Experimental control of floral reversion in isolated shoot apices of the long-day plant Silene coeli-rosa

The fate of shoot meristems of the long day (LD) plant Silene coeli-rosa in culture was examined (complete, reverted or arrested flowers) to establish whether these different patterns were related to a particular stage of morphogenesis and the extent to which the fate of the pattern was regulated by either added plant growth regulators (PGRs) or changing the carbohydrate source in the medium. In particular, the frequency of reversion was measured to test the stability of the determined state for each whorl. The plants were given various inductive treatments (4–7 LD, 7 LD + 1 to 3 SD) and the apices were explained onto Murashige-Skoog medium supplemented with 3% sucrose (controls) ± IAA, ± kinetin, ± GA₃ or onto the basal medium containing 1 or 3% sucrose, glucose or fructose or 7% sucrose. The apices were examined 12 weeks later. When the data were pooled from all inductive treatments, IAA resulted in more reversions, GA₃ caused more arrested flowers while kinetin hardly affected the pattern of meristem fate compared with the controls. However, each PGR treatment did not perturb the pattern of organ formation for those apices that formed either arrested or complete flowers. The time for determination (days) of the earlier formed whorls (determination times for the controls in brackets): sepals (2), stamens 1–5 (3) and petals (3), was shortened by about a day in all PGR treatments whereas the corresponding times for the later formed whorls: stamens 6–10 (4) and carpels (4), were either lengthened to 5 days or unaffected. The response of the apices to the various sugars was simply a reflection of concentration. Hence, more complete flowers formed at 7 or 3% and more flowers were arrested at 1 % regardless of the sugar moiety. However, the frequency of reversion was similar on each of the media. Pooling all data from all treatments enabled a statistical analysis of the pattern of reversion and the pattern of arrest. Reversion was more common from apices which exhibited the later-formed whorls (stamens 6–10 and carpels) than from the earlier whorls. Moreover, the stronger the inductive treatment the less frequent was reversion. The most common stage of arrest was at the stamen 6–10 whorl and this was particularly so for the GA₃ treatment. The data indicated that reversion could occur from any whorl, which suggests that determination of each whorl is independent of the next. This conclusion is underlined by the more frequent occurrence of reversion from the carpel whorl. However, the longer the inductive treatment the less likelihood of reversion; this suggests that in Silene, the floral stimulus is required continuously to stabilise the determined state of each whorl and to ensure smooth completion of floral morphogenesis.     

Determination of floral organ type in cultured Silene shoot apices

Shoot apices of the long day plant, Silene coeli-rosa , were cultured on a basal medium (+3% sucrose) in non-inductive short days (SD) following their excision from plants which had been exposed to long day (LD) treatments in order to examine the period for determination of each floral whorl. In response to the inductive LD treatments, the pattern of whorl formation in vitro reflected their normal appearance in Silene : sepals, stamens 1–5, petals, stamens 6–10 and carpels, although the number of apices initiating each whorl was lower in vitro compared with apices in vivo. However, supplementing the medium with 7 instead of 3% sucrose corrected this deficiency and, for the first time, resulted in apices initiating floral whorls in SD. The interval between the shortest treatment to result in whorl initiation in vitro, 4 LD (which also resulted in 50% flowering in vivo), and the treatment which gave 50% initiation of the corresponding whorl in vitro, was taken to be the period for determination of that whorl. The determination times on the 3% medium were: sepals (2 days), stamens 1–5 (3 days), petals (3 days), stamens 6–10 (4 days) and carpels (4 days); all of these periods shortened to about 1 day on the 7% medium. Tissue culture did not perturb the pattern of initiation of each whorl since apices excised and cultured from plants which had received 7 LD + 2 SD, exhibited each whorl over the same time scale as those of intact plants which received the same treatment. The data are consistent with a sequential determination and initiation of each whorl in the order that they appear normally in Silene . Synchronisation of cell division, as represented by peaks of the mitotic index and G₂/G₁ ratios on day 8 (7 LD + 2 SD), did not occur in vitro but the mitotic index did not descend to zero, further emphasising that tissue culture did not perturb the Silene apex.     

