高山松种实性状与生殖适应性

高山松(Pinus densata)是云南松(P. yunnanensis)与油松(P. tabulaeformis)自然杂交产生的二倍体杂种,是植物同倍体杂交物种形成的典型案例。高山松分布于青藏高原东南缘,占据了两个亲本种都不能正常生长的高海拔地带。良好生殖适应性的产生是物种形成的关键,但对高山松在高海拔生境下生殖适应性的变异与杂交起源遗传背景关系的研究尚未见报道。该研究通过对来自该种分布区内6个代表居群样本、13个反映高山松生殖适应性的种实性状的分析,探讨了其生殖性状在居群水平的变异模式,揭示了具有不同遗传组成和起源历史的高山松居群的生殖特性。研究结果表明:6个研究居群在种实性状上存在显著差异;可育种鳞数、总种鳞数、总种子数、可育种鳞率和可育种鳞密度等与纬度呈显著负相关关系;球果结种率与经度和生态梯度值呈显著的正相关关系;胚珠败育率则与经度和生态梯度值呈显著的负相关关系;球果长度也呈现了与经度的显著负相关。高山松球果结种率很高,平均为74%;球果的结种数、种子长和种翅长与云南松、油松及其它松属双维管亚属多数种接近;球果长度、球果总种鳞数接近油松的报道。这些结果表明,高山松在亲本种不能正常生长、繁衍的高原环境下具备正常的生殖能力;其种实特征在居群间分化显著并呈现一定的地理梯度变化。居群间的显著差异反映了其杂种起源特性,与高山松居群的遗传背景有关,也反映了处在异质生态环境中的高山松居群具有各自的生殖生态进化趋向。     

Comparative ovule and megagametophyte development in Hydatellaceae and water lilies reveal a mosaic of features among the earliest angiosperms

Background and Aims: The embryo sac, nucellus and integuments of the early-divergentangiosperms Hydatellaceae and other Nymphaeales are comparedwith those of other seed plants, in order to evaluate the evolutionaryorigin of these characters in the angiosperms. Methods: Using light microscopy, ovule and embryo sac development aredescribed in five (of 12) species of Trithuria, the sole genusof Hydatellaceae, and compared with those of Cabombaceae andNymphaeaceae. Key Results: The ovule of Trithuria is bitegmic and tenuinucellate, ratherthan bitegmic and crassinucellate as in most other Nymphaeales.The seed is operculate and possesses a perisperm that developsprecociously, which are both key features of Nymphaeales. However,in the Indian species T. konkanensis, perisperm is relativelypoorly developed by the time of fertilization. Perisperm cellsin Trithuria become multinucleate during development, a featureobserved also in other Nymphaeales. The outer integument issemi-annular (‘hood-shaped’), as in Cabombaceaeand some Nymphaeaceae, in contrast to the annular (‘cap-shaped’)outer integument of some other Nymphaeaceae (e.g. Barclaya)and Amborella. The megagametophyte in Trithuria is monosporicand four-nucleate; at the two-nucleate stage both nuclei occurin the micropylar domain. Double megagametophytes were frequentlyobserved, probably developed from different megaspores of thesame tetrad. Indirect, but strong evidence is presented forapomictic embryo development in T. filamentosa. Conclusions: Most features of the ovule and embryo sac of Trithuria are consistentwith a close relationship with other Nymphaeales, especiallyCabombaceae. The frequent occurrence of double megagametophytesin the same ovule indicates a high degree of developmental flexibility,and could provide a clue to the evolutionary origin of the Polygonum-typeof angiosperm embryo sac.     

Reproductive Biology of Plantago: Shift from Cross- to Self-pollination

The breeding systems of an obligate outbreeder (Plantago lanceolata)and an obligate inbreeder (P. patagonica) were compared. Outbreedingin the former and inbreeding in the latter species is achievedby self-incompatibility and preanthesis cleistogamy, respectively.The difference in breeding system is accompanied by a differencein the pollen output, pollen to ovule ratio, stigma and anthersize, and seed weight. P. ovata, a third species known onlyin cultivated form, is intermediate. This species has two typesof plants, some of which are protogynous and others where stigmareceptivity and anther dehiscence synchronize. Although thedifferences between the two intraspecific variants are not large,they nevertheless suggest that the species is in evolutionaryflux. Domestication is known to have modified the breeding systemin many crop plants and there is evidence that, in P. ovata,a start in this direction has already been made. Plantago lanceolata, P. ovata, P. patagonica, protogyny, anther, stigma, pollen to ovule ratio     

