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。     

Host influence on germination and reproduction of the facultative hemi‐parasitic weed Rhamphicarpa fistulosa

Rice Vampireweed, Rhamphicarpa fistulosa, was a minor parasitic weed until recently when rice cultivation in sub‐Saharan Africa was expanded into marginal wetlands, that are the parasite's natural habitat. Unlike most of the parasitic weeds, R. fistulosa is facultative, meaning that the parasite is able to complete its life cycle without a host. However, when not connected to a host plant, its biomass and seed production is lower. Because very little is known regarding the germination ecology of the parasite, the main objective of our study was to identify the cues that favour germination. We hypothesised that, first, being a wetland species, germination of R. fistulosa is stimulated by light and high soil moisture. Second, we hypothesised that if host plant presence increases its reproductive output then a germination stimulatory effect from host presence is likely to have developed. A Petri‐dish and pot experiment showed that light and completely saturated soils were a requirement for germination, demonstrating that germination requirements of R. fistulosa are typical of species that grow in environments with fluctuating water levels. A pot experiment in which five infestation levels of R. fistulosa were installed in the absence and presence of a rice plant, showed that host plant presence resulted in a 3.7 times higher seed production rate and a 15% larger average seed size. Despite this reproductive advantage, a pot experiment with three rice cultivars, selected because of their difference in strigolactone production, showed that host plant presence, regardless of the development stage, did not influence the emergence rate of R. fistulosa. In a follow‐up study, the germination stimulation effect of root exudates collected from the same three rice cultivars and a treatment consisting of an artificial germination stimulant (GR24) was compared with a treatment consisting of plain water. In these treatments, seeds of R. fistulosa were compared with seeds of the obligate parasite Striga hermonthica. Germination of S. hermonthica was strongly advanced by the presence of root exudates and GR24 but was completely absent in water, whereas germination of R. fistulosa in all treatments was similar to that in plain water. The absence of a host recognition mechanism at the germination stage suggests that the regulation of germination through light and soil moisture is near optimal. Our finding might also indicate that for this facultative parasitic plant species, a more opportunistic germination strategy is superior. Implications of the findings for management of R. fistulosa in rice cultivation are discussed.     

<Emphasis Type="Italic">Pityopus californicus</Emphasis>: structural characteristics of seed and seedling development in a myco-heterotrophic species

Pityopus californicus (Eastw.) H. F. Copel., a monotypic member of the Monotropoideae in the family Ericaceae, is a myco-heterotrophic species with distribution limited to the Pacific Northwest of the USA. Young embryos of P. californicus developed mycorrhizal associations in seed packets that had been buried for up to 681 days, suggesting that seeds of P. californicus may require the presence of a fungus to achieve germination. Samples of nongerminated seeds and early stages in embryo and root development were subsequently processed for light microscopy, histochemistry, and transmission electron microscopy (TEM). Nongerminated seeds possessed a thick testa, lacked a shoot and root meristem, and consisted of an embryo with large parenchymatous cells containing protein bodies and starch grains as storage reserves. In the earliest developmental stage (seed coat still attached), fungal hyphae were present on the testa surface and between the testa and embryo. This stage was followed by embryo elongation, the organization of a root apical meristem, and the development of a well-developed fungal mantle surrounding the elongated embryo. At least two morphotypes were identified based on structural characteristics of the mantle. One of these, with ascomycetous septa, had Cenococcum-like features. Late-stage embryo/early root development revealed a typical mantle and Hartig net, with fungal pegs penetrating the outer tangential walls of epidermal cells. Transfer cell-like deposits of wall material, similar to those described in Monotropa spp., enclosed fungal pegs. The development of a Hartig net and fungal pegs suggests that nutrient exchange interfaces are required for seedling development.     

