Local positive feedback regulation determines cell shape in root hair cells

The specification and maintenance of growth sites are tightly regulated during cell morphogenesis in all organisms. ROOT HAIR DEFECTIVE 2 reduced nicotinamide adenine dinucleotide phosphate (RHD2 NADPH) oxidase-derived reactive oxygen species (ROS) stimulate a Ca2+ influx into the cytoplasm that is required for root hair growth in Arabidopsis thaliana. We found that Ca2+, in turn, activated the RHD2 NADPH oxidase to produce ROS at the growing point in the root hair. Together, these components could establish a means of positive feedback regulation that maintains an active growth site in expanding root hair cells. Because the location and stability of growth sites predict the ultimate form of a plant cell, our findings demonstrate how a positive feedback mechanism involving RHD2, ROS, and Ca2+ can determine cell shape.     

护发素对蚕豆根尖细胞有丝分裂不同时期染色体的影响

以蚕豆根尖为试验材料,探讨护发素对蚕豆根尖细胞有丝分裂过程染色体的影响.结果表明.本试验所使用的3个品牌护发素均对蚕豆根尖产生毒性效应.     

护坡木本植物根系的力学特性及其与细胞壁成分的关系

为研究人工边坡立地条件下木本植物根系固土护坡的力学机制,以京承高速(3期)边坡为例,对榆树、紫穗槐、刺槐、胡枝子4种木本植物共395个根样进行室内单根拉伸试验,然后按5个根系径级分类并分别测定其半纤维素、纤维素、木质素含量,系统分析植物根系材料的力学性能。结果表明:4种木本植物根系直径为0.95~5.42 mm,抗拉强度为7.66~36.94 MPa,抗拉力为22.18~464.50 N。4种植物之间抗拉力、抗拉强度差异显著,从大到小依次为榆树＞紫穗槐＞胡枝子＞刺槐,根系抗拉力随根系直径增大以幂函数增大,抗拉强度随根系直径增大以逆函数或幂函数减小。4种木本植物5个径级根系半纤维素质量分数为1.37%~29.26%,纤维素质量分数为20.57%~36.91%,木质素质量分数为15.12%~29.84%,综纤维素质量分数为28.18%~66.17%,木纤比比值为0.45~1.31。不同树种间及不同径级根系间细胞壁成分差异显著。根系抗拉力与木质素显著负相关;抗拉强度与木质素正相关,与半纤维素负相关。根系拉伸的应力--应变曲线随树种根系结构组成的不同而不同。单根拉伸的应力--应变特征初始阶段为线性关系,拉力继续增大会逐渐表现出塑性特征,根系最大应力随直径增大而减小。综合4种植物的抗拉特性,榆树和紫穗槐的护坡作用较大。      

油菜素内酯对拟南芥和水稻根毛发育的影响

油菜素内酯(Brassinosteroids,BRs)是植物生长发育所必需的一类植物激素。本研究以拟南芥和水稻为研究对象,借助BR相关突变体,通过外源施加BR及BR合成抑制剂研究BR和根毛生长发育的关系。结果表明:在双子叶模式植物拟南芥中,BR抑制根毛的生长发育;在单子叶模式植物水稻中,BR对的根毛的发育存在剂量反应,在一定的浓度范围内促进根毛的生长发育。     

