Ovule Fertilization and Seed Number per Pod Determination in Oil Seed Rape (Brassica napus)

Ovule fertilization in relation to seed number determinationin spring rapeseed, Brassica napus var. Maris Haplana, was investigated.Failure of fertilization was found to be the major factor limitingthe number of seeds per pod in both the basally and apicallylocated pods on the terminal inflorescence. Sufficient pollengermination on a stigma did not guarantee full seed set andeven when pollen tubes were present at the micropyle regions,ovules were not penetrated. Some seeds aborted: in some, triplefusion did not take place while other seeds were small and deemedat disadvantage to compete for available nutrients. Brassica napus, fertilization, ovules, seeds     

INVESTIGATIONS OF NORTH AMERICAN CYCADEOIDS: WELTRICHIA AND WILLIAMSONIA FROM THE JURASSIC OF OAXACA,MEXICO

Specimens of cones of members of the family Williamsoniaceae, order Cycadeoidales, from Jurassic deposits of Oaxaca, Mexico, demonstrate the first bona fide evidence of the pollenbearing Weltrichia from the Mexican Jurassic as well as provide new information on ovulebearing Williamsonia.     

On the Structure of the Seeds of Williamsonia Collected from the Middle Jurassic Rocks of Amarjola in the Rajmahal Hills, India

Seeds of Williamsonia collected from Amarjola in the RajmahalHills, Bihar, are described. Mature seeds are found in ripe,naked, bractless fructifications. Seeds are oblong or ovate,stalked, dicotyledonous, partially endospermic, and have longmicropyles. The seed coat is differentiated into an outer coveringof tubular cells, middle parenchymatous true integument, andan inner vascularized layer which forms after fertilizationand as a result of modification of the peripheral portion ofnucellus.     

Pollen Viability and Pollen-tube Growth Following Controlled Pollination and their Relation to Low Fruit Production in Teak (Tectona grandisLinn. f.)

Pollen released at 1100 h has the highest viability (92.2%)but is no longer viable 3 d (84 h) after anthesis.In vitropollen-tubegrowth is fast (140 µm h^-1) and increases significantlywithin the first 8 h.In vivopollen tubes also grow quickly andreach the base of the style within 2 h after pollination andenter the micropyle 8 h after pollination. There is no significantdifference between self- and cross-pollination in either therate and the number of pollen tubes in the pistil and the numberof ovules penetrated by a pollen tube. Teak has late-actinggametophytic self-incompatibility; the majority of pollen tubesgrow through the style but some do not continue to grow fromthe style towards the embryo sacs. Pollen-tube abnormalitiesinclude swollen, reversed, forked and tapered tips and irregularand spiralling tubes. These are most prevalent in self-pollination(20.4%). The index of self-incompatibility of 0.17 and low fruitset following self-pollination (2.49%) indicates that teak ismostly self-incompatible. Drastic fruit abortion occurs withinthe first week following controlled pollination. Within 14 d,fruit size and fruit set from cross-pollination is generallymuch greater than from self-pollination. Tectona grandis; pollen viability; pollen-tube growth; pollination; controlled pollinations; incompatibility.     

Haustorial Role of Pollen Tubes

In angiosperms, the pollen tube is siphonogamous and its mainfunction is to carry the male gametes for double fertilization.In some taxa, as in Cucurbitaceae, the tube branches after enteringthe ovule, prior to fertilization. The tube may even swell andform a bulla. During post-fertilization development of the ovule,a portion of the tube may persist in the micropyle, or in theembryo sac, or in both, sometimes even in the micropyle of themature seed. Haustorial function has been presumed in a numberof taxa. In Grevillea, following fertilization, the pollen tube branchesat the micropyle, and the branches grow intercellularly intothe ovarian tissue where further branching occurs. A haustorialrole of the pollen tube is presumed from circumstantial evidence.In gymnosperms (for example, Cycas, Zamia and Ginkgo) the pollentube is nonsiphonogamous, arises from the distal (upper) poleof pollen grain, and grows laterally in the apical region ofthe nucellus. The tube branches in Cycas and Ginkgo but remainsunbranched in Zamia. These pollen tube branches are enucleate,and are not concerned with the transport of male gametes forfertilization. However, the haustorial role has been well documented.In Podocarpus, the pollen tube is siphonogamous and arises fromthe proximal (lower) pole of pollen grain. After traversingthe nucellus, the tube forms a bulla at the point of contactwith the female gametophyte, and several branches originatefrom the bulla. The pollen tube branches grow along the innersurface of the nucellus and the outer surface of the femalegametophyte. The haustorial role of the pollen tube branchesis uncertain. Procedures for convincingly demonstrating thehaustorial role of pollen tubes are discussed. Angiosperms, gymnosperms, pollen tube, bulla, fertilization, haustorial role     

