The Ultrastructure of Tetrasporogenesis in the Marine Red Alga Chondria tenuissima (Good, et Woodw.) (Ceramiales, Rhodomelaceae)

Tetraspore development has been studied in Chondria tenuissimausing light and electron microscopy. The transformation of tetrasporangialmother cells into mature tetrasporangia involves a series ofstructural changes, especially of dictyosomes and of the nucleus.The youngest stage of tetrasporogenesis consists of a uninucleatetetraspore mother cell with synaptonemal complexes present duringearly prophase of meiosis I. Mitochondria are aggregated aroundthe nucleus, dictyosome activity is low, and proplastids occurin the peripheral cytoplasm. The cleavage furrows are initiatedalmost concomitantly with commencement of meiosis. When thecleavage furrows are initiated, spherical bodies bounded bytwo membranes are found within the cytoplasm; they develop intovacuoles with fibrillar contents (fv₁), which increase in sizeduring tetraspore development by fusing with each other andwith Golgi vesicles. The Golgi vesicles and the vacuoles withfibrillar contents (fv₁) contribute material to the developingtetraspore wall. During the middle stage of tetraspore formationthe vacuoles with fibrillar contents (fv₁) are dominant, dictyosomeactivity increases, as well as the number of plastids and mitochondria;starch formation also increases. Stacked cisternae of the endoplasmicreticulum are found within the peripheral part of the nucleus.The same nuclear structures are also observed in tetrasporangiaof the marine red alga Gastroclonium clavalum. The final stageis characterized by the disappearance of vacuoles with fibrillarcontents (fv₁) and of the stacked ER within the nucleus, presenceof straight, large dictyosomes which produce cored vesicles,an abundance of starch grains and by the formation of fullydeveloped chlorqplasts. The cored vesicles contain Thiéry-positivematerial and contribute to the formation of vacuoles with fibrouscontents (fv₂) as they are dominant in the tetraspores beforetheir liberation. Rhodophlyla, Chondria, tetrasporogenesis, ultrastructure, Golgi apparatus     

Nanoscale Similarities in the Substructure of the Exines ofFagusPollen Grains andLycopodiumSpores

The exine substructure of an angiosperm,Fagus sylvatica(beech)pollen and a pteridophyte,Lycopodium clavatum(a club moss) sporewas investigated by scanning tunnelling microscopy. These pollenand spores, despite their distinct differences in structureand morphology on a micrometre scale, have very similar substructureon a nanometre scale. The substructure appears to consist ofa multi-helix, i.e. a helical chain in turn wound into a helixwith a self-similarity at smaller and smaller length scales.A simple vectorial form is proposed to describe quantitativelythe multi-helical substructure. Copyright 1998 Annals of BotanyCompany Fagus sylvatica,beech,Lycopodium clavatum, club moss, pollen, spores, exine substructure, scanning tunnelling microscopy.     

棉铃虫幼虫感染棉铃虫微孢子虫后的组织病理变化

1997年田间调查时发现一种寄生于棉铃虫Helicoverpa armigera（Hübner）的微孢子虫Nosema sp.,它对棉铃虫有较强的致病力并可经卵垂直传播。利用透射电镜对棉铃虫幼虫感染该微孢子虫后的组织病理变化进行了初步观察。结果表明：该微孢子虫可侵染棉铃虫的中肠、马氏管、脂肪体、神经等组织;侵染后可导致寄主中肠的微绒毛脱落,线粒体内脊排列方向发生变化,线粒体整体发生变形并最终瓦解;内质网发生断裂;细胞核体积变小并变形,但该微孢子虫并不入侵细胞核;马氏管膨大,边缘向外突出隆起;神经细胞的细胞核变成长条形,细胞界线模糊;在神经细胞内也发现了微孢子虫孢子,证明该微孢子虫也入侵寄主神经细胞。     

THE GONADS OF MARGARITIFERA AURICULARIA (SPENGLER, 1793) AND M. MARGARITIFERA (LINNAEUS, 1758) (BIVALVIA: UNIONOIDEA).

