芡个体发育早期的研究

本文研究了芡个体发育的早期, 即心形胚至种苗。心形胚至成熟胚表现为:苗端先发育, 根端弱育;胚芽叶节上的节生根原基先发育, 根端无明显分化。种子胚至种苗表现为:种子萌发时, 下胚轴末端产生多细胞分枝下胚轴毛;种苗形成中, 节生根先发育, 胚根后发育, 且长达1mm左右即停止生长。这些器官发育顺序上的特点在被子植物中是很特殊的, 应该是系统发生上的原始性状。下胚轴毛是水生或湿生被子植物比较普遍的性状, 是区分下胚轴与胚根的指示性状。     

EMBRYOGENESIS AND SEEDLING DEVELOPMENT IN CASSIPOUREA ELLIPTICA (SW.) POIR. (RHIZOPHORACEAE)

Embryogenesis in Cassipourea elliptica (Sw.) Poir, begins with a first division of the zygote which may be oriented transversely, obliquely, or rarely longitudinally. The orientation of the second division is also variable. Though the differentiation of suspensor and embryo proper occurs early, some derivatives of the terminal cell sometimes contribute to the suspensor. Provascular tissue “differentiates” after the initiation of the cotyledons. The radicle apical meristem originates subterminally, 5–10 cell layers from the juncture of the embryo proper and the suspensor. After germination, during early seedling establishment, radicle apical organization is of an unspecialized, columellate type. Vascular differentiation occurs before germination, and there are two loci of initial xylem differentiation: one in the hypocotyl and another in the median trace of the cotyledons. After germination, additional xylem differentiates de novo (without lateral or longitudinal continuity with already-mature vessels) inside the arcs of phloem in the hypocotyl, a pattern reported in few angiosperms. The cotyledonary node is one-trace, unilacunar.     

THE DEVELOPMENT OF THE SEED OF ABUTILON THEOPHRASTI I. OVULE AND EMBRYO

Winter , Dorothy M. (Iowa State U., Ames.) The development of the seed of Abutilon theophrasti. I. Ovule and embryo. Amer. Jour. Bot. 47(1): 8–14. Illus. 1960.—Abutilon theophrasti Medic, is a widespread annual weed which produces an abundance of seed in capsules which mature within 20 days after pollination. Ovule differentiation may be observed at least 8 days before anthesis when a sporogenous cell becomes evident and 2 integuments are initiated. An 8-nucleate embryo sac is produced from the chalazal megaspore approximately 2 days before anthesis. The outer integument of the mature campylotropous ovule consists of 2 cell layers, the inner integument has 6 to 15 cell layers. The initially free-nucleate endosperm becomes cellular betwen 3 and 7 days after pollination. At maturity a thin layer of gelatinous endosperm encases the embryo. The Asterad-type proembryo of Abutilon has a stout suspensor and develops rapidly. Four days after pollination cotyledons are initiated; 4 days later a leaf primordium is evident. Fifteen days after pollination the embryo, which has essentially completed its growth, consists of a large hypocotyl with root promeristem and root cap at its basal end, and 2 flat, folded, leaflike cotyledons enclosing a small epicotyl at its upper end. The epicotyl consists of an embryonic leaf and a stem apex.     

ULTRASTRUCTURE OF THE TRANSFER TISSUES DURING VIVIPAROUS SEEDLING DEVELOPMENT IN RHIZOPHORA MANGLE (RHIZOPHORACEAE)

All water and nutrients required for the growth of the huge viviparous seedlings of Rhizophora mangle must be transported from the inner surface of the integument (maternal tissue), across a layer of persistent endosperm cells (seedling tissue), and to the surface of the cylindrical cotyledonary body. We describe the ultrastructure of these tissues at two functionally different stages of embryo and seedling development (i.e., 2–3 wk and 2–3 mo postgermination, respectively). Integumentary cells adjacent to the endosperm have unique plastids and divide more frequently than cells further away from the endosperm/integument interface. Later, fibrillar inclusions develop in vacuoles of the integument cells. The outermost layer of endosperm cells differentiates into transfer cells with wall ingrowths on the external walls, and the remainder of the endosperm degenerates during the embryo to seedling transition. The wall ingrowths gradually occlude the lumena of the transfer cells, a process which is complete long before the seedling abscises; therefore, the seedling may be photosynthetically independent throughout most of its development. The outer surface of the seedling cotyledonary body is minimally papillate and exhibits several ultrastructural specializations: centripetal degeneration of external walls which are bounded by electron-dense deposits; numerous mitochondria; and plastids of unusual structure with many plastoglobuli, and which contain unique yellow pigments having absorption spectra characteristic of carotenoids. HPLC residence times of these pigments are unlike those of β-carotene or other common carotenoids. Transfer tissues of Rhizophora may have functions not found in other plants, such as salt exclusion and facilitating viviparous germination, but the ultrastuctural correlates of these functions remain uncertain.     

