George Grammatikopoulos

Effects of enhanced UV-B radiation on Mentha spicata essential oils

Abstract In vitro propagated plantlets representing two distinct chemotypes of Mentha spicata, viz. plants producing essential oils rich in piperitone oxide and piperitenone oxide (chemotype I) and rich in carvone and dihydrocarvone (chemotype II), were grown in the field under ambient or ambient plus supplemental UV-B radiation, biologically equivalent to a 15% ozone depletion over Patras (38.3°N, 29.1°E), Greece. Enhanced UV-B radiation stimulated essential oil production in chemotype II substantially, while a similar, non-significant trend was observed in chemotype I. No effect was found on the qualitative composition of the essential oils, whereas the quantitative composition was slightly modified in chemotype I. This is the first investigation reporting an improved essential oil content under UV-B supplementation in aromatic plants under field conditions.

Effects of UV-B radiation on cuticle thickness and nutritional value of leaves in two mediterranean evergreen sclerophylls

Summary Seedlings of Laurus nobilis L. and Ceratonia siliqua L., grown for 1 year in the field under ambient radiation conditions were subsequendy allowed to produce their new spring growth in a glasshouse in the absence or presence of UV-B radiation. The UV-B radiation dose was biologically equivalent to that which would have being received by the plants in their natural environment. Plant height, number of leaves, total and mean leaf area, the biomass allocated to both above and below ground parts, photochemical efficiency of PS II and chlorophyll content were not affected. However, UV-B radiation resulted in slighdy thicker leaves in L. nobilis and considerably thicker cuticles in both plants. UV-B absorbing compounds were increased only in L. nobilis. In addition, the leaf nutritional quality of this plant was considerably reduced by UV-B radiation, since phenolics and tannins were increased but nitrogen was decreased. No such changes were observed in C. siliqua . We may conclude that L. nobilis and C. siliqua are not only resistant against UV-B radiation damage, but the observed changes may benefit the plants through their anti-transpirant and anti-herbivore functions.

The use of the portable, non-destructive, spad-502 (minolta) chlorophyll meter with leaves of varying trichome density and anthocyanin content

Summary The credibility of the portable, non-destructive SPAD (Minolta) chlorophyll meter was tested in the particular cases where the optical properties of a leaf change, irrespectively of its chlorophyll content. In greening Eukalyptus sp., Rosa sp. and Ricinus communis leaves, whose anthocyanin content declines dramatically with leaf age, the SPAD values versus actual chlorophyll concentration curves were not distorted by the different levels of anthocyanins. In Teucrium sp., Populus sp. and Buddleia sp., whose abaxial surfaces are highly reflective due to a dense indumentum, but their adaxial surfaces are glabrous, the SPAD values obtained from both surfaces were the same. It is concluded that the use of the chlorophyll meter can be extended to both highly pubescent and red leaves.

Seasonal and diurnal gas exchange characteristics and water relations of the drought semi-deciduous shrub Phlomis fruticosa L. under Mediterranean field conditions

Summary Diurnal and seasonal fluctuations in gas exchange and water relations were examined in the field during a 21 months period in the drought semi-deciduous shrub Phlomis fruticosa L., in an attempt to reveal environmental factors that may limit its growth and distribution. P.fruticosa is an eastern Mediterranean malacophyllous plant dominating the so called “phryganic” ecosystem in Greece (synonym to coastal sage in California and garrigue in France). Maximum photosynthetic rates (c.a. 30 μmol CO 2 m −2 s −1 ) were observed during the spring, with a secondary maximum at late autumn, a deep minimum during summer and early autumn and a secondary minimum during mid-winter. The deep minimum (c.a. 2 − 3 μmol CO 2 m −2 S −1 ) coincided with minimal shoot water potentials and a well-developed stomatal regulation of excessive water loss and CO 2 assimilation. Photosynthesis, however, was additionally limited during the dry period by a substantial drop in photosynthetic capacity, as judged by CO 2 exchange measurements at saturated (5 %) CO 2 . The secondary minimum in photosynthesis during mid-winter, occurring at a period of relatively high pre-dawn shoot water potentials and low atmospheric evaporative demand, was partly related to low temperatures in a rather indirect way. Indeed, diurnal changes in shoot water potential revealed a characteristic delay in the replacement of evaporated water at low temperatures, leading to leaf water shortage and stomatal closure, even during the wet period. We may conclude, therefore, that growth in P.fruticosa is restricted by low water potentials during the warm dry period and, possibly, by increased hydraulic resistance when the winter temperatures fall to relatively low values.

