Embryo Sac Development in Almond [Prunus dulcis (Mill.) D. A. Webb] as Affected by Cross-, Self- and Non-pollination

Embryo sac development in ‘Nonpareil’ almond wasstudied following cross-, self- and non-pollination under fieldand greenhouse conditions. The embryo sac, which develops accordingto the Polygonum type, does not begin to differentiate untilanthesis in contrast to other Prunus spp. where a well-developedembryo sac is present at the time of flower opening. The developingmegagametophyte appears to be isolated from surrounding nucellartissue by the deposition of a ring of callose, which, as indicatedby aniline blue-induced fluorescence in the walls of nucellarcells, encloses the embryo sac during its elongation. Developmentand growth of the embryo sac following the different pollinationtreatments indicated that embryo sac development was stimulatedby the presence of compatible pollen tubes in the style andfinal elongation growth of the embryo sac was promoted by cross-pollination.Irregularities in megagametophyte development, including delayeddifferentiation of the megaspore mother cell, embryo sac abortionand lack of polar nuclei fusion and embryo sac elongation, werefrequently noted in ovules of self- and non-pollinated flowers. Almond, callose, embryo sac, megagametophyte, pollination, Prunus dulcis (Mill.) D. A. Webb.     

Proline, Hydroxyproline, and Lily Pollen Tube Elongation

Cytoplasm of freshly-harvested, ungerminated Lilium longiflorum,cv. Ace pollen contains 0.14 per cent soluble and 0.35 per centprotein-bound proline (pro). Their metabolic fates in germinationand tube elongation are not known with certainty. Here is reportedconversion of pro to hydroxyproline (hyp)—containing constituentsas well as distribution and isolation of these constituents.Colorimetry revealed pro and hyp in wall, trichloroacetic acid(TCA)—precipitable, and TCA-soluble cytoplasmic fractions.A balance sheet summarizing quantitative changes in pro andhyp for these fractions revealed that TCA—precipitablecytoplasmic pro could be a precursor to wall-bound pro and asubstrate for hydroxylation yielding cytoplasmic and wall-boundhyp. To determine whether hyp was a component of tube and/orgrain walls, pollen was allowed to germinate 1.5 h and thentransferred to sorbitol medium which prevented further tubeelongation. Hyp was absent from walls of transferred pollen.Electron microscope autoradiography of tubes exposed to ²H-prosuggested that a pro- and/or hyp-containing constituent waslocalized in the growing tip. Light microscope autoradiographyof intact tubes labelled with ¹⁴C-pro showed that the constituentwas distributed throughout the pollen tubes. Gel filtrationof hyp-containing material enzymically released from walls supportedthe view that they contained hyp-glycopeptides.     

The Effects of GA3 on Weeping of Growing Shoots of the Japanese Cherry, Prunus spachiana

The effects of GA₃ on weeping were examined in the Japanesecherry, Prunus spachiana. Current-year branches first elongateupward then gradually bend to elongate downward. GA₃ appliedto apical buds promoted the upward elongation and inhibitedthe bending. Thus, GA₃ changed the direction of branches duringtheir growth. (Received April 12, 1993; Accepted February 2, 1994)     

Involvement of Polypyrimidine Tract-Binding Protein (PTB)-Related Proteins in Pollen Germination in Arabidopsis

The pollen grains of most angiosperms contain stores of RNAsand their translation products required for pollen germinationand subsequent early elongation of pollen tubes. Polypyrimidinetract-binding protein (PTB), which is involved in the regulationof pre-mRNA alternative splicing, internal ribosomal entry site(IRES)-mediated translation and mRNA localization/sorting, isknown to act as a bridging molecule between RNAs and a varietyof cellular factors to fulfill cellular functions in both thenucleus and cytoplasm. Moreover, it has been reported that PTBplays roles in the differentiation and development of animalcells and tissues. In the Arabidopsis genome, there are twoPTB-related genes, tentatively termed AtPTB1 and AtPTB2. Inthe present study, the physiological functions of AtPTBs wereinvestigated using genetic and cytological approaches. The AtPTBpromoter was highly active in vegetative cells of mature pollengrains, and AtPTB was localized in the nucleus and cytoplasmof these vegetative cells. Mutations in the AtPTB genes resultedin decreased germination efficiency, and this effect was rescuedby introduction of the AtPTB2 promoter::AtPTB2–GFP. Takentogether, these findings suggest that AtPTB is involved in pollengermination through possible RNA metabolism processes in late-maturingand mature pollen grains.     

