A Role for Cytokinins in De-Etiolation in Arabidopsis (det Mutants Have an Altered Response to Cytokinins)

When grown in the absence of light, Arabidopsis thaliana deetiolated (det) mutants develop many of the characteristics of light-grown plants, including the development of leaves and chloroplasts, the inhibition of hypocotyl growth elongation, and elevated expression levels of light-regulated genes. We show here that dark-grown wild-type seedlings exhibit similar phenotypic traits if any one of a variety of cytokinins are present in the growth medium. We further show that the striking phenotype of det mutants is unlikely to be caused by different levels of cytokinins in these mutants. The three major Arabidopsis cytokinins, zeatin, zeatin riboside, and isopentenyladenosine, accumulate to similar levels in wild-type seedlings grown in either the light or the dark. There is no consistently different pattern for the levels of these cytokinins in wild-type versus det1 or det2 mutants. However, det1 and det2 have an altered response to cytokinin in a detached leaf senescence assay and in tissue culture experiments. A model is proposed in which light and cytokinins act independently or sequentially through common signal transduction intermediates such as DET1 and DET2 to control the downstream light-regulated responses.     

Effects of secondary mutation in det2-1 on root growth and development in Arabidopsis

Brassinosteroids (BRs) are plant steroidal hormones that regulate a wide range of developmental processes. Most BR mutants display impaired growth and responses to developmental and environmental stimuli. Here, we found a BR-deficient mutant det2-1 that displayed exceedingly short roots and agravitropic growth, which were not present in other BR mutants. By back-crossing det2-1 with the wild type, we isolated a secondary mutation named det2-1 phenotype modifier 1 (dpm1) and demonstrated that those aberrant phenotypes in the original det2-1 were independent of the BR deficiency. Phenotypic analysis showed that impaired root growth of dpm1 appeared in BR-deficient condition, but not in a normal condition. In the light condition, the mutant showed enhanced shoot growth which was suppressed in the det2-1 background. Starch granules in the columella cells of the root tip were highly accumulated and expanded in dpm1. Agravitropic roots and the expanded starch granules of dpm1 could not be recovered by BR. Taken together, these results suggest that DPM1 is required for gravitropic growth, and that its functions on root and shoot growth are BR-dependent.     

过量表达大叶补血草LgNHX1基因对拟南芥耐盐性的影响

利用植物表达载体pCAMBIA1301和农杆菌GV3101将LgNHX1(全长1 656 bp)基因在拟南芥中过量表达.在含30 mg/L潮霉素的培养基上筛选获得LgNHX1的纯合转化子,并对其进行了分子鉴定和耐盐性分析.结果显示,经PCR和RT-PCR鉴定,野生型植株(对照)没有出现扩增条带,而转基因株系有相应的扩增条带,表明LgNHX1的确已经整合到拟南芥的基因组中,并已正常转录.在不同盐浓度处理下,转基因株系生长情况好于野生型对照;转基因植株地上部分和根的干重、鲜重相对高于野生型对照,但差异没有达到显著水平;当盐浓度达到150-200 mmol/L时,两个特基因株系的Na+含量显著高于野生型,K+含量极显著高于野生型.以上结果表明,过量表达LgNHX1基因可能增强了拟南芥将Na+区隔化至液泡的能力,提高了转基因拟南芥的耐盐能力.     

拟南芥耐低钾突变体的筛选及遗传分析

利用乙酰甲基磺酸（ＥＭＳ）诱变方法,以幼苗根在重力作用下的弯曲生长为指标、筛选得到了拟南芥（Ａrabidopsis thaliana)耐低钾突变体。经过对突变体杂交后代的遗传分析证明,其中两株突变体的耐低钾性状为隐性单基因突变所致。鉴定、分离与植物耐低钾性状连锁的基因将有可能与对培育钾高效作物品种有重要意义。     

Evidence for a Ustilago maydis steroid 5alpha-reductase by functional expression in Arabidopsis det2-1 mutants