A detailed study of the gonads of two endangered species of thegenus Margaritifera living in the Iberian Peninsula, Margaritiferaauricularia (Spengler, 1793) and Margaritifera margaritifera(Linnaeus 1758), based on macroscopic and histological observationsis presented. In both species, gonadal tissue occurs withinthe visceral mass without a specific location. In hermaphrodite specimens,male and female acini are mixed in the visceral mass but canbe clearly distinguished by detailed macroscopic study. The gonadaltopography and cycle of Margaritifera auricularia is described forthe first time, indicating that the species is a female hermaphroditeand that gametogenesis occurs from December to March. Fiftypercent of Margaritifera margaritifera specimens studied werehermaphrodites and 50% females. (Received 6 March 2000; accepted 5 June 2000)     

Stalked Glandular Hairs in the Pappophoreae (Gramineae)

Stalked glandular hairs on the vegetative parts of grasses areapparently confined to the tribe Pappophoreae. They have beenrecorded from three of the genera in this tribe, Enneapogon,Schmidtia, and Kaokochloa; the first occurs mainly in the OldWorld and the remaining two in Africa only. The hairs are absentfrom one of the genera (Pappophorum) confined to the New World,but investigation showed that they are present in the other(Cottea).     

Glandular Trichomes of Fagonia L. (Zygophyllaceae) Species: Structure, Development and Secreted Materials

The glandular trichomes ofFagoniaconsist of one secretory celland a multicellular stalk, which develops by division, elongationand elevation of epidermal cells. The latter become seperatedfrom the mesophyll and a subepidermal chamber is formed. Thelength of the stalk, which differs in the various species orvarieties is determined by the number of cell divisions and/or the extent of cell elongation. Although the basic morphologyand development of the trichomes of the species and varietiesexamined are similar, two types of mature trichomes can be distinguished:one occurs in the two examined varieties ofF. mollisand thesecond inF. glutinosaandF. arabica. The secretory cells of thesecond type possess a very thick wall and bear a porous cupuleon their top. Histochemical tests revealed that the sticky substancesecreted by the secretory cells contains mainly polysaccharidesand lipophilic compounds. The secreted material exhibits autofluorescence.InF. mollisvar.hispidachanges in the amount and shape of thefluorescent material inside the secretory cell, during the courseof development, have been observed. The contribution of theglandular trichomes inFagoniaspecies to survival in hot desertconditions is discussed. Fagonia; glandular trichomes; subepidermal chamber; secreted material; adaptation to desert conditions; stalk; fluorescence     

Fruit Development in Bambarra Groundnut (Voandzeia subterranea)

Flowers of Voandzeia subterranea are positively geotropic andthis helps their entry into the ground. The ovary develops onlywhen it is on the surface of, or inside, the soil. The transformationinto fruit occurs in two stages: (a) definite development of pod, followed by (b) development of seed. The first stage occurs during the first 30 days after fertilizationand the second stage lasts for about 10 days. Maturity is characterizedby dryness and browning of the interior of the shell and appearanceof brown patches on it. The part of the pod on which the pedicelsubsists is the upper part and the lower part is the portionwhere the style is attached.     

Discovery Of Genetically Distinct Sympatric Lineages in the Freshwater Mussel Cyprogenia Aberti (Bivalvia: Unionidae)