Effect of Cutting During Reproductive Development on the Regrowth and Regenerative Capacity of the Perennial Grass, Phalaris aquatica L., in a Controlled Environment

Two cultivars of phalaris (Phalaris aquatica L.), Australianand Sirolan, were cut at four stages of development in a controlledenvironment to study factors involved in the sensitivity ofphalaris to grazing during spring. Effects on tillering, regrowthafter cutting and regenerative capacity after an artificiallyimposed summer dormant period were observed. Compared with Australian,Sirolan cut after the commencement of stem elongation was characterizedby a higher degree of decapitation due to more synchronous elevationof its apices, and displayed a more severe reduction in regrowth,size of tiller bases and dormant buds and levels of carbohydratereserves in summer relative to plants cut before stem elongation.Suppressed bud activity in tillers of Sirolan decapitated atearly stem elongation, and the potential for profuse tilleringassociated with low bud dormancy after cutting at the earlyboot stage, could reduce persistence under field conditions. Relative to plants cut before stem elongation, regenerationgrowth after 'summer' by plants cut during reproductive developmentwas depressed more severely for Sirolan (56-70%; P 0·05)than Australian (28%; n.s), a result more closely related toregenerating tiller size than number. Regeneration growth didnot differ significantly with stage reproductive developmentat cutting in either cultivar. Regenerative capacity of phalariscut during reproductive development can be considered to dependon an increasing contribution from buds on bases of tillersdecapitated when cut and a contribution from buds on intacttiller bases which declines as the stage of cutting becomeslater. The balance between these source will depend on the environment.Copyright1993, 1999 Academic Press Phalaris aquatica L., phalaris, regrowth, persistence, defoliation, cutting, perennial grass, tillering     

A Fine Structural Analysis of Auxin-induced Elongation of Cucumber Hypocotyls, and the Effects of Calcium Antagonists and Ionophores

The fine structure of epidermal cells, particularly in relationto dictyosomes, has been examined in different regions of dark-growncucumber hypocotyls and in response to auxin treatment, usingboth dot overlay and image analysis techniques. The most noticeablechange in cell structure along the hypocotyls is the increasein vacuolar volume. The volume fraction occupied by dictyosomesand secretory vesicles also increased, whereas that for mitochondriaremained relatively constant. During auxin treatment, the volumefraction for dictyosomes showed an increase after 30 min followedby a fall, whereas that occupied by secretory vesicles fellsteadily over 90 min. The number of cisternae per dictyosomeshowed some increase after 2 h of auxin treatment, althoughthe increase in dictyosomal material with cell expansion waslargely accounted for by an increase in the number of dictyosomes. Auxin-stimulated elongation growth of the hypocotyls was inhibitedby a range of calcium antagonists, chelators and ionophores.The most marked inhibitions were observed with calcium chloride,the chelator chlortetracycline and the ionophores verapamil,nigericin and monensin. Linear transducer experiments showedthat these compounds generally caused an immediate reductionin the rate of growth. Fine structural observations carriedout on epidermal cells showed the most obvious effects withmonensin and nigericin which caused dictyosomes and secretoryvesicles to swell. EGTA and LaCl₃ caused secretory vesiclesto accumulate around dictyosomes, while the ionophore A23187had little effect. The results suggest that the concentration of Ca²⁺ in the cytoplasmmay be critical for cell elongation. Compounds which chelateCa²⁺ appear to be more effective inhibitors of growth in theinitial acid-induced phase, whereas those which affect ionicgradients are more disruptive in the second phase.Copyright1993, 1999 Academic Press Calcium, Cucumis sativus hypocotyle, dictyosomes, elongation growth, indoleacetic acid, stereology     

