Observations with the Electron Microscope on a Species of Saprolegnia

Electron micrographs are presented to show the morphology ofthe flagella in each of the two motile phases of Saprolegniaferax, and one visual light photograph of a stained cell ofthe second stage is added. The front flagellum of both phasesis a Flimmergeissel with hairs between 2µ and 3µlong arranged in two rows and each ending in a thin hair-point.The axis is covered by a wide transparent sheath made of somematerial which appears to liquefy after death. The hind flagellum,which is devoid of Flimmer, is covered by a similar sheath,though there are signs that this is flattened into a fin inthe hind flagellum of the second stage. Some very fine shorthairs 0?5µ long are interpreted as a possible internalframework to this fin. The axis of both flagella is fibrillar,but accurate numerical details have not yet been obtained. Theskins discarded from cysts have also been examined and shownto be covered with characteristic double-headed hooks, whichare strong enough to attach a cyst to passing objects.     

Further Observations with the Electron Microscope on Spermatozoids in the Brown Algae

Observations are recorded for Ascophyllum, Pelvetia, Himanthalia,and Dictyota in addition to Fucus which has already been describedin a previous paper. Fibrillar disintegration of cilia has beenobtained in all except Pelvetia, in each case to give nine peripheralstrands and a central pair. This corrects a previous error forthe hind flagellum of Fucus. Some facts are given regardingthe internal organs associated with the parts of the cilia insidethe body in Himanthalia and Dictyota. A proboscis similar tothat previously described for Fucus has been demohstrated inAscophyllum and Pelvetia, but is absent from Himanthalia andDictyota. Himanthalia differs from the other Fucoids in therelative lengths of front and hind flagella. Dictyota has onlya single flagellum. In all, the front flagellum is a Flimmergeisselwith two rows of hairs, which, in certain cases, notably Himanthalia;have very long hair points. In Himanthalia there is a largespine near the distal end of the front flagellum borne on onefibril of the peripheral series. In Dictyota there is a rowof smaller spines at the front end of the flagellum borne ina line between the two lateral rows of hairs. These spines inDictyot can be used as evidence regarding the internal symmetryof the whole cilium which is summarized in a diagram.     

Further Observations on the Structure of Plant Cilia, by a Combination of Visual and Electron Microscopy

By combining visual microscopy of stained material with electronmicroscopy it has been possible to demonstrate fibrillar disintegrationin the cilia of Saprolegnia (front and back), Chlorosaccus (frontand back), Allomyces, and Olpidium. These represent three fungiand a yellow-green alga. All flagella showed eleven componentstrands, in most cases clearly differentiated into nine strandsand a central pair. In addition, stained and unstained materialof Saprolegnia and Chlorosaccus have been closely compared inthe electron microscope and the comparison has included observationson one and the same cell with die electron microscope and thelight microscope. The nature of the artifacts produced by staininghas been investigated and the value of the combination of thesevarious technical processes demonstrated. The phyletic importanceof the hairs on the front flagellum in the yellow-green algae,brown algae, and water moulds is discussed.     

Observations on the Internal Structure of the Spermatozoid of Dictyota

The spermatozoid of Dictyota is shown to be structurally morelike a vegetative zoospore than was the case in Fucus. The mitochondria,golgi, overall shape of the nucleus, nuclear membrane, fat bodies,and miscellaneous vesicles are as in a zoospore; there is, however,a vestigial chromatophore without an eyespot and the ciliaryapparatus is specialized. In spite of the single flagellum thereare two basal bodies inside the cell, one of which is apparentlyvestigial, ending blindy in the cytoplasm; both the a similarinternal structure with nine fibres in the wall. A fibrous ‘root’,possibly homologous with the ‘proboscis’ of Fucus,arises near the outer side of the functional basal body; itis a band of about eight fibres passing through the cell withouttouching the nucleus but closely pressed to the inner facesof at least two mitochondria before ending in an unknown mannerat the cell surface. The internal structure of the flagellumis normal but the fact that the median strand is marked by arowspines has been used to demonstrate is a conclusive way thefacts of bilateral symmetry in the whole organ; Dictyota agreesexactly with Fucus and a previous error based on incompleteinformation has been corrected. The process of unwinding ofthe flagellum from the surface of the body after liberationfrom the antheridium is described and used to illustrate someunexpected properties of the surface membrane.     

