A Scanning Electron Microscope Study of Theobroma cacao Somatic Embryogenesis

This study describes the somatic embryogenesis of Theobromacacao L. with a scanning electron microscope. It revealed earlydevelopmental stages as globular and incipient heart-shaped.Morphological abnormalities, such as the occurrence of threeand four cotyledons and round or long forms of embryoids witha long and thin or short and thick stalk-like structure whichseems to equate to a suspensor, were also observed. A suspensorwas found in some embryoids. cacao, Theobroma cacao, embryoids, somatic embryogenesis, SEM     

Cytokinins and the Growth Responses of Seedlings of Betula pendula Roth. and Acer pseudoplatanus L. to Nitrogen and Phosphorus Deficiency

Deficiencies in the supply of nitrogen and phosphorus broughtabout the cessation of shoot extension and the formation ofterminal resting buds in seedlings of Acer pseudoplatanus maintainedunder long days, whereas seedlings of Betula pendula maintainedunder the same conditions continued extension growth of themain axis over a long period, although they showed symptomsof nitrogen deficiency, including a reduced chlorophyll content.The endogenous cytokinin levels of the base/nucleoside fractionin leaves of B. pendula were significantly lower in the nitrogen-deficientplants than in the controls only 3 d after transfer to deficientconditions. Similar, though less marked, changes were observedin response to phosphorus deficiency. Changes in the levelsof cytokinin activity in the nucleotide fraction in responseto nitrogen deficiency were much less marked. No significantchanges in cytokinin levels of the base/nucleoside or nucleotidefractions could be detected in leaf material from seedlingsof A. pseudoplatanus, even after a nitrogen or phosphorus deficiencytreatment of 4 weeks. Application of exogenous benzyladenineto seedlings of B. pendula subjected to nitrogen deficiencyresulted in a rapid regreening and to outgrowth of inhibitedlateral buds after only 2 d.     

Development of Meristems of Weigela florida Variety 'Bristol Ruby' Following Reproductive Induction in Long Days

Weigela florida variety ‘Bristol Ruby’ has longday requirements for its growth and, in general, for its flowering.Vegetative development, floral initiation and floral organogenesisare described using scanning electron microscopy during photoperiodictreatment in long days, under controlled conditions. Flowering of axillary buds of cuttings has been studied. Theapex of Weigela at the vegetative phase is characterized bya very small hollow meristem. After 9 long days, the meristemenlarges and, after 12 long days, early axillary buds are initiatedin the axils of the leaves, which become bracts. When the numberof long days was increased, flowers were initiated in the budson the induced branches; first at the proximal part of the branchwhere development afterwards slowed down, then on the medianparts of the branch where development was accelerated. Two bracteoles are differentiated soon after floral initiation;first initiation of the calyx required 18 long days. Petals,stamens and ovary were rapidly initiated after that. Weigelaflowers are clustered; the inflorescence ceased growth by abortionof the terminal meristem or by formation of a terminal flower.In axillary buds of the fifth node the formation of the clusterwas completed about 20 days after the beginning of floral induction. Weigela florida ‘Bristol Ruby’, scanning electron microscopic analysis, vegetative meristem, floral development stages, long days induction     

Determination and Differentiation of Leaf and Petal Primordia in Impatiens balsamina

The development of primordia as leaves, petals, or as organsintermediate between leaves and petals can be regulated by photoperiodin Impatiens. In intermediate organs only some parts of theorgan differentiated as petal, and then only in some cell layers.Allometric measurements of primordium shape suggested that intermediateorgans may begin development as petals, and that their intermediatecharacter at maturity resulted from a switch of some parts ofthe organs from petal to leaf development when the primordiawere between 0.5 and 1 mm long. In reverted apices made to re-flower,primordia were not completely determined as leaves until theywere about 750 µm long. Determination typically occurredfirst at the tips and last at the bases of these primordia.The determination of primordia as leaves or petals in Impatiensis discussed in relation to primordium determination in otherspecies. It is suggested that the lack of commitment to flowermay result in relatively late primordium determination in Impatiens. Impatiens balsamina, determination, differentiation, leaf and petal development, flowering, reversion     

Assessing Costs of Reproduction in Mountain Birch: The Importance of Considering the Modular Level

