Acetogenins and alkaloids during the initial development of Annona muricata L. (Annonaceae).

In plants, the presence and distribution of specialized metabolites during the early stages of development are not documented enough, even though their biosynthesis is one of the most important strategies for survival. In this study, five alkaloids and four acetogenins were detected in Annona muricata L. during early development seedling, including three phases of root emergence and three of seedling formation. Hexane and alkaloid extracts were obtained from each organ, which were analyzed in a gas-mass chromatograph and in a high-performance liquid chromatograph coupled with a photodiode array UV detector (HPLC-DAD). This research shows the presence of the acetogenins cis-uvarimicin IV, mosinone, muricina B, and cis-annonacin-10-one, as well as of the alkaloids reticuline, coreximine, anonaine, asimilobine, and nornuciferine, both groups with a variable organ-specific distribution, related with the formation of organs and tissues.

Beetle pollination and flowering rhythm of Annona coriacea Mart. (Annonaceae) in Brazilian cerrado: Behavioral features of its principal pollinators.

The conservation and sustainable management of Annona coriacea requires knowledge of its floral and reproductive biology, and of its main pollinators and their life cycles. In this work, we analyzed these aspects in detail. Floral biology was assessed by observing flowers from the beginning of anthesis to senescence. The visiting hours and behavior of floral visitors in the floral chamber were recorded, as were the sites of oviposition. Excavations were undertaken around specimens of A. coriacea to determine the location of immature pollinators. Anthesis was nocturnal, starting at sunset, and lasted for 52-56 h. The flowers were bisexual, protogynous and emitted a strong scent similar to the plant´s own ripe fruit. There was pronounced synchrony among all floral events (the period and duration of stigmatic receptivity, release of odor, pollen release and drooping flowers) in different individuals, but no synchrony in the same individuals. All of the flowers monitored were visited by beetle species of the genera Cyclocephala and Arriguttia. Beetles arrived at the flowers with their bodies covered in pollen and these pollen grains were transferred to the stigmata while foraging on nutritious tissues at the base of the petals. With dehiscence of the stamens and retention within the floral chamber, the bodies of the floral visitors were again covered with pollen which they carried to newly opened flowers, thus promoting the cycle of pollination. After leaving the flowers, female beetles often excavated holes in the soil to lay eggs. Larvae were found between the leaf litter and the first layer of soil under specimens of A. coriacea. Cyclocephala beetles were the main pollinators of A. coriacea, but Arriguttia brevissima was also considered a pollinator and is the first species of this genus to be observed in Annonaceae flowers. Annona coriacea was found to be self-compatible with a low reproductive efficiency in the area studied. The results of this investigation provide ecological data that should contribute to the conservation and economic exploitation of A. coriacea.

Microspore development in Annona (Annonaceae): differences between monad and tetrad pollen.

UNLABELLED: • PREMISE OF THE STUDY: Permanent tetrads are the most common form of pollen aggregation in flowering plants. The production of pollen in monads is plesiomorphic in angiosperms, but the aggregation into tetrads has arisen independently different times during the evolution of flowering plants. The causes behind the recurrent evolution of pollen aggregation from monads remain elusive. Permanent tetrad pollen is quite common in the Annonaceae, the largest family in the early-divergent order Magnoliales. In some genera, such as Annona, both tetrad- and monad-producing species can be found.• METHODS: In this comparative study of pollen development, we use immunolocalization, cytological characterization, and enzymatic assays of four species in the genus Annona and one species in its closely related genus Asimina that release pollen in tetrads and two species in the genus Annona that release pollen in monads.• KEY RESULTS: The main difference between species with tetrad and monad pollen is a delayed digestion of callose and cellulose at the pollen aperture sites that resulted in nonlayering of the exine in these areas, followed by a rotation and binding of the young microspores at the aperture sites.• CONCLUSIONS: Small changes in development resulted in clear morphological changes on pollen dispersal time and open a window on the possible selective advantage of the production of aggregated pollen.