Transition of bacterial flagella from helical to straight forms with different subunit arrangements.

We have found that several kinds of helical flagella from Salmonella and Escherichia become straight in the presence of 0·5 m-citric acid at pH values below 4·0, while the straight flagella from a mutant Salmonella (SJ814) are transformed into a helical shape under the same conditions. These transformations are reversible and transitional.Current models of bacterial flagella (Calladine, 1976,1978; Kamiya, 1976) predict that the family of distinct wave-forms should include two types of straight flagella, which have either an extreme right-handed twist (about 7 ° at the surface of the flagellum) or an extreme left-handed twist (2 ° to 3 °). As the inclination of the near-longitudinal rows of subunits in the Salmonella SJ814 flagellum (O'Brien &; Bennett, 1972) agrees closely with the degree of twisting predicted for the right-handed type, this flagellum has been considered to be the right-handed type. We have determined that the basic (1-start) helix in flagella is right-handed, using the method of Finch (1972). This fact, together with the selection rule (O'Brien &; Bennett, 1972), strongly suggests that the near-longitudinal rows in an SJ814 flagellum are right-handed, in agreement with the prediction. However, our optical diffraction and X-ray diffraction studies have revealed that the near-longitudinal rows of subunits in the citric acid-induced straight flagella and in the straight flagella from a mutant E. coli (Kondoh &; Yanagida, 1975) tilt at an angle of 2 ° to 3 ° with respect to the flagellar axis. This inclination is probably left-handed. Thus the predicted presence of the two types of straight flagella seems to be proved.     

Stomatal Pattern in Four Species of Monocotyledons

The distribution of stomata has been investigated in the leafepidermis of Chlorophytum comosum, Galanthus nivalis, Schizostyliscoccinea and Scilla lancifolia. The epidermis was consideredto consist of units of construction of two kinds: type A, along epidermal cell with a stoma at its distal end, and typeB, a long epidermal cell without an associated stoma. Exceptin Scilla, the probability of an epidermal unit being type Aincreases approximately with its length. Considering the epidermisas rows of units, alternating sequences of type A and type Bdo not occur randomly along the rows. In Chlorophytum, Galanthusand Schizostylis, both type A and B units tend to be aggregatedinto longer sequences than would be expected on a random basis.It is suggested that homoeogenetic induction (i.e. of like bylike) may be occurring during development. No case can be madefor homoeogenetic induction of units in Scilla. There is a slighttendency to periodicity of distribution of type A units in Galanthus,Schizostylis and Scilla, but this does not seem to representa primary element of pattern. There is interaction between rowsin the sense that unit ends (transverse walls) tend to avoidthose in neighbour rows; this affects the relative distributionof stomata, but there is no evidence of any direct interactionbetween stomata in different rows. Chlorophytum comosum, Galanthus nivalis, Schizostylis coccinea, Scilla lancifolia, leaf, epidermis, stomata, pattern     

On the Embryogeny of Three Taxa of Paepalanthoideae (Eriocaulaceae)

Embryo development in Leiothrix nubigena, Paepalanthus bifidusand Syngonanthus nitens is described. Distinct differentiationof cotyledonary and epicotyledonary sectors in the three taxais demonstrated. The cotyledonary and the epicotylary loci shareequal amounts of the embryonic shoot apex as in most monocotyledons.The cotyledon and its adjacent epicotyl are both terminal onthe embryonic axis. The basal cell of the two-celled proembryocontributes two basal rows of cells at the radicular pole inthe ripe seed. A typical radicle is not organized. Leiothrix nubigena, Paepalanthus bifidus, Syngonanthus nitens Paepalanthoideae, Eriocaulaceae, embryogeny     

A Comparative Ultrastructural Study of Cyanidium caldarium and the Unicellular Red Alga Rhodosorus marinus