Comparative floral development in Lardizabalaceae (Ranunculales)

Lardizabalaceae, one of seven families of Ranunculales, represent a monophyletic group. The family has functionally unisexual flowers with the organs in trimerous whorls, petaloid sepals and sometimes nectariferous petals. Among Ranunculales, Lardizabalaceae share several floral characters and climbing habit with Menispermaceae, but molecular analyses indicate that Circaeasteraceae and Lardizabalaceae form a strongly supported clade. Morphological and ontogenetic studies of flowers have proved to be a good complement to molecular data in clarifying relationships. Floral organogenesis has been studied in very few species of the family. This study investigates the comparative floral development of three species from three genera (Decaisnea, Akebia and Holboellia) of Lardizabalaceae using scanning electron microscopy. Flowers have a whorled phyllotaxis. Within each whorl, the organs are initiated either simultaneously or in a rapid spiral sequence. In Akebia, six sepals are initiated, but one to three sepals of the second whorl do not further develop. The presence of three sepals in Akebia is thus a developmentally secondary simplification. The petals (if present) are retarded in early developmental stages; stamens and petals are different in shape from the beginning of development. The retarded petals may not be derived from staminodes in Lardizabalaceae. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 166 , 171–184.     

Floral evolution in Lithospermum (Boraginaceae): independent origins of similar flower types

In Lithospermum (Boraginaceae), floral diversity is quite large, with variation in individual quantitative and qualitative traits as well as suites of floral characteristics. The present study utilizes phylogenetic, morphometric and developmental methodologies to investigate patterns of floral evolution, of individual and suites of traits, in the genus and among related genera. The evolutionary patterns of eight quantitative and five qualitative traits were reconstructed, and morphometrics and the evolution of floral morphospace were examined in the genus. Floral developmental patterns were established with light and scanning electron microscopy. Phylogenetic analyses provided evidence that derived flower types have each evolved multiple times, with differences in the manner in which these flower types arose. Floral morphospace has increased throughout the evolution of Lithospermum. Floral developmental patterns and cell lengths of floral organs at anthesis provided evidence that, in Lithospermum, an increase in the length of the sexual organs of flowers involves both longer cells and a greater number of mitotic divisions, but an increase in the length of the corolla is primarily a result of a larger number of cell divisions. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2016, 180 , 213–228.     

Developmental study on the inflorescence and flower of Caldesia grandis Samuel (Alismataceae)

The inflorescence and floral development of Caldesia grandis Samuel is reported for the first time in this paper. The basic units of the large cymo‐thyrsus inflorescence are short panicles that are arranged in a pseudowhorl. Each panicle gives rise spirally to three bract primordia also arranged in a pseudowhorl. The branch primordia arise at the axils of the bracts. Each panicle produces spirally three bract primordia with triradiate symmetry (or in a pseudowhorl) and three floral primordia in the axils of the bract primordia. The apex of the panicle becomes a terminal floral primordium after the initiations of lateral bract primordia and floral primordia. Three sepal primordia are initiated approximately in a single whorl from the floral primordium. Three petal primordia are initiated alternate to the sepal primordia, but their subsequent development is much delayed. The first six stamen primordia are initiated as three pairs in a single whorl and each pair appears to be antipetalous as in other genera of the Alismataceae. The stamen primordia of the second whorl are initiated trimerously and opposite to the petals. Usually, 9–12 stamens are initiated in a flower. There is successive transition between the initiation of stamen and carpel primordia. The six first‐initiated carpel primordia rise simultaneously in a whorl and alternate with the trimerous stamens, but the succeeding ones are initiated in irregular spirals, and there are 15–21 carpels developed in a flower. Petals begin to enlarge and expand when anthers of stamens have differentiated microsporangia. Such features do not occur in C. parnassifolia. In the latter, six stamen primordia are initiated in two whorls of three, carpel primordia are initiated in 1–3 whorls, and there is no delay in the development of petals. C. grandis is thus considered more primitive and C. parnassifolia more derived. C. grandis shares more similarities in features of floral development with Alsma, Echinodorus, Luronium and Sagittaria. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 140 , 39–47.     

