Regime shift by an exotic nitrogen-fixing shrub mediates plant facilitation in primary succession.

Ecosystem invasion by non-native, nitrogen-fixing species is a global phenomenon with serious ecological consequences. However, in the Mediterranean basin few studies addressed the impact of invasion by nitrogen-fixing shrubs on soil quality and hydrological properties at local scale, and the possible effects on succession dynamics and ecosystem invasibility by further species. In this multidisciplinary study we investigated the impact of Genista aetnensis (Biv.) DC., an exotic nitrogen-fixing shrub, on the Vesuvius Grand Cone (Southern Italy). Specifically, we tested the hypotheses that the invasion of G. aetnensis has a significant impact on soil quality, soil hydrological regime, local microclimate and plant community structure, and that its impact increases during the plant ontogenetic cycle. We showed that G. aetnensis, in a relatively short time-span (i.e. ~ 40 years), has been able to build-up an island of fertility under its canopy, by accumulating considerable stocks of C, N, and P in the soil, and by also improving the soil hydrological properties. Moreover, G. aetnensis mitigates the daily range of soil temperature, reducing the exposure of coexisting plants to extremely high temperatures and water loss by soil evaporation, particularly during the growing season. Such amelioration of soil quality, coupled with the mitigation of below-canopy microclimatic conditions, has enhanced plant colonization of the barren Grand Cone slopes, by both herbaceous and woody species. These results suggest that the invasion of G. aetnensis could eventually drive to the spread of other, more resource-demanding exotic species, promoting alternative successional trajectories that may dramatically affect the local landscape. Our study is the first record of the invasion of G. aetnensis, an additional example of the regime shifts driven by N-fixing shrubs in Mediterranean region. Further studies are needed to identity specific management practices that can limit the spread and impacts of this species.

Exploiting the therapeutic potential of 8-ß-d-glucopyranosylgenistein: synthesis, antidiabetic activity, and molecular interaction with islet amyloid polypeptide and amyloid ß-peptide (1-42).

8-ß-d-Glucopyranosylgenistein (1), the major component of Genista tenera, was synthesized and showed an extensive therapeutical impact in the treatment of STZ-induced diabetic rats, producing normalization of fasting hyperglycemia and amelioration of excessive postprandial glucose excursions and and increasing ß-cell sensitivity, insulin secretion, and circulating insulin within 7 days at a dose of 4 (mg/kg bw)/day. Suppression of islet amyloid polypeptide (IAPP) fibril formation by compound 1 was demonstrated by thioflavin T fluorescence and atomic force microscopy. Molecular recognition studies with IAPP and Aß1-42 employing saturation transfer difference (STD) confirmed the same binding mode for both amyloid peptides as suggested by their deduced epitope. Insights into the preferred conformation in the bound state and conformers' geometry resulting from interaction with Aß1-42 were also given by STD, trNOESY, and MM calculations. These studies strongly support 8-ß-d-glucopyranosylgenistein as a promising molecular entity for intervention in amyloid events of both diabetes and the frequently associated Alzheimer's disease.

[Genista tinctoria in vitro]. / Genista tinctoria in vitro.

The paper deals with the effects of different growth regulators on the growth of the culture and production of isoflavonoids in the cultivation of the callus culture Genista tinctoria on MS medium under varying light regimens. Of the regulators tested, the highest growth of the culture was found when using BAP 10 mg/l under continuous lighting. With the use of BAP 0.1 mg/l and under normal light regimen, the production of genistine and daidzenin was even higher than in the intact plant. Of the five isoflavonoids determined, four were demonstrated in the callus culture: genistine, genistein, daidzein, and formononetin. In the intact plant the authors managed to determine daidzein, genistein, and biochanin A.

Capillary electrophoresis-mass spectrometry characterisation of secondary metabolites from the antihyperglycaemic plant Genista tenera.

Genista tenera is endemic to the Portuguese island of Madeira, where an infusion of the aerial parts of the plant is used in folk medicine as an antidiabetic agent. Consequently the medicinal properties of the secondary metabolites of this plant have been the subject of an ongoing study. A recently reported LC-MS method using a 100 min separation allowed identification of five flavonoid components in an extract of the aerial parts of this plant. In order to obtain additional information on the range and complexity of the plant's secondary metabolite components a CE-MS method has been developed and applied for the analysis of an extract of G. tenera. Twenty-six different components are distinguished in an analysis time of only 10 min. Results demonstrate that CE-MS/MS rapidly generates data complementary to those obtainable by LC-MS/MS and is particularly suited to the analysis of plant metabolites where concentration is not limiting.

Genista tinctoria hairy root cultures for selective production of isoliquiritigenin.

Hairy root cultures were established after inoculation of Genista tinctoria in vitro shoots with Agrobacterium rhizogenes, strain ATCC 15834. In transformed roots of G. tinctoria grown in Schenk-Hildebrandt medium without growth regulators the biosynthesis of isoflavones, derivatives of genistein and daidzein, and flavones, derivatives of luteolin and apigenin, characteristic for the intact plant, was completely inhibited. The only compound synthesized in G. tinctoria hairy roots was isoliquiritigenin (2.3 g/100 g DW), a daidzein precursor absent in the intact plant. This compound was stored entirely within cells and it was not until abscisic acid was added (37.8 microM supplement on day 42) that approx. 80% of it was released into the experimental medium. The paper discusses the effect of abscisic acid on the growth of G. tinctoria hairy root cultures, the biosynthesis of isoliquiritigenin and the way it is stored. A prototype basket-bubble bioreactor was designed and built to upgrade the scale of the G. tinctoria hairy root cultures. With immobilized roots and a new aeration system, large amounts of biomass were obtained (FWmax 914.5 g l(-1)) which produced high contents of isoliquiritigenin (2.9 g/100 g DW). The abscisic acid-induced release of the metabolite from the tissue into the growth medium greatly facilitated subsequent extraction and purification of isoliquiritigenin.

Application of composted urban residue enhanced the performance of afforested shrub species in a degraded semiarid land.

Improvement of physical-chemical soil quality is a key step for carrying out revegetation programs of degraded lands in Mediterranean semiarid areas. Organic residue addition may restore the quality of these areas. A field experiment was conducted in a silt-loam soil (Typic Petrocalcid) from a degraded semiarid Mediterranean area to evaluate the effect of the addition of a composted urban residue on soil aggregate stability, bulk density and chemical properties and on the establishment of Pistacia lentiscus and Retama sphaerocarpa seedlings. The composted residue was applied at a rate of 6.7 kg m(-2) before planting. The nutrient content (NPK), total organic C and water soluble C were increased and bulk density was decreased, in the rhizosphere soil of both shrub species, by the composted residue. The addition of composted residue significantly increased the soil aggregate stability by about 22% for both shrub species. The beneficial effect of the composted residue on soil quality still persisted 18 months after addition. Eighteen months after planting, the addition of composted residue to soil had increased significantly the production of shoot biomass by P. lentiscus and R. sphaerocarpa, by about 160% and 320% respectively, compared to control values. Composted residue addition to soil can be considered an effective preparation method of a degraded area for carrying out successful revegetation programs with Mediterranean shrubs under semiarid conditions.