Pistil Exudate Production and Pollen Tube Growth in Lilium longiflorum Thunb.

Exudate production in the pistil of Lilium longiflorum was studiedin relation to pollen tube growth, using scanning electron microscopy(SEM), transmission electron microscopy and light microscopy.In contrast with conventional fixation for SEM, during whichthe exudate of L. longiflorum largely washes away, the exudateremains present through freezing in case of cryo-SEM. Usingthe latter method we observed that exudate production on thestigma and in the style started before anthesis. Just underneaththe stigma the exudate was first accumulated at the top of eachsecretory cell, followed by a merging of those accumulationsas exudate production proceeded. Exudate is also produced bythe placenta. It was however not possible to determine whetherany of this fluid originated from the micropyle. Apart fromthe cell shape and the cuticle present in between the secretorycells, the ultrastructure of the secretory cells covering theplacenta was comparable to those of the stylar canal. The transferwall of the secretory cells of the placenta originated fromfusing Golgi vesicles but the endoplasmic reticulum seemed tohave an important role as well. After pollination the pollen tubes grew across the stigma andentered the style through one of the slits in the three stigmalobes. The pollen tubes grew straight downward through the styleand were covered by exudate. As the pollen tubes approachedthe ovary their growth was restricted to the areas with secretorycells. In the cavity the pollen tubes formed a bundle and theybent from this bundle in between the ovules towards the micropylarside. There they bent again to stay close to the secretory cells.After bud pollination the pollen tube growth was retarded. Laterarriving pollen tubes had a tendency to grow close to the secretorycells of the style, which resulted in a growth between thesecells and preceding pollen tubes. If there was still a littleexudate produced, it resulted in a lifting up of the pollentubes, out of the exudate. The relationship between exudateproduction and pollen tube growth is discussed. Both the speedand the guidance of the pollen tube seemed determined by theproperties of the exudate.Copyright 1994, 1999 Academic Press Cryo-scanning electron microscopy, exudate, Lilium longiflorum, lily, ovary, pollination, pollen tube growth, secretory cell, stigma, style     

Micropylar exudates in Douglas fir – timing and volume of production

 In Pseudotsuga menziesii, a secretion fills the micropylar canal about 7 weeks postpollination until fertilization. Micropylar volumes were measured and found to show variation. Dissection of the ovuliferous scales caused excess fluid to be exuded from the micropylar canal, forming a drop at the tip of the micropyle. This drop was collected, and its production quantified in three trees. Volume and percentage of ovules with drops were greatest when the archegonia in the female gametophyte were at central cell and/or egg cell stage. The volume of exuded drops far exceeded that of the micropyle. Production of subsequent drops by the ovules further confirms that the fluid is actively produced upon dissection Received: 19 September 1998 / Revision accepted: 26 October 1998     

Floral development of Phyllanthus chekiangensis (Phyllanthaceae), with special reference to androecium and gynoecium

