Acropetal Succession Research Articles

Seasonal dynamics of flowering of Calluna vulgaris (L.) Hull and its cultivars in conditions of Kyiv regarding to peculiarities of the flower structure

The aim of our study was to research the connection between the flower structure and the duration of flowering of Calluna vulgaris (L.) Hull and its cultivars. Our tasks were to investigate the flower structure of bud bloomers and double-flowered Calluna vulgaris (L.) Hull cultivars, to compare it with the structure of C. vulgaris flower; to analyze the data of phenological observations of C. vulgaris and its 10 cultivars flowering phase during 2015–2018. The methods were phenological observations and microscopic examinations. Results. Common features for C. vulgaris and cultivars concerning to their flowering are racemose inflorescences, an arrangement of flowers, acropetal succession. The flower structure of ‘Dirry’, ‘Mullion’, ‘Golden Carpet’, ‘Winter Red’ is similar to that of C. Vulgaris. Among this group, ‘Winter Red’ finishes blooming the first and ‘Dirry’ is the last due to its compound inflorescence. An increased number of petals, full sterility and long flowering period characterize flowers of double-flowered cultivars. Bud bloomers ‘Alicia’, ‘Bonita’ belong to f. diplocalyx Jansen. They are characterized by different flowering periods. ‘Alicia’ blooms the longest (85±7 days) among investigated C. vulgaris cultivars and ‘Bonita’ blooms about 53 days. Conclusions. C. vulgaris cultivars that have the same flower structure as species begin to bloom, as well as common heather, in the third decade of July. The duration of C. vulgaris cultivars flowering period depends also on the peculiarities of the inflorescence structure. Therefore, in order to predict the duration of cultivars flowering, it is necessary to study the features of their inflorescences structure. Double-flowered cultivars are worth to be used more often in gardening due to their high decorativeness and long flowering period. The issue of preserving the color of bud bloomers flowers needs further research. When using the cultivars of C. vulgaris with different types of flowers and duration of flowering, we can create landscapes of high and long decorative features

First Report of Black Stem Caused by Botryosporium longibrachiatum on Statice in Korea.

Perennial statice is widely cultivated worldwide. In Korea, hybrid statice (Limonium latifolium × bellidifolium) is grown as a commercial cut flower crop in polyethylene-film-covered greenhouses. In April 2013, hundreds of hybrid statice plants of the cvs. Yellow Cream and Pinky Cream were found symptomatic of a previously unknown disease, with 10 to 15% incidence in 10 greenhouses of 1,600 m2 surveyed in Gochang County, Korea. Affected stems turned dark brown and were usually covered with a fungus resembling the hoar-frost fungus, Botryosporium longibrachiatum (3), especially in a cool and humid environment. Symptoms consisted of stem blackening, as is typical for burley tobacco (1) and sweet basil (2). According to the farmer of the hybrid statice, stems blackened in the winter and spring of January to April when the tunnels were mostly closed, thus reaching 100% relative humidity (RH) every night due to poor ventilation. The fungus had an elongate main axis with lateral fertile branches in acropetal succession. Conidiophores were simple, erect, macronematous, 32 to 79 μm in length, with a terminal cluster of three to five ampullae. Conidiogneous cells were polyblastic. Conidia were ellipsoidal, elliptical-fusiform, hyaline, 7.6 to 9.5 × 3.0 to 4.2 μm. Colonies on potato dextrose agar (PDA) were floccose, non-pigmented, and chalk-white in color. Morphological and cultural characteristics of the fungus were consistent with previous reports of B. longibrachiatum (Oudem.) Maire (2,3). A voucher specimen was deposited in the Korea University Herbarium (KUS). Isolate KUS-F27305 was submitted to the Korean Agricultural Culture Collection (Accession No. KACC47263). Fungal DNA was extracted from isolate KACC47263 with DNeasy Plant Mini Kits. The complete internal transcribed spacer (ITS) region of rDNA was amplified with the primers ITS1/ITS4 and sequenced. The resulting sequence of 604 bp was deposited in GenBank (Accession No. KF372591). A BLAST search in GenBank exhibited ≥99% nucleotide identity with the ITS sequence of B. longibrachiatum (JX666334) from sweet basil in Korea. To confirm pathogenicity, colonized mycelial agar blocks from isolate KACC47263 were transferred individually onto stem apices and leaves of five statice plants of the cv. Yellow Cream. Five control plants were treated similarly with non-colonized agar blocks. The plants were incubated in a humid chamber at 22 ± 2°C with a 12-h photoperiod for 48 h, and then maintained in 100% RH. After 3 to 4 days, necrotic lesions identical to those observed in the original greenhouses, started to develop on the stem and leaves of inoculated plants, leading to blackened stems covered with the hoar-frost fungus after 14 days. B. longibrachiatum was re-isolated from the lesions of inoculated plants, fulfilling Koch's postulates. No symptoms were observed on control plants. The pathogenicity test was repeated with the cv. Pinky Cream with identical results. To our knowledge, this is the first report of B. longibrachiatum infecting perennial statice globally as well as in Korea. We propose the name black stem of statice for this disease, analogous to the disease on basil (2).