Effects of three endophytic entomopathogens on sweet sorghum and on the larvae of the stalk borer Sesamia nonagrioides

Various endophytic fungi of native plants and crops are important entomopathogens. The objective of this study was to investigate the entomopathogenic action of Beauveria bassiana (Balsamo) Vuillemin, Metarhizium robertsii (Metchnikoff) Sorokin, and Isaria fumosorosea (Wize) Brown & Smith (all Ascomycota: Hypocreales) against larvae of Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae) artificially introduced into Sorghum bicolor L. (Moench) (Poaceae) plants under natural environmental conditions. Sorghum bicolor is an economically important crop cultivated for grain, fiber, forage, and lately for biofuel, and S. nonagrioides is its main pest in Mediterranean areas. Young sorghum plants were inoculated with the entomopathogens by spraying in the field. Plant water status, chlorophyll concentration, photosynthesis, and transpiration were not affected. Thirty days after endophyte establishment, plants were infested with fourth instars of S. nonagrioides. The endophytes prevented 50–70% of larvae from entering stalks. Larval mortality was 70–100% and tunnel lengths were reduced by 60–87%. Larval infestation resulted in reduced electron transport capacity and net photosynthetic rate, which was ameliorated in the presence of I. fumosorosea and reversed by B. bassiana and M. robertsii. The growth of sorghum was unaffected in all treatments during the experimental period. Beauveria bassiana and M. robertsii can protect sweet sorghum from damage induced by S. nonagrioides under natural environmental conditions without affecting plant physiology and growth.

Induction of Ageotropic Response in Lettuce Radicle Growth by Epicuticular Flavonoid Aglycons of Dittrichia viscosa

Thirteen flavonoid aglycons, contained in the strongly allelopathic epicuticular exudates of Dittrichia viscosa, were investigated for their effects on lettuce seedling radicle growth. Concerning radicle length and mass, variable results were obtained, with most of the substances having no effect, some being inhibitory and some even promotive. Shoot mass was slightly reduced in four cases. Seed germination rates, root hair and lateral root formation were not affected either. Three of the compounds (namely quercetin 3,3-dimethylether, naringenin and eriodictyol) induced a strong ageotropic response in radicle growth.

Microalgal post-treatment of anaerobically digested agro-industrial wastes for nutrient removal and lipids production

The aim of this study was to investigate the effectiveness of cultivating Parachlorella kessleri and Acutodesmus obliquus, in anaerobic digestion effluent (ADE) derived from the co-digestion of end-of-life dairy products with mixtures of agro-industrial wastes. To this end, their performance under sterile and non-sterile conditions and different ADE loadings was evaluated, in terms of biomass and lipid production, nutrient removal efficiency and vitality of the photosynthetic apparatus. 10% (v/v) ADE loading inhibited growth over 9-12days of cultivation, however biomass yields of 1.1 and 1gL-1, 22.7% and 19.5% (w/w) fatty acids concentration, as well as NH3-N assimilation of 49.7mgL-1 and 32.3mgL-1 and TP removal of 84.2% and 84% were recorded for P. kessleri and A. obliquus, respectively. Among all the ADE-based treatments tested, P. kessleri outperformed A. obliquus, with no differences observed between sterilized and non-sterilized ADE.

Reduction of ambient UV-B radiation does not affect growth but may change the flowering pattern of Rosmarinus officinalis L.