The floral development of Phyllanthus chekiangensis has been studied by scanning electron microscopy. The perianth organs are initiated in two whorls, dimerous in male flowers and trimerous in female flowers, with a longer plastochron between whorls than between the organs within a whorl. Male flowers have two stamens. The prominent connective protrusions begin development simultaneously with the floral disk. The disk is two-lobed in male flowers but continuous in female flowers. In female flowers, the developing gynoecium remains open relatively long, so the developing ovules are visible from the outside for some time. The direction of the hemitropous ovules in the carpels is antitropous (epitropous). Two small obturators are formed per carpel, one above each ovule. The prominent nucellar beak extends far beyond the “micropyle”. A micropyle in the classical sense formed by integuments closing over the nucellus apex is not present at any stage of development. Thus, it is not correct to say that the nucellar beak “grows through the micropyle”. The exposed nucellar beak continues the curvature of the antitropous (epitropous) ovule and becomes contiguous with the obturator. The unusual length of the nucellar beak may be a potential synapomorphy of the enlarged Phyllanthus clade as inferred from molecular phylogenetics.     

The evolution of fertilization modes independent of the micropyle in Fagales and `pseudoporogamy'

In contrast to a majority of angiosperms showing porogamous fertilization, several fagalean families such as Betulaceae and Casuarinaceae are known to show chalazogamy, where fertilization is effected by a pollen tube passing through the chalaza instead of the micropyle. Our developmental study of pollen-tube growth in pistils of Myrica rubra (Myricaceae, Fagales) further shows that pollen tubes reached the nucellus before the micropyle is formed by the integument. Since fertilized ovules appeared as if the pollen tube had passed through the micropyle for fertilization, we propose the new term `pseudoporogamy' to this mode. By mapping diverse modes of fertilization, dependent or independent of the micropyle, onto a phylogenetic tree of Fagales, it appears that fertilization mode evolved from porogamy to chalazogamy and then further from chalazogamy to pseudoporogamy. Possible reasons for the evolution of fertilization modes independent of the micropyle in Fagales are discussed.     

On the Vascular Organization of the Receptacles of Seedbearing Williamsonias from the Middle Jurassic Rocks of Amarjola in the Rajmahal Hills, India

The anatomical structure of the naked receptacles of seed-bearingWilliamsonias collected from Amarjola in the Rajmahal Hills,Bihar, is described. The main stele of the receptacle consistsof a large number of poorly developed, inverted, collateral,exarch bundles. In the pedicel portion of the receptacle thereare present double bundle traces of the bracts, while in theupper part of the receptacle there are present isolated, collateral,endarch bundles in the peripheral region of the cortex whichsupply traces to the seminiferous and interseminal scales. Onthe basis of this study it is concluded that the receptacleof Williamsonia is a modified axis of two noded inflorescence.     

A Comparison of Floral Structures of Anisophylleaceae and Cunoniaceae and the Problem of their Systematic Position

Flowers of Anisophyllea(Anisophylleaceae, Cucurbitales) andCeratopetalum(Cunoniaceae, Oxalidales) are surprisingly similar in appearance.To date, these families have never been interpreted as closelyrelated, and even in present molecular (rbcL) studies they appearin different orders of eurosids I (APG, Annals of the MissouriBotanical Garden85:531–553, 1998). In this investigation,flowers of selected taxa of both families are morphologicallyand anatomically compared. In addition, previous work on thetwo families is reviewed. The results strongly emphasize thegreat similarity in all floral organs. Some special similaritiesinclude the occurrence of trimerous flowers, isomerous organwhorls (including the gynoecium), valvate sepals, digitate petals,obdiplostemony, incurved filaments in bud with similar anthers,similar pollen, similar nectaries, carpels with free styles,a canal in the centre of each individual carpel as well as inthe centre of the entire gynoecium along the symplicate zone,and similar ovules with a slit-shaped micropyle. In addition,recently recovered Late Cretaceous floral fossils that sharefeatures of both families further emphasize a potential closerelationship. However, if more extensive molecular studies areperformed in the future that support the current disparate positionof the two families, then an explanation of the biological/functionalsimilarities in floral structure should be attempted: specifically,whether this suite of features is a symplesiomorphy for basalrosids, or an autapomorphy for each family. Copyright 2001 Annalsof Botany Company Anisophylleaceae, Cucurbitales, Cunoniaceae, eudicots, floral structure, molecular systematics, Myrtales, Oxalidales, Saxifragales     

In vitro Transformation of Ovules into Rudimentary Pistils in Nicotiana tabacum L.