Synchronous monoecy in Ecdeiocoleaceae (Poales), in Western Australia

The Western Australian plant family Ecdeiocoleaceae includes only three species but DNA data show them as the closest living sister-group of the Poaceae. Ecdeiocoleaceae are wind-pollinated and monoecious; spikes produce separate zones of pistillate and staminate flowers, in acropetal succession. Spikes of Ecdeiocolea have up to 45 flowers, with a sequence of zones up the spike, commonly pistillate–staminate–pistillate–staminate–pistillate, with potentially high fruit set in both of the lower pistillate zones. Rainfall in their habitats in semiarid south-western Australia is highly variable and shorter spikes with fewer zones are formed in drought conditions. Georgeantha, with fewer flowers per spike, shows the same general pattern but fewer switches. Synchrony of zonal flowering gives an effective barrier to self-pollination, a form of ‘temporal dioecy’. All spikes on many stems of a plant flower with the conspicuous white stigmas of a pistillate zone or, at a different time, all with the yellow anthers of a staminate zone. Such synchrony is between the many spikes on the plant, not between plants in a population. Features of vegetative and flowering structures and habitat are briefly mentioned.

First Report of Black Stem Caused by Botryosporium longibrachiatum on Sweet Basil in Korea.

Sweet basil, Ocimum basilicum L., is cultivated mainly for fresh consumption in Korea. In March 2009, in Icheon, Korea, several dozen plants showing symptoms of black stems were found in an organic farm that used polyethylene tunnels for production. The black stems were usually covered with a fungus that gave the appearance of hoar-frost on the stems, especially when plants were grown under a cool and humid environment. According to the farmer, black stems appear during the winter season of November to March when the tunnels were mostly closed. The relative humidity (RH) during that period was around 100% every night due to poor ventilation. Beginning the middle of April when both sides of the tunnels were open, providing good ventilation, no further disease development was observed. The fungus on the stems had an elongate, upright conidiophore, reaching 5 mm in length. At intervals along its length, the main axis of conidiophores produced lateral fertile branches in acropetal succession. Each lateral branch terminated in a cluster of four or five ampullae. Conidia were hyaline, oval, and 5.5 to 9.5 × 3.5 to 6 μm. The fungus was non-pigmented and colonies on potato dextrose agar were chalk white. Morphological and cultural characteristics of the fungus were consistent with the previous reports of Botryosporium longibrachiatum (Oudem.) Maire (3,4). Voucher specimens (n = 4) were housed at Korea University Herbarium (KUS). An isolate from KUS-F24010 was deposited in the Korean Agricultural Culture Collection (Accession No. KACC44849) and used for molecular analysis and pathogenicity tests. The complete internal transcribed spacer (ITS) region of rDNA was amplified with the primers ITS1/ITS4 and sequenced. The resulting sequence of 592 bp was deposited in GenBank (Accession No. JX666334). A BLAST search in GenBank showed that there was no comparable sequence of B. longibrachiatum and thus this was the first ITS sequence for the species submitted in GenBank. To confirm the pathogenicity, colonized mycelial plugs (3 mm in diameter) from 10-day-old PDA cultures were placed onto the stem apices (n = 10) of 2-month-old sweet basil pot plants, which were topped as normally harvested. Control plants were inoculated with uncolonized agar plugs. All plants were incubated at 22 ± 2°C in a humidified chamber with a 12-h photoperiod for 48 h, and then maintained in a greenhouse (22 ± 2°C). Three to four days after inoculation, necrotic lesions developed around the points of inoculation on all stems and expanded downwards, leading to black stems covered with the hoar-frost like fungus after 14 days. B. longibrachiatum was successfully reisolated from all inoculated stems, while control plants remained symptomless. The pathogenicity test was conducted twice with the same result. The association of B. longibrachiatum and sweet basil was previously reported (4). Several other plants including burley tobacco are also reported to be infected by this fungus (1,2). To our knowledge, this is the first etiological report of B. longibrachiatum on sweet basil globally as well as in Korea.