The western fanshell, Cyprogenia aberti, occurs in the CentralHighlands region of North America and is the only congener ofthe federally endangered fanshell, C. stegaria. Due to a reductionin range size and local extirpations, extant populations ofC. aberti have become increasingly isolated. Consequently, C.aberti has been the focus of numerous conservation efforts,yet no work has examined the degree of genetic variation amongthe species' disjunct populations. Phylogenetic analyses ofnucleotide sequences from two mitochondrial gene portions (CO1and ND1) revealed results important to the conservation managementof C. aberti. First, phylogenetic analyses do not support amonophyletic C. aberti. Second, C. aberti is comprised of asmany as five independent lineages, one of which includes thefederally endangered C. stegaria. Third, analysis recoveredtwo genetically distinct sympatric lineages of C. aberti inthe Ouachita River Drainage. These phylogenetic results suggestthat the five distinct evolutionary lineages of C. aberti shouldbe managed as separate conservation units. This study illustrateswhy it is critical to evaluate genetic variability in endangeredand threatened ‘species’ prior to implementing arecovery program. These data also reveal the value of assessingbiological diversity of nonimperiled taxa before populationsare extirpated and valuable genetic data necessary for reconstructionof evolutionary relationships is lost. (Received 24 October 2005; accepted 8 June 2006)     

Nuclear genome characterization of the carrageenophyteAgardhiella subulata (Rhodophyta)

DNA reassociation kinetics were used to determine nuclear genome organization and complexity inAgardhiella subulata (Gigartinales, Rhodophyta). Results indicate the presence of three second-order components corresponding to fast (22%), intermediate (68%) and slow (10%) fractions. Thus, the genome consists of 90% repetitive sequences. Microspectrophotoometry with the DNA-localizing fluorochrome DAPI was used to confirm ploidy level differences in the gametophytic and tetrasporophytic phases. Results indicate that meiosis occurs during tetrasporogenesis. Comparison of mean nuclear DNA (I_f) values to chicken erythrocytes (RBC) resulted in an estimate of 0.9 pg/2C genome forAgardhiella. Karyological studies using aceto-orcein revealed a chromosome complement of 2N = 44 in carposporangia and the presence of 22 bivalents during diakinesis of tetraspore mother cells.     

Pollination Ecology ofChloranthus serratus(Thunb.) Roem. et Schult. andCh. fortunei(A. Gray) Solms-Laub. (Chloranthaceae)

Flowering and pollination biology ofChloranthus serratusandChloranthusfortuneiwere studied. Flowering took place from early Marchto mid–April inCh. fortunei, and from April to September,the whole growth period, inCh. serratus.The flowering periodof an inflorescence ofCh. serratusaveraged about 8 d and anthesisof a single flower was 5–6 d. Flowers are slightly protogynous.The flower emitted fragrance when the androecium became white.Both species are entomophilous with thrips as exclusive pollinators.Under natural conditions, fruit set occurs mainly as a resultof cross-pollination, but self-pollination and agamospermy mayoccur in some cases. In flowers ofCh. fortuneiandCh. serratus,theincurved androecium, the carpel and the spike axis form a nearlyclosed chamber that contains the anthers and stigma. The developmentof a floral-axial chamber may be an important step towards amore economical and effective pollination system. Floral morphology,pollination biology and fossil evidence suggest that the mainevolutionary trend in the genusChloranthusis towards developmentof ‘closed’ flowers. The fidelity of the relationshipbetweenChloranthusand thrips is regarded as a specialized featureof pollination biology and this relationship may have originatedearly in the evolutionary lineage.Copyright 1999 Annals of BotanyCompany Chloranthaceae,Chloranthus, Thysanoptera,flowering, floral-axial chamber, pollination, evolution trends.     

THE ECOLOGY OF THE HONG KONG LIMPETS CELLANA GRATA (GOULD, 1859) AND PATELLOIDA PYGMAEA(DUNKER, 1860): DISTRIBUTION AND POPULATION DYNAMICS

