黄精种子萌发过程发育解剖学研究

采用石蜡切片技术对成熟黄精种子形态及萌发过程中的形态学变化及解剖结构特征进行了研究,以阐明黄精种子繁殖的生物学机制。结果显示:(1)成熟的黄精种子由外而内依次为种皮、胚乳和胚等3部分组成。其中种皮由一层木质化的细胞组成;胚乳占据种子的大部分结构,胚乳细胞含有大量淀粉,细胞壁增厚;胚处于棒型胚阶段。(2)黄精种子在萌发过程中棒型胚靠近种脐端分化为吸器、子叶联结和子叶鞘,靠近种孔的部位分化出胚根、胚轴和胚芽。(3)黄精种子萌发首先由子叶联结伸长将胚芽和胚根原基推出种孔,紧接着下胚轴膨大形成初生小根茎,吸器留在种子中分解吸收胚乳中的营养物质。(4)通过子叶联结连通吸器和初生小根茎,将胚乳中的营养物质由吸器-子叶联结这个通路转移到初生小根茎中,为初生根茎上胚芽和胚根的进一步分化提供物质保障。(5)黄精种子自然条件下萌发率较低,而且当年不出土。研究表明,黄精种子的繁殖生物学特性是其生态适应的一种重要机制。     

罗布麻种子形态结构的初步观察

阿白7号种子棕红色,线状圆柱形,种脐着生在基部一端,种脐到珠孔一端有1条显著与种子纵轴平行的沟。红4号红麻成熟种子呈黄棕色,枣核状,种脐在整个种子长度约1／2处。阿白7号种子一般长2.62mm,直径为0.42-0.71mm,千粒重400－500mg。阿红4号种子一般长2.74mm,直径0.38-0.58mm,千粒重350mg左右。罗布麻种皮由内,外两种皮构成。外种皮为1层细胞,除种脐外,形成一个连续组织包裹在整个种子表面,细胞排列紧密,胞壁木质化。内种皮由2层到多层薄壁细胞构成,红,白麻种皮构造基本相似,但白麻厚。种子的胚由子叶,胚茎生长点,胚轴和胚根组成,胚乳不甚明显,似与种皮紧密联结在一起的1层薄壁细胞。     

象牙参种子的解剖学和组织化学研究

象牙参种子解剖学和组织化学的研究结果表明, 种子包括假种皮、种皮、外胚乳、内胚乳和胚。假种皮没有完全包被种子, 由约4~5 层薄壁细胞构成。种皮可以分为外种皮、中种皮和内种皮。外种皮由1 层表皮细胞构成, 细胞壁明显增厚;中种皮包括下皮层、半透明细胞层和3~4层细胞的色素层, 下皮层和色素层细胞均充满红棕色色素;内种皮由1 层体积小、壁局部增厚的砖形薄壁细胞构成。种子在珠孔端分化出珠孔领、孔盖和种阜状结构, 珠孔领为同形型, 孔盖不具石细胞硬层。合点区内种皮出现缺口, 缺口间充满合点区色素细胞, 其整体轮廓成新月形。外胚乳可分为厚区与薄区两部分, 外胚乳细胞壁平直, 细胞内充满淀粉。内胚乳细胞主要含蛋白质, 也有少量脂类物质, 细胞界限不清楚。胚棒状, 两端略膨大, 含大量脂类物质, 也含蛋白质和多糖。     

赤霉素代谢与信号转导及其调控种子萌发与休眠的分子机制

种子的萌发能力由胚周围组织(种皮和胚乳)强加的物理限制与胚的生长潜能之间的平衡所决定.覆盖胚根尖端的珠孔端胚乳细胞的弱化被植物激素赤霉素(gibberellin, GA)促进但被脱落酸抑制,是胚根伸出的重要前提.GA是一种调控植物许多关键生理过程,如种子萌发、根和茎的伸长、开花、座果和种子发育的重要激素. GA在种子萌发与休眠解除中的作用主要受其生物合成与分解代谢和信号转导途径的调控.本文主要综述了GA的生物合成与代谢、GA的信号转导以及它们对种子萌发和休眠解除调控的研究进展.此外,本文也提出了本领域需要进一步研究的科学问题,试图为解释GA调控种子萌发与休眠的分子机理提供新的研究信息.     