Floral developmental morphology of three Indigofera species (Leguminosae) and its systematic significance within Papilionoideae

Inflorescence and floral development of three species of Indigofera (Leguminosae-Papilionoideae), I. lespedezioides, I. spicata, and I. suffruticosa, were investigated and compared with that of other papilionoid groups, especially with members of the recently circumscribed Millettioid clade, which was merged as sister to Indigofereae in a recent cladistic analysis. Although Indigofera is a genus of special interest, because of its great richness in species and its economic importance, few studies have been made of floral development in the genus or in Indigofereae as a whole. Flower buds and inflorescences were analysed at several stages of development in the three species. Our results confirmed that Indigofera species bear a usual inflorescence type among legumes, the raceme, which comprises flowers initiated in acropetal succession, each with a subtending bract and no bracteoles initiated. The inception of the floral organs is as follows: sepals (5), petals (5), carpel (1), outer stamens (5), and, finally, inner stamens (5). Organ initiation in the sepal, petal, and both stamen whorls is unidirectional, from the abaxial side; the carpel cleft is adaxial. The vexillum is larger than other petals at maturity, covering the keels, which are fused edge-to-edge. Nine filaments are fused to form an adaxially open sheath, and the adaxial stamen of the inner whorl remains free (diadelphous androecium) in the mid-stage of development. Most of the infra-generic differences occurred in the later stages of development. Data on floral development in Indigofera obtained here were also compared with those from other members of Papilionoideae. This comparison showed that the early expression of zygomorphy is shared with other members of the Millettioid clade but is rarely found in other papilionoids, corresponding to a hypothetically morphological synapomorphy in the pair Indigoferae plus millettioids.

Floral morphogenesis and proliferation in Poa labillardieri (Poaceae)

Inflorescence and spikelet development in Poa labillardieri Steud. were investigated by scanning electron microscopy. Thirteen developmental stages were described in detail, starting with the vegetative shoot apex which was shown to be of the short type (stage zero), followed by a conversion from vegetative to floral meristem at Stage 1 and ending at Stage 12, with a mature panicle consisting of a variable number of florets at anthesis within each spikelet. The occurrence of short-type vegetative apices in this perennial grass adds further support to the view that there is no correlation between life span and the apex type. The branches of the P. labillardieri panicle are formed in acropetal succession; however, it is the upper branches that first bear rudiments of the spikelets, starting at the tip of the branches. In contrast differentiation of florets within each spikelet occurs in acropetal succession, so that the basal floret is farthest advanced and each successively upper floret less advanced. P. labillardieri occasionally produces inflorescences containing spikelets in which some or all of the florets are replaced by a plantlet that is structurally similar to a vegetative tiller. Proliferous development ranged from a situation where all florets were converted to vegetative propagules that can be detached and rooted readily in soil, to cases where proliferation extended only as far as an enlargement of the lemma, with either functional or non-functional sexual organs in its axil. Under greenhouse conditions, there was a shift from occasional cases of partially proliferating spikelets that occur in the wild to complete vigorous proliferation stimulated by unknown factor(s). Departure from the normal sexual pattern took place from early Stage 5 (initiation of spikelet primordial) to late Stage 6 (differentiation of florets).