Cellana grata is a high-zoned, exposed-shore limpet with a lifespanof 3 years. Patclloida pygmaeais a low-zoned, sheltered-shorelimpet with a lifespan of I year. C. grata migrates up-shorein winter, but occurs lower on the shore in summer. This migrationis synchronized with variations in algal availability high onthe shore; such variations are, however, themselves relatedto seasonal changes in wave height. P. pygmaea is restrictedto the low shore, year round. The movements upwards in winterand downwards in summer are still evident. Algal species richnessincreased from September to reach a peak between December andMarch, and to abruptly diminish between May and June. The encrustingalgae Brachytrichia maculans, Hildenbrandia prototypus, Lithothamnionsp. and Ralfsia vcrrucosa were present year round. The timingof juvenile recruitment of C. grata and P. pygmaea was fromOctober to July and February to October, respectively. Temperaturemay be important in enhancing juvenile survival by affectingthe seasonal pattern of algal occurrence on the shore. Seasonalfluctuations in the rate of growth were recorded for both specieswith the time of fastest growth of C. grata and P. pygmaea occurringbetween October and March and September and February, respectively.Mortality of both species occurred mainly in summer. Summerheat, predation and intra-specific competition for food appearto be the major causes of death. (Received 1 December 1992; accepted 5 May 1993)     

LEARNING AS A FACTOR IN DIET SELECTION BY ELYSIA VIRIDIS (MONTAGU) (OPISTHOBRANCHIA).

Elysia viridis (Montagu) occurs naturally in populations feedingon the fleshy, siphonalean green alga Codium or on the coarse,filamentous green alga Chaetomorpha. Only about half of theE. viridis transferred from Codium to Chaetomorpha in the laboratorywere able to learn to feed on this alga. Handling time decreasedsignificantly during the learning-period. All E. viridis transferredfrom Chaetomorpha to Codium in the laboratory were able to learnto feed on the latter alga. Handling time also decreased withexperience in these animals. Ingestive conditioning occurredin animals transferred from Chaetomorpha to Codium. These animalshad to go through a learning-period again when they were offeredChaetomorpha after 6–9 weeks with Codium Ingestive conditioningwas also evident from preference experiments; animals preferredthe food they had been kept on prior to the experiments. Thesefindings are discussed in relation to optimal diet theory. (Received 14 December 1987; accepted 22 March 1988)     

Egg trading in the simultaneously hermaphroditic polychaete worm Ophryotrocha gracilis (Huth)

Ophryotrocha gracilis (Huth 1934) is a simultaneously hermaphroditicpolychaete worm with external fertilization and a brief protandrousphase. The mating system of this species seems to meet conditionsleading to the establishment of egg-trading behavior. Experimentsshowed that mating occurs in pairs composed of two simultaneoushermaphrodites; sex roles are sequentially alternated and self-fertilizationis avoided. Egg reciprocation is kept evolutionarily stableby laying eggs in multiple, small-sized egg clutches and reducingthe reproductive success of pairs in which one of the two partnersdoes not reciprocate egg exchange. The frequency of ovigeroushermaphrodites in mass cultures of O. gracilis is about 50".Such a high mate availability preadapts hermaphrodites of O.gracilis to change partners very frequently and to reduce investmentin parental care, contrary to what is observed in another egg-trading,simultaneously hermaphroditic species, O. diadema. Laboratorypopulations of O. diadema have a frequency of only 17% ovigeroushermaphrodites     

Callus Growth and Plantlet Regeneration in Taro, Colocasia esculenta var. esculenta (L) Schott (Araceae)

Explants of taro cultivars belonging to Colocasia esculentavar. esculenta have been nearly impossible to culture untilrecently. Here, we describe a method which induces callus formationfrom bud explants of Colocasia esculenta var. esculenta cv.Akalomamale, brings about shoot and root production, and leadsto plantlet regeneration. The medium used is half-strength Murashige-Skoog(HMS) solution containing 25 ml taro tuber extract (TE), 2 mg2, 4, 5-trichlorophenoxyacetic acid and 200 mg glutamine 1^–1.TE is an important requirement for bud explants and callus tissues.Root induction on callus-derived shoots (i.e. plantlet formation)occurs on HMS containing only 25 ml TE and 100 ml coconut water1^–1. Taro, Colocasia esculenta var. esculenta (L) Schott (Araceae), coconut water, micropropagation, plantlet regeneration, root formation, taro extract, tissue culture     