水分亏缺对玉米根毛区皮层解剖结构的影响

【目的】从解剖学角度探讨水分亏缺对苗期和拔节期玉米根毛区皮层结构的影响,为玉米抗旱机理研究提供参考。【方法】以有一定抗旱能力的高农901玉米种子为试材,采用盆栽试验,在苗期和拔节期分别设正常供水(CK)、轻度水分亏缺(LS)、中度水分亏缺(MS)和重度水分亏缺(SS)4个处理,使其土壤含水量分别达到田间最大持水量的75%～85%,65%～75%,55%～65%,45%～55%,处理结束后,分别取玉米根毛区(距离根尖端10cm)的根系样品制作半薄切片,常规甲苯胺蓝染色、番红-固绿和苯胺蓝荧光染色后,用Olympus BX51显微镜观察皮层细胞以及内皮层马蹄形加厚的变化情况,用image pro plus 6.0计算皮层厚度及内皮层细胞的长度和高度。【结果】随着水分亏缺程度的加剧,苗期和拔节期根毛区皮层厚度逐渐减少,皮层薄壁细胞减小变形,排列不规则;苗期和拔节期各水分亏缺处理的内皮层细胞长度和高度均逐渐减小,且在苗期时表现较为明显。荧光观察结果显示,苗期只有轻度水分亏缺处理的内皮层细胞两侧的马蹄形加厚程度较明显;拔节期轻度、中度水分亏缺处理的内皮层细胞出现了不同程度的马蹄形加厚,且在内切向壁上也出现了明显加厚,拔节期重度水分亏缺处理玉米内皮层细胞的加厚程度较小,且细胞发生了明显变形。【结论】苗期玉米对水分亏缺的反应比拔节期敏感;适度水分亏缺条件下,玉米通过缩减皮层厚度,增加内皮层木质化、栓质化程度,降低水分在根部径向运输的阻力,阻止根中水分的流失,使细胞保持基本形状,从而在一定程度上增强了对干旱环境的适应性。     

Subcellular Cd accumulation characteristic in root cell wall of rice cultivars with different sensitivities to Cd stress in soil

The variations of grain cadmiun(Cd) concentrations, translocation factors(TFs) of Cd from roots to shoots/grains of six rice cultivars, characterized with different Cd-sensitivities in polluted soil were studied, the selected rice cultivars were Xiangzao 17(R1), Jiayu 211(R2), Xiangzao 42(R3), Zhuliangyou 312(R4), Zhuliangyou 611(R5), and Jinyou 463(R6), respectively. The Cd subcellular distribution and Cd binding characteristics on subcellular fractions of rice root cell wall(CW) were further investigated. The results showed that the rice grain Cd contents varied significantly, with a maximum variation of 47.0% among the cultivars, the largest grain Cd content was observed with cultivar R1(Cd-sensitivity cultivar) and the smallest with R5(Cd-tolerance cultivar). The translocation factors of Cd from roots to shoots(TF_(shoot)) and roots to grains(TF_(grain)) varied greatly among the cultivars. In general, the TFgrain of the cultivars followed the order of R1R2R3R4 R6-R5. The Cd concentration(mg kg~(–1) FW) in the fraction of root CW, the fraction of cell wall removing pectin(CW-P) and the fraction of cell wall removing pectin and hemicellulose(CW-P-HC) of the cultivars generally followed the order of CW-PCWCWP-HC; the ratios of Cd concentration(mg kg–1 FW) in the fraction of CW-P to that of CW were mostly more than 1.10, while the ratios of Cd concentration in the fraction of CW-P-HC to that of CW were mostly less than 0.60, indicating that Cd was mainly stored in the hemicellulose of the root CW. The ratios of Cd of CW-P-HC to CW generally followed the descending order of R1~R2R3R4R5~R6 for the cultivars, which implied that hemicellulose is probably the main subcellular pool for transferring Cd into rice grain, and it restrains the translocation of Cd from shoot to the grain, especially for the Cd-tolerance cultivars(R5 and R6), the compartmentation of more Cd in hemicellulose in root CW is probably one of the main mechanisms for Cd tolerance of rice cultivars.     

Phycomyces: modification of spiral growth after mechanical conditioning of the cell wall

Mature stage IVb Phycomyces sporangiophores show left-handed spiral growth; that is, viewed from above, the sporangium rotates clockwise. Mechanical conditioning of the cell wall by the Instron technique increases the ratio of the rotational to the elongational growth rate. This result is in agreement with the fibril reorientation model of spiral growth, which suggests that cell wall microfibrils, initially oriented in a nearly transverse right-handed direction in the upper region of the growing zone, are displaced during growth toward the longitudinal axis, causing the observed left-handed spiral growth.     

