Comparative Biology of the Pollination Mechanisms in Acmopyle pancheri and Phyllocladus hypophyllus(Podocarpaceae s. l.)

The pollination mechanisms of Acmopyle pancheri(Brongn. &Gris) Pilg. andPhyllocladus hypophyllus Hook.f. were investigatedby conventional microscopical techniques and by nuclear magneticresonance (NMR) imaging. Dissimilarities include the orientationof the ovule and type of pollen;Phyllocladus has erect ovulesand wettable pollen with vestigial sacci, whereas Acmopyle hasmore-or-less erect ovules and non-wettable, functionally saccatepollen. Similarities include the mode of formation of the pollinationdrop and its response upon pollination. In both genera, pollinationtriggers pollination drop retraction and drop secretion ceases.Neither NMR imaging nor conventional histology of Phyllocladusovules revealed any specific tissue beneath the ovule whichcould be responsible for pollination drop retraction. It ismore likely, therefore, that the drop is channelled into thevascular supply or the apoplast. These findings invalidate thetaxonomic value of the pollination mechanism as a suite of characterstraditionally used to separate Phyllocladaceae from Podocarpaceae.Copyright 2000 Annals of Botany Company Acmopyle pancheri, gymnosperms, NMR imaging, nuclear magnetic resonance imaging, Phyllocladaceae,Phyllocladus hypophyllus , Podocarpaceae, pollination drop, pollination mechanism     

Seed Morphology, Anatomy and Ultrastructure ofPhyllocladusL. C. & A. Rich. ex Mirb. (Phyllocladaceae (Pilg.) Bessey) in Connection with the Generic System and Phylogeny

To analyse the status and phylogeny of the genusPhyllocladus,seedsof all seven species of the genus were studied. The complexof features of thePhyllocladusreproductive system point to theisolated position of the genus within the conifers. Relationswith Podocarpaceae s. l., Taxaceae s. l. and Cephalotaxaceaeappeared to be remote because a complex of features clearlydistinguishesPhyllocladusfrom the afore-mentioned taxa. We findit advisable to circumscribe the family Phyllocladaceae as Bessey(1907) did, and place it into the order Taxales Knobl. in Warming(1890). From investigations of the seeds it appears the genusPhyllocladusconsistsof seven species, forming five groups. There is a significanttendency for transformation of the female reproductive structureswithin the generic boundaries ofPhyllocladus—seeds, originallysolitary, tending to aggregate in various kinds of compact clusters.Copyright1999 Annals of Botany Company PhyllocladusL. C. & A. Rich, ex Mirb., seed anatomy, seed morphology, systematics, phylogenetic relationships, Phyllocladaceae, Podocarpaceae s. str., Acmopyleaceae, Nageiaceae, Austrotaxaceae, Amentotaxaceae, Torreyaceae, Taxaceae, s. str., Cephalotaxaceae, Taxales.     

Seedlessness and Parthenocarpy inPistacia veraL. (Anacardiaceae): Temporal Changes in Patterns of Vascular Transport to Ovules

Pistacia vera‘Kerman’ (pistachio nut) typicallyproduces high numbers of seedless or blank fruits. Patternsof vascular transport into fruits and ovules were studied over3 years by following the movement of disodium fluorescein solutionfrom cut branches into developing fruitlets. Early in the season,vascular conductivity is intact through to the chalazal endof the ovule. Soon afterwards, the percentage of ovules withvascular conductivity through to the chalaza declines, and ina variable fraction of fruits, movement of the fluorochromesolution becomes blocked either at the placenta or in the funiculus.Six to 9 weeks after anthesis there is blockage in 90 (1 year)to 100% (2 years) of fruits. Subsequently, vascular conductivityresumes in 83.3% (3 year mean) of ovules, a percentage thatcorrelates well with the mean percentage of seeded nuts at harvest(77.5%). Ovules from fruits with dysfunctional vascular conductionearly in the season are smaller than those with fully functionalvascular tissue. At the time conductivity declines, a high percentageof those ovules with blocked vascular movement lack endospermand appear to be unfertilized; none of the ovules that retainfull vascular flow lack endosperm. Pollination using gamma-irradiatedpollen (⁶⁰Co, 1.0 kGy) led to a nearly three-fold increase inthe production of blank nuts. The results indicate that fluoresceintransport may be a valuable tool to predict the fate of ovules,and are consistent with the hypothesis that parthenocarpic fruitset may be an important factor in blank nut production in pistachio.Copyright1999 Annals of Botany Company Pistachio,Pistacia veraL., fluorescein, seed set, seedlessness, parthenocarpy, blanking, ovule, funiculus, chalaza, embryo.     