We have identified a gene (udh1) in the basidiomycete Ustilago maydis that is induced during the parasitic interaction with its host plant maize (Zea mays). udh1 encodes a protein with high similarity to mammalian and plant 5alpha-steroid reductases. Udh1 differs from those of known 5alpha-steroid reductases by six additional domains, partially predicted to be membrane-spanning. A fusion protein of Udh1 and the green fluorescent protein provided evidence for endoplasmic reticulum localization in U. maydis. The function of the Udh1 protein was demonstrated by complementing Arabidopsis det2-1 mutants, which display a dwarf phenotype due to a mutation in the 5alpha-steroid reductase encoding DET2 gene. det2-1 mutant plants expressing either the udh1 or the DET2 gene controlled by the cauliflower mosaic virus 35S promoter differed from wild-type Columbia plants by accelerated stem growth, flower and seed development and a reduction in size and number of rosette leaves. The accelerated growth phenotype of udh1 transgenic plants was stably inherited and was favored under reduced light conditions. Truncation of the N-terminal 70 amino acids of the Udh1 protein abolished the ability to restore growth in det2-1 plants. Our results demonstrate the existence of a 5alpha-steroid reductase encoding gene in fungi and suggest a common ancestor between fungal, plant, and mammalian proteins.     

Mutants in Arabidopsis thaliana Altered in Epicuticular Wax and Leaf Morphology

We report eight new mutants in Arabidopsis thaliana possessing altered leaf morphology and epicuticular wax. These were isolated from a T-DNA-mutagenized population using a visual screen for altered leaf reflectance, i.e. increased glaucousness or glossiness. The mutants were placed into three distinct classes based on alterations in overall plant morphology: knobhead (knb), bicentifolia (bcf), and wax. The four knb mutants formed callus-like growths in the axillary region of the rosette leaves and apical meristem, the two bcf mutants produced hundreds of narrow leaves, and the two wax mutants had leaves and stems that were more glossy than wild type and organs that fused during early development. Leaves of knb and bcf were more glaucous and abnormally shaped than wild type. Epicuticular wax crystals over knb and bcf leaf surfaces (where none were present on wild type) likely contributed to their more glaucous appearance. In contrast, the glossy appearance of the wax mutants was associated with a reduced epicuticular wax load on both leaves and stems. One representative from each phenotypic class was selected for detailed analyses of epicuticular wax chemistry. All three lines, knb1, bcf1, and wax1, had dramatic alterations in the total amounts and relative proportions of their leaf epicuticular wax constituents.     

Isolation and Genetic Analysis of Arabidopsis Mutants with Low-K+ Tolerance

Ethyl methane-sulfonate (EMS)-mutagenized Arabidopsis M2 populations were screened in low-K+ medium using the root-bending assay. Forty-two putative low-K+-tolerant ( lkt ) mutants were selected from 150?000 tested M2 seedlings, and two of these mutants maintained their low-K+-tolerant phenotype in their M3 generations, respectively. Genetic analysis showed that either one of these two mutants has a monogenic recessive mutation in a nuclear gene, and that the two mutations in two independent mutants are allelic to each other.     

The Negative Regulator OsSDS1 Significantly Reduces Salt and Drought Tolerance in Transgenic Arabidopsis

In this report, we present data on OsSDS1 (Oryza sativa L. salt and drought sensitive gene 1)—an uncharacterized gene isolated from rice Pei’ai 64S (O. sativa L.). Expression of OsSDS1 was strongly up-regulated by a wide spectrum of stresses, including cold, drought, and heat, in different tissues at different developmental stages of rice, as revealed by both microarray and quantitative RT-PCR analyses. Subcellular localization revealed that an OsSDS1: GFP fusion protein was distributed to the nucleus. Expression of OsSDS1 conferred decreased tolerance to salt and drought in Arabidopsis thaliana, accompanied by altered expression of stress-responsive genes and altered K⁺/Na⁺ ratio. The results suggest that OsSDS1 may act as a negative regulator of salt and drought tolerance in plants.     

过量表达星星草PtSOS_1提高拟南芥的耐盐性

将星星草中分离的质膜型Na+/H+逆向转运蛋白基因PtSOS1(GenBank登录号EF440291)构建到pGWB2植物表达载体上,转化拟南芥,获得抗卡那霉素的抗性植株.PCR和Northern检测表明,PtSOS1已整合到拟南芥基因组中并过量表达.耐盐性实验表明,PtSOS1过量表达提高了拟南芥植株的耐盐性.盐分测定表明,盐胁迫下PtSOS1转基因植株中Na+积累低于野生型的,K+含量则高于野生型的,转基因植株中K+/Na+比值高于野生型.     