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。     

桃儿七种子解剖结构及其萌发生长期形态特征

为探明种皮和胚乳是否是限制桃儿七种子萌发的主要因素,利用组织切片和显微技术,对桃儿七种子及其不同萌发期（1、7、14、21、28 d）解剖结构和播种后一定时期内（7~210 d）的植株生长形态进行观察。桃儿七种子由种皮、胚乳和胚构成。种皮包括外种皮和内种皮,外种皮致密规整,由外至内分别为栅状石细胞和表皮层细胞,内种皮由5~6层海绵细胞组成。胚乳占种子体积的绝大部分,包括珠孔胚乳和外胚乳。胚由胚根、胚轴和子叶组成,被致密种皮、多层珠孔胚乳和外胚乳包围。萌发期1~7 d胚根和胚轴开始伸长,7~14 d两片子叶分离,14~21 d胚根突破珠孔胚乳和种皮,21~28 d胚根、胚轴和子叶继续扩张伸长。种子播种210 d后可平均形成3片功能真叶和5条不定根。致密种皮（物理休眠）和多层胚乳（机械休眠）是限制桃儿七种子萌发的两个主要因素。     

Structure of the zygotic embryos and seedlings of Butia capitata (Arecaceae)

Butia capitata, an endemic palm of the Brazilian savanna threatened by deforestation, demonstrates low germinability due to seed dormancy. The present study characterizes the structure of the zygotic embryo and describes germination and seedling development. Pyrenes were sown into sandy soil substrates to germinate, and their embryos were also cultivated in vitro in MS medium; structural evaluations were made during their development. Seedling growth through the endocarp germ pore culminates in the protrusion of the cotyledonary petiole, with the root and leaf sheaths subsequently being emitted laterally from its extremity. The embryos are composed of the cotyledon (whose proximal third has a haustorial function) and a diminutive embryo axis that is contained within the cotyledonary petiole. The protoderm, ground meristem, and procambium can be observed in their typical positions in the embryo axis and cotyledon. The development of the vegetative axis could be observed on the second day of in vitro cultivation, with elongation of the embryo axis and the beginning of the differentiation of the first eophyll. Elongation of the cotyledonary petiole and the differentiation of the parenchyma and tracheary elements were observed during the second to fifth day. Although the hypocotyl–radicle axis is less differentiated than the plumule, root protrusion occurs on the eighth day, and the leaf sheaths are only emitted between the twelfth and the sixteenth days; the haustorium atrophied during this stage. The embryonic structure of B. capitata does not impose limitations on seed germination as dormancy is of the non-profound physiological type, and the 50 % elongation of the cotyledonary petiole serves as a morphological indicator of germination.     

长喙毛茛泽泻胚中营养物质的积累与消耗

长喙毛茛泽泻是一种水生濒危植物。它的种子中没有胚乳,营养物质以淀粉和帽白体的形式贮藏在胚中。胚不同部位物质积累情况差异较大,下胚轴和子地细胞中的淀粉,蛋白体数目多,体积大,胚芽和胚根分生细胞中只贮藏有少量的淀粉粒和蛋白体。     

Preliminary Studies of Root-Stem Transition in Brassica napus L.

Seedlings of Brassica napus L. 2–11 days after germination were used. However, the most investigation was concentrated on the 6-day old seedlings. The primary root has a diarch protostele, the two groups of primary phloem alternate with the primary xylem. At higher level, the metaxylem is gradually differentiated in a lateral direction. Being coincident with this changes of the metaxylem, the groups of phloem cell are extended. The stele of the lower hypocotyl is root-like and has no pith. In the middle hypocotyl, there is a further lateral differentiation of the metaxylem. At the higher level, four metaxylem arms appear and the groups of phloem are extended circumferentially to form two crescent shaped sectors. In the upper hypocotyl below 0.2 cm of the cotyledonary node, a central pith has been formed which separates the differentiating primary xylem into two distinct units. At a slightly higher level, each primary phloem divides into two small groups, at this time, each xylem unit and the two adjacent groups of phloem constitute a cotyledonary trace. The foliar traces of the first two foliage leaves appear in the inter-cotyledonary plane between the vascular elements of the cotyledonary traces. At this level, the vascular tissue of the hypocotyl forms a siphonostele made up of two cotyledonary traces and the two foliage leaves, where the root-stem transition has nearly been completed, while the endarch condition is not attained in the hypocotyl. At incresing distances from the cotyledonary node upwards, in the cotyledonary petiole, the protoxylem occupies a more and more adaxial position and the metaxylem a more and more abaxial direction and, thus, the endarch condition is attained. The primary system of the root, hypocotyl, and cotyledons forms a complete circular system, the plumular vascular elements are directly connected by secondary elements formed by the cambium in the region of the hypocotyl. As for the results mentioned above, the authers have not detected that the primary xylem has a rotation of 180˚, as described by Van Tieghem.     