拟豆寇种子的解剖学和组织化学研究

拟豆寇（Paramomum petaloideum)种子包括假种皮,种皮,外胚乳,内胚乳和胚,假种皮膜质,由5－7层薄壁细胞构成,种皮分外种皮,中种皮和内种皮,外种皮由一层细胞构成,其壁增厚并木质化,中种皮包括下皮导,透明细胞层和色素层,下皮由一层细胞构成,细胞近长方形,半透明细胞层由一层细胞组成,细胞近长方形或长条形,形态上与色素层细胞相似,但可通过染色方法把二者区分,色素层由一至二层细胞构成,最内层细胞形态有时难以分辨,内种皮由一层内切几壁非常增厚的石细胞构成,珠孔区分化出珠孔领,孔盖和珠孔区薄壁细胞,珠孔领导形型,孔盖具有石细胞硬具,合点区内种皮内凹陷并出现缺口,缺口位于种子近顶部偏向背侧,缺口间的合点区色素细胞群整体轮廓呈喇形,壁呈波浪形的外胚细胞富含淀粉粒,内胚乳最外一层细胞体积小,富含脂类物质,内胚乳合点端多层细胞,珠孔端为一层细胞,含丰富蛋白质,脂类物质主要存在于胚中,本文还从种子解剖学角度讨论了拟豆寇的系统位置。     

桃儿七种子休眠解除过程中细胞壁代谢及种皮超微结构的变化北大核心CSCD

为探究低温层积过程中桃儿七种子细胞壁代谢及种皮超微结构与休眠解除的内在联系,该研究通过低温层积解除桃儿七种子休眠,分析休眠解除过程中种子不同部位细胞壁组分及相关代谢酶的变化,同时利用扫描电镜对种皮的超微结构进行观察。结果表明,(1)桃儿七种皮主要由角质层、栅状石细胞层及海绵组织层3层构成,在层积过程中,种皮内部的海绵组织逐步疏松膨胀,种皮表面破损加剧;(2)种子不同部位的细胞壁组分具有明显差异,整个层积过程中,种胚、种皮和胚乳中的纤维素含量均在层积中期(45 d和60 d)降至最低,3个部位的纤维素酶活性在层积中期对应升高;种胚和种皮内的半纤维素含量均在层积中期显著下降,种皮中甘露聚糖酶活性和木糖苷酶活性在层积中期时相应达到最大;3个部位的果胶含量均在层积后期(75 d和90 d)时显著下降,而种皮和胚乳中多聚半乳糖醛缩酶活性也在层积后期相应升高;(3)种胚和胚乳内过氧化物酶活性在层积75 d和90 d时明显下降,而SOD活性在此时显著上升。(4)种子不同部位3种木质素单体的组成比例具有明显区别,同时3种木质素单体含量均随层积时间的延长而显著降低,且胚乳和种皮中的S-木质素含量对种子萌发存在显著的负向影响关系。研究认为,在低温层积过程中,桃儿七种子内细胞壁组分纤维素、半纤维素及木质素的逐步酶解,活性氧作用下的细胞壁松弛以及海绵组织层的疏松膨胀和种皮的破裂,破坏了细胞壁的刚性结构,促使种子机械束缚力降低,吸水性能提高、胚根生长能力增强,最终导致其休眠解除。     