过量表达棉花CBF2基因提高转基因拟南芥抗旱耐盐能力

CBF/DREB是一类植物中特有的转录因子,在植物抵抗逆境胁迫过程中发挥重要功能。本研究从陆地棉(Gossypium hirsutum L.)Coker 312中克隆获得1个棉花CBF/DREB基因,命名为Gh CBF2,该基因编码一个由216个氨基酸组成的CBF蛋白。序列分析结果显示,Gh CBF2与其他植物的CBF蛋白类似,含有AP2转录因子典型的保守结构域。干旱或高盐胁迫处理明显增加了Gh CBF2基因的表达量。亚细胞定位分析结果发现Gh CBF2定位在细胞核中。将Gh CBF2基因构建到由35S启动子调控的植物表达载体p MD上并转化拟南芥(Arabidopsis thaliana L.),结果表明,在干旱和盐胁迫条件下,过量表达Gh CBF2基因拟南芥的成活率显著高于野生型,并且游离脯氨酸和可溶性糖含量也高于野生型,说明转Gh CBF2基因提高了拟南芥的耐盐抗旱能力。采用实时荧光定量PCR方法分析胁迫相关标记基因COR15A、RD29A和ERD6的表达情况,结果显示转基因株系中的表达量显著高于野生型,说明Gh CBF2参与调控拟南芥干旱和盐胁迫相关基因的表达。     

微丝骨架通过调控线粒体膜透性影响拟南芥耐盐性

植物微丝参与了许多重要的细胞生理活动,与植物耐盐性有密切的联系。在微丝解聚剂Latrunculin B（LatB）存在的情况下,拟南芥会表现出盐胁迫敏感。本研究结果表明盐胁迫下LatB可增加拟南芥线粒体膜通透性转换孔（mitochondrial permeability transition pore,MPTP）开放度,导致线粒体膜电势下降和细胞色素C的释放。而加入MPTP抑制剂环孢素A（CsA）后,膜电势下降程度降低,细胞色素C释放减少,解聚微丝造成的盐敏感表型得到一定程度恢复。     

Identification of Photosynthetic Mutants of Arabidopsis by Automatic Screening for Altered Effective Quantum Yield of Photosystem 2

Quantification of chlorophyll (Chl) fluorescence is a versatile tool for analysing the photosynthetic performance of plants in a non-intrusive manner. A pulse-amplitude modulated fluorometer was combined with a CNC router for the automated measurement of the effective quantum yield of photosystem 2 (₂) of Arabidopsis thaliana plants. About 90 000 individual plants representing 7 500 lines derived from En-transposon and T-DNA mutagenised Arabidopsis populations were screened for mutants with altered ₂. Forty-eight recessive ₂ mutations were identified of which most exhibit also altered pigmentation and increased photosensitivity. For three ₂ mutants the corresponding mutated genes were identified that code all for chloroplast-located proteins. Comparison of the ₂ mutant screen with other screening methods based on the measurement of Chl fluorescence shows that the ₂ mutants identified are different to mutants identified by high Chl fluorescence. Some ₂ mutants, on the contrary, are common to mutants identified by screens based on non-photochemical quenching.     

SOD 活性增高的拟南芥晚花突变体具有增强的非生物胁迫耐受性

为了研究晚花突变表型和非生物胁迫耐受性之间是否存在相关性, 以遗传背景同为Wassilewskija (Ws-2)的7个拟南芥(Arabidopsis thaliana L.)晚花突变体(CS2235、CS2238、CS2239、CS2240、CS2246、CS2248和CS6208)为材料,通过干旱胁迫、盐胁迫和氧化胁迫实验, 发现晚花突变体的耐旱、耐盐和耐氧化性都较野生型(wildtype, WT)强。对叶片失水速率和超氧化物歧化酶superoxide dismutase, SOD)活性测定结果也表明, 晚花突变体的保水能力和SOD活性均高于野生型。相关性回归分析表明SOD活性与耐氧化性、耐旱性、耐盐性之间呈正相关, 耐旱性和耐盐性随耐氧化性增强而增强。实验结果表明, 这些晚花突变体的表型和非生物胁迫耐受性之间存在相关性。     