The presence of nucleus, chloroplasts, mitochondria, microbodiesand a vacuole are confirmed in Cyanidium caldarium strain CCAP1355/1. Chloroplasts usually contain parallel rows of unstackedthylakoids surrounded by a peripheral thylakoid, although theconcentric arrangement has also been observed. The chloroplastenvelope consists of two closely appressed membranes which canonly be resolved after gluteraldehyde—osmium fixation.The chloroplast of Rhodosorus marinus also contains parallel,unstacked thylakoids surrounded by a peripheral thylakoid but,in addition, a prominent, stalked pyrenoid projects into thecytoplasm and is bounded by both the peripheral thylakoid andthe chloroplast envelope. This structure is covered by a capof starch grains and contains membranous vesicles in the matrix.Phycobilisomes are absent from the chloroplasts of both algae.The recognition of C. caldarium as a rhodophyte is supportedby these observations. Cyanidium caldarium, Rhodosorus marinus, chloroplast ultrastructure     

Twist (and rotation?) of central-pair microtubules in flagella ofPoterioochromonas

Summary The chrysoflagellate algaPoterioochromonas bears two unequal flagella. There is a short naked one and a long flagellum with mastigonemes. Ultrastructural investigation reveals that the centralpair microtubules in both flagella have no fixed position with respect to the flagellar base and root system, or the mastigoneme rows in the long flagellum. The central-pair microtubules are twisted several times along the length of the flagellum. This might indicate active or passive rotation of the central-pair microtubules during flagellar beat.     

Effect of divalent cations on flagellar scales in the green flagellateTetraselmis cordiformis

Summary The structure and topography of flagellar scales (underlayer scales, rodshaped scales, hair-scales) in the green flagellateTetraselmis cordiformis has been studied in detail and the effect of divalent cations and fixation conditions on scale structure and topography was followed quantitatively. Hair-scales occur in two rows on opposite sides of a flagellum and are linked to the flagellar membrane and to two axonemal doublets by B-tubule-flagellar membrane connectives. Underlayer scales form about 24 longitudinal rows along the flagellum and occur in two distinctive shapes (pentagonal and square). The square shaped underlayer scales are related in position to the attachment sites of the hair-scales. Rod-shaped scales occur in about 20 longitudinal rows along the flagellum and are characteristically positioned as double scales. Calcium in the culture medium is necessary to retain rod-shaped scales on the flagellum, absence of calcium or chelation with EGTA or pyrophosphate leads to disappearance of rod-shaped scales from the flagellum. Other divalent cations can only partially substitute for calcium. It is suggested that calcium provides the linkage between underlayer scales and rod-shaped scales inTetraselmis. Flagellar scales inTetraselmis apparently fall into two categories: a) hair-scales (not affected by fixation or absence of divalent cations, firmly bound to axonemal microtubules via the flagellar membrane), b) underlayer scales and rod-shaped scales (affected by fixation and absence of divalent cations, kept on the flagellum mainly by electrostatic forces). The function of flagellar scales inTetraselmis is discussed.     

高温对小地老虎和东方粘虫精子发生和形成的影响

小地老虎和东方粘虫精子发生之后,开始分化出真核精子和无核精子。当温度超过32℃时,出现大量的畸形精细胞囊,精子形成受阻,核与鞭毛明显缩短,鞭毛中微管所受影响最大。但32℃温度以下不影响真核到无核精子的发生和二叉发生的转换。由此可见,小地老虎和粘虫夏季由南向北迁飞也是一种回避高温的适应性行为。     

RADULAR PRODUCTION RATES IN TWO SPECIES OF LACUNA TURTON (GASTROPODA: LITTORINIDAE)

The molluscan radula is a dynamic organ, both in terms of itsuse and production. New rows of teeth are constantly producedat the posterior end of the radula, while older, worn teethare shed anteriorly, producing a dynamic equilibrium. We useda cold-shock to mark the radular ribbon and measure tooth rowproduction rates in two gastropod species, Lacuna vincta (Montagu)and L. vanegata Carpenter. We found that the average tooth rowproduction rate at 10–11°C did not differ betweenthese two species, and was 2.94 (SE = 0.002) rows per day forLacuna vincta and 2.97 (SE = 0 002) for L. vanegata Inter-individualvariability in production rate was very low, and was correlatedwith shell length, smaller individuals had slightly higher productionrates. The total length of the radular nbbon varied greatlyamong individuals, ranging from 47 to 94 (2.57 to 5.68 mm) rowsin L vincta and 53 to 99 rows (2.80 to 7.14 mm) in L vanegata,and was only somewhat correlated with the length of the shelLThis great variability will result in large differences amongindividuals in the time it takes to replace the radula totally,from 14.96 to 35.44 days in L vincta and from 17 43 to 39 69days in L. vanegata. (Received 1 September 1995; accepted 20 November 1995)     