Floral Organogenesis of Triglochin maritimum Linn.（Juncaginaceae）

The floral organogenesis of Triglochin maritimum Linn.was observed under scannning electron microscope(SEM).Floral development of T.maritimum consists of the sequential initiation of alternating,trimerous whorls of floral appendages in centripetal and acropetal succession:two whorls of tepals,two of stamens,and two of carpels in the typical monocotyledonous pattern.Our observation did not find an association of the tepal and stamen primordia(the "CA complex").The common base of the stamen and its opposing tepal in later stage maybe a result of subsequent intercarary upgrowth,which is secondary result.There are differences in position,timing and rates of development between whorl of tepals and stamens.Differential timing and rates of growth of the inner tepals and outer stamens result in the former appearing to be located internal to the latter in the mature flower.In the late stage of floral development,we observed the decreasing case of the number of carpel.It seems that the present observation of T.maritimum does not support the interpretation of the flower of Triglochin as a reduced lateral branch of the inflorescence,though a more detailed study would be requried to confirm this.

Reproductive ecology of medicinally important Kashmir Himalayan species of Digitalis L.

AbstractReproductive biology, encompassing phenology, floral biology, pollination and breeding systems, was investigated in three pharmaceutically important and anthropogenically exploited species of Digitalis in the montane habitats of the Kashmir Himalaya. Flowers in all three species (Digitalis purpurea, Digitalis grandiflora and Digitalis lanata) are aggregated in racemes. Corollas are characteristically bell shaped enclosing four, didynamously arranged stamens. The stigma is deeply bifid only in D. purpurea. The three species over‐winter as underground tubers and sprouting during the following spring occurs first in D. lanata, followed by D. purpurea and D. grandiflora. Floral bud opening in an inflorescence in all three species occurs sequentially from the bottom upwards in an acropetal succession and male and female phases are temporally separated with basal flowers entering the male phase first followed by the upper flowers in a regular sequence. Only after shedding the pollen grains completely do the flowers shift to the female phase. Resource allocation in all three species is more towards maleness than femaleness during anthesis. The species are principally insect pollinated and selfing is denied because of protandry and spatial separation of the stigma and anthers. Copious amounts of viable pollen grains produced by these species aid in successful pollination, fertilization and seed production. Studies revealed that none of these species operates autogamy because hand‐pollinated flowers with self‐pollen or bagged flowers (foreign pollen excluded) failed to set seed. High seed output in open‐pollinated flowers and high pollen–ovule ratios also indicate the outbreeding nature of these species. Thus, any reduction in the number of individuals constituting a population would significantly reduce the floral display and consequent rewards to the pollinators, with a subsequent influence on seed production. Hence, data on the reproductive biology of overexploited species, such as Digitalis spp., is of pivotal importance in formulating effective conservation strategies.

Is auxin a diffusible signal mediating abscission of recessive sinks?

Flowering and pod set pattern were examined in racemose inflorescences of cowpea ( Vigna unguiculata). Anthesis occurs in acropetal succession where basal flowers set into pods while those at the distal end abscise either as flowers or immature pods. Increase in the time lag between anthesis on successive racemes reduced chances of pod set in flowers that are produced late. Application of triiodobenzoic acid (TIBA) to the pedicel of the dominant developing pod enhanced transport of 14C sucrose to the upper racemes indicating that auxin transport from the dominant sink suppresses metabolite transport to recessive sinks thereby inhibiting development. The signal auxin moving from early produced dominant sink accelerates abscission of later formed sinks. This was tested in experiments using well defined debladed cotton ( Gossypium hirsutum) petiole explants. In the various explants used, application of IAA to one of the petioles hastened abscission of untreated petioles. However, inhibition of IAA transport by TIBA overcame auxin induced abscission. Radiolabel studies using 14C IAA indicate that high concentration of diffusible IAA moving from a dominant sink inhibits basipetal movement of IAA from other competing sinks, thereby causing accelerated abscission. These observations support the hypothesis that diffusible IAA moving from a dominant sink acts as a correlative signal regulating abscission of other recessive sinks.

First Report of Alternaria Leaf Spot of Almond Caused by Species in the Alternaria alternata Complex in California.