Pollen performance, cell number, and physiological state in the early-divergent angiosperm Annona cherimola Mill. (Annonaceae) are related to environmental conditions during the final stages of pollen development.

Pollen performance is an important determinant for fertilization success, but high variability in pollen behavior both between and within species occurs in different years and under varying environmental conditions. Annona cherimola, an early-divergent angiosperm, is a species that releases a variable ratio of bicellular and tricellular hydrated pollen at anther dehiscence depending on temperature. The presence of both bi- and tricellular types of pollen is an uncommon characteristic in angiosperms and makes Annona cherimola an interesting model to study the effect of varying environmental conditions on subsequent pollen performance during the final stages of pollen development. In this work, we study the influence of changes in temperature and humidity during the final stages of pollen development on subsequent pollen performance, evaluating pollen germination, presence of carbohydrates, number of nuclei, and water content. At 25 °C, which is the average field temperature during the flowering period of this species, pollen had a viability of 60-70 %, starch hydrolyzed just prior to shedding, and pollen mitosis II was taking place, resulting in a mixture of bi- and tricellular pollen. This activity may be related to the pollen retaining 70 % water content at shedding. Temperatures above 30 °C resulted in a decrease in pollen germination, whereas lower temperatures did not have a clear influence on pollen germination, although they did have a clear effect on starch hydrolysis. On the other hand, slightly higher dehydration accelerated mitosis II, whereas strong dehydration arrested starch hydrolysis and reduced pollen germination. These results show a significant influence of environmental conditions on myriad pollen characteristics during the final stages of pollen development modifying subsequent pollen behavior and contributing to our understanding of the variability observed in pollen tube performance.

Liriodenine alkaloid in Annona diversifolia during early development.

Plants of the Annonaceae family produce a series of alkaloids, including liriodenine oxoaporphine. Its distribution in these primitive angiosperms suggests that it plays an important role, but very little is known about which plant organs it accumulates in, or in which developmental stages it is synthesised. Accordingly, liriodenine production was studied during the early stages of germination and seedling development in Annona diversifolia Saff. Liriodenine samples were obtained from the roots and were characterised on the basis of spectroscopic data. Quantification was done by HPLC in the organs and tissues of newly collected seeds, seeds following 1-, 2-, 5- and 10-day imbibitions, upon emergence of the radicle and at the seedling stage. According to our results, liriodenine could not have originated from the parent plant, nor during embryogenesis because it appears for the first time in the endosperm approximately 5 days after the start of imbibition. Therefore, its synthesis does not depend directly on photosynthesis. During the seedling stage it is found in the root and the stem but it is absent from the cotyledonary leaves and the first true leaves. Liriodenine biosynthesis begins during the early stages of development in the endosperm and seed radicles.

Pollen development in Annona cherimola Mill. (Annonaceae). Implications for the evolution of aggregated pollen.

BACKGROUND: In most flowering plants, pollen is dispersed as monads. However, aggregated pollen shedding in groups of four or more pollen grains has arisen independently several times during angiosperm evolution. The reasons behind this phenomenon are largely unknown. In this study, we followed pollen development in Annona cherimola, a basal angiosperm species that releases pollen in groups of four, to investigate how pollen ontogeny may explain the rise and establishment of this character. We followed pollen development using immunolocalization and cytochemical characterization of changes occurring from anther differentiation to pollen dehiscence. RESULTS: Our results show that, following tetrad formation, a delay in the dissolution of the pollen mother cell wall and tapetal chamber is a key event that holds the four microspores together in a confined tapetal chamber, allowing them to rotate and then bind through the aperture sites through small pectin bridges, followed by joint sporopollenin deposition. CONCLUSION: Pollen grouping could be the result of relatively minor ontogenetic changes beneficial for pollen transfer or/and protection from desiccation. Comparison of these events with those recorded in the recent pollen developmental mutants in Arabidopsis indicates that several failures during tetrad dissolution may convert to a common recurring phenotype that has evolved independently several times, whenever this grouping conferred advantages for pollen transfer.