The effects of sub-ambient levels of UV-B radiation on the shrub Rosmarinus officinalis L. were investigated in a field filtration experiment in which the ambient UV-B was manipulated by a combination of UV-B transmitting and UV-B absorbing filters. As a result, the plants were receiving near-ambient or drastically reduced UV-B radiation doses. Drastic reduction of UV-B radiation had no effect on mean, total and maximum stem length, number of stems per plant, dry mass of leaves, stems and roots and leaf nitrogen and phenolic contents. However, flowering was more pronounced under reduced UV-B radiation during the winter period which coincides with ascending ambient UV-B radiation. In contrast, during autumn and early winter, a period which coincides with descending ambient UV-B radiation, flowering was unaffected by reduced UV-B radiation. We can conclude that natural UV-B radiation does not affect growth of Rosmarinus officinalis, but its reduction could influence the flowering pattern of the species.

Photosynthesis in developing leaf of juveniles and adults of three Mediterranean species with different growth forms

Leaf development is influenced by almost all the prevailing environmental conditions as well as from the conditions at the time of bud formation. Furthermore, the growth form of a plant determines the leaf longevity and subsequently the investment in biomass and the internal structure of the mesophyll. Therefore, photosynthetic traits of a growing leaf, though, partly predetermined, should also acclimate to temporal changes during developmental period. In addition, the age of the plant can affect photosynthesis of the growing leaf, yet, in the majority of studies, the age is associated to the size of the plant. To test if the reproductive status of the plant affects the time kinetics of the photosynthetic capacity of a growing leaf and the relative contribution of the plants’ growth form to the whole procedure, field measurements were conducted in juveniles (prereproductive individuals) and adults (fully reproductive individuals) of an evergreen sclerophyllous shrub (Nerium oleander), a semi-deciduous dimorphic shrub (Phlomis fruticosa), and a winter deciduous tree with pre-leafing flowering (Cercis siliquastrum). PSII structural and functional integrity was progressively developed in all species, but already completed, only some days after leaf expansion in P. fruticosa. Developing leaf as well as fully developed leaf in adults of C. siliquastrum showed enhanced relative size of the pool of final PSI electron acceptors. Photosynthetic traits between juveniles and adults of P. fruticosa were similar, though the matured leaf of adults exhibited lower transpiration rates and improved water-use efficiency than that of juveniles. Adults of the evergreen shrub attained higher CO2 assimilation rate than juveniles in matured leaf which can be attributed to higher electron flow devoted to carboxylation, and lower photorespiration rate. The reproductive phase of the plant seemed to be involved in modifications of the PSII and PSI functions of the deciduous tree, in carboxylation and photorespiration traits of the evergreen shrub, and in water conductance efficiency of the semi-deciduous shrub. However, it is interesting, that regardless of the growth form of the plant and the prospective leaf longevity of the developing leaf, adults need to support flowering outmatch juveniles, in terms of photosynthesis.

Selection of microalgae intended for valorization of digestate from agro-waste mixtures

Digestates have been recently recognized as valuable substrates for microalgal cultivation, effectively combining wastewater remediation and biofuels production. In this regard, selection of the appropriate species for such a process is of utmost importance. In this study, the performance of seven different microalgal strains in 10% (v/v) digestate which derived from the co-digestion of several agro-waste streams was investigated. Parachlorella kessleri, Acutodesmus obliquus, Chlorella vulgaris and Tetraselmis tetrathele were able to acclimate to this new medium, resulting in biomass yields and fatty acids (FAs) content which varied between 570-1117 mg L-1 and 3.9-24.5%, respectively. The main FAs detected in the four species were oleic, palmitic and linolenic acid, with significant differences in their relative abundance. Concerning nutrients removal, almost complete NH3-N removal was observed, while % TP removal exceeded 80% for three of the four strains tested. Furthermore, induction kinetics of prompt chlorophyll fluorescence was used as a screening tool indicative of the reactions of the photosynthetic machinery of different microalgal species cultivated in digestate.