Ecological investigations on the zooplankton community of Balsfjorden, northern Norway: population dynamics of the euphausiids Thysanoessa inermis (Kroyer), Thysanoessa raschii (M.Sars) and Meganyctiphanes norvegica (M.Sars) in 1976 and 1977

The population dynamics of the euphausiids Thysanoessa inermis(Kröyer), T. raschii (M.Sars), and Meganyctiphanes norvegica(M.Sars) have been followed in Balsfjorden in 1976 and 1977.Seasonal variations in length-frequency distributions, growthin carapace length, sex-ratio, and spermatophore productionand attachment are presented and discussed in relation to changesin hydrography and phytoplanlcton standing-crop. An annual generationof T. inermis and T. raschii was spawned in April and May. Eggsand larvae of M. norvegica were not found in Balsfjorden, indicatingthat recruitment occurs from outside the fjord. T. inermis andT. raschii reached maximum carapace lengths of 7–8 mmand 6–7 mm respectively and had life-spans of c. 2 years3 months. M. norvegica had a life-span of c. 2 years 6 monthsand reached a maximum carapace length of c. 12.5 mm. In bothT. inermis and T. raschii 0-group underwent the greatest lengthincreases from May to October, I-group from March to Augustand II-group from April to June. The population structure, growthpatterns and growth periods of M. norvegica were difficult todiscern. The phytoplanlcton cycle appears to be the dominantfactor regulating both growth and spawning of the Thysanoessaspp in Balsfjorden, while temperature has no obvious influence.     

Perianth Abscission in Montbretia (Crocosmia x crocosmiiflora)

The anatomy, histochemistry, kinetics and hormonal regulationof perianth abscission in Crocosmia x crocosmiiflora (Montbretia)has been investigated. The abscission zone is anatomically welldefined, with cell divisions occurring in this region at anthesis.Abscission is first detectable 3 d after perianth opening, whenthe walls of a group of cells beneath the adaxial epidermisshow reduced staining with polyanion-specific stains, and adecline in penanth break strength also occurs. Abscission isachieved by cell wall breakage in thc abscission zone, whichprogresses eccentrically from the adaxial epidermis throughthe abscission zone, rather than the separation of intact cellsas occurs in flowers of dicotyledons. Experiments on detachedflowers suggest similarities in the hormonal regulation of abscissionin Crocosmia to that of dicotyledons, in that an ethylene promotion,and possibly an auxin inhibition, mechanism may exist in Crocosmia.Ovary expansion occurs throughout the development and senescenceof unpollinated flowers, but does not appear to be the solecause of wall breakage in the abscission zone. It is suggestedthat hormonally regulated wall hydrolases weaken the cell wallsin the abscission zone, and allow wall breakage and subsequentabscission to occur. Cdrocosmia x crocosmiiflora, Montbretia, anatomy, breakstrength, cell wall changes, histochemistry, flowers, monocotyledons, perianth, senescence, ethylene, auxin     

松突圆蚧花角蚜小蜂的生物学

松突圆蚧花角蚜小蜂Cocvobius azumai Tachikawa是松突圆蚧Hemiberlesla pitysophila Takagi的重要寄生蜂,1987-1989年从日本引入我国广东省。对松突圆蚧花角蚜小蜂的形态、发育、繁殖、成虫寿命和取食寄主行为等生物学特征进行了观察。该蜂的雌性幼虫是松突圆蚧雌蚧的初级内寄生蜂,而雄性幼虫则是次级寄生蜂,重寄生在同种或它种膜翅目的老熟幼虫、预蛹和蛹上。雌雄两性的形态在所有发育阶段均不相同。交配过的雄蜂喜欢寄生产卵初期和盛期的雌成蚧,对巳寄生的寄主具有识别能力。在19.7℃一30.9℃变温条件下每头雌蜂平均产卵14.95粒,约60%的卵是在最初3天内产出。松突圆蚧花角蚜小蜂雌性蜂在21℃,24℃,27℃和30℃时从卵发育到成虫的平均历期分别为41.24,32.60,25.60和23.00天,发育起点温度10.1℃,有效积温448.3日度。该蜂在广东省一年发生。9-10代。     