A new leaf spot disease of almond (Prunus dulcis [Mill.] D. Webb) was observed in California in the late 1980s and was first associated with severe defoliation in the mid-1990s (1). Orchards in areas with frequent summer dews, high humidity, and little air movement sustained severe defoliation, resulting in yield losses often exceeding 50%. Symptoms occur only on leaf blades in late spring and summer. Lesions develop as small, circular, tan spots 1 to 3 mm in diameter that may enlarge to 5 to 20 mm in size. Semicircular lesions frequently develop along the leaf margins and tips. The centers of mature lesions become black with fungal sporulation. The fungi isolated from the margins of sporulating and non-sporulating lesions were identified as three species in the Alternaria alternata complex: A. alternata, A. arborescens, and A. tenuissima (2,3). Cultures grown in the dark on potato dextrose (PDA) or potato-carrot agar are grayish white to olivacious green in the former two species and dark gray and wooly in the latter species. On 5% PDA, cultures of all three species produced catenulate dictyospores that were granular to punctate (-verrucose), pale yellowish to brown or black, and had visible apical and basal pores. Conidial morphology depended on chain position; apical conidia ranged from ovoid to ellipsoid, whereas basal conidia were elliptical to obclavate. Average conidial dimensions of A. alternata and A. arborescens ranged from 20 to 28 × 8 to 10 μm. Conidia of A. alternata were produced in acropetal succession in branching chains on single, short suberect conidiophores. A. arborescens produced conidia similarly but mostly in dichotomously branching chains on short to long conidiophores. Average conidial dimensions of A. tenuissima ranged from 20 to 34 × 8 to 12 μm and they were produced in simple chains with one or two branches forming occasionally. In preliminary studies, the optimum temperature for mycelial growth on PDA for all three species ranged from 24 to 28°C. Fifty mature leaves on each of four 7- or 8-year-old almond cv. Butte trees were inoculated at 2- to 3-week intervals from mid-spring through summer in 1999 and 2000. Leaves were sprayed with aqueous suspensions containing 105 conidia per milliliter for one isolate each of A. alternata and A. arborescens and two isolates of A. tenuissima or with sterile distilled water. The shoots were covered for 72 h with plastic-lined brown paper bags containing wet paper towels. Leaves were examined for infection after 7 and 14 days. All isolates were pathogenic and produced non-sporulating lesions similar to those observed in natural infections. No symptoms were observed on noninoculated control plants. Disease incidence was low (<15%) until late June 1999 and July 2000. Inoculations in summer produced increasingly more infections, reaching incidences of 40 to 52% in September 1999 and 18 to 80% in August 2000.

Variations in floral development in Peperomia (Piperaceae) and their taxonomic implications

The floral development of two species of Peperomia, Peperomia reflexa A. Dietr. (P. tetraphylla (G. Forst.) Hook. et Arn.) and P. serpens C. DC., is described. The initiation order is in an acropetal succession and resembles that in P. metallica L. Lind. et Rod., P. pellucida (L.) Kunth and Il rubella Hook., although many more bracts are produced in these two species than in P. metallica. The arrangement of bracts and floral primordia is orthostichous in P. reflexa: but parastichous in P. serpens. The floral apices in P. reflexa are transversely ellipsoidal protuberances at first, then become saddle-shaped when they begin to produce simultaneously staminal primordia. They are similar to those of P. metallica, P. pellucida and P. rubella. However, their initiation of floral primordia is much delayed compared to the size of the bracts. The triangular ol transversely cuneate ridges then become L-shaped in P. serpens; this shape is related to the parastichous phyllotaxy of the bracts. So, the staminal primordia are successively initiated and develop at different rates. Therefore, they are not always the same size. The staminal primordia are initiated above the level of the floral apex in P. reflexa and P. serpens but below it in P. metallica, P. pellucida and P. rubella. The abaxial position of the carpel primordium on the apex and the closure of the ovary in 19 reflexa and 19 serpens are also similar to those in P. metallica, P. pellucida and P. rubella. The shape of the upper part of the ovary, stigmas and indumentum vary between the species. In P. reflexa, the upper part of the ovary becomes ovoid and acclivous, or leaning acropetally, to the axis of inflorescence. In P. serpens, it becomes helmet-shaped. The flowers of P. serpens are surrounded by the outgrowth of the axis of the inflorescence. The ontogenetical features of ovaries in Peperomia indicate that the fruit characters are useful in the taxonomy of the genus. (C) 1999 The Linnean Society of London.