In our experiments with in vitro cultured young ovaries of Nicotianatabacum, var. havanensis we observed greening and extensivegrowth of the ovular primordia. Four to 6 weeks after inoculationa mass of rudimentary pistils bearing secondary ovules was tobe seen on the protruding placenta. Histological investigationproved these pistilloids not to be adventive organs arisingfrom callusing tissue, but the result of altered growth of theoriginal ovu1ar prirnordia. Though comparatively rare, reportson spontaneous ovular pistillody, including two Nicotiana species,exist in the teratological literature. However, whereas thesespon taneous ovular transformations are described as carpel-likestructures with marginally inserted secondary ovules, the invitro proliferating ovules develop into rudimentary pistilswith an early differentiating and very prominent central placenta.An interpretation of these differences is proposed.     

Seedlessness and Parthenocarpy inPistacia veraL. (Anacardiaceae): Temporal Changes in Patterns of Vascular Transport to Ovules

Pistacia vera‘Kerman’ (pistachio nut) typicallyproduces high numbers of seedless or blank fruits. Patternsof vascular transport into fruits and ovules were studied over3 years by following the movement of disodium fluorescein solutionfrom cut branches into developing fruitlets. Early in the season,vascular conductivity is intact through to the chalazal endof the ovule. Soon afterwards, the percentage of ovules withvascular conductivity through to the chalaza declines, and ina variable fraction of fruits, movement of the fluorochromesolution becomes blocked either at the placenta or in the funiculus.Six to 9 weeks after anthesis there is blockage in 90 (1 year)to 100% (2 years) of fruits. Subsequently, vascular conductivityresumes in 83.3% (3 year mean) of ovules, a percentage thatcorrelates well with the mean percentage of seeded nuts at harvest(77.5%). Ovules from fruits with dysfunctional vascular conductionearly in the season are smaller than those with fully functionalvascular tissue. At the time conductivity declines, a high percentageof those ovules with blocked vascular movement lack endospermand appear to be unfertilized; none of the ovules that retainfull vascular flow lack endosperm. Pollination using gamma-irradiatedpollen (⁶⁰Co, 1.0 kGy) led to a nearly three-fold increase inthe production of blank nuts. The results indicate that fluoresceintransport may be a valuable tool to predict the fate of ovules,and are consistent with the hypothesis that parthenocarpic fruitset may be an important factor in blank nut production in pistachio.Copyright1999 Annals of Botany Company Pistachio,Pistacia veraL., fluorescein, seed set, seedlessness, parthenocarpy, blanking, ovule, funiculus, chalaza, embryo.     

Translocation of Uranin within the Living Ovules of Vanilla

In the ovules of Vanilla (Vanilla planifolia Andr.) before fertilization, outer integument surrounded the lower part of ovule. Uranin got into ovule through funiculus, forming, the first center of fluorescence at the chalaza zone of ovule. Then uranin was transported to micropyle end along inner integument, forming the second center of fluorescence at micropyle end of inner integument. Soon, fluorescence appeared in the egg apparatua. After fertilization, the outer integument ovule extended upward, forming micropyle ogerber with inner integument. After getting into ovule through funiculus, uranin spreads to- ward several directions: l. transported to outer integument at the entrance of micropyle; 2. transported downward to chalaza zone along outer integument at the side of funiculus; 3. extended from chalaza zone to the inside and to the outer integument at the side far from funiculus The ovules of Vanilla had no vascular bundles. On transporting in inner integument, however, the cells in inner layer next to the embryo sac appeared to be the major passage. In mature embryo sac, there was cuticle between inner integument and embryo sac at the half of micropyle end. But between embryo sac at the half of chalaza end and nucellus, cuticle was absent. Nutrient could get into embryo sac from chalaza end undoubtedly. As egg apparatus showed the fluorescence after formation of fluorescence center of inner integument at micropylar end, the possibility that nutrient got into embryo sac from micropyle could not be excluded.     