Striga seed-germination activity of root exudates and compounds present in stems of Striga host and nonhost (trap crop) plants is reduced due to root colonization by arbuscular mycorrhizal fungi

Root colonization by arbuscular mycorrhizal (AM) fungi reduces stimulation of seed germination of the plant parasite Striga (Orobanchaceae). This reduction can affect not only host plants for Striga, resulting in a lower parasite incidence, but also false hosts or trap crops, which induce suicidal Striga seed germination, thereby diminishing their effectiveness. In order to better understand these AM-induced effects, we tested the influence of root colonization by different AM fungi on the seed-germination activity of root exudates of the Striga hermonthica nonhost plants cowpea and cotton on S. hermonthica. We also tested the effect of AM fungi on the seed-germination activity of the Striga gesnerioides host plant cowpea on S. gesnerioides. Moreover, we studied whether mycorrhization affects the transport of seed-germination activity to above-ground plant parts. Mycorrhization not only resulted in a lower seed germination of S. gesnerioides in the presence of root exudates of the S. gesnerioides host cowpea but also seed germination of S. hermonthica was also lower in the presence of root exudates of the S. hermonthica nonhosts cowpea and cotton. Downregulation of the Striga seed-germination activity occurs not only in root exudates upon root colonization by different AM fungi but also in the compounds produced by stems. The lowered seed-germination activity does not appear to depend on the presence of seed germination inhibitors in the root exudates of mycorrhizal plants. The implication for Striga control in the field is discussed.     

肉苁蓉寄生生长形态发育

肉苁蓉(Cistanche deserticola)是一种沙生根寄生濒危药用植物。利用光镜和电镜手段, 采用人工培养和诱导等方法详细观察并研究了肉苁蓉寄生生长过程中种子萌发、吸器产生以及植物体形态发育的过程。结果表明: (1)人工可以诱导肉苁蓉的种子萌发。肉苁蓉种胚具有明显的极性, 珠孔端细胞小于合点端, 珠孔端细胞分化、生长并产生白色的类胚根状结构。(2)有些化学物质可以诱导初生吸器的产生。用2, 6二甲氧基-对苯醌培养肉苁蓉24-26小时后, 其先端膨大并产生突起, 形成类似根毛状的结构, 即初生吸器。(3) 肉苁蓉属于主动寄生植物, 其在初生吸器与寄主幼根黏连后产生次生吸器。肉苁蓉与寄主梭梭(Haloxylon ammodendron)共培养, 其初生吸器主动与寄主幼根(0.1 mm左右)黏连, 穿过寄主根表皮和皮层后与维管束连通形成次生吸器, 肉苁蓉植物体分化、发育的基本组织形成。被寄生后的寄主根横向发育加快, 同时肉苁蓉植物体开始分化和发育。(4)肉苁蓉可以寄生在寄主幼根(0.1 mm左右)的任意部位。     

Initiation, Development and Structure of the Primary Haustorim in Striga gesnerioides (Scrophulariaceae)

A light-microscopic study is reported on the initiation, establishmentand structure of the primary haustorium of Striga gesnerioideson the host, cowpea (Vigna unguiculata). The radicular apexof the germinated parasite seed dissolves its way through thehost root cortex to the stele. Thus, it is converted into aprimary haustorium. Some of the haustorial front-line cellsin contact with the host endodermis penetrate into the steleand make contact with the xylem vessels. Differentiation ofthese haustorial cells into xylem vessels occurs and extendsbackwards through the median axial region of the haustorialtract in the host cortex to connect with the conductive xylemof the radicle outside the host root. Subsequently the parasite'splumule develops into a leafy shoot. On penetrating the steleof the host, the haustorium stimulates cell division in thehost pericycle whose triggered proliferation together with expansionof the parasite haustorial tissues result in the formation ofa large, tuberous primary haustorium. At various points of thehost-parasite interface, differentiation of xylem elements occurs,presumably maximizing nutrient transfer from host to parasite.In spite of this, many proliferated host cells at the interfaceremain apparently meristematic showing densely-stained cytoplasmand prominent nuclei.     

