Junction Complexes between Sieve Tubes in the Secondary Phloem of Myrtaceae

Junction complexes of unusual structure form between neighbouringsieve tubes in the secondary phloem of Eucalyptus species. Thick-walledribs support thin-walled ‘sieve areas’. In longitudinalsections the structures have a ‘concertina’- likeappearance. They are relatively large, up to 0.2 mm in length.Electron micrographs confirmed that the structures consistedof thin-walled areas perforated with pores, supported by muchthicker ribs. The structures provide a vast surface area fortransfer of metabolites between sieve tubes compared with thatof lateral wall sieve areas of other plants. Hydrolysis of parenchymacell walls occurs during the development of the junction complexes.The structures are only found when sieve tubes are in closeproximity and it is the redifferentiation and partitioning ofintervening parenchyma cells which result in junction complexformation. A survey for the presence of the structures in thephloem of other genera in the family Myrtaceae was made andthey were found in Tristania and Angophora but were not observedin Acmena and Metrosideros. Eucalyptus, sieve tubes, lateral walls, ultrastructure     

Pistil Structure and Pollen Tube Pathways in Leptospermum myrsinoides and L. continentale (Myrtaceae)

Pistil structure and pollen tube growth were investigated inLeptospermum myrsinoides and L. continentale (Myrtaceae). BothL. myrsinoides and L. continentale pistils consist of an ovarywith five locules, a style and a five-lobed dry, papillate stigma.A centrally located stigmatic cleft is present but extends onlyto the base of the stigma. Pollen germinates and grows intercellularlythrough the stigma into the central transmitting tissue of thestyle. Pollen tubes do not grow down the stigmatic cleft. Atthe base of the style the transmitting tissue separates intofive, each tract leading through the placenta to one of thefive locules. The pollen tubes continue to grow intercellularlythrough these five tracts entering the locules between the lobesof the placenta. Pollen tubes are smooth-walled and straightwhilst in the transmitting tissue of the style but produce shortlateral branches at regular intervals when in the locules. Branchingcontinues until pollen tubes enter ovules. It is suggested thatthe observed branching in the locules is a result of pollentubes following a chemotropic or thigmotropic pathway to theovules. This behaviour was consistent in all pistils examinedand no difference was observed in the behaviour of self- orcross-pollen tubes in the style or ovary.Copyright 1994, 1999Academic Press Leptospermum myrsinoides Schldl., Leptospermum continentale J. Thompson, pistil structure, pollen tube pathway, pollen tube branching     

Promotion of the Growth of Self-Incompatible Pollen Tubes in Lily by cAMP

Cyclic AMP, forskolin and 3-isobutyl-1-methylxanthine promotedthe elongation of self-incompatible pollen tubes in Lilium longiflorum.It appears that a functional cAMP-regulated system that involvesadenylate cyclase and phosphodiesterase is present in the lilystyle and is involved in the regulation of elongation of self-incompatiblepollen tubes. (Received January 21, 1993; Accepted June 19, 1993)     

Haustorial Pollen Tubes in Fuchsia boliviana

Persistent pollen tubes have been observed in Fuchsia boliviana.It is proposed that after fertilization the pollen tube becomesan important channel conveying food materials from the surroundingtissues to the embryo. Fuchsia, pollen tubes, callosic channel, Onagraceae     

Tubulin and Male-gamete Interconnections in the Pollen Tubes of the Grass Alopecurus pratensis

Tubulin was localized in pollen tubes of the grass Alopecuruspratensis by immunofluorescence using a rat monoclonal yeastantitubulin as a primary antibody. In tubes fixed in activegrowth with paraformaldehyde fixative and permeabilized withdetergent, the two male gametes were found to be linked by tubulin-containingcytoplasmic bridges. The connections appeared to persist throughoutthe growth of the tube, but they were highly mutable, the distancebetween the gamete pair varying greatly, the gametes sometimesactually overlapping in the tube. Systems of longitudinally disposed, discrete microtubule strandscomparable with those seen in generative cells of species withbicellular pollen grains were not observed in the gametes. However,an envelope of antitubulin-binding material was apparent atthe cell boundary in many instances, possibly to be interpretedas a sheath of closely packed microtubules seen in profile.Irregular masses, probably representing pools of unpolymerizedor partly polymerized tubulin, were also present in most ofthe gametes. Alopecurus pratensis, tubulin, pollen tubes, grass male gametes     

