An overview of secretion in floral bracts of Tillandsioideae (Bromeliaceae), with emphasis on the secretory scales.

Bromeliaceae display many water-use strategies, from leaf impounding tanks to Crassulacean acid metabolism (CAM) photosynthesis and absorbing trichomes. Recent studies show that trichomes in inflorescences of bromeliads can exude viscous secretions, protecting against various stresses, including excessive water loss. In light of this, and considering the knowledge gap regarding inflorescence trichomes in bromeliads, we aimed to investigate the presence, source and chemical nature of inflorescence secretions in species of the Tillandsioideae (Bromeliaceae) and to describe the anatomy of their floral bracts focusing on trichome structure and position. We conducted a prospection of secretory activity and anatomy in floral bracts in 52 species of Tillandsioideae and 1 early divergent Bromeliaceae species. We used histochemical tests to investigate the presence and nature of secretion combined with standard light microscopy methods. Secretion appears in all studied species of tribe Vrieseeae, in Guzmania species, Wallisia cyanea, Tillandsia streptopylla (Tillandsieae) and Catopsis morreniana (Catopsideae). It is absent in Vriesea guttata (Vrieseeae), Racinaea crispa and various Tillandsia species (Tillandsieae). Secretion is produced by peltate trichomes on the adaxial surface of young bracts and comprises hydrophilic and lipophilic substances. Bract anatomy revealed an internal mucilage-secreting tissue with wide distribution within the subtribe Vrieseinae. Our results point to a broad occurrence of secretion associated with bracteal scales in inflorescences of Tillandsioideae. Secretory function is strongly related to trichomes of the adaxial surface, whereas the indumentum of the abaxial side is lacking or likely associated with water absorption; the latter case is especially related to small, xeric plants. Exudates might engage in colleter-like roles, protecting against desiccation, high-radiation and herbivores. Directions for future research are presented.

Cryopreservation and low-temperature storage of seeds of Tillandsia species (Bromeliaceae) with ornamental potential.

Tillandsia (Bromeliaceae) species have high endemism, and due to their strong ornamental potential, predatory extraction is threatening the extinction or drastic population reduction of many of them. In light of this scenario, it is necessary to find strategies for the conservation of these endangered species. The objective of this study was to evaluate two seed preservation strategies (freezing at - 5 °C and cryopreservation at - 196 °C) for 20 Tillandsia species occurring in the state of Bahia. We initially evaluated the morphometry, thousand-seed weight, and water content, followed by tests of germination and desiccation. After selecting the best result of the germination test (Germitest paper and incubation at 30 °C) and desiccation (3 h on silica gel), we established conservation tests utilizing two temperatures (freezing at - 5 °C and liquid nitrogen at - 196 °C), with storage times of 1, 7, 30, 180 and 450 days. Analysis of variance indicated that the 20 species had different behaviors when submitted to the two temperatures and different storage times. After 450 days there was a reduction in the germination percentage and germination speed index (GSI) of all the species studied when the seeds were preserved in the freezer. The storage in liquid nitrogen was efficient for the preservation of Tillandsia seeds when dried to a moisture content of approximately 7%. Our results support the establishment of a cryobank for Tillandsia to conserve these endemic species.

Pollen morphology and viability of Tillandsia (Bromeliaceae) species by light microscopy and scanning electron microscopy.

Tillandsia is the bromeliad genus containing the largest number of species, with wide geographic dispersion and an important ecological role in the ecosystems. Investigations of pollen morphology are important to support taxonomic and conservation studies as well as to choose promising species for cross-pollination to obtain hybrids. The objective of this study was to evaluate the morphology, production, and viability of pollen grains of 24 Tillandsia species that naturally occur in the state of Bahia, Brazil. Pollen grains were acetolized and analyzed by scanning electron microscopy. The pollen were germinated in vitro in two culture media (BM and BKM) and collected at three floral development stages (pre-anthesis, anthesis and post-anthesis). Pollen viability also was analyzed by staining with Alexander's solution and acetocarmine in three floral development stages. Variations in the ornamentation and size of the pollen were observed among the species studied, with the majority having medium size, while T. polystachia and T. juncea had large grains and the subgenera Diaphoranthema and Phytarrhiza had small grains. The pollen of the majority of species had bilateral symmetry, with a single irregularly shaped colpus, semitectate exine and reticulated-heterobrochate surface. The pollen presented high germination percentage, tube length and viability according to the histochemistry, except for T. recurvata, T. usneoides and T. loliacea. The BKM medium and collection of pollen during anthesis produced the best results for the Tillandsia species. The results can support studies of the taxonomy and conservation of these species, which have great environmental importance and high value for ornamental purposes.