Floral development in Nymphaea tetragona (Nymphaeaceae)

We describe in detail the floral ontogeny of Nymphaea tetragona from a wild population to provide evidence regarding the phylogenetic position of Nymphaea and to reveal evolutionary trends of flowers in Nymphaeaceae by comparison with that of the other genera. Four sepals are initiated unidirectionally. The basal petals are initiated unidirectionally and alternate with the sepals. The dome‐shaped floral apex continues to expand and produces more petal and stamen primordia. The remaining petals and all stamens are initiated in spirals or whorls. Later, the periphery of the floral apex grows more quickly than the centre and results in a depression in the centre of the apex after all stamens have been initiated. Carpels are simultaneously initiated in a cycle at the periphery of the depression. They are ascidiate. After all organs have been initiated, the centre of the depression on the floral apex grows and develops into a globular structure. The connected inferior ovary, stigma caps and the globular floral apex together form an extragynoecial compitum. Within Nymphaeaceae, the floral ontogeny of Nymphaea is most similar to that of Euryale and Victoria. It differs more from Ondinea and Barclaya, and differs most from Nuphar. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 211–221.     

Analysis of amino acids in nectar from Silene colorata Poiret (Caryophyllaceae)

Nectar samples were collected from Silene colorata Poiret (Caryophyllaceae), in three different populations from south-western Spain: Zahara de la Sierra (Cádiz), Bornos (Cádiz) and Bormujos (Seville). Samples were analysed for amino acids by reverse-phase high-performance liquid chromatography with precolumn phenylisotiocyanate (PITC) derivatization. The method has the advantage of being highly sensitive, capable of detecting nanogram (ng) quantities of amino acids. Eighteen amino acids were identified and quantified. The mean number of amino acids in a nectar sample was 14 (SD = 2.8). Six amino acids (threonine, alanine, arginine, proline, tyrosine and methionine) were detected in all samples, accounting for 83% of the total amino acids content; proline and arginine were the most abundant amino acids, accounting for 40% and 20% of the total amino acids, respectively. The mean amounts of amino acids in nectar samples per population were 824, 782 and 356 µ m in Zahara de la Sierra, Bornos and Bormujos, respectively. Environmental variations such as temperature and sunlight are factors influencing the metabolic processes of nectar production. Our results may contradict the theory that the chemical constituents of floral nectar vary according to the kinds of pollinators.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 49–56.     

NORMAL FLORAL ONTOGENY AND COOL TEMPERATURE-INDUCED ABERRANT FLORAL DEVELOPMENT IN GLYCINE MAX (FABACEAE)

Floral onset in soybean (Glycine max cv. Ransom) is characterized by precocious initiation of axillary meristems in the axils of the most recently initiated leaf primordium. During floral transition, leaf morphology changes from trifoliolate leaf with stipules, to a three-lobed bract, to an unlobed bract. Soybean flowers initiated at 26/22 C day/night temperatures are normal, papilionaceous, and pentamerous. Sepal, petal, and stamen whorls are initiated unidirectionally from the abaxial to adaxial side of the floral apex. The median sepal is located abaxially and the median petal adaxially on the meristem. The organogeny of ‘Ransom’ flowers was found to be: sepals, petals, outer stamens plus carpel, inner stamens; or, sepals, petals, carpel, outer stamens, inner stamens. The outer stamen whorl and the carpel show possible overlap in time of initiation. Equalization of organ size occurs only within the stamen whorls. The sepals retain distinction in size, and the petals exhibit an inverse size to age relationship. The keel petals postgenitally fuse along part of their abaxial margins; their bases, however, remain free. Soybean flowers initiated at cool day/night temperatures of 18/14 C exhibited abnormalities and intermediate organs in all whorls. The gynoecium consisted of one to ten carpels (usually three or four), and carpel connation varied. Fusion of keel petals was often lacking, and stamen filaments fused erratically. Multiple carpellate flowers developed into multiple pods that were separate or variously connate. Intermediate type organs had characteristics only of organs in adjacent whorls. These aberrant flowers demonstrate that the floral meristem of soybean is not fixed or limited in its developmental capabilities and that it has the potential to produce alternate morphological patterns.     