Freezing injury to ovules, pollen and seeds in winter rape

Winter rapeseed (Brassica napus, cv. Samouraï) flowersearly in spring and, under field conditions, short freezingperiods can occur. Unacclimatized plants were freeze-stressed(–3°C for 4 h) at different developmental stages ofbuds, open flowers and seeds. The dissection of pistils from stressed plants showed that freezingresults in shrivelled ovules. We assessed freezing injury onthe basis of per cent of shrivelled ovules: ovule sensitivitybegins early (8 d before anthesis) but increases up to anthesis.Crosspollination of stressed pistils with non-stressed pollenshowed that recording of freeze-injured ovules is a good methodfor early estimation of the effect of stress on seed yields. On the other hand, stress does not reduce the viability of pollen,except when it was applied at the binucleate pollen stage. Useof frozen pollen x nonstressed pistils has little effect onseed yields. Freeze injury on seeds was assessed by seed filling:seeds are very susceptible just after fertilization until 20d after fertilization (DAF). Freezing seems to inhibit seedfilling. A germination test of stressed seeds during their developmentindicated that embryo viability is not affected if the stressoccurs after 35 DAF. As the embryos develop, resistance to stressincreases. Key words: Brassica napus, rapeseed, freeze injury, pollen and ovule, seed filling     

Timing of Embryo Abortion and the Effect of Ovule Thinning on Nutlet Mass in Cryptantha flava (Boraginaceae)

Just after a size difference was apparent among the four single-ovulatesubunits in developing ovaries of Cryptantha flava (Boraginaceae),either the largest subunit or the three smaller were destroyedand final seed set and nutlet mass were scored. Results indicatethat most irreversible embryo abortion must occur during theestablishment of the size differences, and within a 24–48h period. Thinning a portion of the ovules does not affect finalnutlet mass. Embryo abortion, Cryptantha flava, ovule destruction experiments, seed size     

Parasitic Relationships between a Gall-forming Insect Tomoplagia rudolphi (Diptera: Tephritidae) and its Host Plant (Vernonia polyanthes, Asteraceae)

We studied the impact caused byTomoplagia rudolphi Lutz &Costa Lima (Diptera: Tephritidae) on the architecture, flowerproduction, seed germination and seed viability of its hostplantVernonia polyanthes Less (Asteraceae). We measured thegall influence on the number of lateral shoots, on the productionof flower heads and on seed viability. Gall formation induceda significant increase in the number of lateral shoots modifyingthe host plant normal growth pattern. Galled stems producedan average of 7.3±0.45 shoots, whereas ungalled stemsproduced 5.6±0.60 shoots. Galling also caused a significantreduction in seed viability. Seeds of galled stems had a totalpercent seed germination mean of 28.4%, while seeds of ungalledstems had a mean of 33.8%. However, flower head production andseed germination velocity were not affected by the gall. Thisstudy showed thatT. rudolphi galls influence the architectureand seed viability of its host plant. Insect galls; herbivory; herbivore impact; plant growth; Tomoplagia rudolphi ; Vernonia polyanthes     

Characteristics of Sugar, Amino Acid and Phosphate Release from the Seed Coat of Developing Seeds of Vicia faba and Pisum sativum

After removal of the embryo from developing seeds of Vicia fabaL. and Pisum sativum L., the ‘empty’ ovules werefilled with a standard solution (pH 5.5). Seed coat exudatesof both species were collected during relatively long experiments(up to about 12 h) and the concentration of sugar (mainly sucrose),amino acids and phosphate in the exudate measured. A discussionis presented on the amino acid/sugar ratio and the phosphate/sugarratio in the seed coat exudate. A pretreatment (15 min) withp-chloromercuribenzenesulphonic acid (PCMBS) reduced the releaseof sugar, amino acids and phosphate from broad bean seed coats.After excision of ‘empty’ ovules of Vicia faba andPisum sativum from the maternal plant, 2–4 h after thistreatment a strong difference became visible between sucroserelease from excised seed coats and sucrose release from attachedseed coats. Similarly, when the rate of phloem transport ofsucrose into an ‘empty’ ovule of Vicia faba or Pisumsativum was reduced by a sub-optimal mannitol concentrationin the solution, a reduced rate of sugar release from the seedcoat could be observed. Excision and treatment with a sub-optimalmannitol concentration reduced the release of amino acids toa lesser extent than for sucrose. These treatments did not reducethe rate of phosphate release from the seed coat. Key words: Seed development, Seed coat exudate, Phloem transport     

