Eksperimentalno ispitivanje modela oksidacije 5-CQA klorogene kiseline pomoću polifenolne oksidaze

A set of experiments to investigate the enzymatic oxidation of 5-o-caffeoylquinic acid with polyphenol oxidases was carried out in the temperature range from 18 to 39 °C. The kinetic data were obtained in a batch isothermal reactor made of quartz and operated at an optimum pH (approx. 7.0) for enzyme activity, using citrate-phosphate buffer. The decay of 5-o-caffeoylquinic acid concentrations was experimentally monitored with a spectrophotometer at 323 nm. A coefficient of molar absorptivity equal to 1.96·103 mM–1m–1 was found for 5-o-caffeoylquinic acid, based on absorbance measurements with standard aqueous solutions. The kinetic experimental results were used to calculate the parameters Km and vmax of the Michaelis-Menten model, which were 0.24 mM and 2.77·10–4 mM/s at 25 °C, respectively. The effects of temperature on the maximum velocity of oxidation of 5-o-caffeoylquinic acid and on the rate of enzyme deactivation were well described using the Arrhenius equation.Da bi se ispitala oksidacija 5-CQA klorogene kiseline pomoću polifenolne oksidaze, proveden je niz pokusa u temperaturnom rasponu od 18 do 39 °C. Kinetički su podaci dobiveni u šaržnom izotermičkom reaktoru izrađenom od kvarca, pri pH-vrijednosti optimalnoj za aktivnost enzima, korigiranoj pomoću citratnog pufera. Smanjivanje koncentracije kiseline praćeno je spektrofotometrijski pri valnoj duljini od 323 nm. Mjerenjem apsorbancije uz pomoć standardnih vodenih otopina ustanovljen je koeficijent molarne apsorpcije 5-CQA od 1,96×103 mM-1m-1. Dobiveni kinetički podaci upotrijebljeni su za izračun parametara Michaelis-Mentenova modela, te je utvrđeno da Km pri temperaturi od 25 °C iznosi 0,24 mM, a vmax 2,77×10-4 mM/s. Učinak temperature na maksimalnu brzinu oksidacije 5-CQA i deaktivaciju enzima dobro je opisan pomoću Arrheniusove jednadžbe

The diversity and evolution of pollination systems in large plant clades: Apocynaceae as a case study

Background and Aims Large clades of angiosperms are often characterized by diverse interactions with pollinators, but how these pollination systems are structured phylogenetically and biogeographically is still uncertain for most families. Apocynaceae is a clade of >5300 species with a worldwide distribution. A database representing >10 % of species in the family was used to explore the diversity of pollinators and evolutionary shifts in pollination systems across major clades and regions. Methods The database was compiled from published and unpublished reports. Plants were categorized into broad pollination systems and then subdivided to include bimodal systems. These were mapped against the five major divisions of the family, and against the smaller clades. Finally, pollination systems were mapped onto a phylogenetic reconstruction that included those species for which sequence data are available, and transition rates between pollination systems were calculated. Key Results Most Apocynaceae are insect pollinated with few records of bird pollination. Almost three-quarters of species are pollinated by a single higher taxon (e.g. flies or moths); 7 % have bimodal pollination systems, whilst the remaining approx. 20 % are insect generalists. The less phenotypically specialized flowers of the Rauvolfioids are pollinated by a more restricted set of pollinators than are more complex flowers within the Apocynoids + Periplocoideae + Secamonoideae + Asclepiadoideae (APSA) clade. Certain combinations of bimodal pollination systems are more common than others. Some pollination systems are missing from particular regions, whilst others are over-represented. Conclusions Within Apocynaceae, interactions with pollinators are highly structured both phylogenetically and biogeographically. Variation in transition rates between pollination systems suggest constraints on their evolution, whereas regional differences point to environmental effects such as filtering of certain pollinators from habitats. This is the most extensive analysis of its type so far attempted and gives important insights into the diversity and evolution of pollination systems in large clades

Wind pollination and propagule formation in Rhizophora mangle L. (Rhizophoraceae): resource or pollination limitation?

Rhizophora mangle is considered as a self-compatible mangrove, and is pollinated by wind and insects. However, there is no information about fruit production by autogamy and agamospermy and on the foraging behavior of its flower visitors. Hence, the present study analyzed the pollination and reproductive systems of R. mangle in a mangrove community in northern Pernambuco, Brazil. Floral morphology, sequence of anthesis, and behavior of flower visitors were described; the proportion of flowers that resulted in mature propagules was also recorded. Autogamy, agamospermy, and wind pollination tests were performed, and a new anemophily index is proposed. The flowers of R. mangle are hermaphrodite, protandric, and have high P/O rate. Flies were observed on flowers only during the male phase, probably feeding on mites that consume pollen. Rhizophora mangle is not agamospermic and its fruit production rate by spontaneous self-pollination is low (2.56%) compared to wind pollination (19.44%). The anemophily index was high 0.98, and thus it was considered as a good indicator. Only 13.79% of the flowers formed mature propagules. The early stages of fruit development are the most critical and susceptible to predation. Rhizophora mangle is, therefore, exclusively anemophilous in the study area and the propagule dispersal seems to be limited by herbivory