We studied the effects of production of male catkins on growthand the subsequent year's male catkin production in mountainbirch, Betula pubescens subsp. czerepanovii at both the shootand branch level. (Shoot is defined here as the product of asingle growing season while branch refers to a structure consistingof several shoots.) Like heterophyllous trees in general, mountainbirch canopy expansion takes place via the production of longshoots. We found phenotypic trade-offs between long shoot growthand male reproduction at the shoot level in the year of catkinproduction. Generative parental long shoots (long shoots withmale catkins) were significantly shorter than the vegetativeones (long shoots without a male catkin). In contrast, we foundno effects of male reproduction on the subsequent year's malecatkin production at the shoot level. Although the mean lengthof secondary long shoots (long shoots growing from the lateralbuds of parental long shoots) did not differ between vegetativeand generative parental long shoots, there was considerablebetween-individual variation in the response of individual trees.In addition, production of male catkins diminishes canopy expansionin mountain birch because the number of secondary long shootsproduced by generative parental long shoots was smaller thanthat of vegetative parental long shoots. At the branch level,the association between total long shoot growth and male catkinproduction was positive, i.e. no trade-off was found. This maybe because the strong sink strength (the ability of a branchto import assimilates from elsewhere in the tree) of branchesbearing reproductive long shoots masks possible trade-offs.We emphasize the importance of considering several levels ofthe modular hierarchy when analysing costs of reproduction inmodular organisms. Copyright 2000 Annals of Botany Company Hierarchical structure, modularity, mountain birch, short and long shoots, trade-off, Betula pubescens subsp.czerepanovii (Orlova) Hämet-Ahti     

The Effect of Day Length on the Response of Celery to Vernalization

Regimes of long photoperiods or long skotoperiods interruptedby night breaks during vernalization reduced bolting and floweringin celery (Apium graveolens L.) and decreased the stem length.However, after vernalization long photoperiods promote boltingand markedly enhance flower stalk elongation. The possibilitythat the developing inflorescence itself is the source of endogenousgibberellins which control stem elongation is discussed. It is concluded that the celery plant, in addition to its vernalizationrequirements, is a short-long day plant and not a day-neutralplant.     

Growth responses of sunflower hypocotyl disks inoculated with Escherichia coli and Agrobacterium tumefaciens I. Morphological observations

Disks of sunflower hypocotyls 1 mm thick grown in light anddarkness on agar containing mineral salts and sucrose to whichIAA was added in varying concentrations, were inoculated withE. coli, A. tumefaciens or sterile synthetic medium. Light-growndisks inoculated with E. coli proliferated from the lower surfaceand formed numerous long roots but dark-grown disks were usuallyinhibited in comparison with uninfected disks. Inoculation withA. tumefaciens induced proliferation mainly from the upper surfaceand a few short roots were formed. Uninfected disks grown with0.01 ppm IAA proliferated in a manner similar to that of E.coli-infected light-grown disks on simple medium but in thedark similar treatments produced quite different morphologicaleffects. The form of proliferation induced by E. coli underall conditions of growth could not be equated with that inducedby A. tumefaciens or by different concentrations of IAA. (Received December 5, 1967; )     

Influence of Photoperiod on Culm Elongation and Apical Development in Semi-dwarf and Standard-height Wheats

Flower initiation (FI) coincided with the commencement of culmelongation under both long (18 h) and normal (104–144h) photoperiod in eight spring wheats, including both gibberellicacid-sensitive and -insensitive types, which differed widelyin photoperiod sensitivity At FI the apex was significantly (P = 005) higher (above ground)in three of the wheats under long, compared with normal photoperiod;with no difference between the remaining five. Differences inresponse were not related to photoperiod response or gibberellicacid-sensitivity/insensitivity differences between the wheats. Long photoperiod prolonged the phase from terminal spikeletinitiation (TSI) to anthesis (A) in all the wheats, except Sunset(with the greatest photoperiod insensitivity), with no cleardifferences in response between semi-dwarf and standard-heightwheats. Respective rates of culm elongation from FI to TSI were lowerunder normal, compared with long, photoperiod in all varieties.That from TSI to A was unaffected by photoperiod, except inSunset when it was significantly (P = 001) slower under long,compared with normal photoperiod. Rate of culm elongation from FI to TSI across cultivars andphotoperiods was inversely related to spikelet number per head(r = –053, P = 005) but not to rate of spikelet initiation(r = –014 n.s.). Gibberellin-sensitivity, spikelet number, flower initiation, terminal spikelet initiation     