A Dynamical Phyllotaxis Model to Determine Floral Organ Number

How organisms determine particular organ numbers is a fundamental key to the development of precise body structures; however, the developmental mechanisms underlying organ-number determination are unclear. In many eudicot plants, the primordia of sepals and petals (the floral organs) first arise sequentially at the edge of a circular, undifferentiated region called the floral meristem, and later transition into a concentric arrangement called a whorl, which includes four or five organs. The properties controlling the transition to whorls comprising particular numbers of organs is little explored. We propose a development-based model of floral organ-number determination, improving upon earlier models of plant phyllotaxis that assumed two developmental processes: the sequential initiation of primordia in the least crowded space around the meristem and the constant growth of the tip of the stem. By introducing mutual repulsion among primordia into the growth process, we numerically and analytically show that the whorled arrangement emerges spontaneously from the sequential initiation of primordia. Moreover, by allowing the strength of the inhibition exerted by each primordium to decrease as the primordium ages, we show that pentamerous whorls, in which the angular and radial positions of the primordia are consistent with those observed in sepal and petal primordia in Silene coeli-rosa, Caryophyllaceae, become the dominant arrangement. The organ number within the outmost whorl, corresponding to the sepals, takes a value of four or five in a much wider parameter space than that in which it takes a value of six or seven. These results suggest that mutual repulsion among primordia during growth and a temporal decrease in the strength of the inhibition during initiation are required for the development of the tetramerous and pentamerous whorls common in eudicots.     

Reproductive structures and systematics of Buxaceae

Buxaceae belong to a grade of families near the base of eudicots. Flowers of these families are characterized by a variable number and arrangement of floral organs. In this study, the anthetic structure of the gynoecium and androecium of representatives of all genera of Buxaceae were comparatively studied, and observations on the flowering processes and pollination biology were made. Styloceras and Notobuxus were studied in detail for the first time. Various features of the morphological analysis support our earlier molecular phylogenetic study. Shared reproductive characters among Sarcococca , Pachysandra and Styloceras are the occurrence of two (rarely three) carpels, the lack of interstylar nectaries, a micropyle formed by both integuments, attractive stamens in male flowers, and fleshy fruits. In addition, Styloceras and Pachysandra share a secondary partition in the ovary. Notobuxus does not seem to be clearly distinct from Buxus . Both have a similar inflorescence and perianth structure; female flowers have three carpels, interstylar nectaries, micropyles formed by the inner integument, rudimentary arils, and they develop into capsular fruits; in male flowers stamens are sessile and the central pistillode is lacking in some species. Thus, it is questionable to justify a separation of Buxus and Notobuxus at genus level. The results further strongly support the placement of Buxaceae among basal eudicots.  © The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 140 , 193–228.     

