Cuticle structure and chemical composition of waxes in Phaeoceros laevis (L.) Prosk (Notothyladaceae, Anthocerotophyta).

The development of a hydrophobic cuticle covering the epidermis was a crucial evolutionary novelty ensuring the establishment of land plants. However, there is little information about its structure and chemical composition, as well as its functional implications in avascular lineages such as Anthocerotophyta. The main goal of the present study was to compare the gametophyte and sporophyte cuticles of Phaeoceros laevis. Semithin sections were analyzed through light microscopy (LM), cuticle structure was evaluated by transmission electron microscopy (TEM) and epicuticular wax morphology was analyzed by scanning electron microscopy (SEM). Total waxes were analyzed by CG/MS, and the components were identified based on the mass spectra. A thin lipophilic layer was detected on the sporophyte surface, structured as a stratified cuticular layer, similar to the well-known structure described for vascular plants. On the other hand, the gametophyte cuticle was observed only with TEM as a thin osmiophilic layer. SEM analyses showed a film-type wax on the surface of both life phases. The wax layer was eight-fold thicker on the sporophyte (0.8 µg cm-2) than on gametophyte (0.1 µg cm-2). Possible mechanical and/or drought protection are discussed. Fatty acids, primary alcohols, and steroids were identified in both life phases, while the kauren-16-ene diterpene (3%) was detected only on the sporophyte. Although no alkanes were detected in P. laevis, our findings unveil great similarity of the sporophyte cuticle of this hornwort species with the general data described for vascular plants, reinforcing the conservative condition of this character and supporting the previous idea that the biosynthetic machinery involved in the synthesis of wax compounds is conserved since the ancestor of land plants.

Light and electron microscopies reveal unknown details of the pollen grain structure and physiology from Brazilian Cerrado species.

Pollen grains have a relatively simple structure and microscopic size, with two or three cells surrounded by the protective sporoderm at maturity. The viability and efficiency of pollen transport from anther to stigma depends on pollen physiological properties, especially the relative water content of the vegetative cell. Pollen transport is a crucial fate for most angiosperms that depends on biotic pollinators and studies focusing on understanding the morpho-physiological properties of pollen grains are still scarce, especially to tropical open physiognomies as the Brazilian Cerrado. Therefore, we investigate some structural and physiological aspects of pollen grains from six native species naturally growing in one Cerrado area: Campomanesia pubescens (Myrtaceae), Caryocar brasiliense (Caryocaraceae), Erythroxylum campestre (Erythroxylaceae), Lippia lupulina (Verbenaceae), Pyrostegia venusta (Bignoniaceae), and Xylopia aromatica (Annonaceae). We selected dehiscent anthers and mature pollen grains to analyze (1) the anther wall and pollen microstructure, (2) the pollen water status at the time of anther dehiscence, and (3) the pollen chemical compounds. In all analyzed species, the anther and pollen developed in a successfully way, and except for Caryocar brasiliense, all species were able to emit pollen tubes in the germination tests. As expected for a dry and open environment, most species dispersed their pollen grains in a partially dehydrated form, as indicated by our harmomegathy experiment. As indicated by our study, the pollen ability in preventing dissection, maintaining its viability in a dry and hot environment during its transport from anther to stigma, may be related to the sporoderm apertures and to the reserve compounds, mainly carbohydrates in the form of hydrolysable starch grains.

Toward understanding inflorescence development and architecture in Passiflora: insights from comparative anatomy and expression of APETALA1.

PREMISE: The inflorescence of Passiflora species originates from a bud complex that derives from an initially undivided meristem and ultimately produces flowers and tendrils. Because the development of the inflorescence structures derived from such meristems has been variously interpreted, we investigated the ontogeny of the bud complex and the expression of APETALA1 (AP1) in Passiflora species. METHODS: The anatomical development of 15 species of Passiflora was analyzed using light and scanning electron microscopy. We localized AP1 expression in tissues during inflorescence initiation in two Passiflora species using in situ hybridization. RESULTS: In most species, the first primordium to differentiate from the bud complex is a bract, which develops laterally to what will become the inflorescence first-order axis, in this case, the tendril. The bract axillary meristem originates the second-order inflorescence axis meristem, which produces two bracteoles, subsequently developing into a floral meristem. AP1 is uniformly expressed in the initially undivided meristem, with expression maintained in the organ primordia derived from the bud complex. Signal is particularly strong in tendril tips. CONCLUSIONS: We concluded that what is often understood as the first bract produced by a floral meristem actually is produced by the original axillary meristem. Bracteoles develop from the meristem in the bract axil; bracteoles plus floral meristem constitute the inflorescence second-order axis. Comparison of inflorescence early developmental stages in different subgenera indicates flowers are arranged in a modified cyme, with the tendril representing the inflorescence terminal portion. PasAP1 has a broad expression pattern and may have an important role during inflorescence development.