水稻生殖突变体的外观形态特征研究

通过对3种水稻生殖突变体材料的外观形态进行观察后发现,FM1突变体植株不能由营养生长转入生殖生长,一直保持营养生长状态;FM2突变体植株不能分化发育出小穗,只能在进入生殖生长后分化出穗枝梗;FM3突变体植株在生殖生长过程中不能分化出正常小穗,其颖花内的雌蕊和雄蕊明显退化。已经证实这3种生殖突变体植株都不能产生有性生殖后代,只能通过群体内的显性杂合体分离出隐性突变体植株。     

拟南芥ERD15基因缺失突变体的分子鉴定和表型分析

为探究ERD15基因功能,利用反向遗传学,通过PCR及半定量PCR筛选鉴定出拟南芥(Arabidopsis thaliana) ERD15基因的T-DNA插入纯合突变体,并对其表型进行观察分析。结果表明,erd15突变体莲座叶数目显著增多,提前3～4 d开花,突变体比野生型更早从营养生长转向生殖生长。拟南芥野生型植株主茎为圆柱体,平均直径1.29 mm,而erd15突变体主茎扁平,平均直径达到2.27mm,具极显著差异。与野生型相比,erd15突变体果实心皮发育受到影响,隔膜上排列有多排种子,果荚顶端膨大,长度缩短37.67%,但角果平均结籽数升高。因此,ERD15基因参与了调控拟南芥植株的生殖生长过程。     

小麦小穗、小花的形成过程

近年来,各地学校在开展科学研究和支援农业的活动中,种植过不少小麦丰产試驗田,从水肥管理、合理密植等方面来探討小麦丰产的有效措施,因此,对小麦小穗小花形成过程的了解就显得需要了。例如:何时灌水对小穗小花分化更为有利;何时施什么肥更能促进小穗小花的形成;用什么措施可以增多有效小穗小花数目等等,都需要比較观察对照区和試驗区在小穗小花形成过程中的差异,因此,就要对小麦小穗小花形成的正常过程有一个全面的了解。下面就簡单地进行介紹。小麦穗形成过程一般可分成以下几期: 1.生长錐未伸长期一般小麦在通过春化阶段之前,例如:在过冬前的冬小麦,生长錐尚未伸长,其寬度大于长度,形状呈半球形(图2)。这个时候生长錐上只能形成叶子,不能形成花,也就是只有营养生长,沒有生殖生长。从图1中就可以看到生长錐的旁侧正在形成第五片和第六片叶子的叶原基,新形成的叶原基     

烟草的不同器官薄层培养形成花芽的研究

烟草不同器官薄层离体培养形成花芽受植株生长发育时期的影响。植株处于营养生长时期,茎表皮薄层无花芽分化能力。随着植株营养生长转向生殖生长,在抽苔、现蕾、开花、结籽不同发育阶段,主茎上不同部位的茎表皮出现花芽的频率不同。植株现蕾时,只有接近顶端第一节的茎薄层出现花芽分化,随植株的发育,逐渐延伸到第四、五节。植株果实成熟时,主茎薄层分化花芽能力又复减弱。花芽分化的趋势却向花序分枝、花柄、果柄延伸,使??它们的薄层组织有分化花芽能力。此外,还观察到花序上小叶也可直接分化花芽。培养基内附加不同配比的植物激素对薄层花芽分化有促进作用。     

拟南芥晚花突变co-2和ft-1延迟营养生长时相转变

植物胚后发育主要分为营养生长和生殖生长两个阶段,营养生长阶段又包含幼龄期和成熟期。叶片远轴面表皮毛的出现是拟南芥营养生长时相转变的形态学标志。研究利用拟南芥晚花突变体co-2和ft-1,研究了光周期途径晚花突变对营养生长时相转变(vegetative phase change,VPC)的影响。形态学指标测定和茎端分生组织解剖特征表明,光周期途径相关的两种晚花突变体比野生型Ler晚开花近一倍的时间,莲座叶的数目也比野生型多了一倍;野生型叶片远轴面表皮毛多出现在第4片真叶上,co-2和ft-1多出现在第5片真叶上,茎顶端分生组织高宽比变异趋势亦然,说明拟南芥晚花突变延迟了营养生长时相转变。     

不同光周期条件下新铁炮百合生理指标的对比研究

在长、短两种光周期条件下对新铁炮百合的三种生理指标进行了测定。结果表明:新铁炮百合上、中部叶片的生理活动与植株生长发育状态的关系较为紧密;顶芽形态分化初期,上、中部叶片可溶性糖和淀粉含量降至较低的水平,而总氮含量则升至较高水平;此外,生殖生长状态下,3部分叶片各自C/N值均高于营养生长状态下其各自C/N值。     

Comparative study of physiological indexes of Lilium formolongi under different photoperiod conditions

在长、短两种光周期条件下对新铁炮百合的三种生理指标进行了测定.结果表明:新铁炮百合上、中部叶片的生理活动与植株生长发育状态的关系较为紧密;顶芽形态分化初期,上、中部叶片可溶性糖和淀粉含量降至较低的水平,而总氮含量则升至较高水平;此外,生殖生长状态下,3部分叶片各自C/N值均高于营养生长状态下其各自C/N值.     