内在调节蛋白及生长因子对精原干细胞增殖与分化的调控

文章阐述了在转录水平上精原干细胞在增殖与分化过程中的内在调节蛋白Plzf、Sohlh及其对精原干细胞的调节机制。介绍了胶质细胞源性神经营养因子、干细胞因子、Ets相关分子、骨形态发生蛋白、肝细胞生长因子、斯里兰卡肉桂碱受体等由支持细胞分泌的对精原细胞增殖与分化有重要作用的生长因子。     

水淹对秋华柳根茎细胞壁组分镉含量的影响

为了解水淹胁迫对细胞壁镉富集能力的影响,以秋华柳(Salix variegata Franch)扦插苗为研究对象,设置镉胁迫和水淹胁迫试验,测定了不同处理组下秋华柳根、茎细胞壁不同组分的镉积累特征。结果表明:所有处理组秋华柳存活良好,表现出水淹和镉的双重耐受性;所有镉浓度处理下,秋华柳根、茎细胞壁果胶和半纤维素均具有良好的镉离子结合能力,其中果胶的镉离子结合能力最大;水淹、镉胁迫及两者的交互效应均对秋华柳根、茎细胞壁组分镉含量造成了不同程度的影响。水淹显著降低了茎细胞壁组分镉含量,但对根组分中镉含量无显著影响;水淹条件下,秋华柳根、茎细胞壁果胶和半纤维素镉含量有所降低,但果胶和半纤维素仍为细胞壁镉积累富集的主要组分。上述结果表明,水淹对秋华柳根、茎细胞壁组分中镉的分配策略没有明显改变,镉仍被固定于细胞壁中以减少重金属对植物细胞的伤害,因此秋华柳可以作为三峡库区消落带镉污染土壤修复的备选物种。     

BID, BIM, and PUMA are essential for activation of the BAX- and BAK-dependent cell death program

Although the proteins BAX and BAK are required for initiation of apoptosis at the mitochondria, how BAX and BAK are activated remains unsettled. We provide in vivo evidence demonstrating an essential role of the proteins BID, BIM, and PUMA in activating BAX and BAK. Bid, Bim, and Puma triple-knockout mice showed the same developmental defects that are associated with deficiency of Bax and Bak, including persistent interdigital webs and imperforate vaginas. Genetic deletion of Bid, Bim, and Puma prevented the homo-oligomerization of BAX and BAK, and thereby cytochrome c-mediated activation of caspases in response to diverse death signals in neurons and T lymphocytes, despite the presence of other BH3-only molecules. Thus, many forms of apoptosis require direct activation of BAX and BAK at the mitochondria by a member of the BID, BIM, or PUMA family of proteins.     

破壁方法对葡糖醋杆菌TDY1破壁率及乙醇脱氢酶酶活的影响

分别用超声破碎法、反复冻融法、溶菌酶法和细菌裂解液法等4种不同破壁方法对葡糖醋杆菌TDY1进行破壁处理,通过比较细胞的破碎率和乙醇脱氢酶的活力,确定适合于菌株TDY1的细胞破壁方法和最佳条件.结果表明,超声破碎法获得的乙醇脱氢酶活力最高、为4004(±224)U/mg,破壁率为97.3(±1.26)％,与其他3种方法比较差异极显著;处理2 mL菌数为1.3×1010CFU/mL的菌液时,超声破碎的最佳条件为:超声9s、破碎总时间75 s、功率95 W.     

一氧化氮在植物根系生长发育过程中的作用研究进展

一氧化氮作为重要的气体信号分子,在植物体内参与的生理调节和信号转导功能已经成为新的研究热点.近年来,有关NO在植物根系生长发育过程中的作用研究取得了较大进展,特别是在植物根系中NO的合成和产生、NO调节植物根系生长和发育的详细具体过程以及这些过程中参与的信号转导途径等方面.本文对植物根系中NO的产生方式、NO在调节植物...     