STUDIES ON THE SEED OF BANANA. II. THE ANATOMY AND MORPHOLOGY OF THE SEEDLING OF MUSA BALBISIANA

Mc Gahan , Merritt W. (Central Research Labs., United Fruit Co., Norwood, Massachusetts.) Studies on the seed of banana. II. The anatomy and morphology of the seedling of Musa balbisiana. Amer. Jour. Bot. 48(7): 630–637. Illus. 1961.—The first external evidence of germination of the seed of Musa balbisiana is the displacement of the micropylar plug by the elongation of the hypocotyl-radicle axis. As the hypocotyl and epicotyl emerge from the micropylar collar, the seminal adventitious roots become apparent and the cotyledonary sheath surrounding the epicotyl emerges as a coleoptile-like structure. Subsequent growth results in the elongation of the first leaves beyond the cotyledonary sheath and the rapid elongation of the adventitious root system. The vascular transition occurs between the cotyledon and the radicle. The sheath is considered to be only analogous to the coleoptile of the grasses.     

Reserve mobilization in the Arabidopsis endosperm fuels hypocotyl elongation in the dark, is independent of abscisic acid, and requires PHOSPHOENOLPYRUVATE CARBOXYKINASE1

Arabidopsis thaliana is used as a model system to study triacylglycerol (TAG) accumulation and seed germination in oilseeds. Here, we consider the partitioning of these lipid reserves between embryo and endosperm tissues in the mature seed. The Arabidopsis endosperm accumulates significant quantities of storage lipid, and this is effectively catabolized upon germination. This lipid differs in composition from that in the embryo and has a specific function during germination. Removing the endosperm from the wild-type seeds resulted in a reduction in hypocotyl elongation in the dark, demonstrating a role for endospermic TAG reserves in fueling skotomorphogenesis. Seedlings of two allelic gluconeogenically compromised phosphoenolpyruvate carboxykinase1 (pck1) mutants show a reduction in hypocotyl length in the dark compared with the wild type, but this is not further reduced by removing the endosperm. The short hypocotyl phenotypes were completely reversed by the provision of an exogenous supply of sucrose. The PCK1 gene is expressed in both embryo and endosperm, and the induction of PCK1:beta-glucuronidase at radicle emergence occurs in a robust, wave-like manner around the embryo suggestive of the action of a diffusing signal. Strikingly, the induction of PCK1 promoter reporter constructs and measurements of lipid breakdown demonstrate that whereas lipid mobilization in the embryo is inhibited by abscisic acid (ABA), no effect is seen in the endosperm. This insensitivity of endosperm tissues is not specific to lipid breakdown because hydrolysis of the seed coat cell walls also proceeded in the presence of concentrations of ABA that effectively inhibit radicle emergence. Both processes still required gibberellins, however. These results suggest a model whereby the breakdown of seed carbon reserves is regulated in a tissue-specific manner and shed new light on phytohormonal regulation of the germination process.     

Degradation of the endosperm cell walls of Lactuca sativa L., cv. Grand Rapids

The timing of mobilisation of lipid, sucrose, raffinose and phytate in lettuce seeds (achenes) (cv. Grand Rapids) has been examined. These reserves (33%, 1.5%, 0.7%, 1.4% of achene dry weight, respectively) are stored mostly in the cotyledons. Except for a slight degradation of raffinose and increase in sucrose, there is no detectable reserve mobilisation during germination. The endosperm (8% of seed dry weight), which has thick, mannan-containing cell walls (carbohydrate, 3,4% of seed dry weight), is completely degraded within about 15h following germination. Mannanase activity increases about 100-fold during the same period and arises in all regions of the endosperm. Also during this period sucrose and raffinose are degraded and fructose and glucose accumulate in the embryo. The endosperm hydrolysis products are taken up by the embryo, and are probably used as an additional reserve to support early seedling growth. However, endosperm cell-wall carbohydrates, such as mannose, are not found as free sugars. Lipid and phytate are degraded in a later, second phase of mobilisation. Low levels of sucrose are present in the embryo, mostly in the cotyledons, and large amounts of fractose and glucose (14% of seedling dry weight at 3 days after sowing) accumulate in the hypocotyl and radicle. It is suggested that sucrose, produced in the cotyledons by gluco-neogenesis, is translocated to the axis and converted there to fructose and glucose.     