Growth and flowering of Lemna paucicostata I. General aspects and role of chelating agents in flowering

Lemna paucicostata HEGELM. is normally a short-day plant andflowers only in the presence of a chelating agent (EDTA or EDDHA)in the medium. The plant can be induced to flower even by asingle long night treatment; the flowering percentage, however,increases with further inductive cycles. The length of the criticaldark period depends upon the chelating agent employed in themedium. It is between 10 and 12 hr in the medium containingEDTA and about 8 hr in the EDDHA-supplemented medium. Red lightinterruption in the middle of the dark period—even fora minute—is inhibitory for flowering. Attempts to identify the metal ion(s) chelated reveal that thechelating agents affect flowering by facilitating iron uptake.This is also supported by the fact that the requirement of achelating agent for flowering can be overcome with an excessof iron in the medium. Interestingly, provision of EDDHA andexcess of ferric citrate, together, can bring about floweringeven under long days. ¹Originally HEGELMAIER (1) designated L. paucicostata as a separatespecies; however, THOMPSON (2) and DAUBS (3) have treated itsynonymous to L. perpusilla. More recently, based on physiologicaland chemotaxonomic studies, the distinctiveness of L. paucicostatafrom L. perpusilla has been favoured (4, 5). (Received September 8, 1969; )     

In Vitro Culture of a Root Parasite, Aeginetia indica L. II. The Plane of Cell Division in the Tendril

Factors affecting septation (cell division) of the tendril whichfacilitates the organic connection with the host were studiedin a root parasite Aeginetia indica L. Transverse cell division,which occurs perpendicular to the long axis of the tendril,was promoted by additions of sucrose, glucose and cytokininsto the basal medium. Longitudinal cell division of the tendril,which takes place parallel or obliquely to the long axis, wasstimulated by cytokinins, but not by sucrose. The latter typeof cell division was frequent in basal and sub-basal cells ofthe tendril but was extremely rare in apical cells. The orientationof the planes of these cell divisions was closely related tocell shape. Abnormal growth of the tendril was seen in germinatingseeds grown for six weeks or more in media containing both Miscanthus(a host) root extract and cytokinin. (Received February 23, 1984; Accepted June 12, 1984)     

Effect of nitrate concentration in the medium on the flowering of Lemna paucicostata 6746

Addition of copper or tungstate to or exclusion of molybdenumfrom M-sucrose medium induced long-day flowering in Lemna paucicostata6746 provided the medium contained sufficient nitrate. By contrast,ferricyanide, cyanide or silver induced long day flowering evenin nitrate-deficient, M-sucrose medium. (Received August 26, 1977; )     

Differential Accumulation of Heterochromatin as a Cause for Karyotype Variation in Phalaenopsis Orchids

Karyotypes of nine Phalaenopsis species and the closely relatedDoritis pulcherrima were compared based on Feulgen- and DAPI-stainedsomatic metaphase chromosomes prepared from root tips. All specieshad the same chromosome number (2n = 2x = 38), but their karyotypesdiffered markedly in absolute chromosome size, relative chromosomesize, and the position of the centromere. Both genome size andthe amount of constitutive heterochromatin (CH) varied widelyamong the species studied, and there was a positive correlationbetween these two parameters. The distribution of CH in thegenomes was non-random: one or both arms of long chromosomesusually possessed large blocks of CH, while the small chromosomescontained little or no CH. DAPI-staining revealed that mostCH regions are rich in AT base pairs. We suggest that differentialaccumulation of CH is a major cause for karyotype variationin Phalaenopsis orchids. Copyright 2001 Annals of Botany Company Phalaenopsis, Doritis pulcherrima, karyotype differentiation, constitutive heterochromatin, total chromosome volume, nuclear DNA content     

The Structure of the Gonads, Gametogenesis, and Sperm-Egg Interactions in the Anthozoa