澄黄滨珊瑚、大管孔珊瑚和丛生盔形珊瑚排卵前后小穗生长特征

澄黄滨珊瑚、大管孔珊瑚和丛生盔形珊瑚排卵前后分别采集珊瑚小穗,在实验室条件下进行为期60 d的养殖,观察其生长特性,结果表明:3种珊瑚排卵前后骨骼密度变化在1.541—2.137 g/cm3之间,差异不显著。3种珊瑚小穗的生长率表现出相对一致的变化趋势,同一规格珊瑚小穗排卵前期生长率明显高于排卵后期;同一时期大规格珊瑚小穗生长率明显高于小规格珊瑚小穗,而且养殖中后期生长较快,养殖前期生长较慢,差异显著(P0.05)。澄黄滨珊瑚小穗边缘组织延伸度排卵后期大于排卵前期,大管孔珊瑚小穗边缘组织延伸度排卵前期大于排卵后期,以上两种珊瑚的小规格珊瑚小穗与大规格珊瑚小穗组织延伸度相当。随着养殖时间的持续,丛生盔形珊瑚小穗螅体增殖速率加快,各养殖阶段螅体数差异显著(P0.05),珊瑚小穗规格和养殖季节对其小穗螅体增殖数量没有显著影响。3种珊瑚小穗生长指标间多呈显著正相关,仅大管孔珊瑚小穗初始直径、初始重量与组织延伸度间,以及丛生盔形珊瑚小穗初始重量与初始螅体数量、生长率间相关性不明显。     

棉花li突变体生长素极性运输的减弱

陆地棉(Gossypium hirsutum L.)li突变体叶片卷曲,植株扭曲,种子表皮毛明显偏短。通过扫描电子显微镜(SEM)观察发现,li突变体的纤维发育在起始期与野生型植株并无明显差异,但在伸长期开始后,如开花后3d(3 day post anthesis,DPA),纤维伸长受阻;li突变体茎的形成层和韧皮部分化发育不完全,生长素由顶端向基部的极性运输能力下降,仅为野生型植株的大约三分之一。推测棉花li突变体包括纤维发育不良在内的多效性异常表型,与其生长素极性运输能力的下降有关。     

渤海湾津唐沿海野生大豆(Glycine soja)种群高盐碱胁迫反应

以渤海湾津唐沿海地带895份野生大豆种群在高盐碱(3%)环境下的全生育期鉴定试验,分析不同种群(株系)的生长发育动态以及对盐碱土壤生态适应性的分化。结果表明,出苗阶段存在3种耐盐碱能力类型:耐高盐碱胁迫发芽出苗;耐低盐碱胁迫发芽出苗;盐胁迫不能发芽出苗。在高盐胁迫下营养生长早期阶段种群死亡率最高,中期以后相对降低,成熟期死亡率较低。种群植株形态建成和生殖生长受到高盐胁迫的强烈抑制,表现早期严重而后期较轻。植株和产量性状的受害程度由大到小依次为:单株的地上干物质重、单株产量、种子数、百粒重和收获指数。株系间变异系数从大到小依次为:单株产量、种子数、荚数、收获指数、地上干物质重、百粒重。研究揭示该地域种群内对盐碱土壤有很高的适应性分化,存在高耐盐碱生态型。     

The Arabidopsis compact inflorescence genes: phase-specific growth regulation and the determination of inflorescence architecture

During their life cycle, higher plants pass through a series of growth phases that are characterized by the production of morphologically distinct vegetative and reproductive organs and by different growth patterns. Three major phases have been described in Arabidopsis: juvenile vegetative, adult vegetative, and reproductive. In this report we describe a novel, phase-specific mutant in Arabidopsis, compact inflorescence (cif). The most apparent aspect of the cif phenotype is a strong reduction in the elongation of internodes in the inflorescence, resulting in the formation of a floral cluster at the apical end of all reproductive shoots. Elongation and expansion of adult vegetative rosette leaves are also compromised in mutant plants. The onset of the cif trait correlates closely with morphological changes marking the phase transition from juvenile to adult, and mutant plants produce normal flowers and are fully fertile. Hence the cif phenotype appears to be adult vegetative phase-specific. Histological sections of mutant inflorescence internodes indicate normal tissue specification, but reduced cell elongation compared to wild-type. compact inflorescence is inherited as a two-gene trait involving the action of a recessive and a dominant locus. These two cif genes appear to be key components of a growth regulatory pathway that is closely linked to phase change, and specifies critical aspects of plant growth and architecture including inflorescence internode length.     