SOD活性增高的拟南芥晚花突变体具有增强的非生物胁迫耐受性

为了研究晚花突变表型和非生物胁迫耐受性之间是否存在相关性,以遗传背景同为Wassilewskija(Ws-2)的7个拟南芥(Arabidopsis thaliana L.)晚花突变体(CS2235、CS2238、CS2239、CS2240、CS2246、CS2248和CS6208)为材料,通过干旱胁迫、盐胁迫和氧化胁迫实验,发现晚花突变体的耐旱、耐盐和耐氧化性都较野生型(wildtype,WT)强。对叶片失水速率和超氧化物歧化酶(superoxide dismutase,SOD)活性测定结果也表明,晚花突变体的保水能力和SOD活性均高于野生型。相关性回归分析表明SOD活性与耐氧化性、耐旱性、耐盐性之间呈正相关,耐旱性和耐盐性随耐氧化性增强而增强。实验结果表明,这些晚花突变体的表型和非生物胁迫耐受性之间存在相关性。     

拟南芥耐盐突变体stg2的筛选

采取在高盐平板上萌发的方法,对一个雌激素诱导激活型拟南芥突变体库进行了耐盐突变体的筛选,最终得到了2株稳定的耐盐突变体。本文中对其中的一株耐盐突变体,命名为stg2(salt tolerance during germination 2),进行了研究。遗传实验表明它的耐盐特性是受雌激素诱导的,是功能获得型的耐盐突变体。本实验中还探讨了stg2突变体的筛选过程及耐盐生理特点。     

过表达水稻OsAQP增强转基因拟南芥耐盐性

水稻OsAQP是实验室前期从cDNA文库中筛选的功能未知的水通道蛋白质编码基因。本文采用DNA重组技术构建其植物过表达载体,并对拟南芥进行了遗传转化,筛选获得转基因拟南芥。采用50、100、125和150 mmol/L梯度盐胁迫处理,结果显示,转基因拟南芥的发芽率、根长以及鲜重分别比对照至少高17%、40.8%和14.29%,且差异达到显著水平（P<0.05）。在正常条件下,转基因植株叶片中抗坏血酸过氧化物酶(APX)活性显著高于WT;经300 mmol/L NaCl处理,转基因拟南芥叶片中超氧化物歧化酶(SOD)、过氧化物酶(POD)、APX酶活性均升高,与处理前相比分别提高7.37倍、30.87倍和1.77倍,且与WT的酶活性差异达到显著水平（P<0.05）;丙二醛(MDA)含量也在处理后上升,但在转基因植株中的含量低于WT,分别是WT的0.74倍、0.68倍和0.62倍,差异同样达到显著水平（P<0.05）。本研究提示,OsAQP过表达不仅能够促进拟南芥种子萌发和根系生长,而且在盐胁迫下通过提高拟南芥内源抗氧化酶活性、降低膜脂过氧化程度,增强了转基因植株对一定程度盐胁迫的耐受性。     

植物耐盐相关基因：SOS基因家族研究进展

土壤盐渍化是影响农业生产和生态环境的一个非常重要的非生物胁迫因素,也是现代生物科学迫切需要解决的问题。利用拟南芥研究植物耐盐相关基因成为该领域的研究热点。几年来,该领域研究成果斐然。本文就SOS基因家族的三个耐盐基因SOS1、SOS2和SOS3的克隆、功能及相互关系作一概要的评述。 Abstract:The soil salination is a significant abiotic stress for agricultural production and ecological environment. The research on salt tolerance represents an important part for basic plant biology. Genetic analysis of salt tolerance genes in Arabidopsis has become a central issue in this research areas. In recent years, efforts from some laboratories in the world have led to some significant progresses in this field. In this paper, we will review the progress in salt tolerance genes SOS(salt overly sensitive):SOS1,SOS2 and SOS3.