Despina Vokou

Geographic variation of Greek oregano (Origanum vulgare ssp. hirtum) essential oils

Essential oils of Origanum vulgare ssp. hirtum from twenty-three localities, scattered all over Greece, were analysed in order to determine their quantitative and qualitative features. The total oil content of plants and the percentage contribution of the major oil constituents, carvacrol, thymol, γ-terpinene and p-cymene, varied remarkably between localities. The contents of carvacrol and thymol were significantly correlated, varying inversely. The same holds for their sum and the sum of the two major monoterpene hydrocarbons. Altitude seems to be the most important environmental factor influencing the oil content; high values were recorded at low altitudes, coinciding with Mediterranean-type ecosystems. The sum of the four major oil constituents, representing the phenol pathway, seems influenced by the climates thermal efficiency. The hotter the climate, the higher their total concentration.

Effects of Monoterpenoids, Acting Alone or in Pairs, on Seed Germination and Subsequent Seedling Growth

We compared the potential allelopathic activity of 47 monoterpe- noids of different chemical groups, by estimating their effect on seed germination and subsequent growth of Lactuca sativa seedlings. Apart from individual compounds, eleven pairs at different proportions were also tested. As a group, the hydrocarbons, except for (+)-3-carene, were the least inhibitory. Of the oxygenated compounds, the least inhibitory were the acetates; whenever the free hydroxyl group of an alcohol turned into a carboxyl group, the activity of the resulting ester was markedly lower (against both germination and seedling growth). Twenty-four compounds were extremely active against seedling growth (inhibiting it by more than 85%), but only five against seed germination. The compounds that were most active against both processes belonged to the groups of ketones and alcohols; they were terpinen-4-ol, dihydrocarvone, and two carvone stereoisomers. We used a model to investigate whether compounds acted independently when applied in pairs. The combined effect varied. In half of the cases, it followed the pattern expected under the assumption of independence; in the rest, either synergistic or antagonistic interactions were found in both germination and elongation. However, even in cases of synergistic interactions, the level of inhibition was not comparable to that of a single extremely active compound, unless such a compound already participated in the combination. The specific structural factors that operate and determine the activity of monoterpenoids still remain rather obscure. The same holds true for the combined effect; its character cannot in general be predicted on the basis of individual compounds acting alone.

Pattern of geographic variations of Origanum vulgare trichomes and essential oil content in Greece

Abstract The variation of the total plant pubescence and essential oil content of Origanum vulgare plants grown all over the species range in Greece has been studied. In respect to their glandular and non-glandular trichomes. o. vulgare plants are differentiated along a direction fromeastern and central Aegean islands, through Crete and Peloponnese, to the northern part of Greece. The same variation pattern is found when the essential oil content of O. vulgare plants is considered. Along this direction, a gradual change of the climate from the Real Mediterranean to the Continental Mediterranean type occurs. Plants grown in the Mediterranean climatic zones are characterized by numerous sessile glands and are essential oil-rich (ssp. hirtum), whereas those of the Continental type climate have few glands and are oil-poor (ssp. viridulum and ssp. vulgare).

Bacterial colonization of the phyllosphere of nineteen plant species and antimicrobial activity of their leaf secondary metabolites against leaf associated bacteria

Summary.The scope of this work was to examine whether leaf constitutive secondary metabolites play a role in determining bacterial colonization of the phyllosphere. To this aim, we surveyed nineteen native or cultivated plant species that share a common bacterial pool in a North Mediterranean area, and estimated the size of total and ice nucleation active (INA) bacterial populations on their leaves. Large differences in the colonization of their phyllosphere were found; the population size of epiphytic bacteria ranged from 7.5 × 102 to 1 × 106 CFU/g fresh weight, in eucalypt and celery, respectively. Species native in Mediterranean-type climate areas, particularly those belonging to the group of aromatic plants, are characterized by scarce presence of INA bacteria. The antibacterial activity of essential oils, surface phenolics and leaf tissue extracts was also estimated against the INA strains P. syringae and E. herbicola, isolated from two of these plant species. E. herbicola proved more sensitive than P. syringae. Of the species examined, oregano [Origanum vulgare L. subsp. hirtum (Link.) Ietswaart], an aromatic plant, had the highest antimicrobial activity, whereas six species showed no activity at all. Further experiments were performed with oregano and bean (Phaseolus vulgaris L.) that represent two extremes in their secondary metabolite content. Both plants were inoculated with P. syringae. By the end of incubation, the bacterial population on bean plants was about 100 times higher than that on oregano leaves. Scanning electron micrographs showed that bacterial growth on oregano leaves was confined to sites away from glandular hairs. Results from the bacterial colonization survey together with those from the toxicity tests showed that all species rich in antibacterial secondary metabolites harbored low leaf bacterial populations. These results provide substantial evidence that leaf secondary metabolites function as constitutive defense chemicals against microbial invasions. However, the fact that species with non- or moderately active leaf secondary metabolites are not always highly colonized suggests mediation of other unknown factors, the contribution of which requires further investigation.