Variations in floral development in Peperomia (Piperaceae) and their taxonomic implications

The floral development of two species of Peperomia, Peperomia reflexa A. Dietr. (P. tetraphylla (G. Forst.) Hook. et Arn.) and P. serpens C. DCis described. The initiation order is in an acropetal succession and resembles that in P. metallica L. Lind. et Rod P. pellucida (L.) Kunth and P. rubella Hookalthough many more bracts are produced in these two species than in P. metallica. The arrangement of bracts and floral primordia is orthostichous in P. reflexa, but parastichous in P. serpens. The floral apices inP. reflexa are transversely ellipsoidal protuberances at first, then become saddle-shaped when they begin to produce simultaneously staminal primordia. They are similar to those of P. metallica>, P. pellucida and P. rubella. However, their initiation of floral primordia is much delayed compared to the size of the bracts. The triangular or transversely cuneate ridges then become L-shaped in P. serpens; this shape is related to the parastichous phyllotaxy of the bracts. So, the staminal primordia are successively initiated and develop at different rates. Therefore, they are not always the same size. The staminal primordia are initiated above the level of the floral apex in P. reflexa and P. serpens but below it inP. metallica, P. pellucida and P. rubella. The abaxial position of the carpel primordium on the apex and the closure of the ovary in P. reflexa and P. serpens are also similar to those in P. metallica, P. pellucida and P. rubella. The shape of the upper part of the ovary, stigmas and indumentum vary between the species. In P. reflexa, the upper part of the ovary becomes ovoid and acclivous, or leaning acropetally, to the axis of inflorescence. In P. serpens, it becomes helmet-shaped. The flowers of P. serpens are surrounded by the outgrowth of the axis of the inflorescence. The ontogenetical features of ovaries in Peperomia indicate that the fruit characters are useful in the taxonomy of the genus.

An analysis of the early floral development of Pittosporum tobira (THUNB.) AITON and some remarks on the systematic position of the family Pittosporaceae

AbstractIn Pittosporum tobira all floral organs are initiated in a strictly acropetal succession. It is striking that sepals and petals show an extremely early hyponastical development. Important floral characters for placing the family Pittosporaceae near the Apiales (Araliaceae and Apiaceae) are the early sympetaly, only gradual differences in the gynoecium development and placentation, and the fact that a nectar secreting area is situated at the base of the dorsal carpel flanks (ovary superior in Pittosporaceae, inferior in Apiales).Viscid latex, which plays an important role in the dispersal of the seeds by exozoochory, is produced by the multicellular epidermal hairs in the septal (placental) region.

Senescence and Receptivity of Maize Silks

Ears of maize (Zea mays L.) fail to produce kernals if pollination is delayed more than a few days after silks emerge. Reproductive failure in aging flowers could be due to loss of silk receptivity to pollen. To test this possibility, we examined the capacity of silks to support pollen germination, tube growth, and the passage of the tube to the ovary as flowers aged. Plants were grown in the greenhouse and silks were pollinated by hand up to 14 d after emergence from the husks. Flowers in the mid‐base region of the ear failed to set kernels when pollinated 7 or more days after their silks emerged. This corresponded to the day the base of the silks began to collapse (senesce). The remaining flowers on the ear failed to set kernels in acropetal succession, coincident with the occurrence of silk senescence. During the first 24 to 36 h of senescence, pollen germination and tube growth proceeded normally. However, once the basal tissue collapsed, tube growth was restricted and fertilization did not occur. These results indicate that kernel set on an ear was closely related to the number of flowers having silks that are not senesced at pollination. Silks of aging flowers lost receptivity initially because the base of the silk collapsed, and pollen tubes were blocked from reaching the ovary. Silk senescence is the primary cause for reproductive failure in maize if pollination does not occur soon after silks emerge from the husk.

Microscopy studies of powdery mildew on summer squash

Powdery mildews are characterized by the appearance of spots or patches of a white to grayish, powdery, mildewy growth on plant tissues, entire leaves or other organs. Ervsiphe cichoracearum, the powdery mildew of cucurbits is among the most serious parasites, and the most common. The conidia are formed similar to the process described for Ervsiphe graminis by Cole and Samson. Theconidial chains mature basipetally from a short, conidiophore mother-cell at the base of the fertile hypha which arises holoblastically from the conidiophore. During early development it probably elongates by polar-tip growth like a vegetative hypha. A septum forms just above the conidiophore apex. Additional septa develop in acropetal succession. However, the conidia of E. cichoracearum are more doliform than condia from E. graminis. The purpose of these investigations was to use scanning electron microscopy (SEM) to demonstrate the nature of hyphal growth and conidial formation of E. cichoracearum on field-grown squash leaves.