Sexual harassment in live-bearing fishes (Poeciliidae): comparing courting and noncourting species

Sexual harassment by males has been reported from several live-bearingfishes (Poeciliidae) and has been shown to inflict costs onfemales. For example, poeciliid females have reduced feedingopportunities when accompanied by a male because females dedicateattention to avoiding male copulation attempts. Poeciliid speciesdiffer considerably in male mating behavior, such as the presenceor absence of courtship. Courting males display in front ofthe females, but males attempting to sneak-copulate approachfemales from behind, that is, in the blind portion of theirvisual field, and force copulations, which can be viewed asa male persistence trait. We predicted that poeciliid femalesneed to be more vigilant in the presence of noncourting males,and costs of harassment by noncourting males might be stronger.In a comparative approach we examined the costs of male sexualharassment for females as reduced feeding time in 9 speciesof live-bearing fishes, including courting (Poecilia latipinna,Poecilia reticulata, Xiphophorus cortezi, Xiphophorus variatus)and noncourting species (Poecilia mexicana [surface- and cave-dwellingform], Poecilia orri, Gambusia affinis, Gambusia geiseri, Heterandriaformosa). In all species examined except for the cave form ofP. mexicana, focal females spent significantly less time feedingin the presence of a male than when together with another female.The time females spent feeding was found to significantly declinewith increasing male mating activity (sum of all sexual behaviors),but there was no support for the idea that females would spendmore time feeding in the presence of courting males comparedwith noncourting ones.     

Responses of the Root Systems of Sunflower and Maize to Unidirectional Stem Flexure

Plants of two contrasting species of herbaceous annuals, thedicot sunflower (Helianthus annuusL.) and the monocot maize(Zea maysL.), grown in the glasshouse were subjected to regularunidirectional stem flexure. Differences in morphology and mechanicalproperties of roots and shoots were then investigated. Rootsystems were divided into quadrants around the axis of stimulationand differences in root morphology and mechanics between thezones were investigated. There were considerable differencesbetween roots in the leeward and windward zones compared withroots perpendicular to the axis of stimulation. First-orderlateral roots in both species were thicker, more rigid and morenumerous. These results suggest that plant roots respond locallyto mechanical stimulation. There were, however, also differencesin the responses of the two species. In sunflower, the tap rootand stem base became elliptical in cross section with the majoraxis lying in the plane of stimulation. The lateral roots offlexed sunflowers in both the leeward and windward zones showedsimilar growth responses: roots were thicker, more numerousand weighed more than those in the perpendicular zones. However,only leeward roots showed significant differences in their mechanicalproperties; roots were more rigid, stronger and stiffer. Incontrast, the leeward roots of maize were thicker and more numerous,with a greater biomass than the windward roots. However, onlyroots in the windward zone were stiffer than those in the perpendicularzone. These differences between sunflower and maize are relatedto their contrasting anchorage mechanics.Copyright 1998 Annalsof Botany Company Anchorage, biomechanics, adaptive growth, roots, thigmomorphogenesis,Helianthus annuusL.,Zea maysL.     