Effective Pollination Period and Nature of Pollen-collecting Apparatus in the Gymnosperm, Larix leptolepis

In controlled environment, the effective pollination periodin Larix leptolepis is characterized by its brevity, lastingfor less than 1 d. It is associated with the opening of thepapillae of the pollen collecting apparatus which possess surfaceesterase activity, a condition that has its parallel in thesurface pellicle of angiosperm stigmas. Larix leptolepis, ovule receptivity, morphometric analysis, pollination, stigma surface, esterase activity     

The Endosperm in Rothia trifoliata Pers

After fertilization the ovule in Rothia trifoliata shows thedevelopment of a large multinucleate endosperm, which extendsby haustoria at the expense of the cells in the base of theovule. Later, this endosperm is almost entirely replaced bya relatively massive embryo.     

Embryo Rescue in Wide Crosses in Arachis. 1. Culture of Ovules in Peg Tips of Arachis hypogaea

Interspecific hybridization in Arachis is restricted by earlyembryo abortion for many cross-combinations. Rescue of youngembryos in vitro within a week after fertilization is necessaryto recover these embryos before they abort. Peg tips, with theovule and embryo tissues, of A. hypogaea L. cv. ‘NC 6’,were cultured to compare ovule growth, callus production andpeg elongation. Tissues were collected 1, 2, 3 and 4 d afterself-pollination, after which peg meristems were removed fromhalf the pegs and cultured on five media combinations. One-day-oldpegs had significantly (P = 0.01) more ovule growth than oldertissues. Presence of the meristem had a greater inhibition toovule growth for 2- to 4-d pegs than for 1-d-old pegs. Significantlymore callus was produced on 4-d pegs than younger tissues, andkinetin had the greatest stimulatory effect on callus. Elongationof pegs with the meristem attached was observed most often inmedia with high sucrose levels. The observations indicate thatvery young ovules can be grown in vitro, and techniques maybe applicable to rescue of young embryonic tissues of Arachis. Ovule culture, interspecific hybridization, Arachis hypogaea, peanuts     

Comparative Biology of the Pollination Mechanisms in Acmopyle pancheri and Phyllocladus hypophyllus(Podocarpaceae s. l.)

The pollination mechanisms of Acmopyle pancheri(Brongn. &Gris) Pilg. andPhyllocladus hypophyllus Hook.f. were investigatedby conventional microscopical techniques and by nuclear magneticresonance (NMR) imaging. Dissimilarities include the orientationof the ovule and type of pollen;Phyllocladus has erect ovulesand wettable pollen with vestigial sacci, whereas Acmopyle hasmore-or-less erect ovules and non-wettable, functionally saccatepollen. Similarities include the mode of formation of the pollinationdrop and its response upon pollination. In both genera, pollinationtriggers pollination drop retraction and drop secretion ceases.Neither NMR imaging nor conventional histology of Phyllocladusovules revealed any specific tissue beneath the ovule whichcould be responsible for pollination drop retraction. It ismore likely, therefore, that the drop is channelled into thevascular supply or the apoplast. These findings invalidate thetaxonomic value of the pollination mechanism as a suite of characterstraditionally used to separate Phyllocladaceae from Podocarpaceae.Copyright 2000 Annals of Botany Company Acmopyle pancheri, gymnosperms, NMR imaging, nuclear magnetic resonance imaging, Phyllocladaceae,Phyllocladus hypophyllus , Podocarpaceae, pollination drop, pollination mechanism     

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     

Early Inbreeding Depression and Pollen Competition inCalluna vulgaris(L.) Hull.

We investigated whether partial self-sterility inCalluna vulgarisresultsfrom abortion of selfed offspring owing to inbreeding depressionor a late-acting self-incompatibility mechanism, and whetherself-pollen interferes with normal functioning of cross-pollen.Self-pollination resulted in 75% less seed set than cross-pollination.Self-pollen tubes reached ovaries and penetrated ovules as oftenas those of cross-pollen. Following self-pollination, examinationof the size of undeveloped seeds showed that at least 70% resultedfrom ovule fertilization and arrest of development occurredat various stages. All self-pollinated plants produced seedsand self-fertility varied among plants. These results indicatethat the reduced seed set observed in self-pollination is morelikely the result of inbreeding depression rather than a late-actingself-incompatibility system. The fecundity component of inbreedingdepression was high (0.762). Seed set was reduced by an averageof 40% when self-pollen was mixed with cross-pollen, comparedto pure cross-pollination. Using genetic markers, we found about20% of seeds resulted from self-pollination in mixed-pollinatedfruits.C. vulgarisis likely to experience self-pollination innature and our data suggest this will reduce the number of ovulesthat might otherwise mature after cross-pollination.Copyright1999 Annals of Botany Company Calluna vulgaris(heather), self-pollination, pollen tube, ovule fertilization, early inbreeding depression, pollen interference.     