ANATOMY AND ASPECTS OF DEVELOPMENT OF THE STAMINATE INFLORESCENCES AND FLORETS OF SEVEN SPECIES OF ALLOCASUARINA (CASUARINACEAE)

The morphology, ontogeny, and vascular anatomy of the staminate inflorescences and florets of seven species of Allocasuarina are described. The generally terminal but open‐ended inflorescences occur on monoecious or staminate dioecious trees and consist of whorls of bracts, each subtending a sessile axillary floret. Each floret consists of one terminal stamen with a bilobed, tetrasporangiate anther enclosed typically by cuculliform appendages, commonly considered bracteoles, an inner median pair and an outer lateral pair. The mature stamen is exerted, the anther is basifixed and is extrorsely dehiscent. In early development of a male inflorescence very little internodal elongation occurs and enclosing cataphylls appear. The inflorescence apex is a low dome with a uniseriate tunica and a small group of central corpus cells. Bract primordia are initiated by periclinal divisions of C1 followed by further divisions of the corpus and anticlinal divisions in the tunica. The bracts are epinastic and become gamophyllous except apically by cell divisions in both sides of each primordium. Stomata are restricted to the axis furrows and the abaxial tips of the bracts. The axillary florets arise in acropetal succession initiated by periclinal divisions in C1 accompanied by anticlinal divisions in the tunica. The lateral floral appendages are also initiated by C1 followed by anticlinal divisions in the tunica. They become adnate basally later with the subtending bract. The median sterile appendages are initiated in a manner similar to the initiation of the outer appendages. The stamen is initiated by divisions in the outer layers of the corpus and in the tunica, and then develops first by apical growth followed by intercalary growth. The vascular system of the inflorescence is identical to that of the vegetative stem. Each floret is supplied by a single bundle that has its source in a branch from each of the two traces supplying a bract. Six bundles arise from the floral bundle; four of these terminate in the base of the stamen and two form an amphicribal bundle that supplies the anther. Pollen is binucleate, 3‐ to 7‐porate. The exine is tegillate.

The role of growth regulators in the differentiation of flowers and inflorescences

Growth regulators participate in the differentiation of floral parts, determining the developmental path of the respective type of inflorescence. The effect depends on the expression of the peculiarities of floral part differentiation, the recognition of the character of endogenous substances in certain stages and the choice of the suitable regulator for application. In the primitive flower ofPapaver petals and stamens are formed from the peripheral meristem with a lower content of auxins and a higher level of gibberellic substances. The pistil arises later from central tissues with a higher level of auxins and inhibitory substances. The stamens are more sensitive to the higher level of auxin substances, and by a suitable application of GA3 and BAP they can be transformed into petals; in this way double flower forms arise. In the differentiation of floral parts ofCampanula, Rosa andMelandrium similar regularities assert themselves in time successions, but in another spatial arrangement. Sex differentiation of diclinous flowers ofMelandrium is based on differences in heterochromosomes XY and XX. The rise of the zygomorphic flower ofVeronica is accompanied by a different distribution of endogenous substances which affect the development of petals, stamens and the pistil. The differentiation of flowers in the racemose inflorescence occurs in the acropetal succession, and lateral primordia inCampanula develop into actinomorphic regular flowers, whereas inDigitalis they are zygomorphic and only the terminal flower is peloric. In the initial phases the staminate tassel and the pistillate ear in maize are identical. Earlier differentiation of the terminal pistillate tassel is connected with a higher level of gibberellins and the later development of the lateral pistillate ear is accompanied by the increase in auxin-like substances and inhibitions. Similar correlations were found in the development of staminate catkins and the differentiation of pistillate flowers in terminal buds ofJuglans regia. By the application of auxin-like substances it is possible to achieve the transformation of primordia of the staminate tassel into the pistillate ear in maize or to regulate the number of staminate catkins and pistillate flowers on twigs of the walnut tree. In the capitulum of the sunflower differences arise between peripheral pistillate ray flowers and hermaphrodite tubular ones. By applying GA3 and BAP the number of ray flowers is increased. If the normal course of inflorescence differentiation is affected with a suitable type of regulator, a range of floral abnormalities appears which permit to assess the intervention in different developmental stages and the reaction of the primordium to the applied type of regulator. Abnormalities also suggest some phylogenetic correlations.

