The Role of Baccharis dracunculifolia and its Chemical Profile on Green Propolis Production by Apis mellifera.

The botanical source of Brazilian green propolis (BGP) is Baccharis dracunculifolia DC, which interacts not only with Apis mellifera, but also with galling insects. In the last decade, because of green propolis´ important biologic activities, the international demand for BGP overcame the production capacity, consequently, new approaches are required to increase this production. Hence, the understanding of the chemical ecology interactions of B. dracunculifolia with galls and bees in field conditions may provide insights to increase BGP's production. A "bee pasture" experiment aiming to better understand this plant-insect interaction was therefore performed. For that, 48 B. dracunculifolia individuals, being 24 females and 24 males, were cultivated and investigated for the following parameters: (1) phenolic and volatile compounds in both B. dracunculifolia leaves and green propolis, (2) environmental variables, (3) visiting rate by bees, (4) time of resin collection, and (5) number of galls. Regression analyses by independent linear mixed-effect models were run to correlate phenolic and volatile compounds concentration with the environmental and field variables. Significant differences in chemical profile and field variables were observed between male and female plants. Male plants showed higher infestation by galling insects while female plants showed higher number of visiting bees, time of resin collection and terpenes concentration, contributing to the differences observed in the field. The obtained results suggest that increasing the percentage of female B. dracunculifolia plants in the field may attract more bees and therefore enhance propolis production.

Aluminium detoxification in facultative (Passovia ovata (Pohl ex DC.) Kuijt and Struthanthus polyanthus Mart. - Loranthaceae) and dependent (Psittacanthus robustus (Mart.) Marloth - Loranthaceae) Al-accumulating mistletoe species from the Brazilian savanna.

Mechanisms to detoxify aluminium (Al) is a hot topic for cultivated plants. However, little information is known about the mechanisms used by native plants to deal with Al-toxicity. In Cerrado, some generalist mistletoe species, such as Passovia ovata (Pohl ex DC.) Kuijt and Struthanthus polyanthus Mart. can parasitize Al-accumulating and Al-excluding plant species without any clear symptoms of toxicity and mineral deficiency, while Psittacanthus robustus (Mart.) Marloth, a more specialist mistletoe, seems to be an Al-dependent species, parasitizing only Al-accumulating hosts. Here we (i) characterized the forms and compartmentalization of Al in leaves of P. robustus; (ii) compared Ca and Al leaf concentration, and leaf concentration of organic acids and polyphenols between facultative Al-accumulating (P. ovata and S. polyanthus) and Al-dependent (P. robustus) mistletoe species infecting Miconia albicans (Sw.) Steud. (Al-accumulating species). P. robustus chelated Al3+ with oxalate and stored it in the phloematic and epidermic leaf tissues. Leaf Ca and Al concentration did not differ among species. Leaf oxalate concentration was higher in the Al-dependent species. Concentrations of citrate and phenolic compounds were higher in the leaves of the facultative Al-accumulating species. These results show that facultative Al-accumulating and Al-dependent species use different mechanisms to detoxify Al. Moreover, this is the first report on a mistletoes species (P. robustus) with a potential calcifuge behaviour in Cerrado.

A proteomic approach to the mechanisms underlying activation of aluminium resistance in roots of Urochloa decumbens.

The mechanisms of extreme Al-resistance in Urochloa decumbens are not established. Full resistance expression requires a lag time of 72-96h and is preceded by a sensitive phase (24-48h) with Al-induced root growth inhibition. The aim here was to identify key processes of the activation phase of Al-resistance analysing both root exudates and comparative root proteome. Samples were taken after 0, 24 and 96h exposure to 0 or 200µM Al. Al-induced stimulation of citrate and oxalate efflux was limited to the sensitive phase. Only 11 proteins revealed Al-induced abundance differences; six were identified. After 24h, phenylalanine ammonium lyase (PAL), methionine synthase (MS), and deoxymugineic acid synthase (DMAS) decreased, while acid phosphatase (APase) abundance increased. Coincident with growth recovering, PAL and MS, but not DMAS, returned to initial levels. After 96h, γ­carbonic anhydrase (γ­CA) and adenylate kinase (AK) along with two unidentified proteins were more abundant. In conclusion, few protein changes characterize the initial response to Al in signalgrass. During the alarm phase, changes are related to P-mobilization, downregulation of Fe-acquisition, reduction of phenolic biosynthesis, and small stimulation of organic acid exudation. After recovering (resistant phase), biosynthesis of phenolics and methionine, but not Fe-mobilization are re-established. Full expression of Al-resistance is characterized by enhanced γ­CA mediating mitochondrial complex I assembly and increased AK abundance indicating higher root respiration and better provision of ADP and Mg2+ to ATP synthase, respectively. The unidentified proteins and the specific role of γ­CA in Al resistance of U. decumbens will centre future research.