九翅豆蔻种子的解剖学和组织化学研究

九翅豆蔻种子包括假种皮、种皮、外胚乳、内胚乳和胚．由外珠被发育而来的种皮可划分为外种皮、中种皮和内种皮．外种皮由一层表皮细胞构成,其壁增厚并略木质化．中种皮包括下皮层、油细胞层和含２—５层细胞的色素层;各为一层薄壁细胞的下皮层与油细胞层非常压扁．内种皮由一层石细胞构成,极厚,占种皮厚度的１／３—２／３,是种皮主要的机械层;内种皮整体外观呈波浪形,在珠孔端和合点端的内种皮除外．种子在珠孔端分化出珠孔领和孔盖,在合点端分化出下皮细胞垫、大型薄壁细胞区、维管束和合点端色素细胞区．外胚乳细胞内充满淀粉,内胚乳细胞含有大量蛋白质和多糖,胚细胞含有蛋白质、多糖和脂类物质．脂类物质不存在于油细胞中,而存在于胚细胞、部分假种皮细胞、外种皮细胞和内胚乳最外层细胞中．建议将油细胞（层）改称为半透明细胞（层）．     

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。     

距药姜种子解剖学和组织化学研究

距药姜种子解剖学和组织化学研究表明,种子包括种皮、外胚乳、内胚乳和胚。外皮由1层表皮细胞构成,细胞壁纤维素质且明显增厚,中种皮可分为1层细胞的下皮层、半透明细胞层和2-4层细胞的色素细胞层,下皮层和色素细胞层的细胞内充满棕红色色素;内种皮由1层砖形薄壁细胞构成。珠孔区有珠孔领和孔盖的分化,但珠孔领分化不完善。合点区内种皮出现缺口,缺口间充满合点区色素细胞,其整体轮廓成新月形。外胚乳细胞壁平直,细胞内充满淀粉。内胚乳可分为多细胞区简细胞区两部分,内胚乳细胞界限不清,内含物主要是蛋白质,胚少有分化,含脂类、蛋白质、多糖,另外,还对姜花族的种子解剖学特征进行了初步的系统学分析。     

龙胆个体发育早期器官发育形态学研究

为进一步了解被子植物个体发育早期形态与结构的多样性,研究了龙胆合子至种苗阶段的发育过程及特征。结果表明:龙胆的胚发育属于茄型,胚乳发育为核型,蒴果开裂时散落出来的种子内的胚分化不完全,大部分处于心形胚或鱼雷胚阶段。种子萌发时胚根依靠下胚轴细胞伸长突破种皮,在下胚轴和胚根交界处形成根环,随后根环上发育出根环毛,毛的生长在早期快于胚根,随着胚根的发育,正常根毛在其先端逐渐出现。子叶状态的种苗至少停滞约10 d才见真叶发育,但在地上停滞发育的同时,地下的胚根却继续生长。这些器官发育顺序上的特点既反映祖先的水生孑遗原始性状,又反映了其对现存偏旱生境的适应性状,是次生陆生的进一步演化。     

Antisense-transformation reveals novel roles for class I beta-1,3-glucanase in tobacco seed after-ripening and photodormancy

Little is known about the molecular basis for seed dormancy, after-ripening, and radicle emergence through the covering layers during germination. In tobacco, endosperm rupture occurs after testa rupture and is the limiting step in seed germination. Class I beta-1,3-glucanase (betaGLU I), which is induced in the micropylar endosperm just prior to its penetration by the radicle, is believed to help weaken the endosperm wall. Evidence is presented here for a second site of betaGLU I action during after-ripening. Tobacco plants were transformed with antisense betaGLU I constructs with promoters thought to direct endosperm-specific expression. Unexpectedly, these transformants were unaffected in endosperm rupture and did not exhibit reduced betaGLU I expression during germination. Nevertheless, antisense betaGLU I transformation delayed the onset of testa rupture in light-imbibed, after-ripened seeds and inhibited the after-ripening-mediated release of photodormancy. It is proposed that betaGLU I expression in the dry seed contributes to the after-ripening-mediated release of seed dormancy.     