The Role of DNA Synthesis During Hypocotyl Elongation in Light and Dark

Fluorodeoxyuridine, an inhibitor of DNA synthesis, did not affectgermination and post-germinative growth in the aerial part oflettuce and Haplopappus gracilis seedlings when grown in thelight. In the dark, however, elongation of the hypocotyl wasinhibited by fluorodeoxyuridine, strikingly in lettuce and onlyslightly in Haplopappus gracilis. This could imply that thecontrolling mechanism of hypocotyl elongation is in some casesrelated to DNA synthesis, either because mitotic processes (oftenlittle taken into account in considering hypocotyl growth) areinvolved in the elongation of hypocotyls only when they aregrown in the dark, or because DNA synthesis affects cell elongationdirectly, or through the production of a greater number of endopolyploidcells in the dark. Using mainly autoradiographic and cytofluorimetricmethods, these possibilities were tested. Besides lettuce (Lactucasativa L. var. Great Lakes) and H. gracilis (Nutt.) Gray, radish(Raphanus sativus L. var. Tondo rosso quarantino) and soybean(Soya hyspida Sieb. and Zucc. var. Tokyo) seedlings were alsostudied. Fluorodeoxyuridine drastically inhibits cell elongation onlywhen it is preceded or accompanied by mitotic or endomitoticevents. Need for DNA synthesis during hypocotyl elongation,as well as during early post-germinative growth, seems to beof particular importance when endomitotic processes are involved. DNA synthesis, elongation, endoreduplication, fluorodeoxyuridine, Haplopappus gracilis (Nutt.) Gray, Lactuca sativa L., Raphanus sativus L., Soya hyspida Sieb and Zucc     

Use of Longitudinally Bisected Pistils of Lilium longiflorum for Studies on Self-Incompatibility

The longitudinally bisected pistil of Lilium longiflorum cv.Hinomoto was shown to be useful for the study of self-incompatibility.When pollen grains of cv. Hinomoto or cv. Georgia were placedon the stigma of the bisected pistil, pollen tube elongationof each cultivar occurred with almost the same time course aswhen placed on the stigmaof the whole pistil. Tube elongation of cv. Hinomoto was retarded after 24 hours(self combination), whereas the tubes of cv. Georgia elongatedwell (cross combination). The selfincompatibility reaction detectedas retardation of pollen tube elongation occurred in all portionsof the inner surface of the stylar canal; it was not restrictedto a specific portion of the style. ¹Present address: Laboratory of Pomology, Faculty of Horticulture,Chiba University, Matsudo, Chiba 271, Japan. (Received October 20, 1982; Accepted February 9, 1983)     

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     

Arrangement of Cortical Microtubules in Avena Coleoptiles and Mesocotyls and Pisum Epicotyls

Cortical microtubules (MTs) in coleoptiles and mesocotyls ofAvena sativa and epicotyls of Pisum sativum were examined byimmunofluorescence. In elongating Avena coleoptiles whose elongationis less localized, the orientations of cortical MTs of parenchymaand adaxial epidermal cells, and abaxial epidermal cells aretransverse, and oblique or longitudinal, respectively, and doesnot differ between the upper, middle and lower parts. The transverseMTs in parenchyma and adaxial epidermal cells turns to obliqueor longitudinal ones after elongation stops. The obliquity ofMTs in abaxial epidermal cells also tends to become steeperas elongation comes to a stop. In Avena mesocotyls and Pisumepicotyls whose elongation is localized, the orientation ofcortical MTs of cortical cells in the elongating region is relativelytransverse. The epidermis has intermingling cells of transverseor oblique MTs. In the non-elongating region, MT orientationbecomes steeper both in the cortex and epidermis. The present results indicate that whatever the degree of localizationof the elongation, the obliquity of MTs in these organs is steeperin epidermal than in inner tissue cells and becomes steeperas elongation stops in both tissues. (Received October 26, 1987; Accepted April 19, 1988)     

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     

Gibberellin A3 and Abscisic Acid Cause the Reorientation of Cortical Microtubules in Epicotyl Cells of the Decapitated Dwarf Pea