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     

A New Species of Abietaceous Gone from the Lower Greensand of the Isle of Wight

An account is given of a hitherto undescribed species of Pityostrobusthe specimens of which come from the Lower Greensand of theIsle of Wight and for which the name Pityostrobus jacksoni issuggested. Structurally it has the general characters of thecones of the modern genus Pinus but no immediate affinity toan individual species of that genus is proposed. As a highlycharacteristic feature of the cone the seed-scale complexespossess much inflated apophyses, definite bract scales are alsopresent. The information obtained from sections through variousplanes is embodied in a reconstruction of one seed-scale complextogether with its bract scale.     

Timing of Embryo Abortion and the Effect of Ovule Thinning on Nutlet Mass in Cryptantha flava (Boraginaceae)

Just after a size difference was apparent among the four single-ovulatesubunits in developing ovaries of Cryptantha flava (Boraginaceae),either the largest subunit or the three smaller were destroyedand final seed set and nutlet mass were scored. Results indicatethat most irreversible embryo abortion must occur during theestablishment of the size differences, and within a 24–48h period. Thinning a portion of the ovules does not affect finalnutlet mass. Embryo abortion, Cryptantha flava, ovule destruction experiments, seed size     

Fruit Development and Structure in Some Indian Bamboos

Fruit structure and development of seven species belonging tofive genera of Indian bamboos are described. The fruit in fourspecies is a caryopsis typical of the family Poaceae. The ovuleis bitegmic; the outer surface of the cells of nucellar epidermisbecomes cutinized and forms the seed coat. Three species beara fleshy fruit with a unitegmic ovule. In a mature fruit theendosperm is either completely absorbed by the embryo or ispresent only in small quantity. The developing embryo comesin direct contact with the fruit wall due to the disintegrationof the nucellus and integument. The embryo is covered by a thickbrown mat from the disorganized cells of the inner layers ofthe fruit wall. Poaceae, Bambusoideae, Bambusa, Dendrocalamus, Melocalamus, Ochlandra, Pseudostachyum (fleshy fruits), fruit wall     

Localization of Phenolic Compounds in the Covering Tissues of the Embryo of Brassica napus (L.) during Different Stages of Embryogenesis and Seed Maturation

During embryogenesis and maturation of an embryo the tissuescovering it produce phenolic compounds the localization of whichchanges during maturation of the embryo. In the ovary containinga globular embryo, phenolics are located in the epidermis ofthe integumentum externum and the innermost layer of the integumentuminternum. In the ovule at the stage at which heart- and torpedo-shapedembryos are present, phenolic compounds are visible in the stellarcells, the innermost cells of the integumentum internum andthe endosperm. In hard, green seeds, after the integumentuminternum and layers over the stellar cells gradually disappear,the remaining tissue contains cell walls impregnated with phenolics.Mature, black seeds contain only one distinct layer of cells—stellarcells, which, like the other compressed cell walls, are impregnatedwith phenolics. In this way they constitute a barrier betweenthe embryo and its environment.Copyright 1994, 1999 AcademicPress Brassica napus, seed coat, integumentum, phenolic compounds     

Influence of Temperature and Ageing of Ovules and Pollen on Reproductive Success in Trifolium repens L.

Four clones of Trifolium repens L., originating from Iceland,Denmark and Israel, were cultivated in controlled environmentchambers at 10, 14, 18 and 22°C. Seed set at 10°C was,on average, 45% lower than at 18°C. Generally, seed frequencieswere higher in the stylar ovule positions than in the basal.This polarization became more pronounced at low temperatures.At least 30% of the decrease in seed set was caused by inadequatepollen tube growth. This was further supported by in vitro studieswhich showed that pollen developed significantly shorter pollentubes at low temperatures and a strong positive correlationbetween the capacity of male parents to induce seed set in basalovule positions and the length of pollen tubes in vitro. Femaleage, determined by days relative to anthesis, was also foundto have a significant influence on seed set, i.e. when pollinationwas delayed until the fifth day of flowering, seed set decreasedby an average of 60% when compared to florets pollinated onthe first day of anthesis. Pollen age did not influence seedset. Ageing of pollen decreased in vitro germinability, tubeelongation and the percentage of pollen tubes with sperm cells.Seed set, pollen germinability, pollen tube lengths, and abilityto form sperm cells in vitro varied significantly among clones.Copyright1994, 1999 Academic Press Trifolium repens, white clover, temperature, pollen tube, sperm cells, ovule fertility, seed set     