Floral Development of Hydrocharis morsus-ranae (Hydrocharitaceae)

In both male and female flowers of H. morsus-ranae the primordia of the floral appendages appear in an acropetal succession consisting of alternating trimerous whorls. In the male flower a whorl of sepals is followed by a whorl of petals, three whorls of stamens, and a whorl of filamentous staminodes. The mature androecial arrangement therefore consists of two antisepalous stamen whorls, an antipetalous whorl of stamens, and antipetalous staminodes. Shortly before anthesis, basal meristematic upgrowth between filaments of adjacent whorls produces paired stamens, joining Whorls 1 and 3, and Whorl 2 with the staminodial whorl. A central domelike structure develops between the closely appressed filaments of the inner stamen and staminodial whorl, giving the structure a lobed appearance. After petal inception in the female flower a whorl of antisepalous staminodes develop, each of which may bifurcate to form a pair of staminodes. During staminode development a girdling primordium arises by upgrowth at the periphery of the floral apex. The girdling primordium rapidly forms six gynoecial primordia, which then go on to produce six free styles with bifid stigmas. Intercalary meristem activity, below the point of floral appendage attachment, leads to the production of a syncarpous inferior ovary with six parietal placentae. The styles and carpels remain open along their ventral sutures. During the final stages of female floral development, several hundred ovules develop along the carpel walls, and three nectaries develop dorsally and basally on the three antipetalous styles.

FLORAL DEVELOPMENT OF HYDROCHARIS MORSUS‐RANAE (HYDROCHARITACEAE)

In both male and female flowers of H. morsus‐ranae the primordia of the floral appendages appear in an acropetal succession consisting of alternating trimerous whorls. In the male flower a whorl of sepals is followed by a whorl of petals, three whorls of stamens, and a whorl of filamentous staminodes. The mature androecial arrangement therefore consists of two antisepalous stamen whorls, an antipetalous whorl of stamens, and antipetalous staminodes. Shortly before anthesis, basal meristematic upgrowth between filaments of adjacent whorls produces paired stamens, joining Whorls 1 and 3, and Whorl 2 with the staminodial whorl. A central domelike structure develops between the closely appressed filaments of the inner stamen and staminodial whorl, giving the structure a lobed appearance. After petal inception in the female flower a whorl of antisepalous staminodes develop, each of which may bifurcate to form a pair of staminodes. During staminode development a girdling primordium arises by upgrowth at the periphery of the floral apex. The girdling primordium rapidly forms six gynoecial primordia, which then go on to produce six free styles with bifid stigmas. Intercalary meristem activity, below the point of floral appendage attachment, leads to the production of a syncarpous inferior ovary with six parietal placentae. The styles and carpels remain open along their ventral sutures. During the final stages of female floral development, several hundred ovules develop along the carpel walls, and three nectaries develop dorsally and basally on the three antipetalous styles.

Ultrastructural ontogeny of leaf cavity trichomes inAzolla implies a functional role in metabolite exchange

Anabaena azollae is associated with two types of multicellular epidermal trichomes inAzolla leaf cavities, the simple and branched hairs. The observation of transfer cell ultrastructure in some hair cells led to speculation that the cavity hairs might participate in metabolite exchange between the symbionts. The developmental ontogeny of cavity trichomes is described here, using transmission electron microscopy, with a goal of improving our understanding of possible functions of these structures in the symbiosis. The observations have established that all cells of simple and branched hairs develop the structural characteristics of transfer cells, but not simultaneously. Rather, there is an acropetal succession of transfer cell ultrastructure beginning in terminal cells, moving to body cells where present, and ending in stalk cells. The transfer cell stage is followed immediately by senescence in all hair cells. The timing of transfer cell differentiation, considered together with information from other studies, suggests that branched hairs may be involved in exchange of fixed nitrogen between the symbionts, while simple hairs may participate in exchange of fixed carbon fromAzolla toAnabaena.