Seed after-ripening and over-expression of class I beta-1,3-glucanase confer maternal effects on tobacco testa rupture and dormancy release

'Coat-imposed' seed dormancy of many non-endospermic and endospermic species is released during after-ripening. After-ripening-mediated promotion of tobacco ( Nicotiana tabacum L.) seed germination is mainly due to a promotion of testa rupture and a similar promotion of subsequent endosperm rupture. Treatment of after-ripened or freshly harvested mature seeds with abscisic acid (ABA) delays endosperm rupture and inhibits the induction of class I beta-1,3-glucanase (betaGlu I) in the micropylar endosperm, but does not affect the kinetics of testa rupture. After-ripening-mediated release of photodormancy is correlated with a decreased gibberellin (GA) requirement for testa rupture during dark-imbibition. Reciprocal crosses between wild-type tobacco and sense-betaGlu I transformant lines showed that betaGlu I over-expression in the seed covering layers can replace the promoting effect of after-ripening on testa rupture in light, but only if the mother plant is a sense-betaGlu I line. This maternal effect supports the model of two sites for betaGlu I action: (i) betaGlu I contribution to the after-ripening-mediated release of dormancy in the dry seed state, which is manifested in the promotion and ABA-insensitivity of testa rupture during imbibition. (ii) ABA-sensitive expression of betaGlu I in the micropylar endosperm, which contributes to endosperm rupture. The importance of GA-signaling and testa characteristics appear to be a common feature during the after-ripening-mediated release of coat-imposed dormancy in endospermic and non-endospermic seeds.     

The emergence of embryos from hard seeds is related to the structure of the cell walls of the micropylar endosperm, and not to endo-beta-mannanase activity

BACKGROUND AND AIMS: Seeds of carob, Chinese senna, date and fenugreek are hard due to thickened endosperm cell walls containing mannan polymers. How the radicle is able penetrate these thickened walls to complete seed germination is not clearly understood. The objective of this study was to determine if radicle emergence is related to the production of endo-beta-mannanase to weaken the mannan-rich cell walls of the surrounding endosperm region, and/or if the endosperm structure itself is such that it is weaker in the region through which the radicle must penetrate. METHODS: Activity of endo-beta-mannanase in the endosperm and embryo was measured using a gel assay during and following germination, and the structure of the endosperm in juxtaposition to the radicle, and surrounding the cotyledons was determined using fixation, sectioning and light microscopy. KEY RESULTS: The activity of endo-beta-mannanase, the major enzyme responsible for galactomannan cell wall weakening increased in activity only after emergence of the radicle from the seed. Thickened cell walls were present in the lateral endosperm in the hard-seeded species studied, but there was little to no thickening in the micropylar endosperm except in date seeds. In this species, a ring of thin cells was visible in the micropylar endosperm and surrounding an operculum which was pushed open by the expanding radicle to complete germination. CONCLUSIONS: The micropylar endosperm presents a lower physical constraint to the completion of germination than the lateral endosperm, and hence its structure is predisposed to permit radicle protrusion.     

Analyses to determine the role of the megagametophyte and other seed tissues in dormancy maintenance of yellow cedar (Chamaecyparis nootkatensis) seeds; morphological, cellular and physiological changes following moist chilling and during germination