Carpology, Seed Anatomy and Taxonomic Relationships ofGalbulimima(Himantandraceae)

The fruit and seed anatomy and morphology ofGalbulimima belgraveana(F.Muell.) Sprague, a solitary species of the monotypic genus inthe Himantandraceae, have been studied in an effort to clarifyits systematic position. The indehiscent fleshy multicarpellary,two- or three-ranked capsetum ofGalbulimimaconsists of follicles(capseoles) with lignified fibrous five- or six-layered endocarp.Such construction of the himantandraceous capsetum suggestsderivation from free cone-like fruits similar to those of Annonaceaeand Magnoliaceae. Seeds ofGalbulimimaare relatively large, flattened,winged, with a solitary vascular bundle extending to the micropyle,and a cup of hypostase. They are abundantly albuminous and havea small dicotyledonous embryo. The seed coat ofGalbulimimaismesotestal with testal-tegmic ruminations and unspecializedtwo- or three-layered tegmen; a single-layered exotesta representedby thin-walled tanniniferous cells; a two (–three)-layeredmesotesta, composed of thick-walled lignified longitudinal fibres;and an endotesta composed of two or three layers of unspecializedaerenchymatous parenchyma. Evidence, mainly from seed morphologyand anatomy of seed coats, emphasizes the anomaly of the traditionalaffiliation of Himantandraceae with MagnolialessensuTakhtajan,being quite distinct in spermoderm structure and origin fromboth Magnoliaceae and Degeneriaceae in particular. Furthermore,seed anatomy does not confirm any relationships with Myristicaceaeor Canellaceae. Among all Magnoliidae, the structure of theseed coats ofGalbulimimais similar to that of some advancedAnnonaceae and Eupomatiaceae. It is suggested that Himantandraceaetogether with Eupomatiaceae and Annonaceae constitute a distinctrelic blind branch of magnoliid ancestry. On the basis of availabledata of seed coat anatomy, it is appropriate to remove Himantandralesfrom the order Magnolialessensu stricto, and to place it intoits own monotypic order, Himantandralesord. nov.,grouping togetherwith orders Eupomatiales and Annonales in Magnoliidae.Copyright1998 Annals of Botany Company Galbulimima belgraveana(F. Muell.) Sprague; carpology; pericarp; seed anatomy; systematics; phylogenetic relationships; Himantandraceae; Magnoliaceae; Eupomatiaceae; Degeneriaceae; Annonaceae; Liriodendraceae; Myristicaceae; Canellaceae.     

The Ovule and 'Seed' of Araucaria Bidwillii with Discussion of the Taxonomy of the Genus: III. Anatomy of Multi-ovulate Cone Scales

This paper deals with the anatomy of two- and three-ovulatecone scales which are found occasionally in the cones of A.Bidwillii. The manner in which each ovule receives its vascularsupply from bundles lateral to the ovule is discussed, togetherwith a hypothetically primitive type of araucarian cone scalewith three ovules possibly resembling the fossil Schizolepis.The interpretation of the vascular system of the scales as givenin this paper is a correction of that presented in the firstpaper of this series by the same authors.     

Seed cone and ovule ontogeny in Metasequoia, Sequoia and Sequoiadendron (Taxodiaceae–Coniferales)

TAKASO, T. & TOMUNSON, P. B., 1992. Seed cone and ovule ontogeny in Metasequoia, Sequoia and Sequoiadendron (Taxodiaceae–Coniferales). Structural features of seed cones, up to the initiation of ovules, are developed in the three genera in the summer and late fall prior to pollination in the following spring, when cones renew their further development. Bracts are initiated in a decussate manner in Metasequoia but spirally in Sequoia and Sequoiadendron. No ovuliferous scale is initiated, at most there is a shallow mound of tissue on the adaxial surface of the bract from which the ovules are developed. Metasequoia produces a single series of up to eight ovules in acropetal (centripetal order), Sequoia and Sequoiadendron produce a double series of six to nine ovules, also in acropetal order, since a second series of ovules appear distal to and alternate with the first series. Common features that unite the genera are the somewhat peltate configuration of the cone scales due to late intercalary expansion, the derivation of the vascular supply to the bract-ovule complex from a single bundle and the usual inversion of the seed during late development, to which can be added developmental features. The absence of tooth-like structures, present in some other Taxodiaceae, is discussed in relation to cone evolution in the family being determined by changes in developmental timing. Emphasis is made on the way in which features of morphogenesis, determine cone organization in the three genera independent of an interpretation that relies solely on hypothetical ancestral forms.     