冠果草种子萌发过程的组织化学动态

冠果草的种子中没有胚乳,营养物质贮藏在胚中,其成分主要是淀粉和蛋白质。胚各部分的物质积累情况差异较大,子叶和下胚轴细胞中的淀粉粒、蛋白体数目多、体积大,胚芽和胚根分生细胞中则只贮藏少量的淀粉粒、蛋白体。在种子萌发过程中,胚各部分的淀粉粒逐渐解体,至二叶幼苗期全部消失。蛋白体的降解有严格顺序,远离胚芽的细胞中蛋白体降解较早,胚芽附近细胞中的降解较晚,而且胚芽细胞中还有新的蛋白体形成。单个蛋白体的降解     

伊贝母种子萌发和籽苗建立

在子叶出土萌发的植物类型中,伊贝母种子萌发过程是罕见的。萌发初期,子叶优先生长。首先伸长而突破种皮,接着长出地面,此后,胚根才开始生长并产生不定根。种子萌发后形成特殊籽苗。在地上部分,子叶变绿,成为第一生长季唯一的同化叶;在地下部分,上胚轴扁平化,芽鳞肉质化,于是形成小鳞茎。籽苗形态属于最简化的类型。伊贝母的籽苗与其营养更新苗相比,是很弱小的。     

Mechanism and control of Genipa americana seed germination

Genipa americana (Rubiaceae) is important for restoration of riparian forest in the Brazilian Cerrado. The objective was to characterize the mechanism and control of germination of G. americana to support uniform seedling production. Morphology and morphometrics of seeds, embryo and endosperm were assessed by light and scanning electron microscopy during germination. Imbibition and germination curves were generated and over the same time interval endosperm digestion and resistance were measured by puncture force analysis and activity assay of endo-β-mannanase (EBM) in water and in abscisic acid (ABA). The gene encoding for EBM was partially cloned and its expression monitored by quantitative real-time-polymerase chain reaction. Embryos displayed growth prior to radicle protrusion. A two-phase increase in EBM activity coincided with the two stages of weakening of the micropylar endosperm. The second stage also coincided with growth of the embryo prior to radicle protrusion. Enzyme activity was initiated in the micropylar endosperm but spread to the lateral endosperm. ABA completely inhibited germination by inhibiting embryo growth, the second stage of weakening and expression of the EBM gene, but EBM activity was not significantly inhibited. This suggests that a specific isoform of the enzyme is involved in endosperm weakening. EBM may cause a general 'softening' of micropylar endosperm cell walls, allowing the embryo to puncture the endosperm as the driving force of the decrease in puncture force.     

SEEDLING MORPHOLOGY IN MARAH (CUCURBITACEAE) RELATED TO THE CALIFORNIAN MEDITERRANEAN CLIMATE

Studies in reproductive ecology were made in indigenous, western American plants in the genus Marah (Cucurbitaceae), with particular attention given plants of M. oreganus occurring in the Berkeley Hills near San Francisco Bay in California. These tuberous perennials produce capsular fruits on their annual aboveground shoots; the fruits dehisce in early summer, each one exposing about three large seeds with an average seed weight of 1.05 g. The embryo of a M. oreganus seed has two thick and fleshy cotyledons packed with protein granules. The embryonic axis, with shoot and root apices, is ca. 0.5-1.0 mm long, roughly ½0 or less the length of the seed. In the Berkeley Hills dispersal of the seeds is accomplished by nocturnal rodents, after which germination begins with the fall rains and cooler temperatures of November and December. Instead of a radicle emerging first from the seed at germination, the minute radicle and epicotyl are pushed or carried far out of the seed, down into the soil, by the elongating bases of the cotyledons. These cotyledon bases, or petioles, are fused, and as they elongate they form a hollow tube that bears the embryonic axis at its extreme tip. The cotyledonary petiole tube ceases elongation by January, when it may be 5-25 or more cm long in a seedling of M. oreganus. Then, from its tip, the radicle grows downward and the epicotyl upward—up the hollow petiole tube. The green shoot (epicotyl) reaches the soil surface by early March in this area, completes the first season's growth, and dries up by late May, when the arid summer season is beginning. But even before the epicotyl grows out of the petiole tube and above ground, the seedling's hypocotyl begins to enlarge, forming a tuber. The fleshy cotyledon blades remain in the seed coat below ground, and some food from the blades is transferred to the tuber that produces shoots in the following growing seasons. This pattern of germination and seedling establishment is now known for species of Marah and for a very few other dicotyledonous plants, all of them growing mainly in areas of hot and dry habitat that are generally referred to as having Mediterranean climate. This elongation of the fused hypogeal cotyledons is considered a complex adaptation in dicotyledons that helps ensure fast and successful seedling establishment in seasonally arid areas such as “Mediterranean” California.     