In the Anthozoans Metridium sp. and Bunodosoma cavernata thetestes are located in the secondary septa. The cysts of thetestis are surrounded by mesoglea. Bounding the mesoglea oneach side of the septa is the gastrodermis. The gastrodermalcells exhibit interesting flagellar specializations. Each cellhas a flagellum which extends into the gastrovascular cavityand is surrounded by long microvillus-like extensions. It issuggested that these specializations may serve in a sensorycapacity. The periphery of the testicular cysts contains the early spermatogenicstages, while spermatids and sperm are more centrally located.In both Metridium sp. and B. cavernata the early spermatidsare connected by intercellular bridges. These spermatids exhibitearly flagellar formation. The distal centrioles have two associatedspecializations, satellites and pericentriolar processes. Duringspermiogenesis there is a general polarization of the cytoplasmand several maturational events occur more or less simultaneously.Nuclear condensation begins, mitochondria aggregate and fuse,and lipid-like inclusions associate with this mitochondrialcomplex. Concave or "donut" shaped vesicles are noted in associationwith Golgi complexes. The sperm of both species contain electron dense nuclei, lackdistinct acrosomes but have vesicles associated with the lateralsides of their heads between the nuclear envelopes and plasmamembranes. In both sperm, lipid-like inclusions are associatedwith complex mitochondrial bodies. The sperm of Metridium exhibit an interesting membrane responsewhen exposed to eggs. The plasma membrane along the side ofthe head of the sperm sends out long finger-like protrusions. The eggs of both Metridium sp. and B. cavernata exhibit corticalreactions. In Metridium the dehisced cortical substance appearsto be lost to the environment, while in B. cavernata it formsa flocculent coat around the egg.     

Intracellular Silica Deposition in Mature and Senescent Leaves of Sieglingia decumbens (L.) Bernh

Following 1, 2, 4, or 8 weeks of growth in a silica-minimalsolution, tillers of Sieglingia decumbens (Heath Grass) weretransferred for 8 days to a nutrient solution which contained50 or 100 ppm silica. The resultant formation of intracellularopal phytoliths (silica bodies) was compared for the four developmentalstages of leaf 3. Characteristically different phytolith typesoccurred in leaves of different ages. Senescent, in contrastto younger, mature leaves, typically exhibited extensive extracellularsilicification of the mesophyll, in addition to deposits instomatal, long, and bulliform cells of adaxial epidermis; depositionin abaxial silica cells and long cells, characteristic of youngleaves, was much reduced, or absent. Physico-chemical factors and cytoplasmic changes associatedwith senescence are discussed in relation to intracellular opalphytolith formation in mature leaves of S. decumbens. In thisrespect, the tendency of silicic acid sols to polymerize inthe presence of an organic matrix and mineral cations is consideredto be significant.     

Nucleotide and copy-number polymorphism at the odorant receptor genes Or22a and Or22b in Drosophila melanogaster

In Drosophila, odorant receptors are encoded by an old and moderatelysized multigene family. Or22a and Or22b are two tandemly arrangedgenes of this family that have proved to be the result of arather young duplication. Nucleotide variation in the regionspanning both duplicates was surveyed in four natural populations(two African and two non-African) of Drosophila melanogasterand also analyzed in species of the melanogaster subgroup. Theintraspecific survey revealed a particular copy-number polymorphismin some of the studied populations, with the two genes (Or22aand Or22b) present in the long variant and a single chimericgene (Or22ab) present in the short variant. Estimated nucleotidediversity was higher in the short than in the long variant,despite the ancestral character of the latter variant in D.melanogaster. The general skew toward low-frequency variantsdetected in the non-African long variant and its reduced levelof silent polymorphism relative to divergence is consistentwith the recent fixation of an advantageous mutation at, ornearby, the Or22 long variant region. The nonnegligible frequencyof the short variant and the presence of a highly divergenthaplotype in the East African sample would point to direct orindirect selection for its maintenance in the species. Therewas evidence for a generally more rapid evolution of the Or22bcopy at both synonymous and nonsynonymous sites. However, anexcess of nonsynonymous substitutions was only detected in theearly history of this copy.     