Genetic Variation in Sorghum for the Inhibition of Maize Pollen Tube Growth

Aniline blue fluorescence was used to study the growth of maizepollen tubes in the stigmas of 13 diverse sorghum accessions.In 12, only short maize pollen tubes were formed, but in thesingle exception (Sorghum nervosum Nr481) maize pollen tubesgrew at least as far as the base of the style. The S. bicolorgenotypes S9B and CMS (a cytoplasmic male sterile line) werehybridized with Nr481, and analysis of maize pollen tube growthin F₁ plants, and BC₁ plants using Nr481 as the recurrent parent,suggested that differences in inhibition of pollen tube growthwere due to variation at a single locus, which we propose todesignate lap (Inhibition of alien pollen tubes). AccessionNr481 appears to be homozygous for a recessive allele permittingmaize pollen tube growth. Attempts were made to produce sorghumx maize hybrids using Nr481 and CMS derivatives which were knownto allow maize pollen tube growth to the base of the style.A putative hybrid endosperm was obtained in one Nr481 x Seneca60 maize cross, but this was not repeatable and no hybrid plantswere produced. A fundamental problem may be the large size ofthe maize pollen tube, which could have difficulty growing throughthe sorghum ovary and in entering the micropyle. Sorghum bicolor spp. bicolor (L.) Moench, Zea mays L, sorghum, maize, pollen tube growth, hybridization barriers     

The Significance of the Obturator in the Control of Pollen Tube Entry into the Ovary in Peach (Prunus persica)

Changes in the obturator of the peach (Prunus persica) havebeen investigated and related to pollen tube growth in thisregion. At anthesis, the cells of the obturator are active andrich in starch reserves. Twelve days after anthesis these cellsproduce a secretion that stains for carbohydrates and for proteins.As the secretion is produced, starch vanishes from these cellsand they degenerate and collapse as callose is accumulated.Secretion is independent of pollination as it takes place ina similar fashion both in pollinated and in unpollinated flowers. Pollen tube growth along the obturator surface depends on thissecretion for, although pollen tubes reach the base of the styleseven days after pollination, they cannot grow on the obturatoruntil five days later, when the secretion is produced. Thisdiscontinuous secretion taking place at the obturator may providea mechanism that controls the entrance of pollen tubes intothe ovary in the peach. Prunus persica, peach, obturator, pollen tube     

The Fine Structure of the Sieve Tubes of the Petiole of Nytnphoides peltatum (Gmel.) O. Kunze

A study has been made by electron microscopy of the fine structureof the peti-olar sieve tubes of the water plant Nymphoides peltatum.These are found to have very well-developed nacreous walls.The pores of the sieve plates appear to be filled in functioningsieve tubes with densely staining cytoplasm. The peripheralcytoplasm of the sieve tubes seems to contain an extensive developmentof the endoplasmic reticulum, whose elements become finer nearthe plates and crowd together through the pores. These findingsappear to be compatible with more than one theory of translocation,including the electro-osmotic theory of mass flow.     

Factors Inducing Successful Anhydrobiosis in the African Chironomid Polypedilum vanderplanki: Significance of the Larval Tubular Nest

The African chironomid Polypedilum vanderplanki exhibits anhydrobiosis,i.e., the larvae can survive complete desiccation. Recoveryrate and trehalose content were investigated in larvae desiccatedslowly or at a rate more than 3 times faster. Upon slow desiccation(evaporation rate 0.22 ml day^–1) larvae synthesized 38µg trehalose/individual before complete desiccation, andall of them recovered after rehydration, whereas larvae thatwere dehydrated quickly (evaporation rate 0.75 ml day^–1)accumulated only 6.8 µg trehalose/individual and noneof them revived after rehydration. In the pools that are theirnatural habitat P. vanderplanki larvae make tubes by incorporatingdetritus or soil with their sticky saliva. This tubular structureis a physical barrier not only to protect the larva from naturalenemies but also induces successful anhydrobiosis by reducingthe dehydration rate. When larvae were dehydrated with 100 µldistilled water (DW) in soil tubes, they accumulated 37 µgtrehalose/individual and more than half of them could reviveafter rehydration, whereas larvae without tubes accumulatedlower level of trehalose and none recovered after rehydration.     

Tension in the Phloem?

The hydrostatic pressure in sieve tubes may probably be estimatedreasonably accurately from experimental measurements of theosmolarity of the sieve tube sap and of the tension in the xylem.The possibility of the existence of phloem tension is advanced.     