Analysis of the Variation Potential Induced by Wounding in Plants

Following burning of a leaf portion, a bioelectrical wave called"variation potential" spread throughout the whole plant. Bioelectricalvariations are recorded by two types of electrodes (platinumwires and Ag/AgCl nonpolarizable electrodes) in the stem ofVicia faba and in the petiole of Lycopersicon esculentum andMimosa pudica. The time course of the variation potential thusrecorded can be divided into two components respectively calledcomponents "A" and "B". Component A looks like a negative spikybioelectrical change lasting about 1 min with an amplitude of20–50 mV spreading in front of the component B depictedby a more smooth and long-lasting (several min) wave of negativity.An attenuation of the signals recorded under the Ag/AgCl electrodesis noted compared to that recorded under the platinum wires.Moreover, component B is more attenuated than the componentA. Attenuation of the component A is nearly the same as thatnoted for the action potential in Mimosa pudica. All the parameters depicting the variation potential increaseapproximately in direct proportion to the amount of the damagedarea up to 400 mm² in Vicia faba; above this value, a maximalresponse is reached. (Received October 18, 1984; Accepted January 14, 1985)     

Motion of the Longitudinal Flagellum in Ceratium tripos (Dinoflagellida): A Retractile Flagellar Motion1

The longitudinal flagellum of Ceratium tripos moves in two dissimilar ways: undulation and retraction. The undulatory wave is planar and has a wavelength of 74.3 ± 9.6 μm and an amplitude of 14.2 ± 2.3 μm in sea water. The beat frequency is 30 Hz at 20°C, pH 8.0. The retractile motion is unique to Ceratium and is triggered by mechanical stimulation on the cell body, especially at the tip of the apical horn. When it retracts, the longitudinal flagellum folds every 4–5 μm along the flagellum. Cinematographic study showed that the flagellum folded from tip to base and was finally installed into the sulcus, a groove on the ventral side of the cell. This motion is completed in sea water within 28 msec. The retracted flagellum then re-extends and restores the undulation within a few seconds. The flagellum unfolds in the proximal portion first, then the distal, and finally the middle portion. Fixation always triggers the retraction. Scanning electron microscopy showed that the flagellum is folded and secondarily twisted in a helix. A new fiber in addition to the flagellar axoneme was found in the retracted flagellum by phase microscopy. This fiber (R-fiber) seems to contract during the retraction to fold the flagellum.     

Early scale development in Heterodontus (Heterodontiformes; Chondrichthyes): a novel chondrichthyan scale pattern

In two species of Heterodontus, H. portusjacksoni and H. galeatus, the first scales to develop form two opposing rows along the caudal fin axis on both the left and right sides of the fin. The opposing rows originate from an initial scale located on either side of the posterior tip of the caudal fin, with subsequent scales erupting in a posterior to anterior direction along the tail axis. These scale rows may strengthen tail movements, providing aeration in the egg case, but are lost later in ontogeny. Development of subsequent body scales shows a more irregular origin and arrangement, from anterior to posterior, to cover the dorsal and ventral lobes of the caudal fin. Although the early developmental pattern of the scale associated with the Heterodontus caudal fin has not been previously described, several chondrichthyan taxa, including chimeroids, likewise possess ordered rows of flank scales early in ontogeny that are subsequently lost. These ordered scales contrast with previous suggestions that chondrichthyan scale development is entirely random. Instead, regulated and sequential development of scales may be a plesiomorphic character for both chondrichthyans and osteichthyans, with the less organized arrangement in later ontogenetic stages being a derived condition within Chondrichthyes.     

Ultrastructure of the flagellar apparatus inPyramimonas octopus (Prasinophyceae)

Summary While green algae usually lack one of the outer dynein arms in the axoneme, flagella of the octoflagellated prasinophytePyramimonas octopus possess dynein arms on all peripheral doublets. The outer dynein arm on doublet no. 1 is modified, and additional structures are associated with doublets no. 2 and 6. The flagellar scales are asymmetrically arranged. Thus the two rows of thick flagellar hairscales are displaced towards doublet no. 6,i.e., in the direction of the effective stroke of each flagellum. The underlayer of small scales includes two nearly opposite double rows scales, arranged in the longitudinal direction of the flagellum. The hairscales emerge from these rows. The double rows are separated on one side by 9, on the other by 11 rows of helically arranged scales. The central pair of microtubules twists, but the axoneme itself (represented by the 9 peripheral doublets), does not seem to rotate. The flagella are arranged in two groups, showing modified 180° rotational symmetry. The effective strokes of the two central flagella are exactly opposite, while the other flagella beat in six intermediate directions.