Embryo and Endosperm Function and Failure inSolanumSpecies and Hybrids

Although the importance of the endosperm as a food store inmany angiosperm seeds is well known, its significance duringearly embryogenesis has been neglected. In many interspecifichybrids, and in some other situations, embryos do not developfully and abort. It has often been stated that this is causedby the endosperm failing to conduct sufficient nutrients tothe embryo, but seldom has it been suggested that the endospermactively controls most of the early stages of morphogenesisof the embryo. Information gleaned from a broad survey of theliterature, combined with additional evidence presented here,obtained fromSolanum incanumand interspecific hybrids, indicatethat the endosperm is dynamic and very active in regulatingearly embryo development. This requires highly integrated geneticcontrol of rapidly changing metabolism in the endosperm. Ininterspecific hybrids, lack of coordination may cause unbalancedproduction of growth regulating substances by the endospermand hence abortion of the embryo, or even unregulated productionof nucleases and proteases resulting firstly in autolysis ofthe endosperm and then digestion of the embryo. The endospermmay thus serve to detect inappropriate hybridization of speciesor ploidy levels and so prevent waste of resources by producingseeds that would result in sterile hybrids or unthrifty subsequentgenerations. This discriminatory function of the endosperm hasdiminished during evolution and domestication of the crop plantSolanummelongenaL.Copyright 1998 Annals of Botany Company Solanum, embryo morphogenesis, endosperm, hybrid, seed development.     

The Methylation Cycle and its Possible Functions in Barley Endosperm Development

Barley endosperm development can be subdivided into the pre-storage, intermediate, storage and desiccation phase. Nothing is known about DNA methylation events involved in different endosperm-specific developmental programmes. A complete set of methylation cycle enzyme genes was identified and investigated by mRNA expression analysis. During the pre-storage phase, methionine synthase and S-adenosylmethionine (AdoMet) synthase genes are expressed at high levels, mainly to produce AdoMet, which might be used for methylation processes as indicated by high expression of methyltransferases HvMET1, HvCMT1 and HvDnmt3-1 as well as AdoHcy hydrolase genes. The methyltransferases, core histones and DNA-unwinding ATPases are co-expressed at the mRNA level. On the contrary, storage protein (prolamin) gene expression is repressed due to CpG methylation. Expression of genes responsible for starch biosynthesis is also developmentally regulated but not methylation-dependent. Thus, during pre-storage phase, activity of HvMET1 and HvCMT1 possibly maintains DNA replication and suppresses specific pathways of maturation. Besides, HvDnmt3-1 might be responsible for differentiation-specific de novo methylation. Expression of methyltransferases HvDnmt3-2 and HvCMT2 peaks during the onset of massive starch accumulation. The enzymes are likely responsible for DNA methylation involved in determining plastid division and amyloplast differentiation as concluded from the patterns of co-expressed genes. Levels of AdoMet decarboxylase mRNA, but not methyltransferase- and AdoHcy mRNA, increase at the beginning of desiccation together with methionine synthase and AdoMet synthase levels. This increase may be indicative for utilization of AdoMet in polyamine production protecting aleuron and embryo cell membranes during desiccation.     

Embryo and Endosperm Metabolism of Barley Seeds during Early Germination

Embryos detached from germinating barley seeds were immersedin tritiated water or solutions containing ¹⁴C-labelled compounds.Amino acids rapidly became radioactive and later acids of theKrebs cycle. Labelled alanine did not give rise to radioactivesucrose.     

The Relationship between Embryo and Endosperm in Interspecific Hybrids in PennisetumL. Rich

In the interspecific cross [diploid Pennisetum typhoides X hexaploid(P. typhoides X P. purpureum)] X diploid P. typhoides, embryosand endosperms in the same ovule may respond differently totreatment with the growth substance gibberellic acid, as maydo different genotypes. Size of embryo and size of its endospermare positively correlated in some genotypes but not in others.Large fully developed normal embryos may be associated withnormal, retarded, degenerate or even no endosperm at all. Conversely,large normal endosperms, even in mature seeds, may contain large,small, or no embryos. Fully developed embryos may be viableregardless of whether they had been associated with normal,retarded or degenerate endosperm, or even no endosperm at all. It is concluded that the embryo is not always dependent on theendosperm during its early development and that a degeneratingendosperm need not have a detrimental effect on the developmentof its embryo or on the viability of the latter.     