Monitoring, Modelling and Forecasting of the Pollen Season

The section about monitoring covers the development of phenological networks, remote sensing of the season cycle of the vegetation, the emergence of the science of aerobiology and, more specifically, aeropalynology, pollen sampling instruments, pollen counting techniques, applications of aeropalynology in agriculture and the European Pollen Information System. Three data sources are directly related with aeropalynology: phenological observations, pollen counts and remote sensing of the vegetation activity. The main future challenge is the assimilation of these data streams into numerical pollen forecast systems. Over the last decades consistent monitoring efforts of various national networks have created a wealth of pollen concentration time series. These constitute a nearly untouched treasure, which is still to be exploited to investigate questions concerning pollen emission, transport and deposition. New monitoring methods allow measuring the allergen content in pollen. Results from research on the allergen content in pollen are expected to increase the quality of the operational pollen forecasts.

The scale of analysis determines the spatial pattern of woody species diversity in the Mediterranean environment

We examine the spatial pattern of woody species diversity at different scales, in two sites of Mt. Holomontas in northern Greece, which falls within the transitional zone between temperate forests and Mediterranean-type ecosystems. We investigate how diversity is distributed in space and whether the perceived pattern changes with the scale of observation. We use two different metrics of diversity: species richness and species turnover. Our main finding is that the spatial pattern of diversity changes with the scale of observation or analysis. For a given scale, the pattern of species richness (alpha diversity) is negatively correlated with the pattern of species turnover (beta diversity). Species-rich areas have more species in common with their neighbors than species-poor areas. The between-scale disparity of the spatial pattern of diversity may be a general feature of ecological systems. For this to be validated, studies with different groups of species in different biomes and in different biogeographical areas are required; our study contributes to this direction providing evidence that this holds true for woody species in Mediterranean communities. Finally, we discuss how these findings might affect important issues in theoretical and applied ecology, such as identifying the environmental factors driving biodiversity.

The hybrid Origanum × intercedens from the island of Nisyros (SE Greece) and its parental taxa; comparative study of essential oils and distribution

Abstract The hybrid Origanum × intercedens Rech. is reported for the first time to occur in the Aegean Archipelago, on the volcanic island of Nisyros (SE Greece), in particular. The qualitative and quantitative features of its essential oil are studied in comparison to those of the parental taxa. O. onites and O. vulgare ssp. hirtum . Though O. onites is a common element of the flora of Nisyros, O. vulgare spp. hirtum has not been found on the island, which has been fairly well studied from a floristic point of view. On the basis of the essential oil composition, and compared with 23 O. vulgare spp. hirtum samples studied from populations scattered all over Greece, it is concluded that the hybrid from Nisyros resembles most of population from the nearby island of Kos. Possible causes that could explain the seemingly peculiar occurrence of the hybrid at the absence of one of the parental taxa are discussed.

Distribution and essential oils of Salvia pomifera subsp. pomifera (Labiatae) on the island of Crete (S Greece)

Abstract The distribution of Salvia pomifera subsp. pomifera (Cretan sage) on the island of Crete is presented. The essential oils of six populations scattered on the island are studied. The essential oil content varies from 2.1–4.2%, whereas the main oil components were in all cases α - and/or β -thujone (27.4–72.3% and 7.1–40.8%, respectively). The comparison of our results to literature data, suggest that S. pomifera can be distinguished from S. fruticosa (Greek sage), on the basis of its essential oil composition.