To determine whether or not the changes in the orientation ofmicrotubules (MTs) that are induced by GA₃ and ABA result fromchanges in the rate of epicotyl elongation caused by these hormones,we examined the effects of GA₃ and ABA on the orientation ofMTs in epidermal cells of decapitated epicotyls of the dwarfpea (Pisum sativum cv. Little Marvel), in which neither GA₃nor ABA causes changes in the rate of epicotyl elongation. Cuttings taken from GA₃-pretreated seedlings were decapitatedand treated with ABA. ABA eliminated the GA₃-induced predominanceof transverse MTs and treatment with ABA resulted in a predominanceof longitudinal MTs in the decapitated cuttings. However, ABAdid not reduce the rate of epicotyl elongation in these samples.Cuttings taken from ABA-pretreated seedlings were decapitatedand treated with GA₃. GA₃ caused the orientation of MTs to changefrom longitudinal to transverse in the decapitated cuttings.However, GA₃ had no promotive effect on elongation of theseepicotyls. The results indicate that both ABA and GA₃ have the abilityto change the orientation of MTs by mechanisms that do not involvechanges in the rate of cell elongation. (Received August 18, 1992; Accepted January 18, 1993)     

Promotion of tea pollen tube growth by incubated solution of rapeseed cakes

The existence of growth promoters in rapeseed cakes (an organicfertilizer) was tested by measuring tube elongation in pollenculture in vitro. Growth of tea pollen tubes on an agar mediumcontaining sucrose and boron was strikingly promoted by addingthe solution obtained from incubated rapeseed cakes to the medium.Addition of a solution diluted to 1/300 stregnth to the agarmedium increased the pollen tube elongation to 153–170%of the control. Maximum activity was found with the solutionin which rapeseed cakes had been incubated at 30?C for 2 weeks.The promotive substances were not soluble in ethyl ether, ethylacetate or n-butanol, but were soluble in water, and diffusedout by dialysing against distilled water. These substances werefound to be soluble in 50% methanol, and were separated intothree fractions by Sephadex G-25 gel filtration. The promotivesubstances were different from several known growth regulators,amino acids and mineral nutrients. (Received August 31, 1979; )     

High pH Causes Disintegration of the Root Surface in Lupinus angustifolius L.

The effect of high pH on the morphology and anatomy of the rootsof lupin (Lupinus angustifolius L. cv. Yandee) and pea (Pisumsativum L. cv. Dundale) was examined in buffered solution. Themorphology and anatomy of lupin roots were markedly altered,and root growth was reduced by increasing solution pH from 5·2to 7·5, whereas pea roots were unaffected. In lupin roots,pH 7·5 caused disintegration of the root surface andimpaired root hair formation. Lupin roots grown at pH 7·5also had decreased cell lengths but increased cell diameterin both the epidermis and the cortex in comparison to rootsgrown at pH 5·2. High pH reduced cell volume greatlyin the epidermis, to a lesser extent in the outer cortex andnot at all in the inner cortex. It appears that in lupins, theprimary detrimental effects of growth at pH 7·5 is reducedlongitudinal growth of cells near the root surface with a consequentreduction in elongation of the cells in inner cortex.Copyright1993, 1999 Academic Press Lupinus angustifolius L., Pisum sativum L., high pH, root morphology, root anatomy     

The Net Orientation of Wall Microfibrils in the Outer Periclinal Epidermal Walls of Seedling Leaves of Wheat

Use of the dichroic stain chlor-zinc-iodine revealed that thenet orientation of cellulose wall microfibrils in the outerparadermal wall of the epidermis of seedling wheat leaves isprincipally transverse in the extension zone. The net orientationof microfibrils changes abruptly to principally longitudinalat the end of cell elongation. The net angle of orientationof microfibrils in the extension zone was not a function ofRht-dosage (number of dwarfing alleles), and neither leaf extensionrate nor estimated maximum relative elemental rate of elongationwere functions of microfibril orientation. The results indicatethat elongation rates are not regulated by the net angle oforientation of microfibrils and support the concept that leafextension rate is regulated by the length of the extension zone.Copyright1995, 1999 Academic Press Cellulose wall microfibrils, extension zone, elongation, Rht, wheat, Triticum aestivum L     

Relationship between Floret Elongation and Pigment Synthesis in the Flowers of Carthamus tinctorius

Floret elongation and levels of precarthamin were investigatedin freshly collected flowers of Carthamus tinctorius. Accumulationof precarthamin was found to be induced at the early stagesof floret elongation. [U-¹⁴C]Acetate and [U-¹⁴C]phenylalaninewere incorporated into precarthamin in the detached floretsfrom the flower bud. The results suggest that precarthamin issynthesized via the acetate-shikimate pathway. Carthamus tinctorius L, floret elongation, pigment synthesis, precarthamin     

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     

The Effects of Light Irradiation on the Orientation of Microtubules in Seedlings of Avena sativa L. and Pisum sativum L.

