Rates of corolla growth in tobacco determined with the plastochron index

The growth of vegetative and reproductive shoots of Nicotiana tabacum L. cv. Xanthi is analyzed with the plastochron index to estimate the relationship between corolla growth and time. The plastochron of leaves 9 through 20 declines steadily at each successive node. The flower plastochron increases steadily during the growth of an individual cyme, with the most distal flower to open having the longest plastochron. Variation in the flower plastochron is the result of variation in the rate of flower initiation, not the growth rate of individual flowers. The corolla has an extended phase of approximately constant relative growth in length (between 0.2 · d^–1 and 0.3 · d^–1) until a peak of growth (0.5 · d^–1) 2–3 d before anthesis. Corollas also have periodic peaks and troughs of growth that are low in amplitude (0.1 · d^–1), but persist throughout most of corolla development. The pattern of corolla expansion contrasts strongly with earlier reports of the pattern of tobacco leaf growth.Abbreviations PI plastochron index - PR plastochron ratio - RGR relative growth rate in length The authors thank: Drs. T. Sage and E.G. Williams for the considerable time and space they invested; the members of Dr. R. Wyatt's laboratory for allowing us to use their computer facilities; A. Tull and M. Smith for their care taken in the green-house. This research was supported by U.S. Department of Agriculture grant GAM-89-01056 and by National Science Foundation grant DCB-87-15799.     

COMPONENTS OF PHENOTYPIC SELECTION: POLLEN EXPORT AND FLOWER COROLLA WIDTH IN IPOMOPSIS AGGREGATA

In the hummingbird-pollinated herb Ipomopsis aggregata, selection through male function during pollination favors wide corolla tubes. We explored the mechanisms behind this selection, using phenotypic selection analysis to compare effects of corolla width on two components of male pollination success, pollinator visit rate and pollen exported per visit. During single visits by captive hummingbirds, flowers with wider corollas exported more pollen, and more dye used as a pollen analogue, to stigmas of recipient flowers. Corolla width was less strongly related to visit rate in the field, and had no direct effect on visit rate after nectar production and corolla length were controlled for. Moreover, the phenotypic selection differential was 80% higher for the effect on pollen exported per visit, suggesting that this is the more important mechanism of selection.     

Corolla tube formation in six species of apocynaceae

Corolla tube formation inTrachelospermum asiaticum, Nerium indicum var.leucanthum, Anodendrom affine, Vinca major, Catharanthus roseus andAmsonia elliptica was investigated anatomically. The corolla tube formation among these species is basically similar. The bases of petal primordia extend laterally to the interprimordial regions, the upward growth occurrig at those regions just beside the petal bases. The extending petal bases connect with each other at the bases of the abaxial side of stamen primordia in the early stage of the corolla development. The upward growth at the coonnected regions results in the formation of a short corolla tube but is weakened rapidly. At the stage of the mutual connection of petal bases, a common base of petal and stamen primordia is initiated. This common base develops into the lower portion of the corolla tube, i.e. the portion below the stamen insertion. In a relatively late stage, adjacent margins, of the corolla lobes fuse postgenitally at their lower portions, resulting in the formation of almost all of the upper portion of the corolla tube. The corona inNerium andVinca is initiated by the active adaxial growth of the upper portion of the corolla tube.     

Island–mainland difference in <Emphasis Type="Italic">Nicotiana glauca</Emphasis> (Solanaceae) corolla length: a product of pollinator-mediated selection?

A match between floral and pollinator traits, such as that between unique island plants and pollinators, is often thought to be the product of pollinator-mediated selection. I examined whether the floral morphology of an introduced hummingbird-pollinated plant, Nicotiana glauca (tree tobacco, Solanaceae), is under selection by pollinators on the California Channel Islands where it is a recent colonist. I first determined differences in floral morphology and pollinator composition between island and mainland populations of N. glauca. I found that island plants have detectably longer corollas (on average 1 mm) and are visited by hummingbird species with on average 1–2 mm longer bills than common mainland visitors. Corolla length differences were not found to be associated with site abiotic differences. Flower size does not vary consistently with season and corolla width is very consistent across sites. I tested whether island–mainland corolla length differences are the product of pollinator-mediated selection by measuring phenotypic selection and per visit effectiveness. Contrary to expectations, a longer corolla was not consistently associated with higher pollen transfer or seed count on the islands. Per visit effectiveness of longer and shorter-billed hummingbirds did differ; however, effectiveness did not depend on corolla length. Although I failed to detect expected patterns of selection for longer corollas on islands, I cannot rule out weak or past pollinator-mediated selection. It is also possible that despite the apparent match between pollinator and floral traits, island–mainland differences in corolla length are instead due to other environmental effects, selection unrelated to pollinators, or stochastic processes such as drift.     

Lifetime fecundity and floral variation in Tuberaria guttata (Cistaceae), a Mediterranean annual

In Tuberaria guttata, petal length, ovule number, and seeds per capsule raised steeply with increasing plant size (respectively, in the ranges 6-11 mm, 40-100, and 20-80), while the number of stamens varied relatively little (14-20). All flowers set fruit, and the rates of embryo abortion were independent of plant size and low on average. Individual fecundities had a markedly right-skewed frequency distribution (in the ranges 1-20 capsules and 20-1500 seeds per plant), which issued not only from plant size and flower production being positively correlated, but also from per-flower ovule numbers being directly proportional to plant size. Correlated variation of plant and ovary sizes amplified among-plant inequalities regarding fecundity; allowed larger plants to set ca. 50% more seed than expected on the basis of flower number only; and caused the slope of the size-fecundity relationship to be considerably steeper (at the population level) than if ovule number was a fixed trait. Corolla, ovary and androecium plasticity in Tuberaria are discussed in terms of environmental effects and developmental constraints.     