Yellow cedar (Chamaecyparis nootkatensis) seeds exhibit prolonged dormancy following their dispersal from the parent plant. Embryos excised fully from their enclosing seed tissues exhibit 100% germination, indicating that the seed tissues enclosing the embryo (the testa, remnants of the nucellus and the megagametophyte) play an inhibitory role and prevent radicle emergence. As part of an assessment of the role of seed tissues in the dormancy mechanism of yellow cedar seeds, light microscopy was used to examine changes within the major structures of the seed following a 90 d war (26C)/cold (4C) moist treatment ('stratification') and during germination. In the micropylar tip of the seed, the nucellus forms a hard nucellar cap covering the radicle. The nucellar cap is composed primarily of degenerated cells; histological staining with ruthenium red revealed a predominance of pectins. There were no obvious cellular or morphological differences (detected by light microscopy) between mature seeds subjected to a 3 d soak and seeds subjected to a 3 d soak and the 90 d dormancy-breaking treatment. However, just prior to germination there was an outward projection of the nucellar cap through the micropyle, which appeared to be caused by the extension of highly folded proteinaceous strands lying immediately in front of the radicle. When the testa was removed, the embryo enclosed within the intact megagametophyte was incapable of germination. If, however, the megagametophyte surrounding the embryo was slit or the embryo surrounded by an intact megagametophyte was subjected to a 3d rinse in water, some germination occurred, perhaps as a result of an enhanced release of inhibitors from the megagametophyte. After stratification, dormancy of yellow cedar seeds is broken; concurrent with dormancy breakage, there was a mechanical weakening of the megagametophyte. The embryo also underwent changes that included an increase in turgor and a reduced sensitivity to highly negative osmotic potential. It is concluded that coat-imposed dormancy of yellow cedar seeds is enforced by mechanical restraint of the megagametophyte as well as a leachable chemical inhibitor (most probably ABA).     

Endo-β-mannanase activity during dormancy alleviation and germination of white spruce (Picea glauca) seeds

It is not known how embryos of seeds of the Pinaceae protrude from their enclosing tissues to complete germination. Prior to protrusion of the radicle there is an increase in endo-β-1,4-mannanase (EC 3.2.1.78) activity associated with weakening of the micropylar megagametophyte/nucellus from seeds of white spruce ( Picea glauca [Moench.] Voss). Mannanase activity is present as three isoforms (pI values 5.0, 4.8, 4.7) in both the embryo and surrounding structures (megagametophyte and nucellus) prior to and during imbibition. Activity of all the isoforms increases in the chalazal and micropylar megagametophyte during germination. Activity then declines after the testa splits, typically 1 day prior to radicle protrusion, due partially to its leaching from the seed into the surrounding water. Activity increases in the cotyledons and axis as the embryo commences elongation. Seeds from dormant seedlots exhibit a lower germination percentage, relative to seeds from nondormant seedlots, and the force necessary for the embryo to puncture the surrounding structures tends to be greater. Although similar mannanase activities are present in unimbibed seeds of dormant and nondormant seedlots, during germination, enzyme activity in seeds of dormant seedlots is lower. Moist chilling alleviates dormancy in the seeds of the Pinaceae and, during 3 weeks of this treatment, mannanase activity slowly increases. After 3 weeks of moist chilling and regardless of whether the seedlot was dormant or not prior to moist chilling, the force necessary to puncture the micropylar megagametophyte and nucellus is lower, and the speed of germination greater. Seeds from previously dormant seedlots also complete germination to a greater percentage, relative to unchilled seeds from dormant seedlots. Upon transfer to 25°C, mannanase activity in moist-chilled seeds decreases during germination of all seedlots regardless of their previous dormancy status.     

Structures contributing to the completion of conifer seed germination

The variety of interpretations of the origin and role of the tissues surrounding the emerging radicle of conifer seeds prompted us to study changes during germination. The structures contributing to the opening of the seed coat and protrusion of the radicle in pine and spruce seeds were examined using light microscopy and field emission scanning electron microscopy. The opening of the seed coat was mainly mechanical and primarily affected by the enlargement of the imbibed endotesta cells lining the micropylar canal. The hypertrophied nucellar apex, swelling remnants and mucous substances in the micropyle further enhanced the testa splitting which was reinforced by the straightening of the folded nucellar cap. The expansion of the imbibed megagametophyte and the embryo were conducive to the seed coat opening only at a later stage. This was followed almost immediately by the appearance of the root cap showing an early geotropic response typical for taproots and assuring an immediate anchoring of the emerged embryo to the ground. The translucent tissue composed of elongating cell rows preceded and surrounded the protruding radicle and derived mainly from two origins: the micropylar end of the megagametophyte and the root cap. Observations about the origin of the sheath clarify the reasons for previous interpretations about the putative role of the massive embryo root cap in testa splitting and germination. The protective and adhesive function of the sheath is concluded to be essential to the conifer embryos, which present the epigeal type of germination. Received: 7 July 1999 / Accepted: 11 August 1999     