Glia are essential for sensory organ function in C. elegans

Sensory organs are composed of neurons, which convert environmental stimuli to electrical signals, and glia-like cells, whose functions are not well understood. To decipher glial roles in sensory organs, we ablated the sheath glial cell of the major sensory organ of Caenorhabditis elegans. We found that glia-ablated animals exhibit profound sensory deficits and that glia provide activities that affect neuronal morphology, behavior generation, and neuronal uptake of lipophilic dyes. To understand the molecular bases of these activities, we identified 298 genes whose messenger RNAs are glia-enriched. One gene, fig-1, encodes a labile protein with conserved thrombospondin TSP1 domains. FIG-1 protein functions extracellularly, is essential for neuronal dye uptake, and also affects behavior. Our results suggest that glia are required for multiple aspects of sensory organ function.     

Red cell slip at a wall in vitro

Interferometric microscope observations of flowing blood indicate that the absolute number of red cells maintaining sliding contact with a wall is of the order 10(4) per square centi meter at low flow rates. Contacting cell oscillation and orientation results are given. The near wall local hematocrit is found to be relatively low.     

短光照对绒山羊绒毛生长相关激素的影响

为研究控制光周期对绒山羊绒毛生长相关激素的影响,从短光照试验和对照组绒山羊中选择2周岁6对双胞胎绒山羊母羊,采集血液样品利用酶联免疫法进行激素含量测定,利用SAS9.0软件进行显著性检验和相关性分析。结果发现:一天24h当中,绒山羊进入棚圈后褪黑激素MLT(melatonin,mLT)和IGF-1含量显著增加,PRL含量显著减少,EGF和GH含量在2组中差异不显著;一年当中,进入光控棚圈后6月份绒山羊血液中的MLT(P0.05)、IGF-1和EGF(P0.05)含量均增加,PRL含量显著降低;9月份试验组绒山羊MLT、IGF-1和GH含量高于对照组(P0.05),PRL含量依然低于对照组(P0.05)。在相关性分析中,试验组和对照组PRL与其他激素之间的相关系数为负数;与对照组相比短光照明显增加了MLT与PRL、EGF,PRL与IGF-1、EGF、GH,IGF-1与EGF、GH,EGF与GH之间的相互作用(P0.05),减弱了MLT与IGF-1、GH之间的相互作用。结果表明,短光照通过增强各激素间的协同或拮抗作用而提前诱发绒毛生长。     

土壤铝对林木根系的影响

采用孔洞根系生长法、进行铝对杉木和湿地松根系生长影响的研究，结果表明：土壤中加入铝离子后，活性铝含量明显增加，PH值下降；孔洞中根系生物量与对照比较，虽无明显差异，但均表现出铝毒害症，根中铝含量降低，但钙含量继续升高。这说明铝对杉木和湿地松根系有抑制作用，而钙对铝有拮抗作用。表3参7     

Fungal morphogenesis: cell wall construction in Mucor rouxii

An autoradiographic study revealed two different patterns of cell wall constructioni associated with two types of morphogenesis in Mucor rouxii. In hyphae, the cell wall was preferentially synthesized in the apical region; these cylindrical walls seemed to be generated by a sharply descending gradient of wall synthesis radiating from the apex. In spherical cells (germinating spores, yeast cells), wall formation occurred largely, if not entirely, in uniformly dispersed fashion over the entire cell periphery.     

Voltage- and tension-dependent lipid mobility in the outer hair cell plasma membrane

The mechanism responsible for electromotility of outer hair cells in the ear is unknown but is thought to reside within the plasma membrane. Lipid lateral diffusion in the outer hair cell plasma membrane is a sigmoidal function of transmembrane potential and bathing media osmolality. Cell depolarization or hyposmotic challenge shorten the cell and reduce membrane fluidity by half. Changing the membrane tension with amphipathic drugs results in similar reductions. These dynamic changes in membrane fluidity represent the modulation of membrane tension by lipid-protein interactions. The voltage dependence may be associated with the force-generating motors that contribute to the exquisite sensitivity of mammalian hearing.