Micropropagation and in vitroconservation of Alcantarea nahoumii (Bromeliaceae), an endemic and endangered species of the Brazilian Atlantic Forest

Alcantarea nahoumii(Leme) J. R. Grant is a species native to theAtlantic Forest that stands out for ornamental purposes. The objective of this work was to evaluate the in vitrogerminationof A. nahoumiiseeds and establish a micropropagation protocol for production of seedlings so as to minimize the effects of predatory extractivism and develop an in vitroconservation system. Mature seeds were disinfested, established in three culture media (MS, MS½ and MS⅓) and incubated at four temperatures (20, 25, 30 and 35ºC)in a germination chamber. In the micropropagation experiment, stem segments were introduced in MS medium supplemented with 0.5 μM of 1-naphthaleneacetic acid (NAA) and 0.0, 2.2, 4.4 and 6.6 μM of 6-benzylaminopurine (BAP). For the in vitroconservation, plantlets were established in MS or MS½ medium supplemented with 15 g L-1or 30 g L-1of sucrose. The plants were acclimated with commercial substrate. The highest seed germination percentages were promoted by temperature conditions of 20 and 25ºC, with MS culture medium. The highest multiplication rate of shoots was obtained from the treatment without addition of the growth regulator or when combined with 2.2 μM of BAP + 0.5 μM of NAA. The acclimation of the plants occurred with high survival rate. The species can be conserved in vitrounder slow growth condition for 24 months when incubated in MS medium supplemented with 30 g L-1of sucrose.

Trade-off between soluble protein production and nutritional storage in Bromeliaceae.

BACKGROUND AND AIMS: Bromeliads are able to occupy some of the most nutrient-poor environments especially because they possess absorptive leaf trichomes, leaves organized in rosettes, distinct photosynthetic pathways [C3, Crassulacean acid metabolism (CAM) or facultative C3-CAM], and may present an epiphytic habit. The more derived features related to these traits are described for the Tillandsioideae subfamily. In this context, the aims of this study were to evaluate how terrestrial predators contribute to the nutrition and performance of bromeliad species, subfamilies and ecophysiological types, whether these species differ in their ecophysiological traits and whether the physiological outcomes are consistent among subfamilies and types (e.g. presence/absence of tank, soil/tank/atmosphere source of nutrients, trichomes/roots access to nutrients). METHODS: Isotopic (15N-enriched predator faeces) and physiological methods (analyses of plant protein, amino acids, growth, leaf mass per area and total N incorporated) in greenhouse experiments were used to investigate the ecophysiological contrasts between Tillandsioideae and Bromelioideae, and among ecophysiological types when a predatory anuran contributes to their nutrition. KEY RESULTS: It was observed that Bromelioideae had higher concentrations of soluble protein and only one species grew more (Ananas bracteatus), while Tillandsioideae showed higher concentrations of total amino acids, asparagine and did not grow. The ecophysiological types that showed similar protein contents also had similar growth. Additionally, an ordination analysis showed that the subfamilies and ecophysiological types were discrepant considering the results of the total nitrogen incorporated from predators, soluble protein and asparagine concentrations, relative growth rate and leaf mass per area. CONCLUSIONS: Bromeliad subfamilies showed a trade-off between two strategies: Tillandsioideae stored nitrogen into amino acids possibly for transamination reactions during nutritional stress and did not grow, whereas Bromelioideae used nitrogen for soluble protein production for immediate utilization, possibly for fast growth. These results highlight that Bromeliaceae evolution may be directly associated with the ability to stock nutrients.

Population genetics of the endemic and endangered Vriesea minarum (Bromeliaceae) in the Iron Quadrangle, Espinhaço Range, Brazil.

• Premise of the study: Knowledge about genetic variability in plant populations is one of the main branches of conservation genetics, linking genetic data to conservation strategies. Vriesea minarum is a bromeliad endemic to the Iron Quadrangle region (southeastern Brazil), occurring on mountaintop rock outcrops. It is listed as endangered due to habitat loss, particularly from iron ore mining. Thus, determining the structure and genetic diversity of V. minarum populations could help develop strategies to conserve the species.• Methods: We studied the genetic structure of 12 populations of V. minarum using 10 microsatellite loci transferred from other species of Bromeliaceae. Statistical analyses to compare and describe the genetic diversity of each population were performed, and genetic structure within and among populations, isolation by distance, and Bayesian structure were also analyzed.• Key results: Our results show high inbreeding (GIS = 0.376) and low population structure (FST = 0.088), possibly related to high gene flow due to great pollinator efficiency and/or efficient seed dispersal, thus leading to high connectivity among populations of these fragmented rock outcrops. Two clusters were observed, corresponding to the basins of rivers São Francisco and Doce.• Conclusions: Gene flow among populations is high but, given the rate of habitat loss to mining, most populations are vulnerable and will become increasingly isolated if no action is taken to preserve them. Thus, conservation of this species depends on in situ and ex situ actions, such as controlling overexploitation and creating a germoplasm bank.