Observations on the biology of Boschniakia hookeri (Orobanchaceae)

Observations on Boschniakia hookeri Walp. (Orobanchaceae), a root parasite, have been carried out at locations on the Kitsap Peninsula, Washington State, U.S.A.; Bamfield, British Columbia, Canada; and Sand Lake, Tillamook County, Oregon State, U.S.A. The hosts of B. hookeri , all Ericaceae, identified by excavation of the host root–parasite connection, were Arbutus menziesii Pursh., Gaultheria shallon Pursh., Arctostaphylos uva–ursi (L.) Spreng., and an introduced South American species, Pernettya mucronata Gaud. Seasonal development above ground and recurrence of blooming were monitored. It was shown that the plants are autogamous. Predation plays an important role in the biology of Boschniakia hookeri , including infestation by nematodes, destruction of entire plants by rodents, and attack on the inflorescences by a fly, Pegomya sp. A life history of Boschniakia hookeri was assembled from the data of this study.     

Respiratory Mechanisms and the Changes of Glutathione and Ascorbic Acid in Germinating Peas

The respiration of pea seeds during the early stages of germinationwas studied by manometric methods. From analyses of the germinatingseeds estimates were obtained of the oxidized and reduced formsof glutathione and ascorbic acid. Thus it was possible to explorethe relationship between these oxidation-reduction systems andthe resumption of respiratory activities in the dormant seed. Several lines of evidence indicate that partial anaerobiosisis an important feature of metabolism during the first phasesof germination in air. The intact testa, acting as a barrierto diffusion, limits the uptake of oxygen by the seed. Splittingof the testa by the development of the embryo leads to rapidchanges in the mechanism and rate of respiration. An increase in the relative proportions of the reduced formsof both glutathione and ascorbic acid is associated with theestablishment of anaerobic conditions in the seed. This andother available evidence indicate that the glutathione-ascorbicacid carrier system plays only a minor part in aerobic oxidationsduring the early stages of germination. The possibility thatglutathione has an important influence on the activation ofenzymes in the first phase of germination is briefly considered.     

The effect of cereal growth stages on the reproductive activity of Sitobion avenue and Metopolophium dirhodum

Apterous Sitobion avenae on oats were found to have a higher reproductive rate on the ears (5–95 nymphs per day) than on young leaves (3–78 nymphs per day), mature leaves (2–17 nymphs per day) or senescent leaves (2–08 nymphs per day). At each growth stage of the the host plant large aphids gave birth to more young than small aphids, but aphids of the same weight on different growth stages of the host plant had different reproductive rates. On wheat in the field S. avenae gave birth to more young on the ears but less on the leaves than Metopolophium dirhodum on the leaves.
The suitability of ears to S. avenae changed through the flowering and ripening stages. During the latter part of the milky-ripe stage the reproductive rate of S. avenae declined and its mortality increased. The consequences of the variations in reproduction and mortality are discussed in relation to the life history and population dynamics of S. avenae and the assessment of cereal varieties for aphid resistance.     

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     

Seed Germination and Seedling Growth in Sopubia delphinifolia - a Hemi-root Parasite: Germination Requirements

Requirements for seed germination (emergence of radicle) andseedling formation (emergence of both radicle and cotyledons)of a hemi-root parasite Sopubia delphinifolia were studied inthe absence of any host stimulus, in Petri dish and asepticcultures. Both water washing in trickling tap water as wellas cold treatment were effective in inducing/stimulating germinationand seedling formation in the light. Although ethrel, an ethylenereleasing compound, stimulated radicle emergence it inhibitedthe emergence of the cotyledons. Light was found to be essentialfor germination; none of the growth substances could replacethe light requirement. Light responses seem to be mediated throughthe phytochrome system. The results indicate that the emergenceof the radicle, its further growth into the root and the emergenceof cotyledons are controlled by different factors. Sopubia delphinifolia, hemi-root parasite, seed germination requirements, pretreatment, seedling formation     