Endogenous cis,trans-Abscisic Acid and Pea Seed Development: Evidence for a Role in Seed Growth from Changes Induced by Temperature

Measurements were made using GC/MS SIM¹ of the effects of temperatureon cis,trans-ABA levels in developing ovules and embryos oftwo pea genotypes contrasted in seed size. These effects werethen related to differences in the growth of the pods, seeds,embryos, and testae. In both genotypes high temperatures hastenedthe onset and rate of logarithmic and then linear growth, greatlyshortening the duration of pod and seed development but withoutgreatly altering seed size. Cis,trans-ABA was most concentratedxin the ovules immediately after fertilization. It also accumulatedin the embryo, more rapidly in the larger-seeded line, duringseed maturation. The stage when accumulation in the embryo beganwas the same irrespective of temperature. Accumulation ceasedwhen the pods started to desiccate. The effects of differentconstant temperatures on the maximum levels of embryo cis,trans-ABAwere relatively small and confounded in one genotype by variationin ovule abortion and in the other by differences in the stagewhen cis,trans-ABA accumulation ceased. However, when plantswere transferred from 13 °C to 29 °C at two differentstages during seed maturation, further seed growth was greatlyinhibited coincident with a substantial increase in embryo cis-trans-ABA.The results suggested a role for cis,trans-ABA in the controlof cotyledon enlargement during the linear phase of seed growth.     

Sexual Reproduction and Early Plant Growth of the Wollemi Pine (Wollemia nobilis), a Rare and Threatened Australian Conifer

The two known populations of the recently discovered rare andthreatened Wollemi Pine (Wollemia nobilis Jones, Hill and Allen)consist of a small number of large multi-stemmed adult treesand small seedlings. Female and male cones are produced on adulttrees with pollen release occurring in spring (October–November).Seed cones mature 16–19 months later in late summer andautumn and appear to be produced annually. Approximately 10%of seed produced in two consecutive years was viable, 25% ofwhich was damaged by animals. Glasshouse studies showed thatseed germination at 25 °C (day)/16 °C (night) proceededslowly but steadily at approx. 4% per week until, after 6 months,88% of apparently viable seed had germinated with the remainderof the seed rotting. Growth of potted seedlings in this temperatureregime was continuous (after a lag period of 4–6 months)with the monopodial axis growing 0.05–0.25 m in the firstyear, 0.5–0.6 m in the second year and 0.25–0.35m in the third year, attaining a total height of 0.8–1.2m. Multiple orthotropic shoots developed on some plants at thisstage, some of which outgrew the primary shoot in height. Thediameter of the stem below the cotyledon (just above the soil)grew 3–7 mm in the first year, 10–14 mm in the secondand 15–20 mm in the third at which time it was 25–34mm. The average number of lateral branches produced was five–17in the first year, 25–36 in the second year and 24–30in the third year giving a total of 60–77. The establishmentof Wollemi Pine in the wild does not appear limited by the inherentviability of seed and potential for early growth of seedlings.Copyright 1999 Annals of Botany Company Wollemia nobilis, Wollemi Pine, Araucariaceae, conifer, rare and threatened plant, cone, seed, germination, seedling growth.     

Phylogeny of seed dormancy in Convolvulaceae, subfamily Convolvuloideae (Solanales)

Background and Aims: The water gap is an important morphoanatomical structure inseeds with physical dormancy (PY). It is an environmental signaldetector for dormancy break and the route of water into thenon-dormant seed. The Convolvulaceae, which consists of subfamiliesConvolvuloideae (11 tribes) and Humbertoideae (one tribe, monotypicHumberteae), is the only family in the asterid clade known toproduce seeds with PY. The primary aim of this study was tocompare the morphoanatomical characteristics of the water gapin seeds of species in the 11 tribes of the Convolvuloideaeand to use this information, and that on seed dormancy and storagebehaviour, to construct a phylogenetic tree of seed dormancyfor the subfamily. Methods: Scanning electron microscopy (SEM) was used to define morphologicalchanges in the hilum area during dormancy break; hand and vibratomesections were taken to describe the anatomy of the water gap,hilum and seed coat; and dye tracking was used to identify theinitial route of water entry into the non-dormant seed. Resultswere compared with a recent cladogram of the family. Key Results: Species in nine tribes have (a) layer(s) of palisade cells inthe seed coat, a water gap and orthodox storage behaviour. Erycibe(Erycibeae) and Maripa (Maripeae) do not have a palisade layerin the seed coat or a water gap, and are recalcitrant. The hilarfissure is the water gap in relatively basal Cuscuteae, andbulges adjacent to the micropyle serve as the water gap in theConvolvuloideae, Dicranostyloideae (except Maripeae) and theCardiochlamyeae clades. Seeds from the Convolvuloideae havemorphologically prominent bulges demarcated by cell shape inthe sclereid layer, whereas the Dicranostyloideae and Cardiochlamyeaehave non-prominent bulges demarcated by the number of sub-celllayers. The anatomy and morphology of the hilar pad follow thesame pattern. Conclusions: PY in the subfamily Convolvuloideae probably evolved in theaseasonal tropics from an ancestor with recalcitrant non-dormantseeds, and it may have arisen as Convolvulaceae radiated tooccupy the seasonal tropics. Combinational dormancy may havedeveloped in seeds of some Cuscuta spp. as this genus movedinto temperate habitats.     