Germination Preventing Mechanisms in Iris Seeds

The different germination behaviour of the seeds of two irises,Iris lorteti and I. atropurpurea was found to be due to thedifferent mechanical resistance of the integument, at the micropylarend, to radicle protrusion. A pressure of 135 atm was necessaryin l. lorteti seeds for radicle protrusion, while in I. atropurpurea77 atm was sufficient. In contrast Pancratium maritimum requireda pressure of only 10 atm. The outer integument of seeds ofI. lorteti was found to contain a compound which was toxic tothe germinated embryo but did not act as a germination inhibitor.Extracts of the endosperm also had a slight germination inhibitingeffect. An interaction between this weak inhibitor and the effectof the testa could not be ruled out completely. A test assayfor germination using excised embryos was developed. A methodfor germination of Iris seeds, by cutting off the outer integumentat the micropylar end, was developed and is being exploitedcommercially. Iris lorteti, Iris atropurpurea, germination, germination inhibition, embryo culture, seed coat mechanical resistance     

GERMINATION OF LIGHT-INHIBITED SEED OF NEMOPHILA INSIGNIS

Germination of Nemophila insignis seed is inhibited by light over a wide range of temperatures. At low temperatures the light intensity required for inhibition is higher. At 25 C there is little germination (in darkness as well as in light); at 27.5 C germination is inhibited altogether. Virtually complete germination in light is obtained when the endosperm directly covering the radicle is removed. This operation also improves germination in darkness at 25 C. Mechanical scarification performed elsewhere in the seed is without effect. As with Phacelia tanacetifolia, Nemophila seed apparently fails to germinate in light because the endosperm restrains the expansive growth of the embryo. The embryo of dark-imbibed seed develops a force which enables it to overcome the physical resistance of the endosperm. Light inhibits the process which leads to generation of “expansive force.” Gibberellic acid at 5 × 10^–4 m stimulates germination in light and in the dark. Abscisic acid at 10^-4 m inhibits germination; at 10^-6 m it inhibits only root growth. The inhibition of germination or root growth caused by abscisic acid cannot be reversed by gibberellic acid. Eighty per cent oxygen under certain conditions promotes germination. The rate of O₂ uptake is enhanced in oxygen-enriched atmosphere; however, there is no corresponding increase in the rate of CO₂ output. Thus high oxygen tension enhances an oxidative process other than respiration. This reaction is favorable to seed germination.     

Effect of Salicylhydroxamic Acid on Endosperm Strength and Embryo Growth of Lactuca sativa L. cv Waldmann''s Green Seeds

Salicylhydroxamic acid (SHAM) stimulated germination of photosensitive lettuce (Lactuca sativa L. cv Waldmann's Green) seeds in darkness. To determine whether SHAM acts on the embryo or the endosperm, we investigated separately effects of SHAM on growth potential of isolated embryos as well as on endosperm strength. Embryo growth potential was quantified by incubating decoated embryos in various concentrations of osmoticum and measuring subsequent radicle elongation. Growth potential of embryos isolated from seeds pretreated with 4 millimolar SHAM was equal to that of untreated controls. Rupture strength of endosperm tissue excised from seeds pretreated with SHAM was 33% less than that of controls in the micropylar region. To determine if the embryo must be in contact with the endosperm for SHAM to weaken the endosperm, some endosperms were incubated with SHAM only after dissection from seeds. Rupture strength of SHAM-treated, isolated endosperms in the micropylar region was 25% less than that of untreated controls. There was no difference in rupture strength in the cotyledonary region of endosperm isolated from seeds treated with SHAM in buffer or buffer alone. SHAM therefore stimulates germination not by enhancing embryo growth potential, but by weakening the micropylar region of the endosperm enclosing the embryo.