掌叶木种皮障碍及种子各部位内源抑制活性的研究

掌叶木(Handeliodendron bodinieri)是残遗于中国的稀有单种属植物,因人为破坏、生境特殊及自身特性的影响,资源稀少,被列为国家一级重点保护野生珍稀濒危植物。该研究以掌叶木种子为材料,研究了4种不同发芽条件下(带种皮、浓硫酸处理种皮、完全去除种皮、仅露出胚根)种子萌发性、种皮透水性、掌叶木果皮、假种皮、种皮和种仁四个部位不同浓度甲醇浸提物(0、3.125、6.25、12.5、25 mg/m L)对白菜种子萌发及幼苗生长的影响以及掌叶木各部位浸提物对种子萌发的影响。结果表明:(1)掌叶木种皮具有一定的透水性,为掌叶木种子的萌发提供必要的透水透气条件,不影响种子萌发前的水分吸收,但掌叶木种皮的机械阻碍、易霉变对种子的萌发影响较大。(2)掌叶木的果皮、假种皮、种皮和种仁甲醇浸提物对白菜种子的萌发和生长都有影响,尤其对白菜幼根的生长有较强的抑制作用,抑制强度依次是种仁果皮假种皮种皮,且随着浓度的升高,抑制作用增强。该研究结果揭示了掌叶木种子难发芽、发芽率低的原因,为掌叶木的人工扩繁和保护与利用奠定了基础。     

新疆干旱区植物藜的种子异型性及其萌发机理

新疆干旱区分布的植物藜(Chenopodium album)的种子有黑色和褐色两种类型。对藜的异型性种子从形态结构、不同环境因素及激素或化学物质对萌发的影响以及同工酶谱等方面进行了研究,并对其萌发及适应异质环境的机理进行了讨论。结果表明:(1)藜的异型性种子在形态结构、萌发休眠特性等方面都存在明显差异:黑色种子种皮厚且硬,休眠,萌发慢,萌发率低;褐色种子种皮薄而软,不休眠,萌发快且萌发率高;(2)黑色种子的休眠可通过切除胚根外缘种皮得以完全解除;(3)赤霉素、乙烯利对黑色种子的萌发无明显促进作用;KNO3可较显著促进黑色种子的萌发;协同使用乙烯利和KNO3时,可显著提高黑种子萌发率,完全打破休眠;(4)黑色种子和褐色种子的酯酶、过氧化物酶及过氧化氢酶同工酶谱带存在差异;(5)黑色种子的萌发需要光照,而褐色种子则对光不敏感;低温贮藏对二者的萌发均无显著影响,尽管黑色种子的萌发率有波动。研究结果初步显示黑色种子的休眠是内源(胚)和外源(种皮)因素共同所致。藜的种子异型性及其萌发机理的形成是其对新疆干旱区异质化环境的高度适应。     

Primi Processi di Germinazione in Pinus Pinea L. var. Fragilis Du Hamel

Abstract

Early stages of germination in PINUS PINEA L. var. FRAGILIS Du Hamel. — The main stages of the hydration process preceeding germination and accompaning root elongation have been observed in Pinus pinea L. seeds, by means of vital colours (Congo red, neutral red, acid fuchsine).

The results are as follows:

a) water penetrates easily through the outer shell of the seed reaching its deepest layer which is less permeable to water. Two or three days were required in our experience for water could overcome this barrier.

b) The inner shell (known as « soft shell ») is almost water-proof and seems to draw water towards the micropilar pole of the seed, so that the first region of the seed which sucks up water is the micropile.

c) Through the micropile water enters the seed and imbibes the column, the pericolumn and the endosperm cells.

The endosperm swells with water until the seed shell blows up, because of the inside pressure. At this time water freely penetrates the seed everywhere.

In natural conditions we may infer that the first tissues which take contact with the soil water are the column and pericolumn. As a certain amount of time is required for penetration of water as far as the column (two or three days in experience conditions) germination starts only after a given amount of water is available in the soil for a certain period of time.

When seed hydration is performed the embryo root starts elongating and gets out of the seed.

The behaviour of the column, the pericolumn and the root cap during the early stages of germination are dexcribed.     

