Effects of light and temperature on seed dormancy and gibberellin-stimulated germination in Arabidopsis thaliana: studies with gibberellin-deficient and -insensitive mutants.

Effects of light and temperature on gibberellin (GA)-induced seed germination were studied in Arabidopsis thaliana (L.) Heynh. with the use of GA-deficient ( gal ) mutants, mutants with a strongly reduced sensitivity to GA ( gai ) and with the recombinant gai/gal . Seeds of the gal mutant did not germinate in the absence of exogenous GAs, neither in darkness, nor in light, indicating that GAs are absolutely required for germination of this species. Wild-type and gai seeds did not always require applied GAs in light. The conclusion that light stimulates GA biosynthesis was strengthened by the antagonistic action of tetcyclacis, an inhibitor of GA biosynthesis. In wild-type, gal and gai/gal seeds light lowered the GA requirement, which can be interpreted as an increase in sensitivity to GAs. In gai and gai/gal seeds light became effective only after dormancy was broken by either a chilling treatment of one week or a dry after-ripening period at 2°C during some months. The present genetic and physiological evidence strongly suggests that temperature regulates the responsiveness to light in A. thaliana seeds. The responsiveness increases during dormancy breaking, whereas the opposite occurs during induction of dormancy (8 days at 15°C pre-incubation). Since light stimulates the synthesis of GAs as well as the responsiveness to GAs, temperature-induced changes in dormancy may indirectly change the capacities to synthesize GAs and to respond to GAs. GA sensitivity is also directly controlled by temperature. It is concluded that both GA biosynthesis and sensitivity to GAs are not the primary controlling factors in dormancy, but are essential for germination.     

Increased extreme drought events in south–central China since the last century：Evidence from oxygen isotope signatures preserved in tree ring cellulose

Tree-ring cellulose oxygen isotope ratios (δ¹⁸O) is a well-established proxy for hydroclimatic conditions in monsoon Asia. We reconstructed June–October relative humidity (RH_J–O) variations from 1808 to 2017, based on tree-ring cellulose δ¹⁸O data, which explain 46.2% of the actual RH variance in the Nanyue region, south–central China. Extreme wet events occurred frequently prior to the 1900s, but there have been more extreme dry events since the 1900s, apart from the late 1930s and early 1950s. Periodicity analysis revealed that the reconstructed RH_J–O records show obvious 15–30 years cycles from the 1830–1970s. The multi-decadal signals may reflect the effect of the Pacific Decadal Oscillation (PDO) on hydroclimate. In the positive PDO phase, there is drying in south–central China, which is related to a weaker East Asian summer monsoon (EASM) via the Pacific–Japan teleconnection. The decadal signal has weakened since the 1970s. In addition, the reconstructed RH_J–O record shows strong interannual variations, which may be related to the Central Pacific El Niño–Southern Oscillation (CP ENSO). During extreme CP El Niño events, there is a weaker EASM due to the Pacific–Japan teleconnection, and the study site experienced drought. Our reconstructed moisture record is characterized by a decreasing influence from the PDO and increasing influence from the CP ENSO in recent decades. Moreover, the frequency of CP ENSO events is projected to increase under anthropogenic warming. Consequently, more extreme droughts which are related to CP ENSO events may increase in the south–central China in near future.     

Natural variation in life history strategy of Arabidopsis thaliana determines stress responses to drought and insects of different feeding guilds

