Base Of Carpel Research Articles

The ontogenetic bases for variation in ovary position in Melastomataceae.

Although the ovary position is considered a stable character in angiosperms, Melastomataceae species have perigynous flowers in which the ovary varies from superior to inferior. Thus, we investigated the ontogenetic process involved in variation of the ovary position in Melastomataceae. We focused on histogenesis of the floral apex in search of developmental patterns for each type of ovary position. Six species in which the ovary varies from superior to inferior were chosen: Henriettea saldanhae, Leandra melastomoides, Miconia dodecandra, Microlicia euphorbioides, Rhynchanthera grandiflora, and Tibouchina clinopodifolia. Buds and flowers were processed for surface and histological examinations. The floral apex changes from convex to concave, resulting in a perigynous hypanthium. Cell divisions in the margins of the floral apex form an annular intercalary meristem that elevates the base of the primordia of almost all whorls. The joint growth of the carpel base with the gynoecial hypanthium originates semi-inferior ovaries in Leandra melastomoides, Miconia dodecandra, and Tibouchina clinopodifolia and inferior ovaries in Henriettea saldanhae. In Microlicia euphorbioides and Rhynchanthera grandiflora, the carpels are not affected by this hypanthial growth; flowers have a superior ovary. Changes in ovary position of Melastomataceae are due to intercalary meristematic activity, which is one of the main mechanisms for the origin of morphological innovations among plants. Our data illustrate the importance of the intercalary meristems in floral development, and we discuss the implications of this ontogenetic model for understanding the evolution of ovary position in Melastomataceae.

Unique growth paths of heterospecific pollen tubes result in late entry into ovules in the gynoecium of Sagittaria (Alismataceae).

Pollen-pistil interactions are a fundamental process in the reproductive biology of angiosperms and play a particularly important role in maintaining incipient species that exist in sympatry. However, the majority of previous studies have focused on species with syncarpous gynoecia (fused carpels) and not those with apocarpous gynoecia (unfused carpels). In the present study, we investigated the growth of conspecific pollen tubes compared to heterospecific pollen tubes in Sagittaria species, which have apocarpous gynoecia. We conducted controlled pollinations between S.pygmaea and S.trifolia and observed the growth of conspecific and heterospecific pollen tubes under a fluorescence microscope. Heterospecific and conspecific pollen tubes arrived at locules within the ovaries near simultaneously. However, conspecific pollen tubes entered into the ovules directly, whereas heterospecific tubes passed through the carpel base and adjacent receptacle tissue, to ultimately fertilize other unfertilized ovules. This longer route taken by heterospecific pollen tubes therefore caused a delay in the time required to enter into the ovules. Furthermore, heterospecific pollen tubes displayed similar growth patterns at early and peak pollination. The growth pattern of heterospecific pollen tubes at late pollination was similar to that of conspecific pollen tubes at peak pollination. Heterospecific and conspecific pollen tubes took different routes to fertilize ovules. A delayed entry of heterospecific pollen into ovules may be a novel mechanism of conspecific pollen advantage (CPA) for apocarpous species.

Sedum piaxtlaense(Crassulaceae), a New Species from Durango, México

Abstract: Sedum piaxtlaense is described as a new species based on a collection in the Rio Piaxtla Canyon, growing in tropical deciduous forest in the Sierra Madre Occidental near the border of the Mexican states of Durango and Sinaloa. This new species belongs into the section Sedastrum (Rose) A. Berger whose distinctive morphological characteristics are basal rosettes, generally pubescent leaves, concave carpel base, usually paniculate inflorescences, and white corollas, the only exceptions being Sedum glabrum and S. jarocho which do not show any pubescence in their floral structures. S. piaxtlaense is apparently closely related to S. hintonii and S. mocinianum from which it differs in the laxer rosettes, concave leaves of larger diameter, as well as a shorter inflorescence with up to eight flowers per cincinnus and large pedicels, and its distribution in another biogeographical province.

The structure and development of incompletely closed carpels in an apocarpous species, Sagittaria trifolia (Alismataceae).