The physiological basis of seed dormancy in Avena fatua. VIII. Action of malonic acid

Adkins, S. W., Symons, S. J. and Simpson, G. M. 1988. The physiological basis of seed dormancy in Avena fatua . VIII. Action of malonic acid - Physiol. Plant, 72: 477–482.
A low concentration of malonic acid (50 m M ) induced germination in four genetically pure dormant lines of Avena fatua L. Sensitivity to this treatment was poor immediately after harvest but increased markedly during after-ripening, indicating that the mode of action of malonic acid (50 m M ) was similar to that of another organic acid, citric acid. Over the concentration range (10–50 m M ) where malonic acid promoted germination, oxygen uptake was also stimulated, and this was before the first visible signs of germination. At higher concentrations (100–300 m M ) where there was no promotion of germination, malonic acid strongly inhibited oxygen uptake. These results show that malonic acid has a dual effect on oxygen uptake and subsequent germination. Low concentrations (10–50 m M ) act by stimulating the Krebs cycle and germination through an acidification reaction like citric acid, and high concentrations (100–300 m M ) act by inhibiting germination through enzymatic restraint of the Krebs cycle.
The stimulation of both oxygen uptake and germination by three established germination promoters (sodium nitrate, citric acid and ethanol) was inhibited by a high concentration of malonic acid (200 m M ) but unaffected by a low concentration (50 m M ). These results show that oxygen uptake, and hence the activity of the Krebs cycle, are important processes involved in the dormancy breaking mechanism of these three promotors.     

红松种子休眠与种皮的关系

本文探讨红松(Pinus koraiensis)种子休眠与其种皮之间的关系。夹破中种皮后,种子萌发率很低。在离体胚培养基中外加 ABA 及经 ABA 溶液浸泡种子的萌发实验表明,ABA也不是导致休眠的关键因素。试验确认红松种子存在透气障碍,即中、内种皮对氧气的进入都有阻碍作用。经低温砂藏后,种皮的阻碍作用明显减小。种皮的透气性障碍可能是诱导休限的主导因素。     

Seed dormancy patterns in Epipactis palustris (Orchidaceae): Requirements for germination and establishment of mycorrhiza

Some terrestrial orchid species, including Epipactis palustris (L.) Crantz, are considered extremely difficult to germinate and cultivate in vitro. Observations of orchids germinating in nature are very few, and the timing and requirements for seedling establishment are unknown for most species. Seeds of E. palustris were incubated in vitro with an appropriate fungus, but germination was poor unless several other conditions were also met: scarification of the testa in Ca(OCL)₂, an initial incubation for several weeks at 27°C, and a subsequent cold stratification for 8–12 weeks at 4–8°C, With these pretreatments, germnation responses exceeded 50% after incubation for 4 weeks at 20°C. Healthy protocorms with normal organ development were only produced by symbiotic culture following this lengthy seed preparation. The findings suggest that under natural conditions the seeds need some after-ripening, and the testa needs to be partially decomposed before germination. The requirement for chilling suggests that germination of seeds in situ occurs in spring.     

Activity of secreted cell wall-modifying enzymes and expression of peroxidase-encoding gene following germination of <Emphasis Type="Italic">Orobanche ramosa</Emphasis>

Radicle growth of germinated seed of the root parasite O. ramosa is shown to be rapidly accompanied by secretion of proteins including pectinolytic enzymes, polygalacturonase and rhamnogalacturonase. These secretions peaked between 4 to 8 d after induction of germination and remained constant for some further days in the case of polygalacturonases. After 6 d, germinated seeds secreted proteins which exhibit peroxidase activity. The latter may be correlated with expression of OrPOX1, a putative gene encoding for secreted peroxidase. The involvement of these enzymes in host root attack and haustorium formation by the parasite is discussed.     

蔷薇种子的休眠及解除方法

分析了蔷薇(Rosa L.)种子休眠原因、解除休眠方法以及环境条件对休眠与萌发的影响.蔷薇种子休眠的主要原因有瘦果果皮和种皮的限制作用,胚生理休眠以及果肉、瘦果果皮、种皮和胚中的抑制物质.解除休眠的方法包括去除瘦果果皮限制、解除胚的生理休眠、去除抑制物质等.种子发育过程中及成熟后,环境因子,如温度、水分和光照,对种子休眠和萌发有影响.此外,微生物、果实采集时间也对种子休眠及萌发有较大影响.蔷薇种子的休眠机制复杂,且种间差异很大.