Plants are sessile organisms and, consequently, are exposed to a plethora of stresses in their local habitat. As a result, different populations of a species are subject to different selection pressures leading to adaptation to local conditions and intraspecific divergence. The annual brassicaceous plant Arabidopsis thaliana is an attractive model for ecologists and evolutionary biologists due to the availability of a large collection of resequenced natural accessions. Accessions of A. thaliana display one of two different life cycle strategies: summer and winter annuals. We exposed a collection of 308 European Arabidopsis accessions, that have been genotyped for 250K SNPs, to a range of stresses: one abiotic stress (drought), four biotic stresses (Pieris rapae caterpillars, Plutella xylostella caterpillars, Frankliniella occidentalis thrips and Myzus persicae aphids) and two combined stresses (drought plus P. rapae and Botrytis cinerea fungus plus P. rapae). We identified heritable genetic variation for responses to the different stresses, estimated by narrow‐sense heritability. We found that accessions displaying different life cycle strategies differ in their response to stresses. Winter annuals are more resistant to drought, aphids and thrips and summer annuals are more resistant to P. rapae and P. xylostella caterpillars. Summer annuals are also more resistant to the combined stresses of drought plus P. rapae and infection by the fungus Botryris cinerea plus herbivory by P. rapae. Adaptation to drought displayed a longitudinal gradient. Finally, trade‐offs were recorded between the response to drought and responses to herbivory by caterpillars of the specialist herbivore P. rapae.     

Changes in protein synthesis during stratification and dormancy release in embryos of sugar maple (Acer saccharum)

Protein synthesis in dormant embryos of sugar maple ( Acer saccharum ) was investigated in seeds stratified at 4°C or incubated at 15°C. Seeds stratified at 4°C germinated after 27 days; seeds incubated at 15°C failed to germinate. Stratification increased the embryo's capacity for protein synthesis by day 11 as measured by in vivo incorporation of [³⁵S]-methionine into purified protein. At 4°C protein synthesis in the embryonic axis rose in a linear fashion prior to germination, whereas in cotyledons it increased until day 20 and then declined. Analysis of radiolabelled proteins by two-dimensional gel electrophoresis revealed that the levels of specific proteins were altered by temperature, primarily in the cotyledons. Several proteins were expressed in the cotyledons at 15°C but were absent in unstratified embryos and in embryos stratified at 4°C. That is, the expression of these proteins was repressed during stratification and release from dormancy. Levels of other proteins in the cotyledons declined at 4°C during stratification. We suggest that one or more of these proteins may be associated with the inhibition of growth of the embryonic axis imposed by the cotyledons.     

不同处理对银沙槐种子休眠破除和幼苗生长的影响

对银沙槐种子破除休眠的适宜方法及其幼苗生长进行研究。结果表明:破口和沙磨处理休眠破除效果最好,但容易引起种子腐烂死亡;分别用65、80和95℃热水处理种子,以95℃1 min破除种子休眠效果最好,且幼苗长势好,65℃效果最差,80℃可破除部分种子休眠,除80℃外延长热水处理时间可导致死种子数增加,95℃则引致大部分种子死亡;液氮浸种处理效果均显著,其中以液氮处理10 min效果最好,但幼苗多为不正常苗而致死;硫酸处理以浸种120 min效果最好,但处理时间过长可导致死种子数增多,且造成少数幼苗根部腐蚀死亡。综上所述,打破银沙槐种子休眠的较优处理方法是硫酸120 min浸种处理和95℃1 min热水处理。     

濒危植物中甸刺玫种子休眠及其生态学意义

对中甸刺玫Rosa praelucens种子结构及其透水性,赤霉素处理对胚的影响,果壳、种皮、胚乳的粗提物活性进行研究。结果表明：(1) 中甸刺玫外种皮是由多层排列紧密的厚壁细胞组成,内种皮为坚硬致密的栅栏组织;(2) 种皮对种子的吸胀阻碍较大, 未处理的种子吸水率较低,吸水13 d后增加量为18.82%;(3) 果实结籽率为0.69%,多数果实中没有饱满的种子;(4) 赤霉素100 mg·kg-1预处理种子可加快胚的萌发速率;(5) 胚乳、种皮、果壳中存在内源抑制物。中甸刺玫种子的休眠是由其形态和生理特点引起的综合休眠。     

Wheat seed proteins regulated by imbibition independent of dormancy status

Seed dormancy is an important trait in wheat (Trticum aestivum L.) and it can be released by germination-stimulating treatments such as after-ripening. Previously, we identified proteins specifically associated with after-ripening mediated developmental switches of wheat seeds from the state of dormancy to germination. Here, we report seed proteins that exhibited imbibition induced co-regulation in both dormant and after-ripened seeds of wheat, suggesting that the expression of these specific proteins/protein isoforms is not associated with the maintenance or release of seed dormancy in wheat.     