Floral development in Anemoneae (Ranunculaceae)

The floral development of two Clematis species and four Anemone species (including Pulsatilla) (Anemoneae, Ranunculaceae) is described. Shared features are: (1) sepals shortly after initiation broad, crescent‐shaped, as opposed to the other organs, which are narrow and hemispherical; (2) outermost organs of the androecium often smaller than the others and sometimes sterile; (3) carpels ascidiate, with distinctive stalk, stigma papillate, decurrent; the carpels have one median fertile ovule and a few lateral sterile ovules in all species studied; the fertile ovule appears before the carpel closes. Generic differences are: (1) In Clematis, four sepals are initiated in two pairs; sometimes one of the sepals in the second pair appears to be divided into two organs (double position) resulting in a pentamerous perianth; the first eight stamens are positioned in two alternating whorls, the outer whorl alternating with the four sepals. In Anemone, the perianth organs, if five, are initiated in spiral sequence; in the Pulsatilla group of Anemone, six sepals are initiated in two whorls; the first three organs of the androecium (staminodes) alternate with the inner sepals. (2) Further androecial organs are mostly in complex whorls (i.e. including double positions) in Clematis, but in an irregular spiral or in irregular complex whorls in Anemone. (3) Anther maturation is largely centripetal in Clematis, but centrifugal or bidirectional in Anemone. In Clematis macropetala, the outermost organs of the androecium lack anthers and the filaments expand and become petal‐like. In contrast, in the Pulsatilla group of Anemone, these organs retain sterile anthers and become small, capitate organs. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162 , 77–100.     

Intra‐individual variation of flowers in Gunnera subgenus Panke (Gunneraceae) and proposed apomorphies for Gunnerales

A study of inflorescence and flower development in 12 species from four of the six subgenera of Gunnera (Gunneraceae) was carried out. In the species of subgenus Panke, initiation of floral apices along the partial inflorescences is acropetal but ends up in the late formation of a terminal flower, forming a cyme at maturity. The terminal flower is the largest and the most complete in terms of merosity and number of whorls and thus it is the most diagnostic in terms of species‐level taxonomy. The lateral flowers undergo a basipetal gradient of organ reduction along the inflorescence, ranging from bisexual flowers (towards the distal region) to functionally (i.e. with staminodia) and structurally female flowers (towards the proximal region). Our results show that the terminal structure in Gunnera is a flower rather than a pseudanthium. The terminal flower is disymmetric, dimerous and bisexual, representing the common bauplan for Gunnera flowers. It has a differentiated perianth with two sepals and two alternate petals, the latter opposite the stamens and carpels. Comparisons with other members of the core eudicots with labile floral construction are addressed. We propose vegetative and floral putative synapomorphies for the sister‐group relationship between Gunneraceae and Myrothamnaceae. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 262–283.     

A new species of Silene (Caryophyllaceae) from South Anatolia, Turkey

Silene doganii A.Duran & Y.Menemen sp. nov. from the Amanos Mountains (C6: Osmaniye-Turkey) is described and illustrated. It is closely related to S. caramanica Boiss. & Heldr., from which it differs mainly in its habit, hairiness, leaf and floral features.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 109−113.     

Characterization of the Rice Floral Organ Number Mutant fon3

A spontaneous rice mutant named floral organ number 3 (fon3) had major mutations in floral organ numbers. Genetic analysis indicated thatfon3 acted as a single recessive gene. Microscopic observation showed that the number of floral organs infon3 increased centripetally. For example, the number of pistils was the more frequently increased than organs in the outer whorls. Homeotic conversion of lodicules and glumes into palea/lemma-like organs was observed in some flowers. Scanning electron microscopy observation showed that the size of flower meristems was maintained the same or similar until the lemma primordium started to differentiate, at which time the floral meristem became enlarged, suggesting abnormal development of the inner whorls of rice florets. The relationship offon3 with other similar rice mutants is discussed.     

