Differences in Sugar Accumulation and Mobilization between Sequential and Non-Sequential Senescence Wheat Cultivars under Natural and Drought Conditions

Wheat leaf non-sequential senescence at the late grain-filling stage involves the early senescence of younger flag leaves compared to that observed in older second leaves. On the other hand, sequential senescence involves leaf senescence that follows an age-related pattern, in which flag leaves are the latest to undergo senescence. The characteristics of sugar metabolism in two sequential senescence cultivars and two non-sequential senescence cultivars under both natural and drought conditions were studied to elucidate the underlying mechanism of drought tolerance in two different senescence modes. The results showed that compared to sequential senescence wheat cultivars, under natural and drought conditions, non-sequential senescence wheat cultivars showed a higher leaf net photosynthetic rate, higher soluble sugar levels in leaves, leaf sheaths, and internodes, higher leaf sucrose synthase (SS) and sucrose phosphate synthase (SPS) activity, and higher grain SS activity, thereby suggesting that non-sequential senescence wheat cultivars had stronger source activity. Spike weight, grain weight per spike, and 100-grain weight of non-sequential senescence cultivars at maturity were significantly higher than those of sequential senescence cultivars under both natural and drought conditions. These findings indicate that the higher rate of accumulation and the higher mobilization of soluble sugar in the leaves, leaf sheaths and internodes of non-sequential senescence cultivars improve grain weight and drought tolerance. At the late grain-filling stage, drought conditions adversely affected leaf chlorophyll content, net photosynthetic rate, soluble sugar and sucrose content, SS and SPS activity, gain SS activity, and weight. This study showed that higher rates of soluble sugar accumulation in the source was one of the reasons of triggering leaf non-sequential senescence, and higher rates of soluble sugar mobilization during leaf non-sequential senescence promoted high and stable wheat yield and drought tolerance.     

陕西洋县药用植物群落土壤种子库特性研究

采用种子萌发法对洋县药用植物群落土壤种子库物种组成、单位面积种子密度、物种丰富度及与地上群落结构的关系进行了研究。结果显示,研究区内共有种子植物50种(包括药用植物21种),隶属于28科47属,其中草本植物45种、乔木5种;不同药用植物群落间土壤种子库种子密度差异显著,从大到小依次为:2年生凹叶厚朴(Magnolia officinalis Rehd.et Wils.subsp.biloba(Rehd.et Wils.)Law)4年生凹叶厚朴7年生凹叶厚朴11年生凹叶厚朴杜仲-凹叶厚朴(Eucommia ulmoides Oliver-Magnolia officinalis Rehd.et Wils.subsp.biloba(Rehd.et Wils.)Law)7年生厚朴(Magnolia officinalis Rehd.et Wils.)杜仲山茱萸(Cornus officinalis Sieb.et Zucc.)山茱萸-凹叶厚朴;土壤种子库具有表聚性,土层深度与种子数量成负相关;药用植物群落土壤种子库与地上群落结构相似性普遍较低。低林龄群落的土壤种子库密度大于高林龄群落,因此低林龄群落有利于天然更新,它们在植被恢复和生物多样性保护中的潜在价值更大。本研究结果可为洋县药用植物群落天然更新提供理论指导。     

苹果树腐烂病菌非核糖体多肽合成酶基因VmNRPS12的功能

【目的】非核糖体多肽合成酶(NRPS)在植物病原真菌与其寄主互作过程中发挥着重要作用,明确Vm NRPS12基因在苹果树腐烂病菌致病过程中的功能,将为今后深入研究苹果树腐烂病菌NRPS作用机制提供理论依据。【方法】基于苹果树腐烂病菌全基因组数据,得到VmNRPS12基因。运用qRT-PCR技术分析VmNRPS12在侵染初期的表达水平,利用Double-joint PCR和PEG介导的原生质体转化获得该基因抗潮霉素的突变体,对突变体进行PCR检测及Southern blot验证得到敲除突变体,进一步通过重新导入该基因全长片段获得互补突变体,最后对野生型、敲除突变体和互补突变体进行菌落、产孢及致病力观察,对检测数据用SPSS软件进行差异显著性分析。【结果】定量分析显示该基因在侵染初期显著上调表达,且接种48 h后的表达量是对照的138.6倍。该基因的敲除突变体在营养生长及产孢方面与野生型菌株03-8相比无显著性差异,但致病力与野生型菌株03-8相比显著减弱,且互补突变体致病力近似恢复至野生型水平。【结论】VmNRPS12基因与苹果树腐烂病菌致病性相关。     