Influence of Irradiated Pollen on Embryo and Endosperm Development in Kiwifruit

Development of seeds following pollination with irradiated pollenwas studied inActinidia deliciosa(kiwifruit) ‘Hayward’.Pollinations were carried out using two different sources ofpollen (‘Tomuri’ and ‘Matua’) irradiatedwith gamma rays at doses of 700 and 900 Gy. Non-irradiated crosseswere used as controls. Pollen irradiation had little effectonin vitropollen germination. Irradiated pollen affected seedset and seed content, and induced the formation of parthenogeneticembryos. In comparison to the control, the embryo growth ratewas slower and the endosperm contained very low amounts of storageproducts. Seed set was significantly reduced following bothdoses of irradiation. Two types of seeds were observed: (1)seeds with endosperm only; and (2) seeds with both embryo andendosperm. The proportion of seeds containing endosperm onlywas almost ten-fold higher than those containing both embryoand endosperm. Embryo production by gamma-irradiated pollenwas genotype- and dose-dependent. The induction of parthenogenesiswas higher following gamma ray doses of 900 Gy than 700 Gy,which suggests the ‘Hertwig Effect’; the best efficiencywas obtained with ‘Tomuri’ pollen. Ploidy levelof parthenogenetic embryos was evaluated by nuclear size (area)with the use of image analysis. There was a large differencein embryo nuclei size between control and parthenogenetic embryos(mean size 90.8 and 49.1 µm², respectively). It is concludedthat parthenogenetic embryos represent trihaploids.Copyright1998 Annals of Botany Company. Actinidia deliciosa, kiwifruit, pollen irradiation, induced parthenogenesis.     

水稻胚与胚乳分化发育中的内源多胺

稻胚发育过程中,其内源多胺以腐胺、亚精胺为主。在幼胚分化期,腐胺和亚精胺的含量很高;幼胚分化完成时,其含量急剧下降;直至分化后期才趋稳定。在胚及胚乳发育时期,还出现一种未知多胺X_(22),其含量除在胚分化完成时较少外,在胚发育的其他各期中,含量则一直很高。DNA和蛋白质含量的变化,从分化期开始递增直至物质积累成熟期,其趋势均相同。多胺可能参与胚与胚乳中核酸和蛋白质合成的调节。     

Endosperm and Embryo Development in Daucus carota L.

Maximum carrot seed dry weight and maximum endosperm volumewere reached about 35 d after anthesis, although at this timethe endosperm was still soft, the pericarp green and less than50% of the seeds were viable. Fully viable, ripe seeds werenot produced until 44 d later. Seventy per cent of the increasein endosperm volume was due to an increase in cell number, whichceased 35 d after anthesis. The increase in embryo volume wasslower and was due to an increase in both cell number and cellvolume which continued until 49 d after anthesis. At maturitythe embryo was the equivalent of between 2% and 3% of the endospermvolume. The relationship between embryo length and cell number per embryowas unaffected by seed crop plant density, seed crop harvestdate and position of the seed on the mother plant but it wasaffected by the year of seed production, possibly due to differencesin temperature during the period of seed growth. Key words: Endosperm, Embryo, Carrot, Development     

The Development of Embryo and Endosperm of Nelumbo nucifera Gaertn

The development of the embryo and endosperm of Nelumbo nucifera Gaertn can be summarized as follows: 1. Embryogenesis of N. nucifera belongs to Solanad type; the 1st mitotic division of the zygote takes place later than that of the primary endosperm nucleus. 2. The development of endosperm basically conforms to the Helobial endosperm. After fertilization, the primary endosperm nucleus divides first transversely. This division results in the formation of two cells. The wall of this division is a little oblique to the longitudinal axis of the embryo sac. In accordance with the character of the endospermic development, it can be divided into, three stages: (1) two-celled endosperm stage, (2) multicellular endosperm stage, and (3) the stage of the endospermic nutrition being absorbed and cells atrophy. The developments of the embryo and endosperm are well correlated. This relation is relatively stable. 3. The cotyledons of the mature embryo are comparatively developed, but the radicle is extremely reduced. 4. As the seed is ripening, a thin membrane remains outside the plumule, which is the remainder of the endosperm. Therefore, the seed of N. nucifera is exalbuminous.     