Evolution of novel morphological and reproductive traits in a clade containing Antirrhinum majus (Scrophulariaceae)

Phylogenetic analysis of DNA sequences of the chloroplast genes rcbL and ndhf revealed a highly supported clade composed of the families Plantaginaceae, Callitrichaceae, and Hippuridaceae in close association with the model organism Antirrhinum majus and other members of family Scrophulariaceae. Plantago has miniature actinomorphic wind-pollinated flowers that have evolved from zygomorphic animal-pollinated precursors. The aquatic Hippuridaceae have reduced windpollinated flowers with one reproductive organ per whorl, and three, rather than four, whorls. In monoecious aquatic Callitrichaceae, further reduction has occurred such that there is only one whorl per flower containing a single stamen or carpel. Optimization of character states showed that these families descended from an ancestor similar to Antirrhinum majus. Recent studies of plant developmental genetics have focused on distantly related species. Differences in the molecular mechanisms controlling floral development between model organisms are difficult to interpret due to phylogenetic distance. In order to understand evolutionary changes in floral morphology in terms of their underlying genetic processes, closely related species exhibiting morphological Variation should be examined. Studies of genes that regulate morphogenesis in the clade described here could aid in the elucidation of a general model tot such fundamental issues as how changes in floral symmetry, organ number, and whorl number are achieved, as well as providing insight on the evolution of dicliny and associated changes in pollination syndrome.     

Floral morphogenesis in Sinofranchetia (Lardizabalaceae) and its systematic significance

The floral organs of Sinofranchetia chinensis Hemsl. (Lardizabalaceae) are all spiral in initiation. Stamen and petal (nectar‐leaf) primordia initiate independently and are different in shape. The petals and three stamens in the first whorl are retarded in the early developmental stages. The carpel primordia are conduplicate; the stigma is formed around the upper part of the ventral slit and the style is not differentiated. The functionally unisexual flowers are bisexual in organization in the early developmental stages. The development of the flowers on the inflorescence is spiral and centripetal. Some floral characteristics of Sinofranchetia appear to be plesiomorphic in Lardizabalaceae. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 82–92.     

Characterization of the Rice Floral Organ Number Mutant fon3

A spontaneous rice mutant named floral organ number 3 (fon3) had major mutations in floral organ numbers. Genetic analysis indicated that fort3 acted as a single recessive gene. Microscopic observation showed that the number of floral organs infon3 increased centripetally. For example, the number of pistils was the more frequently increased than organs in the outer whorls. Homeotic conversion of lodicules and glumes into palea/lemma-like organs was observed in some flowers. Scanning electron microscopy observation showed that the size of flower meristems was maintained the same or similar until the lemma primordium started to differentiate, at which time the floral meristem became enlarged, suggesting abnormal development of the inner whorls of rice florets. The relationship of fort3 with other similar rice mutants is discussed.     

Flower development schedule and AGAMOUS‐like gene expression patterns in two morphs of Nigella damascena (Ranunculaceae) differing in floral architecture

Love‐in‐a‐mist (Nigella damascena) is an annual species of Ranunculaceae native to the Mediterranean Basin, characterized by delicate flowers lying on long lacy bracts. Two floral morphs of N. damascena, designated [P] and [T], differ in the identity and number of perianth organs and in the position of the perianth–androecium boundary on the meristem. They both occur in the wild. Here we describe a precise comparative schedule of floral development in the two morphs. We divided the sequence of developmental events affecting the floral meristem into six stages and related them to the height of the elongating stem and to the time elapsed after the beginning of stem elongation. In addition, we characterized the expression pattern of C‐class genes in floral organs of both morphs in an attempt to better characterize the differences between the two floral groundplans. In the [T] morph an expansion of the expression domain of AGAMOUS (AG) paralogues outside the fertile organs was observed, correlating with the change in identity of the inner perianth organs. Expression of AG‐like genes in the sepal‐like organs suggests these are not identical to true sepals at the molecular level. The morpho‐temporal framework we have defined will allow us to compare various gene expression profiles at targeted developmental stages in both morphs, providing further insight into the molecular control of the floral dimorphism in N. damascena and into the processes underlying the transition from a differentiated (bipartite) to an undifferentiated (unipartite) perianth. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178 , 608–619.