiosira weissflogii (Grunow) G. Fryxell & Hasle. Steady‐state diatom concentrations and other indicators of biomass (chl a, and total carbohydrate) were inversely related to growth rate, while individual cell volume increased with growth rate. There was no change in total TEP area with growth rate; however, individual TEP were larger at high growth rates and the number of individual TEP particles was lower. TEP concentration per cell was higher at higher growth rates. SYTOX Green staining showed that <5% of the diatom population had permeable cell membranes, with the proportion increasing at low growth rates. However, TEP production rates were greater at high growth rates, refuting our hypothesis that TEP formation is dependent on dying cells with compromised cell membranes in a diatom population. Measurements of particle size distribution in the cultures using laser scattering showed that they were most aggregated at high growth rates. These results indicate a coupling between TEP production and growth rate in diatoms under N limitation, with fast growing T. weissflogii producing more TEP and aggregates.     

采用常规电泳设备建立CLARITY透明脑技术

目的:CLARITY是一种全新的组织形态学研究技术,在脑结构与功能研究中具有重要用途。探讨能否采用常规电泳设备开展该项技术。方法:从ICR雌性小鼠取得新鲜脑组织,依次进行多聚甲醛组织固定、聚丙烯酰胺水凝胶包埋、SDS电泳洗涤,通过拍照记录结果。结果:多聚甲醛固定和水凝胶包埋后的脑组织呈乳白色,柔软富有弹性;电泳洗涤后的脑组织从周边开始逐渐透明化,至洗涤第10 d时呈现均匀的半透明状态,可用于三维神经网络原位分析。结论:研究结果为采用常规电泳设备开展CLARITY技术提供了基础数据。     

No evidence for intra-segment recombination of 2009 H1N1 influenza virus in swine

Hao (2011) reported that the PB2 genes of three swine influenza A viruses were likely generated through homologous recombination between two closely related parental strains. However, we show that Hao's observation is an artifact of incorrect taxon sampling arising through the lack of an appropriate evolutionary context. Through rigorous phylogenetic analyses we explain the evolutionary origins of these stains and confirm the lack of any statistical support for intra-segmental recombination.     

Palynological record of climate change during the last deglaciation from the Song Hong (Red River) delta, Vietnam

The palynological sequence from core ND-1 on the Song Hong delta in the northern Vietnam reveals the climate change during the last deglaciation. The identified pollen in the core is dominated by Castanopsis (Lithocarpus), Elaeocarpus, Ficus, Piperaceae and Quercus. High percentages of temperate taxa including the conifers Dacrydium, Podocarpus, Pinus, Cupressaceae, Txodiaceae and Cryptomeria, and broad-leaved taxa of Carpinus, Alnus, Juglans, Carya, Ulmus, Fagus, Ilex, Castanea, Quercus, which have a mainly upland distribution, is possibly associated with a lowering of the montane vegetation boundary. On the other hand, intensified river influence can also result in an increase in the temperate allochthonous taxa. After analyzing the magnitude of river influence on pollen assemblages during the sedimentary environment evolution, we extracted the climate information and used this to reconstruct climate change during the last deglaciation. A cooler climate during 14.5-10.9 cal. kyr BP than at present is indicated by higher percentage of temperate types than at present under a similar river influence on the floodplain. The Younger Dryas cooling event is recognized by widely developed grasslands between 12.9 and 11.6 cal. kyr BP, adding to the evidences for this period from both terrestrial and marine records in regions influenced by the East Asian monsoon. Two other cooling periods, 9.4-9.0 cal. kyr BP and 6.5-5.2 cal. kyr BP, are indicated by increases of temperate pollen taxa such as Cryptomeria, Alnus, Quercus, and Castanea.