The role of EMF1 in regulating the vegetative and reproductive transition in Arabidopsis thaliana (Brassicaceae)

To understand the genetic regulation of vegetative to reproductive transition in higher plants, further characterization of the Arabidopsis mutant embryonic flower1, emf1, was conducted. Using three flowering symptoms, we showed that emf1 mutants could only grow reproductive and not rosette shoots under five different growth conditions. The mutant embryos did not produce the typical tunica–corpus shoot apical structures at the heart-, torpedo-, and mature stages. The divergent shoot apical development during mutant and wild-type embryogenesis indicated that the wild-type EMF1 gene was expressed in early embryogenesis. Mutations in the EMF1 gene affected the embryonic shoot apical development and caused the germinating embryo and regenerating callus to grow inflorescence, instead of rosette, shoots. Our results support the hypothesis that the EMF1 gene regulates the switch between vegetative and reproductive growth in Arabidopsis.     

Transgenic tobacco plants expressing the bacterial mc gene resist virus infection

A bacterial rnc gene coding for a double-stranded RNA-dependent RNase III endoribonuclease and a mutant, rnc70, were expressed in tobacco plants. The RNase III protein produced in the transgenic plants was the same size as the bacterial protein. Expression of the wild-type gene could cause stunting in some plant lines, but not in others. Expression of the mutant protein did not affect normal growth and development of the transgenic plants. Transgenic plants of the R1 and R2 generations, expressing the wild type, as well as a mutant protein, were resistant to infection by three disparate RNA plant viruses with a divided genome but not against two viruses with a single-stranded RNA genome. Introduction of the rnc gene in crop plants may provide resistance to economically important virus diseases.     

Cytokinin‐dependent specification of the functional megaspore in the Arabidopsis female gametophyte

The life cycle of higher plants alternates between the diploid sporophytic and the haploid gametophytic phases. In angiosperms, male and female gametophytes develop within the sporophyte. During female gametophyte (FG) development, a single archesporial cell enlarges and differentiates into a megaspore mother cell, which then undergoes meiosis to give rise to four megaspores. In most species of higher plants, including Arabidopsis thaliana, the megaspore closest to the chalaza develops into the functional megaspore (FM), and the remaining three megaspores degenerate. Here, we examined the role of cytokinin signaling in FG development. We characterized the FG phenotype in three triple mutants harboring non‐overlapping T–DNA insertions in cytokinin AHK receptors. We demonstrate that even the strongest mutant is not a complete null for the cytokinin receptors. Only the strongest mutant displayed a near fully penetrant disruption of FG development, and the weakest triple ahk mutant had only a modest FG phenotype. This suggests that cytokinin signaling is essential for FG development, but that only a low threshold of signaling activity is required for this function. Furthermore, we demonstrate that there is elevated cytokinin signaling localized in the chalaza of the ovule, which is enhanced by the asymmetric localization of cytokinin biosynthetic machinery and receptors. We show that an FM‐specific marker is absent in the multiple ahk ovules, suggesting that disruption of cytokinin signaling elements in Arabidopsis blocks the FM specification. Together, this study reveals a chalazal‐localized sporophytic cytokinin signal that plays an important role in FM specification in FG development.     

Selection and Characterization of a Gibberellin-Deficient Mutant of Thlaspi arvense L

Field pennycress (Thlaspi arvense L.) is a winter annual weed with a cold requirement for reproductive development. Previous work in this laboratory has demonstrated that the bolting aspect (rapid stem growth) of reproductive development is mediated by gibberellins (GA). The present paper describes the selection and characterization of a mutant lacking the capacity for thermoinduced stem growth. Seeds of an inbred field pennycress line (CR₁) were treated with the chemical mutagen ethyl methane sulfonate, germinated, and allowed to produce seed. Plants derived from these seeds were screened for reduced stem growth. A mutant line, EMS-141, in which the lack of stem growth can be fully overcome with exogenous GA₃, was selected for further analysis. Other phenotypic abnormalities exhibited by the mutant line include reduced petiole growth, slightly delayed floral initiation, and failure of flowers to develop fully. These are also reversed with exogenous GA₃. Evidence is presented indicating that all of the alterations in growth and development exhibited by EMS-141 are conferred by a recessive mutation of a single nuclear gene. Through quantitative analysis of endogenous GA and GA precursors and a comparison of the abilities of various compounds to restore normal growth when applied to plants of EMS-141, the physiological basis for the mutant phenotype was determined to be the result of highly reduced endogenous GA levels. Moreover, the affected site in GA biosynthesis appears to be the accumulation of ent-kaurene, probably at the level of ent-kaurene synthase. The relative abilities of exogenous GA and GA precursors to restore normal growth of petioles and stems are compared, and the results are used to make inferences on the functions of the two different pathways of GA metabolism that exist in field pennycress.     