Flowering in Lentil (Lens culinaris Medic.): The Duration of the Photoperiodic Inductive Phase as a Function of Accumulated Daylength above the Critical Photoperiod

The durations from emergence to the appearance of first flowerbuds and to first open flowers were recorded in three genotypesof lentil (Lens culinaris Medic.) when plants were transferredfrom short days (either 8 or 10 h) to long days (16 h), or viceversa, after various times from emergence. These results werecompared with those of control treatments in which plants remainedin either short or long days throughout. Four developmentalphases were identified: pre-emergence, pre-inductive, inductiveand post-inductive. The first two phases and the last are insensitiveto photoperiod, but are probably sensitive to temperature. Theduration of the inductive phase, which has to be completed beforeflowering can occur at the end of the post-inductive phase,can be predicted by assuming that its reciprocal is a linearfunction of both photoperiod and temperature. It follows thatthe critical photoperiod decreases with increase in temperatureand that the duration of the inductive phase can be calculatedfrom a summation of the amounts by which successive daylengthsexceed the critical photoperiod until a value (‘the photoperiodicsum’) characteristic of the genotype is reached. The implicationsof these findings for predictive field models of time to floweringin lentils are discussed. Lens culinaris Medic., lentil, flowering, critical photoperiod, photoperiodic sum, temperature, developmental phases, field models     

Studies in the Physiology of the Onion Plant: IV. THE INFLUENCE OF DAY-LENGTH AND TEMPERATURE ON THE FLOWERING OF THE ONION PLANT

At temperatures above about 17° C. inflorescence initiationin growing onion plants, as in stored sets, is suppressed whetherthe plants are kept in long or short days. Independently ofcurrent day-length and of previous day-length treatment, ifthe plants are sufficiently large initiation begins very shortlyafter the temperature falls below c. 15° C. Emerged infiorescencesappear some ten or so weeks later. Small plants are unable toinitiate inflores cences under any of the conditions tested,and actual size (perhaps leaf area) rather than leaf or nodenumber seems to be the important factor. Inflorescence emergenceis suppressed at high temperatures in short days or long days;in long days bulb formation also suppresses emergence at lowertemperatures. In long days at temperatures sufficiently lowfor bulbing to be delayed, however, emergence is accelerated.Plants which have produced bulbs in long days in the summershow a delay of inflorescence emergence in the following winter.     

A morphological study of two populations of Bosmina longispina exposed to different predation

Two populations of Bosmina longispina existing in two similarand closely situated Norwegian mountain lakes were investigatedwith respect to morphological variations. The two lakes areinhabited by different predators, Lake Gopollen is dominatedby whitefish and Lake Djupen by a sparse population of browntrout and invertebrate predators. The B. longispina in LakeDjupen were both larger and also longer at maturation than theB. longispina of Lake Gopollen. In Lake Djupen the mucronesof B. longispina were twice as long and their relative antennulalength was also larger than in Lake Gopollen. However, the relativeeye size did not differ between the two populations. The observationsfit the present hypothesis on morphological predator avoidanceadaptations in B. longispina, fairly well. Invertebrate predatorsfavour large B. longispina with long protuberances, body sizeand length of mucro being the most important features.     

Flowering Behaviour of Four Annual Grass Species in Relation to Temperature and Photoperiod

Populations of four co-habiting annual grass species Bromusmollis L. (Soft brome), Hordeum hystrix Roth (Mediterraneanbarley grass), Lolium rigidum Gaud. (Wimmera ryegrass) and Vulpiabromoides (L.) S. F. Gray (Squirrel-tail fescue) were examinedfor the presence and comparative levels of vernalization andphotoperiod response. This was evaluated as the number of daysfrom sowing to heading in both long (16 h) and short (normal,over-winter) photoperiods at two levels of temperature. Wide variation among the species in both vernalization and photoperiodicresponse was detected. L. rigidum possessed a high level ofvernalization response and was comparatively sensitive to photoperiodwhile V. bromoides possessed little or no vernalization responseand was comparatively insensitive to photoperiod. B. mollisand H. hystrix appeared to be intermediate between these twospecies for both responses. There were wide differences in timeto heading under long photoperiod (16 h) and high temperature(20 °C) of plants derived from seed of three of the speciesripened under non-vernalizing temperatures. This variation indicatesthe likely existence of genetic differences in vernalizationresponse between plants of these populations. The implications of these findings to the adaptability of thesespecies to the Australian environment have been outlined. Bromus mollis L., soft brome, Hordeum hystrix Roth, Mediterranean barley grass, Lolium rigidum Gaud, Wimmera ryegrass, Vulpia bromoides (L.) S. F. Gray, Squirrel-tail fescue, flowering, vernalization, photoperiod, temperature