Germination traits and seed-bank dynamics of a biennial plant,Oenothera glazioviana Micheli

A study was conducted on the germination traits and seed-bank dynamics ofOenothera glazioviana (=O. erythrosepala), which sets seed in August in sand-dune systems in Japan. More than 90% of freshly matured seeds germinated over a wide range of temperature in light, but less than 10% did so in continuous darkness. Stratification (chilling under moist conditions) was ineffective in diminishing the light-requirement for germination. When fresh seeds were imbibed for 24 h including a 12-h light period, followed by 7-day air-drying, 94% of them became germinable in the dark at 25°C, but remained dormant at less than 15°C. of seeds collected in March from capsules of dead plants, 58% germinated in the dark at 25°C. After four cycles of alternatc 1-day wetting followed by 2-day drying or 1.5-day wetting followed by 1.5-day drying under a 12-h photoperiod, the fraction of viable seeds declined from 76% to 40% and 22%, respectively, due to germination during the wet periods. Seed-bag experiments were conducted in the field, using seeds given and not given a light-stimulus. Forty percent of the light-stimulated seeds germinated in the soil, whereas the seeds without a light-stimulus remained dormant throughout the experiment. When seeds were placed on the soil surface or at a depth of 0.5-1 cm, the proportion of germinable seeds declined during late spring and autumn, but not during winter and early spring. The seed-bank size of a natural population just prior to current seed dispersal was 2–3% of the seed production in the previous year, suggesting a high turnover rate of the seed-bank.     

Advantages of distinguishing the active fraction in bacterioplankton assemblages: some examples

The difficulty of distinguishing between active and dormant or dead bacterial cells is an important problem for the aquatic microbiologist.Active cells can be detected under the microscope by the presence of an intact electron transport system able to reduce the colourless INT [2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride] to an optically dense intracellular deposit.An improvement of this method has been applied to Lake Geneva and to a fish pond in the Ivory Coast. The portion of INT-reducing bacterial cells ranged from 1 to 71%, depending on place, depth, season and time of the day. In all cases bacterial activity, determined by uptake of ³H Thymidine or ¹⁴C glucose, and frequency of dividing cells were better correlated with the number of INT-reducing cells than with the total number of cells. This means that counts of cells able to reduce INT have a better metabolic significance than total cell counts. Some examples are developed which show the advantages of applying this method in cases where it is useful to distinguish active cells in a bacterial assemblage.     

沙葱萤叶甲成虫不同夏滞育阶段的转录组分析(英文)

【目的】本研究旨在揭示内蒙古草原新害虫沙葱萤叶甲Galeruca daurica专性夏滞育相关的重要基因以及代谢通路。【方法】应用RNA-Seq技术,对沙葱萤叶甲成虫不同夏滞育阶段［滞育前期(PD)、滞育期(D)及滞育后期(TD)］进行转录组测序、分析及基因功能预测,基于RNA-Seq数据筛选夏滞育不同阶段差异表达基因;利用qPCR对基于RNA-Seq数据筛选的10个差异表达基因的表达水平进行验证。【结果】从9个文库中获得202 770 198 clean reads,将12 078 060条转录本组装获得82 292 条unigene,平均长度为783.59 bp,N50为1 545 bp。沙葱萤叶甲D vs PD和TD vs D 比较组分别有2 395(2 119上调和277下调)和62(59上调和3下调)个差异基因。KEGG分析表明,D vs PD和TD vs D比较组差异表达基因分别显著富集于糖孝解/糖异生通路和脂肪酸生物合成通路;此外,许多与钙离子信号转导相关的基因在滞育期间差异表达。10个差异表达基因的qPCR分析表明,RNA-Seq与qPCR结果高度一致。【结论】糖孝解/糖异生、脂肪酸生物合成及钙离子信号通路可能在沙葱萤叶甲滞育调节中起着重要的作用。本研究为进一步研究沙葱萤叶甲成虫专性夏滞育的分子机理奠定了基础。