The effects of light irradiation on the arrangement of corticalmicrotubules (MTs) were examined in etiolated A vena mesocotylsand coleoptiles, and in Pisum epicotyls. Elongation of A venamesocotyls ceased as a result of irradiation with white lightwithin 1 h. The predominant orientation of MTs became more longitudinalwithin 1 h in epidermal cells and changed from transverse tooblique, after the elongation ceased, in parenchymal cells.Irradiation with red and with blue light also caused cessationof cell elongation and the same changes in the orientation ofMTs. Elongation of Avena coleoptiles ceased as a result of irradiationwith white light within 24 h. The predominant orientation ofMTs became more longitudinal in epidermal cells and changedfrom transverse to oblique in parenchymal cells. The changein orientation of MTs in epidermal cells preceded that in parenchymalcells. In Pisum epicotyls, elongation ceased as a result ofirradiation with white light within 1 h. Although the orientationsof MTs in epidermal cells did not show any remarkable change,those in parenchymal cells changed from transverse to obliqueafter cell elongation ceased. The change in orientation of MTs and the cessation of cell elongationof A vena mesocotyls induced by white-light irradiation wereboth significantly retarded by treatment with IAA. This resultsuggests that IAA is involved in maintaining the transverseorientation of MTs in Avena mesocotyls. (Received February 22, 1989; Accepted August 2, 1989)     

Organization of the psaH Gene Family of Photosystem I in Nicotiana sylvestris

The PSI-H subunit of photosystem I has two isoforms of differingmolecular mass in Nicotiana sylvestris [Obokata et al. (1993)Plant Physiol. 102: 1259], and is encoded by a nuclear gene,psaH. We identified three structurally distinct psaH genes inthe nuclear genome of N. sylvestris, designated psaHa, psaHb,and psaHc, and all three genes are expressed in young leaves.Each gene has two introns: one between sequences encoding atransit peptide and the N-terminal acidic domain, and one betweenthe N-terminal domain and a central hydrophobic domain. Thededuced amino acid sequences are identical in the mature proteinsand differ only in the transit peptides. Since PSI-H is presentin two isoforms in N. sylvestris, the psaH products may be subjectedto post-translational modifications. (Received November 8, 1993; Accepted December 28, 1993)     

Some Factors Concerning the Centripetal Disposition of Bundle Sheath Chloroplasts during the Leaf Development of Eleusine coracana

Factors concerning the chloroplast disposition in bundle sheathcells were investigated in finger millet (Eleusine coracanaGaertn.), and NAD malic enzyme type C₄ plant with the centripetalarrangement of bundle sheath chloroplasts. Segments were cutfrom immature regions of emerging leaves in which the centripetalarrangement of bundle sheath chloroplasts had not yet been established.The leaf segments were floated on solutions with or withoutreagents. Sections were made of the segments at time intervalsand the distribution of bundle sheath chloroplasts was observedby light microscopy. The bundle sheath chloroplasts migratedto the vascular bundle and established a centripetal arrangementby 12-16 h in control solutions. Auxins, cycloheximide and cytochalasinB inhibited the disposition of bundle sheath chloroplasts whilechloramphenicol and colchicine had no effect. The inhibitoryeffect of auxins appeared only at early stages of chloroplastmigration while cycloheximide and cytochalasin B were effectiveeven at later stages. Cessation of elongation growth, cytoplasmicprotein synthesis and microfilaments seemed to be associatedwith the centripetal disposition of bundle sheath chloroplasts.Copyright1993, 1999 Academic Press Bundle sheath chloroplast, C₄ plant, chloroplast orientation, Eleusine coracana, finger millet