Explosive flower opening in ornithophily: a study of pollination mechanisms in some Central African Loranthaceae

In many ornithophilous Loranthaceae pollination is accompanied by an explosive opening of the flowers, and diverse mechanisms have evolved in different genera to bring this about. These are described for the African genera Erianthemum, Englerina, Tapinanthus, Globimetula, Vanwykia and Plicosepalus. In many genera tensions within the stamens cause the tubular corolla to split along the petal junctions to form window-like fenestrae. The flowers are pollinated mainly by sunbirds which insert their beaks through the fenestrae in search of the abundant nectar. This action causes the tube to split and the stamens to coil inwards explosively. In Globimetula and many species of Tapinanthus pigment is secreted along the edges of the specialized petal segments of the head, the spathulae. Probing along these secretory junctions causes the spathulae to reflex; further probing splits the corolla tube, and allows the stamens to coil inwards explosively. In Globimetula reflexure of the petals exposes the central column of stamens, between which secondary fenestrae are developed. In Plicosepalus curvature of the corolla tube is connected with a more specialized fenestral structure; flower opening is not explosive, and the open flowers continue to be visited regularly by sunbirds. In Vanwykia an early stage in the development of explosive flower-opening is found.     

Anthocyanin synthesis in a white flowering mutant of Petunia hybrida

In flower buds of the white flowering mutant W19 of Petunia hybrida four biologically active dihydroflavonol intermediates-dihydroquercetin-7-glucoside, dihydroquercetin-4-glucoside, dihydroquercetin, and dihydrokaempferol-7-glucoside-are accumulated. When dihydroquercetin was supplied to in vitro cultured corollas of the white flowering mutant W18, a mixture of cyanidin and delphinidin glycosides was produced, cyanidin-3-glucoside being the major pigment. The quantity of dihydroquercetin accumulated in W19 is very small, but this compound appears to be a more direct precursor of anthocyanins than the glucosides of dihydrokaempferol and dihydroquercetin. The conditions for pigment synthesis in W18 were optimalized. The quantitative uptake of dihydroquercetin was also studied. It was demonstrated that ca. 1/3 of the quantity present in the culture solution entered the corolla. From the absorbed dihydroquercetin only 14% was converted into anthocyanins. Complementation experiments to determine the biosynthetic sequence of the anthocyanin genes An1, An2, and An3 indicated that the genes An1 and An2 are indistinguishable by this technique.Abbreviation DHQ (+) dihydroquercetin     

Are flowers physiological sinks or faucets? Costs and correlates of water use by flowers of Polemonium viscosum

Water loss through inflorescences may place extreme demands on plant water status in arid environments. Here we examine how corolla size, a trait known to influence pollination success, affects the water cost of flowering in the alpine skypilot, Polemonium viscosum. In a potometry experiment, water uptake rates of inflorescences were monitored during bud expansion and anthesis. Corolla volume of fully expanded flowers predicted water uptake during bud expansion (R ²=0.61, P=0.0375) and corolla surface area predicted water uptake during anthesis (R ²=0.59, P=0.044). To probe mechanisms underlying the relationship between corolla size and water uptake, cell dimensions and densities were measured in several regions of fully expanded corollas. Corolla length was positively correlated with cell length in the middle of the corolla tube and cell diameter in the corolla lobe (Pearson's r from 0.26–0.33, n=86, P ≤ 0.05). Cell density was negatively correlated with cell dimensions in the upper corolla tube and lobe (Pearson's r from –0.39 to –0.42, P ≤ 0.0015). These findings suggest that more water may be required to maintain turgor in large corollas in part because their tissues have lower cell wall densities. The carbon cost of water use by flowers was assessed in krummholz and tundra habitats for P. viscosum flowering, respectively, during dry and wet portions of the growing season. For plants in full flower, average leaf water potentials were significantly more negative (P=0.0079) at mid-day in the krummholz (June) than in the tundra (July), but were similar before dawn (P=0.631). Photosynthetic rate at the time of flowering declined significantly with increasing corolla size in the krummholz (P=0.0376), but was unrelated to corolla size on the tundra (P>0.72). Plants losing water through large corollas may close leaf stomata to maintain turgor. If photosynthesis limits growth in this perennial species, then the water cost of producing large flowers should exacerbate the cost of reproduction under dry conditions. Such factors could select for flowers with smaller corollas in the krummholz, countering pollinator-mediated selection and helping maintain genetic variation in corolla size components of P. viscosum. Received: 5 May 1998 / Accepted: 2 October 1998     

Hoofbeats From the Currituck Outer Banks: A Study of the Corolla Wild Horse Fund Adoption Program

Research on the adoption and relinquishment of horses, both domestic and wild, remains limited. As a result, little is known about adopters, their adopted horses, and their adoption experience. This study surveyed and interviewed 17 adopters of Colonial Spanish mustangs through the Corolla Wild Horse Fund (CWHF). Together, they adopted 22 horses of varying ages and genders from 2002 to 2012. The participants, who had a range of previous experience with and knowledge of horses, were generally very satisfied with their horses and their adoption experience. Being able to adopt a gentled/trained mustang and receiving support from the CWHF during the adoption process played key roles in adoption success. Additionally, participants’ strong desire to preserve a perceived endangered species or national treasure appeared to be a major reason for adopting a Colonial Spanish mustang and served as motivation for making the adoption successful. The results of the study provide insights into ways to improve the number and success of adoptions through other equine programs, especially the Bureau of Land Management's wild horse and burro program.