Gynoecium structure and development in core Caryophyllales: a matter of proportions

This review based on a morphological and developmental perspective reveals a striking diversity in shapes and evolutionary trends in the gynoecium of core Caryophyllales that have affected the number of carpels, the formation of septa and the number of ovules. Two major developmental shifts are responsible for the diversity in gynoecial forms and are linked to the proportional development of carpellary tissue (ovary wall) and the floral apex. (1) Meristic change is caused by an expansion or reduction of the diameter of the floral apex. An expansion leads to polygyny linked with the development of more numerous small carpels; a reduction of space leads to lower carpel numbers, eventually resulting in a single carpel. (2) Different ovary shapes can be recognized at a mid-developmental stage predicting the further development of ovaries. With an equal growth of the ovary wall and floral apex, young ovaries take the shape of a salt-shaker; with more extensive development of the floral apex and delay of the ovary wall, a club-shaped ovary is formed; with faster growth of the ovary wall linked with intercalary expansion and a delayed growth of the floral apex, a (half-) inferior cup-shaped ovary develops. The different growth forms are the results of heterochronic shifts and affect the development of septa and ovule numbers. A common trend in the order implies a weakening and break-up of septa during development, leading to residual apical and basal septa and the shift to free-central and basal placentation. The club-shaped ovary is linked with an almost complete loss of septa and a reduction of the ovule number to one. The salt-shaker shape leads to ovaries with a massive placental column and several ovules. The cup-shaped ovary leads to a shift of ovules away from the floral apex. Developmental flexibility is responsible for a disconnection of carpel wall growth from ovular tissue. Subtle shifts in proportional growth lead to a high diversification of ovaries in core Caryophyllales and the establishment of predictable developmental trends. These trends clearly represent apomorphic tendencies, affecting different families of core Caryophyllales in different degrees. The ancestral gynoecium was probably pentamerous and isomerous with the other floral whorls, with ovules clearly separated from the carpellary wall and inserted on axile placentas corresponding to the central axis of the flower.

Anatomy and development of gynoecium in Tapiscia sinensis Oliv. and its implications for the origin of carpels

Tapiscia sinensis Oliv. (Tapisciaceae) is a rare tree endemic in China. Characteristic of its androdioecy is the coexistence of male and hermaphroditic flowers. Its bisexual flower bears five stamens surrounding the gynoecium, which is composed of a terminal style and an ovary at the base. The style has a bifid stigmata, which is hollow and longer than stamens. The ovary is syncarpous, unilocular, formed by two fused carpels, with a basal or subbasal placenta. Ovule is bitegmic, anatropous, borne on the placenta and supplied by an amphicribral vascular bundle arising directly from receptacle. The carpel wall is supplied by a collateral vascular bundle. The ovule’s position changes from initially inserted on the ovary base to later attached to the middle of the ovary wall due to unequal growth of the embryo sac. Based on the present observation and others, the implications of vascular system in Tapiscia for the evolution of carpel are discussed.

Floral ontogeny of Illicium Lanceolatum (Schisandraceae) and its implications on carpel homology

There are two competing hypotheses for the origin of carpels. The traditional hypothesis favors a phyllosporous origin and regards a conduplicate carpel as an ancestral form that is the result of longitudinal folding of a leaf bearing ovules along its margins. Alternatively, the carpel formation is interpreted as the result of a fusion between an ovule-bearing branch and its subtending leaf-like structure. Illicium is a member of the Austrobaileyales, which are one of the three ANA lines that diverged before all other extant angiosperms. This genus with apocarpous gynoecium has various ancestral morphological characteristics in terms of carpel, ovule, and floral apex. Although various aspects of Illicium morphology have been previously investigated, many evolutionary characteristics remain poorly understood. In this study, the development of carpel, ovule, and floral apex of I. lanceolatum was studied using LM and SEM. The results showed that the ovule primordium originates in the axillary position between the flower axis and carpel wall. So the carpel of Illicium is a leaf-like structure that encircles the ovule. This kind of carpel favors the carpel as a result of fusion between two parts, ovule-bearing branch and its subtending leaf-like structure.