Confirmation of Ancient Polyploidy in Dahlia (Asteraceae) Species using Genomic In Situ Hybridization

The successful production of interspecific hybrids between membersof the dysploid chromosome series inDahlia offers a unique opportunityto investigate chromosome evolution. Analysis of meiotic metaphaseI in these hybrids using genomic in situ hybridization (GISH)has shown that pairing occurs both between and within parentalgenomes. These results have provided clear evidence for theallotetraploid origin of Dahlia species with 2n=32 and suggeststhat species with 2n=34 and 2n=36 have also arisen via allopolyploidy.A bivalent promoting mechanism proposed for species with 2n=32also appears to be present in Dahlia species with 2n=34 and2n=36 .Copyright 1999 Annals of Botany Company Dahlia , GISH, dysploidy, chromosome pairing, karyotype analysis, polyploidy.     

The Reproductive Biology of Totara (Podocarpus totara) (Podocarpaceae)

A reproductive cycle of totara (Podocarpus totara) in New Zealandis complete within 2 years. After strobilus initiation in September,there is a 9 month period of winter dormancy until emergenceduring the growth flush in July–August of the followingyear. Female strobili bear only one or two ovules which arepollinated mid-October to mid-November at the megaspore tetradstage. Pollen germination and fertilization occur rapidly duringDecember. The pollen tube carries the body cell, sterile andtube nuclei with at least three prothallial nuclei, and branchesout after reaching the archegonia. The four–six archegoniacontain egg nuclei with no distinct perinuclear zone and a largechalazal vacuole. Fertilization by the larger of the two unequalmale gametes is accompanied by a degradation of egg cell cytoplasm.The three-tier proembryo contains a binucleate embryonal tierof only one cell. Soon after embryo penetration into the megagametophyte,the binucleate embryonal-tier cell undergoes mitosis and cellwall formation resulting in four uninucleate cells. Some ovulescontained secondary embryos thought to be the product of suspensorcleavage. Embryo maturation occurs by February.Copyright 1999Annals of Botany Company Podocarpus totara, totara, conifer, podocarp, reproductive biology, embryology.     

Branching Principles Governing the Architecture of Cornus kousa (Cornaceae)

The complex structure of the crown of Cornus kousa, generallyfive-forked in vegetative branching and two-forked in reproductivebranching, is analysed quantitatively and described by two basicbranching principles: decussate phyllotaxy and the resettingrule for planes of branching. Most Cornus species have opposite,decussate phyllotaxis. The leaf pair (with axillary buds) definesthe branching plane of a node. Because of regular phyllotaxis,the fundamental branching pattern is that every branching planealong an axis is perpendicular to the preceding one. However,the first node of a lateral horizontal shoot always has a horizontalbranching plane; we term this the resetting rule. We observedthat resetting occurs when the first nodes initiated in thevertical plane are repositioned by a twisting of their firstinternodes. All later nodes alternate directions, i.e. showusual decussate alternation. Foliage leaf nodes usually producethree-forked branchings. When vegetative winter buds are formed,a foliar node and adjacent scale leaf node produce a five-forkedbranching. When reproductive winter buds with a terminal inflorescenceare formed, the last foliar node and two adjacent scale leafnodes can produce a variety of branchings but usually producean equal two-forked branching. To understand better the architecturein C. kousa, we contrast it with C. capitata which does notproduce buds with scale leaves and whose vegetative nodes areclearly separated. Copyright 1999 Annals of Botany Company Branching pattern, Cornaceae, Cornus kousa, decussate branching, dogwood, Japanese strawberry tree, tree architecture, tree geometry.