The Early Development of Embryo and Endosperm of Paeonia lactifiora

The present paper reports the early development of embryo and endosperm of Paeonia lactiflora. The main conclusions are as follows: 1 The zygote nucleus divides directly to form a coenocytic proembryo with different number of free nuclei. The result confirms the conclusion of Yakovlev[6] as well as Yakovlev and Yoffe[7] On the occurnce of coenocytic proembryo in Paeonia suffruticosa Andr. (P. moutan Sims), P. albiflora Pall. (P. lactiflora Pall), P. officinalis L., P. tenuifolia L., P. anomala L., P. veitchii Lynch (P. beresowskii Komarov), P. wittmanniana, also it agrees with the report of Cave et al.[4] on the occurence of the coenocytie proembryo in Paeonia californica and P. brownii. From the result of our investigation, there is no basis to support Murgai's conclusion obtained in certain species of Paeonia, i.e., the first division of zygote nucleus is accompanied by wall formation and the coenocyte is a suspensor. The primary endosperm nucleus of P. lactiflora divides often earlier than zygote nucleus, or almost at the same time or later in a few cases; 2 Both mitosis and amitosis occur in the free nuclei in the coenocytic proembryo, and mitosis is dominant. In the later stage of development the amitosis occurs at the micropylar region of the coenocytic proembryo, in the free nuclear endosperm at the chalazal region and the appressed part of the chalazal end of the coenocytic proembryo. In addition, in the region of conenocytic proembryo and endosperm polyploid nuclei, irregular nuclei are also frequently met with; 3 Cell wall formation in the coenocyte and the endosperm initiates by means of both cell plate and freely growthing walls, but in the coenocyte wall formation is earlier than in the free nuclear endosperm. At first, wall formation of the coenocytic proembryo begins at the chalazal end, and then extends toward the micropylar region, and in endosperm it begins at the part appressed to the part of the chalazal end of coenocytic proembryo, and then extends toward the chalazal end. We support Cave’s suggestion of the parallel evolution for Paeonia possessed the coenocytic proembryo has no relation to the coenocytic proembryo of the gymnosperms. Further we consider the evolution tendency of the coenocytic proembryo of Paeonia toward a functional specialization.     

The Development and Abnormality of Embryo and Endosperm in Trigrain Wheat

The development processes of embryos and endosperm of trigrain wheat were observed by using paraffin section method and intact dissection. The results were as follows: 1. Fertilization: the development and progression of embryo and endosperm were similar to those as common wheat. 2. The grain come from the primary pistil embryo developed more early among the three-grains. 3. Many abnormal structures, such as Conversion of position between the top and base, back and belly of embryos, horizontal embryos, embryos moved on top, polyembryony and endosperm deficiency etc, appeared in additional pistils. All abnormalities accounted for 88 percent in whole additional pistils.     

Studies on the Development of the Embryo and Endosperm of Nitraria sibirica Pall

The pollen tube enters the embryo sac through the crassinucellus at the micropylar end, and brings about the porogamy. The embryogeny corresponds to the Solanad type. The defference of the suspensor structure is notable by comparing it with the other genera of Zygophyllaceae that have been studied. The endosperm is of the Nuclear type. Mitosis is the main form of the free endosperm nuclei proliferation. No cell plates develop in the early free nuclear division, however, they appear in late development, without developing into the cell wall and disappear ultimately. At the late globular embryo stage, cell formation in endosperm starts first from the micropylar end. The first anticlinal walls develop from the cell plate that is initiated from tile phragmoplast as a result of normal cytokinesis. Follwing this a wall begins to grow from the base of the cell plates, the outer growing margin soon fuses with the wall of the central cell, and the inner growing margin continues to grow towards the central vacuole. The growing walls branch and eventually fuse on the side nearest the central vacuole. Thus, the first periclinal walls are initiated, and a complete endosperm cell is formed. Along with the development of embryo, cell is gradually formed in the endosperm from the micropylar end towards the chalazal end, but the chalazal endosperm is still coenocytic until the endosperm disintegrate completely. The mature seed has no endosperm.     