Water uptake and distribution in germinating tobacco seeds investigated in vivo by nuclear magnetic resonance imaging

The regulation of water uptake of germinating tobacco (Nicotiana tabacum) seeds was studied spatially and temporally by in vivo (1)H-nuclear magnetic resonance (NMR) microimaging and (1)H-magic angle spinning NMR spectroscopy. These nondestructive state-of-the-art methods showed that water distribution in the water uptake phases II and III is inhomogeneous. The micropylar seed end is the major entry point of water. The micropylar endosperm and the radicle show the highest hydration. Germination of tobacco follows a distinct pattern of events: rupture of the testa is followed by rupture of the endosperm. Abscisic acid (ABA) specifically inhibits endosperm rupture and phase III water uptake, but does not alter the spatial and temporal pattern of phase I and II water uptake. Testa rupture was associated with an increase in water uptake due to initial embryo elongation, which was not inhibited by ABA. Overexpression of beta-1,3-glucanase in the seed-covering layers of transgenic tobacco seeds did not alter the moisture sorption isotherms or the spatial pattern of water uptake during imbibition, but partially reverted the ABA inhibition of phase III water uptake and of endosperm rupture. In vivo (13)C-magic angle spinning NMR spectroscopy showed that seed oil mobilization is not inhibited by ABA. ABA therefore does not inhibit germination by preventing oil mobilization or by decreasing the water-holding capacity of the micropylar endosperm and the radicle. Our results support the proposal that different seed tissues and organs hydrate at different extents and that the micropylar endosperm region of tobacco acts as a water reservoir for the embryo.     

Sense transformation reveals a novel role for class I beta-1, 3-glucanase in tobacco seed germination

'Coat-enhanced' seed dormancy of many dicotyledonous species, including tobacco, is released during after-ripening. Rupture of the endosperm, which is the limiting step in tobacco seed germination, is preceded by induction of class I beta-1,3-glucanase (betaGLU I) in the micropylar endosperm where the radicle will penetrate. Treating after-ripened tobacco seeds with abscisic acid (ABA) delays endosperm rupture and inhibits betaGLU I induction. Sense transformation with a chimeric ABA-inducible betaGLU I transgene resulted in over-expression of betaGLU I in seeds and promoted endosperm rupture of mature seeds and of ABA-treated after-ripened seeds. Taken together, these results provide direct evidence that betaGLU I contributes to endosperm rupture. Over-expression of betaGLU I during germination also replaced the effects of after-ripening on endosperm rupture. This suggests that regulation of betaGLU I by ABA signalling pathways might have a key role in after-ripening.     

外来种无瓣海桑化感作用研究初报*

种子萌发率和胚根长度作为测量指标,以化感效应敏感指数RI为评价指标,研究了无瓣海桑(Sonneratia apetala)各器官的水浸液对海桑(Sonneratia caseolaris)和无瓣海桑种子发芽的影响。结果表明:1)无瓣海桑的各器官水浸液对海桑种子萌发均起抑制作用,高浓度下抑制效应明显;2)不同浓度无瓣海桑根的水浸液对海桑的胚根长均起抑制作用,高浓度下显著抑制,随着浓度降低抑制作用减弱;无瓣海桑的枝、叶和果的水浸液对海桑的胚根长表现为"高抑低促",即高浓度下显著抑制,随着浓度降低抑制作用减弱甚至转为促进;3)无瓣海桑各器官的水浸液对本身种子的发芽表现为"高抑低促";4)无瓣海桑果的水浸液对本身的胚根长表现为高浓度下显著抑制,随着浓度降低抑制作用逐渐减弱;无瓣海桑枝、叶和根的水浸液对本身的胚根长表现为"高抑低促";5)无瓣海桑各器官的水浸液中果的水浸液对海桑或无瓣海桑种子发芽和胚根长的抑制作用最强。