Effect of the Osmotic Environment on K+ and Mg2+ Release from the Seed Coat and Cotyledons of Developing Seeds of Vicia faba and Pisum sativum. Evidence for a Stimulation of Efflux from the Vacuole at High Cell Turgor

After removal of the embryo from developing seeds of Vicia fabaL. and Pisum sativum L., the ‘empty’ ovules werefilled with a substitute medium (pH 5.5) and the effect of theosmolality of the medium on K⁺ and Mg²⁺ release from the seedcoat was examined. In long-term experiments (12 h or longer),with both attached and detached seed coats, the rate of K⁺ andMg²⁺ release from seed coats filled with a solution withoutosmoticum was enhanced, in comparison with release from seedcoats filled with a solution containing 400 mol m     

Pollen Tube Distribution in the Kiwifruit (Actinidia deliciosaA. Chev. C. F. Liang) Pistil in Relation to its Reproductive Process

High resolution light and fluorescence microscopy were usedto investigate the structural and cytochemical features of thekiwifruit(Actinidia deliciosa)pistil and to follow the pollentube pathway after pollination. The multicarpellary ovary issyncarpous only at the ovary level thus leaving 30–40free styles on top. The fusion of the longitudinally-foldedcarpels to form the syncarpous ovary forms a central parenchymatousaxis, the columella, from which the ovules radiate outwardsinto the ovary cavity. A prominent cup shaped depression onthe columella at the top end of the ovary, termed the pollentube distributor cup (PTDC) was detected. Pollen tubes fromthe stigma travel through the transmitting tract and enter thePTDC from where they are distributed towards the ovary. Evenwhen pollination is restricted to two stigmas, the PTDC seemsto ensure that the pollen tubes are evenly distributed aroundthe ovary resulting in an even distribution of seeds. This suggestedrole of the PTDC which could compensate for over and under pollinationof individual stigmatic arms is another adaptive feature whichplays a crucial role in the reproductive process of kiwifruit.The significance of this structure for pollination by insectsis discussed.Copyright 1998 Annals of Botany Company Actinidia deliciosa, kiwifruit, pollination, floral anatomy, reproductive success, pollen tube distribution.     

The Role of Maturation Drying in the Transition from Seed Development to Germination: I. ACQUISITION OF DESICCATION-TOLERANCE AND GERMINABILITY DURING DEVELOPMENT OF Ricinus communis L. SEEDS

Kermode, A. R. and Bewley, J. D. 1985. The role of maturationdrying in the transition from seed development to germination.1. Acquisition of desiccation–tolerance and germinabilityduring development of Ricinus communis L. seeds.—J. exp.Bot. 36: 1906–1915. Seeds of Ricinus communis L. cv. Hale(castor bean) undergo a transition from desiccation–intoleranceto desiccation–tolerance approximately midway throughtheir development. Tolerance of slow desiccation is gained overonly a few days of development (between 20 and 25 d) and isachieved well before the completion of major developmental events,such as reserve deposition and the onset of normal maturationdrying. A tolerance of very rapid water loss brought about bydrying over silica gel is not acquired by this seed until nearmaturity. Coincident with the acquisition of tolerance to slowdesiccation the seeds gain the capacity to germinate upon subsequentrehydration. Germinability and capacity for normal post–germinativegrowth during the tolerant phase are not fully expressed unlessthe seed is dried at an optimal rate, which is dependent uponthe developmental stage of the seed. Drying presumably actsto terminate developmental processes and to initiate those metabolicprocesses necessary to prepare the seed for germination andgrowth. Key words: Desiccation-tolerance, germinability, seed development, castor bean