狭叶柴胡胚及胚乳发育的研究

利用石蜡切片以及半薄切片法对狭叶柴胡的胚及胚乳的发育进行了研究,并对采收期果实中胚的发育情况进行了统计。结果表明:(1)狭叶柴胡胚的发育属于茄型;胚乳核的发育早于合子的分裂,胚乳的发育属于核型。(2)于采收期对狭叶柴胡果实的胚发育阶段观察发现,狭叶柴胡采收期有26%的果实处于球形胚时期,29.6%的果实处于早期心形胚时期,37.4%的果实处于后期心形胚时期,仅有7%果实处于鱼雷胚时期,所有被检测的果实中未发现有双子叶时期胚出现。研究表明,狭叶柴胡采收期果实存在严重的形态后熟现象,是导致在其栽培过程中出现发芽率低和出苗不整齐现象的主要原因。     

小麦×大麦胚胎发育的研究——Ⅰ.小麦×大麦胚和胚乳发育的观察

本试验以206小麦为母本,二棱大麦旱燕3号和六棱大麦原早1号为父本进进杂交。结果表明,两个组合早期的胚胎发育基本上是正常的,前者成胚率为8.75%,后者为16.8%。胚乳核最早于授粉后3天开始形成细胞。当胚乳细胞充满囊后,很快就转入迅速解体,胚随即停止生长,没有能够进一步分化出器官来。胚乳于授粉15天后,几乎全部败育,胚亦相继夭亡。胚胎发育过程中的不正常现象普遍存在。主要是极核受精过程遭受破坏;合子和初生胚乳核发育停滞;原胚虽能正常发育而胚乳没有形成;胚乳细胞过早形成和迅速解体等。讨论了杂交不孕和胚乳败育的原因。同时,提出了幼胚离体培养的适宜时间。     

壶瓶碎米荠(Cardamine Hupingshanesis)胚和胚乳发育的研究

壶瓶碎米荠（Cardamine Hupingshanesis.）是十字花科中以营养体繁殖的多年生植物,在自然条件下,种子不易萌芽成苗。本文以碎米荠、油菜为对照材料对壶瓶碎米荠的胚胎发育进行了观察。壶瓶碎米荠胚发育经球形胚、心形胚、鱼雷形胚和子叶胚四个时期,属柳叶菜型。胚乳发育属核型发育类型,其胚胎发育过程和成熟胚结构与节状聚积和胚乳吸器,而壶瓶碎米荠和碎米荠无此类结构。通过胚胎发育观察证明,壶瓶碎米荠种胚结构完整,其种子不易萌发成苗可能与其特殊的生理原因有关。     

胚和胚乳基因效应对水稻幼苗生物量的影响研究

本文利用和胚乳遗传模型[研究了水稻早期胚后生长生物量性状的遗传控制,结果表明：在两个时期水稻幼苗生物量性状中,除了第16天时根鲜重（RFW）主要受到胚乳显性效应控制外,叶鲜重（LFW）,叶干重（LDW）,根干重（RDW）主要受到胚基因显性效应和胚乳基因加性效应的控制,胚加性和乳乳加性效应占总遗传方差的40－54％,说明对生物量性状进行早期选择有效,各个性状都检测到显著的胚狭义遗传率和胚乳狭义遗传率,说明在早期世代即可估计选择进程,对亲本的遗传效应值的预测表明,对根部性状的选择在第8天进行比较合适,并以亲本P1,P3和P6较好,它们既可提高RFW又可提高RDW,而对地上部分性状的选择在第16天时进行比较合适,并以P4,P9和P10为最好。     

星星草受精作用及其胚与胚乳早期发育的观察

利用常规石蜡切片法对星星草[Puccinellia tenuiflora(Griseb．)Scribn．et Merr．]受精过程及胚与胚乳的早期发育进行了观察,主要结论如下：(1)开花后2h,花粉管破坏1个助细胞,释放2个精子,精子呈逗点状。(2)开花后2～3h,2个精子分别移向卵细胞与极核。(3)开花后3～5h,精核分别贴附于卵细胞与极核的核膜上。(4)开花后5～10h,精核与卵核融合,雄性核仁出现,合子形成。(5)开花后5～6h,精核与极核融合,并出现雄性核仁,形成初生胚乳核,精核与极核的融合比与卵核融合要快。(6)开花后20h左右,合子分裂。(7)开花后8h,初生胚乳核。