Viability and Germination of the Pollen of Sorghum [Sorghum bicolor (L.) Moench]

Previous studies have demonstrated that pollen of sorghum [Sorghumbicolor (L.) Moench] loses capacity to both germinate in vitroand to set seed in vivo soon after being shed. The current studyevaluates the capacity for dehydrated pollen to effect in vitrogermination, reduce tetrazolium chloride, and set seed on cytoplasmicmale sterile plants. Morphological changes during pollen germinationwere examined by scanning electron microscopy (SEM). Close to70% of the pollen germinated in 5 min, or less, when collectedat 80% relative humidity (RH) and stored in sealed glass vials.Pollen tubes elongated autotropically with atmospheric humidityapparently being a controlling factor in the process. Pollendehydrated at 50% RH and 25°C for 15-30 min neither germinatedin vitro, reduced tetrazolium chloride, nor set seed on malesterile plants. Rehydrating the pollen did not restore the capacityfor germination. SEM micrographs demonstrated that elongatingpollen tubes encircled the pollen grain and were contiguousto the surface. A fibrillar-like material existed on the exineof separated pollen grains at the point where the grains hadbeen previously attached.Copyright 1994, 1999 Academic Press Sorghum pollen, germination, seed-set, viability, scanning electron microscopy, Sorghum bicolor (L.) Moench     

The Pollen Tube Pathway in the Pistil of Lycopersicon peruvianum

The pollen tube pathway has been studied in unpollinated andpollinated pistils of Lycopersicon peruvianum using histochemicalstains for detection of proteins, lipids and arabinogalactansby bright-field microscopy, and decolourized aniline blue fordetection of pollen tubes by epifluoresence microscopy. Thepollen tube pathway is a continuous tract of mucilage from thestigma surface to the ovule micropyles, and is associated witha continuous tract of specialized, protein-rich transmittingcells comprising the stigmatic papillae, vertical files of stylartransmitting cells and the placental epithelium within the ovary.The superficial exudate of the stigma is hydrophobic and richin lipids. The mucilage of the style and ovary is hydrophilicand rich in arabinogalactans but low in proteins. Pollen tubesgrow between cells through the mucilage of the stigma and stylartransmitting tract, and across the surface of the placenta inthe ovarian mucilage. The structure of the junction of the stylartransmitting tract with the top of the ovary placenta assistseffective distribution of pollen tubes within the ovary. Lycopersicon, solanaceae, fertilization, pistil, pollen tube, pollination     

Electron Microscopy of the Epidermis and Cuticle of the Needles of Pinus nigra var. maritima in relation to infection by Lophodermella sulcigena

Changes in the ultrastructure of the epidermis and cuticle ofCorsican pine (Pinus nigra var. maritima (Aiton) Melville) inrelation to infection of the needle by Lophodermella sulcigena(Rostr.) v Hohn were recorded throughout a growing season. Epidermalcells when young had thin walls and a thin smooth cuticle: bothstructures thickened with age, and the needle surface becamerough. Densely packed wax tubes developed around the stomatalpore and later became scattered over the needle surface. Themicro-flora present on the needles is briefly noted. Changesin the structure and micro-flora of needles as they aged arethought to contribute to the confinement of infection by L.sulcigena to the needle bases.     

Ultrastructure of Wall Swellings of Germinating Sporangia of Phytophthora palmivora (Butl.) Butl.

Germ tubes of directly germinating sporangia of P. palmivoraincubated in yeast extract solution at 30 ?C usually developedinto prominent swellings from which hyphae later emerged. Thegerm tubes arose as an extension of a new germination wall formedinternal to the sporangial wall prior to germination. The germtube swellings contained typical hyphal organelles. The germtube swelling possessed a thicker wall than both hyphae growingout of it and germ tubes that did not form swellings.     

Retaining the viability of Camellia japonica pollen in various organic solvents

Pollen viability in 31 organic solvents was studied. Pollengrains of Camellia japonica which had been soaked in 28 organicsolvents for 3 days retained their viability and grains in 19solvents such as ethyl acetate, n-amyl alcohol and petroleumether grew longer pollen tubes than fresh pollen. (Received July 20, 1972; )     

Successful Fertilization and Seed Set from Pollination on Immature Non-dehisced Flowers of Eucalyptus globulus