A peptide pair coordinates regular ovule initiation patterns with seed number and fruit size

Ovule development in Arabidopsis thaliana involves pattern formation which ensures that ovules are regularly arranged in the pistils to reduce competition for nutrients and space. Mechanisms underlying pattern formation in plants, such as phyllotaxis, flower morphogenesis or lateral root initiation, have been extensively studied, and genes controlling the initiation of ovules have been identified. However, how a regular spacing of ovules is achieved is not known. Using natural variation analysis combined with quantitative trait locus analysis, we found that the spacing of ovules in the developing fruits is controlled by two secreted peptides, EPFL2 and EPFL9 (also known as Stomagen), and their receptors from the ERECTA (ER) family that act from the carpel wall and the placental tissue. We found that a signalling pathway controlled by EPFL9 acting from the carpel wall through the LRR-receptor kinases ER, ERL1 and ERL2 promotes fruit growth. Regular spacing of ovules depends on EPFL2 expression in the carpel wall and in the inter-ovule spaces, where it acts through ERL1 and ERL2. Loss of EPFL2 signalling results in shorter fruits and irregular spacing of ovules or even ovule twinning. The EPFL2 expression pattern between ovules is under negative-feedback regulation by auxin, which accumulates in the arising ovule primordia. We propose that the auxin-EPFL2 signalling module evolved to control the initiation and regular, equidistant spacing of ovule primordia, which serves to minimise competition between developing seeds. Together, EPFL2 and EPFL9 coordinate ovule patterning and thereby seed number with fruit growth through a set of shared receptors.

CRABS CLAW and SPATULA, two Arabidopsis genes that control carpel development in parallel with AGAMOUS

To help understand the process of carpel morphogenesis, the roles of three carpel development genes have been partitioned genetically. Mutants of CRABS CLAW cause the gynoecium to develop into a wider but shorter structure, and the two carpels are unfused at the apex. Mutants of a second gene, SPATULA, show reduced growth of the style, stigma, and septum, and the transmitting tract is absent. Double mutants of crabs claw and spatula with homeotic mutants that develop ectopic carpels demonstrate that CRABS CLAW and SPATULA are necessary for, and inseparable from, carpel development, and that their action is negatively regulated by A and B organ identity genes. The third carpel gene studied, AGAMOUS, encodes C function that has been proposed to fully specify carpel identity. When AGAMOUS function is removed together with the A class gene APETALA2, however, the organs retain many carpelloid properties, suggesting that other genes are also involved. We show here that further mutant disruption of both CRABS CLAW and SPATULA function removes remaining carpelloid properties, revealing that the three genes together are necessary to generate the mature gynoecium. In particular, AGAMOUS is required to specify the identity of the carpel wall and to promote the stylar outgrowth at the apex, CRABS CLAW suppresses radial growth of the developing gynoecium but promotes its longitudinal growth, and SPATULA supports development of the carpel margins and tissues derived from them. The three genes mostly act independently, although there is genetic evidence that CRABS CLAW enhances AGAMOUS and SPATULA function.

The floral development and floral anatomy of Coris monspeliensis

The floral development of Coris was investigated to clarify its controversial relationship with either Primulaceae (Primulales) or Lythraceae (Myrtales). We demonstrate that Coris is strongly related to the Primulaceae but differs in a few important features, such as the presence of an epicalyx and partial zygomorphy. The saccate calyx and epicalyx with unilateral development encloses an actinomorphic flower. The stamen–petal tube has two sections that arise through three growth processes: a lower common part for stamens and petals and an upper section representing a fused corolla. The central ovule-bearing part of the ovary arises separated from the carpel wall. The formation of ridges with teethlike appendages between the ovules suggests a derivation of the free-central placentation from an axile arrangement. Several characters support the monotypic family Coridaceae near the Primulaceae. Key words: Coridaceae, Primulaceae, Lythraceae, floral development, floral vasculature, epicalyx, free-central placentation, common primordium, zygomorphy.

Further Observations on Dysdercus superstitiosus, F., and other Insects affecting Cotton in Southern Nigeria

Young bolls may be shed owing to the mechanical action of stainer puncturing, apart from the introduction of any specific internal boll disease. One puncture is sufficient to obtain this effect.Unless the carpel wall is pierced, no injury to the boll from insect attack results, and it is highly probable that the piercing of the carpel wall is essential for the introduction of internal boll disease.Internal proliferation does not take place unless the carpel wall is pierced, and is not an essential factor in the shedding of young bolls, but rather an indication of injury from an external source.Puncturing by stainers of the buds and flowers, before the flower petals have fallen off, may cause the shedding of the boll and the introduction of internal boll disease.The surest superficial diagnosis of stainer injury to bolls, as compared with other insect injuries, is the finding of a bead of moisture exuding from the single minute orifice, in the case of a fresh puncture, and of a minute canal in the centre of the corked area of an injury some days old. The regularity of the rim of the corked area is a strong indication of stainer injury, the periphery of the corked area produced by the nibbling of young Lepidopterous larvae being irregular, owing to the action of the mandibles.