Studies in the Genus Elaphoglossum: III. Anatomy of the Rhizome and Frond

The investigation is continued of a number of species of Elaphoglossumfrom Jamaica. Features of interest in the anatomy of the rhizome and frondare described. Information, additional to that previously recorded,is given of the scales. It is shown that, in E. villosum, complexityof stelar structure and the presence of hydathodea in the frondsis accompanied by scales of a specialized type.     

Genetic Regulation of Seed Dormancy in Purshia tridentata(Rosaceae)

Seeds of Purshia tridentata, a shrub of semi-arid North America,require chilling to become non-dormant. Using seeds producedfrom controlled crosses in a common garden, we examined effectsof ovule parent, pollen parent, and year of production on germinationpercentage in response to chilling for 2 weeks at 2°C. Differencesamong ovule parents accounted for most of the variance in chillingresponse, and these differences (2 to 83% germination) wereconsistent across years. Differences among pollen parents werealso significant, producing a two- to five-fold difference inmean germination percentage. Differences among years were significantbut small. Ovule parent by year interactions showed that among-yearvariation in ripening environment did not affect ovule parentsequally. There was no significant pollen parent by year interaction,suggesting that the effect of maturation environment was mediatedthrough maternal tissues. In reciprocal crosses, two plantsthat showed contrasting dormancy levels as ovule parents producedseeds with similar dormancy as pollen parents, indicating thatthe genetic difference between them was at the testa level.Two plants that produced seeds with contrasting dormancy aspollen parents showed a similar but stronger pattern of contrastas ovule parents, showing that the genetic difference betweenthem was at both embryo and endosperm or testa level. Testaor endosperm genotype was primarily responsible for chillingresponse of intact seeds, while embryo genotype affected chillingresponse and also exercised primary control over low temperaturegermination rate, whether of excised embryos or of intact seeds.Copyright 2000 Annals of Botany Company Antelope bitterbrush, bitterbrush, common garden study, germination     

Ovule and Embryo Ontogenesis in Bombacopsis glabra (Pasq.) A. Robyns

Ontogeny of the ovule and development of the embryo in Bombacopsisglabra (Pasq.) A. Robyns were examined. The ovule is bitegmic,crassinucellate, and anatropous. The exostome is eccentric relativeto the endostome; stomata occur on the outer integument. Thesingle archesporial cell functions directly as the megasporemother cell. The embryo-sac is bisporic. The organization ofthe nuclei in the mature embryo-sac is normal. The antipodalcells disintegrate soon after formation. Double fertilization takes place; the zygote undergoes a longperiod of dormancy, but the primary endosperm nucleus dividesimmediately to produce first a nuclear-type, later a cellular-typeendosperm. The zygote is of the caryophyllad type. Adventive embryos arise from single cells of the nucellus inthe vicinity of the micropyle, and develop faster than the sexuallyproduced embryo; this leads to anomictic renroduction.     

A survey for body scales in dinoflagellates and a revision of Cachonina and Heterocapsa (Pyrrhophyta)

Small organic scales 0.2 to 0.4 µm in diameter have beenobserved to form a layer on the surface of three species ofmarine dinoflagellates. Two of the species were originally describedas members of the genus Cachonina; the third is Heterocapsapygmaea Loeblich et al., 1981. The body scales are very similarto those previously described covering cells of Heterocapsatriquetra (Ehrenberg) Stein, 1883. These scales are freely shedfrom the cells of the above four species and can be found inthe culture medium; no scales were observed in the culture mediumof 35 other dinoflagellate species representing 18 genera and11 families. The complete thecal plate pattern of H. triquetra,type species of Heterocapsa, has been determined, and on thebasis of similarities in body scale morphology and thecal platetabulation, the genus Cachonina is placed in the synonomy ofHeterocapsa. Cachonina illdefina and C. niei are transferredto Heterocapsa.