To minimize the number of visits required to achieve seed-setfrom hand pollination whilst maintaining full control of thereproductive process in Eucalyptus globulus, we investigatedthe importance of style maturation on the progamic phase ofreproduction. Controlled pollinations were performed in: (1)fully receptive styles; (2) immature cut styles at or afterflower dehiscence; and (3) immature cut styles before flowerdehiscence. We show here that pollen germination and tube growthto the ovule occurred in all three treatments, and all producedviable seeds. Remarkably, tubes growing on immature sliced stylesof non-dehisced flowers reached the ovules by day 7, 1–2d faster than tubes growing on normal receptive stigmas. Moreover,more tubes entered the ovary in this kind of pollination and,consequently, more viable seeds were produced. We establishedhistochemically that tube growth in immature sliced styles isconcomitant with the presence of lipid secretion. These resultsfully support the efficiency of the so-called ‘one-steppollination’ method in Eucalyptus globulus, which we nowprove can be applied more successfully to immature non-dehiscedflowers. General application of this procedure is likely tohave beneficial impacts on the planning and efficiency of large-scalegenetic improvement programs. Copyright 2001 Annals of BotanyCompany Eucalyptus globulus, one-step pollination, lipids, pollen, fertilization     

Rhizomorph Behaviour in Armillaria mellea (Fr.) Quel.: With one Figure in the text: Saprophytic Colonization of Woody Substrates in Soil

Rhizomorphs put out by Armillaria mellea from small woody inoculain glass tubes of moist soil were tested for their ability tocolonize segments of willow shoots, previously killed by autoclavingand then buried for various periods in soil before inoculationwith A. mellea. The degree of saprophytic colonization of thesesubstrate segments by A. mellea was assessed by reburying themin fresh tubes of moist soil, and recording weekly growth incrementsof rhizomorphs put out from them over a period of 5 weeks. Aperiod of previous burial in soil up to 3 weeks was found notto diminish availability of the substrate segments to A. mellea,but with longer periods substrate value for A. mellea progressivelydeclined. Segments of living, green shoots of willow provideda consistently better substrate for A. mellea than did deadsegments, and these living segments maintained their substratevalue over periods (up to 7 weeks) of previous burial in soil.These results are interpreted in terms of competition betweenA. mellea and other soil fungi. In the infection of living tissues,A. mellea benefits from the exclusion of competitors by hostresistance. In the saprophytic colonization of dead tissues,A. mellea has the advantage of its capacity to decompose celluloseand lignin, which are substrates restricted to a minority ofsoil fungi.     

The Effect of Puncturing Individual Latex Tubes of Euphorbia Wulfenii

A method is described for puncturing single latex tubes in situin the living tissues of a laticiferous plant. The results of this operation are recorded for Euphorbia Wulfenii,and it is shown that the plant possesses a mechanism for closingthe wound so produced, so that rapid turgor recovery of thetube occurs.     

Further Evidence of Apoplastic Unloading into the Stem of Bean: Identification of the Phloem Buffering Pool

Further evidence that sucrose is passively leaked from the sievetubes directly into the apoplast of bean stems and activelyreloaded is reported. The stem apoplast is identified as thepool of sucrose outside the sieve tubes which buffers againstsudden changes in sieve tube sucrose concentration, caused bysudden changes in sink demand or source supply. Key words: Sucrose transport, Phaseolus vulgaris, Apoplast, Phloem unloading     

Preservation of the Tonoplast in Metaphloem Sieve Elements of Embryonic Roots of Zea mays L.

Decortication of embryonic roots of 4- to 5-day-old Zea seedlingsand subsequent chemical fixation permitted comparison of cutand uncut developing sieve elements In a decorticated root wheresieve tubes are not severed, metaphloem sieve elements in latestates of development and some mature sieve elements exhibita highly vacuolate condition When roots are cut or diced inthe course of fixation intact vacuoles are not observed in latestages of sieve-element ontogeny The degree of callose formationat sites of developing sieve-plate pores and in the pores ofmature sieve elements varies greatly with both decorticationand non-decortication treatments Nuclei were not observed insieve elements at the electron microscope level, but they wereseen at the light microscope level in serial sections of sieveelements in the late to mature developmental stages representedAlthough the occurrence and distribution of plastids, mitochondria,endoplasmic reticulum, dictyosomes and nbosomes also vanes insieve elements of decorticated roots, disruption or surgingof sieve-element contents is greater for sieve tubes that aresevered during fixation treatment A discussion is presentedrelating effects of trauma on observed developmental stagesand sieve-element structure Zea mays L, maize, corn, phloem, Sieve elements, tonoplast, ultrastructure