• Premise of the study: Carpel closure is commonly considered as a key innovation in angiosperms; however, some families continue to exhibit a variety of forms of incomplete carpel closure. The carpel of Sagittaria species contains an unusual structure. In this study, we confirm the closure type of the carpel of Sagittaria trifolia and discuss its development and evolution.• Methods: Scanning electron microscopy and light microscopy of semithin sections were used to observe the development and the mature structure of the carpel. Pollen tube growth in the carpel and seed germination in the achene was also studied.• Key results: During late carpel development, the middle parts of the carpel margins underwent postgenital fusion. However, at maturity the lowest and uppermost parts of the carpel margins remained open. The mature carpel was incompletely closed and contained a secretion-filled canal, which extended from the stigma to the opening at the carpel base. At that site, pollen tubes could either grow to the ovule or exit the carpel and grow to other carpels. The basal opening also served as an exit point for the seedling to emerge.• Conclusions: Incomplete carpel closure by S. trifolia differs from the closure types recorded in previous studies because two entrances link the ovary in the carpel to the outside environment. This type of carpel closure occurs as a result of the lack of fusion of the carpel margins at the base of the carpel and could improve the seed set and seedling germination of S. trifolia.

CARPEL DEVELOPMENT IN DRIMYS LANCEOLATA

The dissimilar carpels of representatives of the Tasmannia and Wintera sections of the genus Drimys have been investigated developmentally with particular attention to the presence of peltation. In Drimys winteri of the Wintera section peltation results from an active adaxial meristem, but in D. lanceolata of the Tasmannia section the adaxial “cross‐zone” meristem is weakly developed and contributes little to the carpel. The form of the carpels also shows contrasts; the carpel of D. lanceolata begins growth as paired ridges separated by a cleft extending over the summit. Allometric growth reorients the cleft and it eventually extends from the ventral base of the carpel up over the summit. The cleft elongates greatly, together with the main part of the carpel. In D. winteri, growth is concentrated below the level of the cleft, and the carpel grows as an elongating cylinder. The cleft remains short, not extending with the carpel. In both species, early growth involves subsurface initials: subapical, adaxial (although weak in D. lanceolata), and submarginal. The presence of a disc encircling the base of the solitary carpel is reported for the first time for D. lanceolata.

Carpel Development in Drimys lanceolata

The dissimilar carpels of representatives of the Tasmannia and Wintera sections of the genus Drimys have been investigated developmentally with particular attention to the presence of peltation. In Drimys winteri of the Wintera section peltation results from an active adaxial meristem, but in D. lanceolata of the Tasmannia section the adaxial “cross-zone” meristem is weakly developed and contributes little to the carpel. The form of the carpels also shows contrasts; the carpel of D. lanceolata begins growth as paired ridges separated by a cleft extending over the summit. Allometric growth reorients the cleft and it eventually extends from the ventral base of the carpel up over the summit. The cleft elongates greatly, together with the main part of the carpel. In D. winteri, growth is concentrated below the level of the cleft, and the carpel grows as an elongating cylinder. The cleft remains short, not extending with the carpel. In both species, early growth involves subsurface initials: subapical, adaxial (although weak in D. lanceolata), and submarginal. The presence of a disc encircling the base of the solitary carpel is reported for the first time for D. lanceolata.

COMPARATIVE MORPHOLOGY OF THE CARPEL IN THE ROSACEAE. II. PRUNOIDEAE: MADDENIA, PYGEUM; OSMARONIA

A survey of species of the prunoid genera, Maddenia and Pygeum, and of the genus Osmaronia has been made. The ovules of all are pendent, campylotropous, and epitropic. In the prunoids, the ovular supply is intimately connected with a central vascular plexus in the base of the carpel; that plexus is absent from Osmaronia. The prunoid carpels are marked by an extensive degree of fusion among the ovular and wing bundles, by fusion of the sutural margins, by fusion of the 2 integuments of the ovule to a single massive one, and by the presence of 3 or 5 well‐developed bundles in the base. The carpel of Osmaronia also has a strongly fused bipartite ovular supply, separate bundles of which, however, become very much attenuated before reaching the funiculus; it has independent ovular and wing bundles, completely separate carpellary margins, 2 clearly separate integuments in the ovule, and 6 distinctive bundles in the carpel base. At the funiculus, the wing bundle of Osmaronia is connected with the adjoining weak ovular bundle by a well‐developed vascular branch. Various particularities in the morphology of Osmaronia lend support to its segregation into a unique tribe, the Osmaronieae of Rydberg.