Carbon Partitioning to Whole versus Surgically Modified Ovules of Pea: An Application of the In Vivo Measurement of Carbon Flows over many Hours Using the Short-Lived Isotope Carbon-11

Continuous in vivo measurements of the partitioning of recentlyfixed photo-assimilate to individual ovules within a singlepod of Pisum are reported. Also, partitioning to attached surgicallymodified ovules as well as partitioning to the solution bathingthese ovules is described. Partitioning to whole ovules wasfound to vary up and down by about 10% over a time span of severalhundred minutes, while that to surgically modified ovules continuallyfell and was reduced by about 65% 400 min post surgery. Partitioningfrom the seed coat to the bathing solution was reduced by 80%,so that partitioning of photo-assimilate from the pod to thebathing solution had been reduced by 93% and had virtually stopped.This observation throws some doubt upon the use of long-term(> 200 min) measurements of photo-assimilate efflux fromattached seed coats in the study of photo-assimilate movementinto ovules. This work is based upon a method of analysing carbon-11 tracerprofiles which does not require that these profiles be correctedfor radioactive decay, thus enabling this short-lived isotopeto be used for quantitative studies of indefinite duration bycontinuous or multiple pulse labelling. Key words: Pea, ovules, carbon-11     

Development of ovule,fruit and seed of Xyris (Xyridaceae,Poales) and taxonomic considerations

The development of the ovule, fruit and seed of Xyris spp. was studied to assess the embryological characteristics of potential taxonomic usefulness. All of the studied species have (1) orthotropous, bitegmic and tenuinucellate ovules, with a micropyle formed by both the endostoma and exostoma; (2) a cuticle in the ovules and seeds between the nucellus/endosperm and the inner integument and between the inner and outer integuments; (3) helobial, starchy endosperm; (4) a reduced, campanulate and undifferentiated embryo; (5) a seed coat formed by a tanniferous endotegmen, endotesta with thick‐walled cells and exotesta with thin‐walled cells; and (6) a micropylar operculum formed from inner and outer integuments. The pericarp is composed of a mesocarp with cells containing starch grains and an endocarp and exocarp formed by cells with U‐shaped thickened walls. The studied species differ in the embryo sac development, which can be of the Polygonum or Allium type, and in the pericarp, which can have larger cells in either endocarp or exocarp. The Allium‐type embryo sac development was observed only in Xyris spp. within Xyridaceae. Xyris also differs from the other genera of Xyridaceae by the presence of orthotropous ovules and a seed coat formed by endotegmen, endotesta and exotesta, in agreement with the division of the family into Xyridoideae and Abolbodoideae. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 619–628.     

一叶萩大孢子发生和雌配子体发育

采用石蜡切片法对一叶萩(Flueggea suffruticosa(Pall.)Baill.)雌花大孢子发生及雌配子体的发育过程进行了观察。结果表明:一叶萩子房上位,中轴胎座,三室,每室2枚倒生胚珠,双珠被,厚珠心,具大戟科常见的珠心喙和珠孔塞。胚囊发育为蓼型,成熟胚囊结构为:卵器位于珠孔端,包括2个助细胞和1个卵细胞;中央是1个二核的中央细胞;合点端为3个反足细胞。本研究为大戟科植物生殖生物学和传粉生物学研究提供了基础资料,同时对大戟科植物系统分类研究有一定意义。     

Seed Structure in Cannaceae: Taxonomic and Ecological Implications

The ovules and seeds of Canna show some striking differencesto those in other zingiberalean families. The pachychalazaldevelopment of the ovule results in a seed of which only a smallpart of the testa is of tegumentary origin. A silicified endotesta,characteristic of the order, is lacking. The mechanical layerof the seed is formed by a continuous exotesta of Malpighiancells. The intact seed coat is impermeable. The seed is ableto absorb water after the raising of a preformed imbibitionlid on the raphe. During imbibition the extotesta loses itshardness, allowing the embryo to emerge. The special structuralfeatures of the seed are discussed in relation to records onthe extreme longevity of Canna seeds. Canna tuerckheimii, C. jaegeriana, C. glauca, pachychalaza, Malpighian cells, imbibition lid, seed longevity