Shoot tip culture and cryopreservation for eradication of Apple stem pitting virus (ASPV) and Apple stem grooving virus (ASGV) from apple rootstocks ‘M9’ and ‘M26’

This study attempted to eradicate Apple stem pitting virus (ASPV) and Apple stem grooving virus (ASGV) from virus‐infected in vitro shoots of apple rootstocks ‘M9’ and ‘M26’ using shoot tip culture and cryopreservation. In shoot tip culture, shoot tips (0.2 mm in length) containing two leaf primordia failed to show shoot regrowth. Although shoot regrowth rate was the highest in the largest shoot tips (1.0 mm in length) containing four leaf primordia, none of the regenerated shoots was virus‐free. Shoot tips (0.5 mm in length) containing two and three leaf primordia produced 100% and 10% of ASPV‐free shoots, respectively, while those (1.0 mm) containing four leaf primordia were not able to eradicate ASPV. ASGV could not be eradicated by shoot tip culture, regardless of the size of the shoot tips tested. In cryopreservation, shoot tips (0.5 mm in length) containing two leaf primordia did not resume shoot growth. Although 1.0‐mm and 1.5‐mm shoot tips gave similarly high ASPV‐free frequencies, the latter had much higher shoot regrowth rate than the former. Very similar results of shoot regrowth and virus eradication by shoot tip culture and cryopreservation were observed in both ‘M9’ and ‘M26’. Histological observations showed that only cells in upper part of apical dome and in leaf primordia 1–3 survived, while other cells were damaged or killed, in shoot tips following cryopreservation. Virus immunolocalization found ASPV was not detected in upper part of apical dome and leaf primordia 1 and 2, but was present in lower part of apical dome, and in leaf primordium 4 and more developed tissues in all samples tested. ASPV was also detected in leaf primordium 3 in about 16.7% and 13.3% samples tested in ‘M9’ and ‘M26’. ASGV was observed in apical dome and leaf primordia 1–6, leaving only a few top layers of cells in apical dome free of the virus. Different abilities of ASPV and ASGV to invade leaf petioles and shoot tips were also noted.     

Integrative insect taxonomy based on morphology,mitochondrial DNA,and hyperspectral reflectance profiling

Integrative taxonomy is considered a reliable taxonomic approach of closely related and cryptic species by integrating different sources of taxonomic data (genetic, ecological, and morphological characters). In order to infer the boundaries of seven species of the evacanthine leafhopper genus Bundera Distant, 1908 (Hemiptera: Cicadellidae), an integrated analysis based on morphology, mitochondrial DNA, and hyperspectral reflectance profiling (37 spectral bands from 411–870 nm) was conducted. Despite their morphological similarities, the genetic distances of the cytochrome c oxidase subunit I (COI) gene among the tested species are relatively large (5.8–17.3%). The species‐specific divergence of five morphologically similar species (Bundera pellucida and Bundera spp. 1–4) was revealed in mitochondrial DNA data and reflectance profiling. A key to identifying males is provided, and their morphological characters are described. Average reflectance profiles from the dorsal side of specimens were classified based on linear discriminant analysis. Cross‐validation of reflectance‐based classification revealed that the seven species could be distinguished with 91.3% classification accuracy. This study verified the feasibility of using hyperspectral imaging data in insect classification, and our work provides a good example of using integrative taxonomy in studies of closely related and cryptic species. © 2015 The Linnean Society of London     

Multiple mechanisms contributed to the reduced stability of Inner Mongolia grassland ecosystem following nitrogen enrichment

Plant and Soil - Global nitrogen enrichment has been identified as a major environmental problem that poses a threat to ecosystem functioning. However, there is no consensus on the impact of...