Isolation and characterization of an Arabidopsis mutant, fireworks (fiw), which exhibits premature cessation of inflorescence growth and early leaf senescence

To examine the mechanism underlying the reproductive development in monocarpic plants, we screened for mutants that exhibit premature cessation of inflorescence growth in Arabidopsis. We identified a novel mutant line that exhibited earlier cessation of flower formation and inflorescence stem elongation. This mutant also exhibited accelerated rosette leaf senescence after the cessation of the inflorescence growth. We designated the mutant fireworks (fiw) because flowers and siliques were clustered at the top of the fiw inflorescence. The fiw mutation was a single, recessive mutation and mapped on the lower part of chromosome 4. The fiw phenotype was not observable during vegetative growth, but the inflorescence growth was arrested more than 7 d earlier than the wild type (WT). Microscopic observation revealed that the fiw apical meristem was structurally preserved. The premature arrest of growth was observed not only in the primary inflorescence but also in the lateral inflorescence, which is consistent with the global proliferative arrest observed later in WT. Regardless of such dramatic phenotypic features, the fiw plants bore normal flowers and set fully matured siliques.     

Suppression of OsRAD51D results in defects in reproductive development in rice (Oryza sativa L.)

The cellular roles of RAD51 paralogs in somatic and reproductive growth have been extensively described in a wide range of animal systems and, to a lesser extent, in Arabidopsis, a dicot model plant. Here, the OsRAD51D gene was identified and characterized in rice (Oryza sativa L.), a monocot model crop. In the rice genome, three alternative OsRAD51D mRNA splicing variants, OsRAD51D.1, OsRAD51D.2, and OsRAD51D.3, were predicted. Yeast two‐hybrid studies, however, showed that only OsRAD51D.1 interacted with OsRAD51B and OsRAD51C paralogs, suggesting that OsRAD51D.1 is a functional OsRAD51D protein in rice. Loss‐of‐function osrad51d mutant rice plants displayed normal vegetative growth. However, the mutant plants were defective in reproductive growth, resulting in sterile flowers. Homozygous osrad51d mutant flowers exhibited impaired development of lemma and palea and contained unusual numbers of stamens and stigmas. During early meiosis, osrad51d pollen mother cells (PMCs) failed to form normal homologous chromosome pairings. In subsequent meiotic progression, mutant PMCs represented fragmented chromosomes. The osrad51d pollen cells contained numerous abnormal micro‐nuclei that resulted in malfunctioning pollen. The abnormalities of heterozygous mutant and T2 Ubi:RNAi‐OsRAD51D RNAi‐knock‐down transgenic plants were intermediate between those of wild type and homozygous mutant plants. The osrad51d and Ubi:RNAi‐OsRAD51D plants contained longer telomeres compared with wild type plants, indicating that OsRAD51D is a negative factor for telomere lengthening. Overall, these results suggest that OsRAD51D plays a critical role in reproductive growth in rice. This essential function of OsRAD51D is distinct from Arabidopsis, in which AtRAD51D is not an essential factor for meiosis or reproductive development.     

Towards Defining Nutrient Conditions Encountered by the Rice Blast Fungus during Host Infection

Fungal diseases cause enormous crop losses, but defining the nutrient conditions encountered by the pathogen remains elusive. Here, we generated a mutant strain of the devastating rice pathogen Magnaporthe oryzae impaired for de novo methionine biosynthesis. The resulting methionine-requiring strain grew strongly on synthetic minimal media supplemented with methionine, aspartate or complex mixtures of partially digested proteins, but could not establish disease in rice leaves. Live-cell-imaging showed the mutant could produce normal appressoria and enter host cells but failed to develop, indicating the availability or accessibility of aspartate and methionine is limited in the plant. This is the first report to demonstrate the utility of combining biochemical genetics, plate growth tests and live-cell-imaging to indicate what nutrients might not be readily available to the fungal pathogen in rice host cells.     

The balance between sexual and asexual reproduction in plants living in variable environments

The balance between sexual and asexual propagule production is studied in an evolutionary model where plants produce the two kinds of propagules in genetically determined proportions. The male function of plants producing asexual propagules can be varied, and the sexual and asexual propagules carry different probabilities to turn into new reproductive individuals. These fitnesses may vary over years. The evolution of the population’s reproductive system is studied assuming modifier alleles with small effects. In this setting a balanced, mixed reproductive system can evolve, but only if the difference in fitness between the sexual and asexual propagules varies over years. When the two kinds of propagules are very similar to each other, as is often the case with sexual and asexual seed formation, evolution will tend towards a state dominated by the one or the other reproductive system.