Glasshouse experiments were conducted in winter and spring growing seasons in order to evaluate the effects of shading on production and nutritional quality of lettuce (Lactuca sativa L. cv. Parris Island), under Mediterranean climate conditions. In both seasons, plants were cultivated hydroponically under four different levels of photosynthetically active radiation intensities (26, 47, 73 and 100 % of incident light intensity). The results showed that stomatal conductance and photosynthetic rate significantly decreased in shaded plants. This strong negative correlation of leaf physiological parameters with light deficiency resulted in lower biomass yield production in both growing seasons. Moreover, the nutritional value (ascorbic acid concentration) was also significantly decreased in relation to incident light intensity decrease. In contrary, a strong positive correlation of leaf total chlorophyll content and nitrate content with light deficiency was detected. However, nitrate concentration in all treatments remained within the European Union's permissible levels being significantly lower in plants produced in spring compared to winter.

Objectives: In the present work, five aromatic plants: Origanum vulgare L., Rosmarinus officinalis L., Ocimum basilicum L., Salvia officinalis L. and Achillea millefolium L., are examined in order to determine Gallic Acid (GA) radical generation in them by UV-Vis and EPR spectroscopy. Methods: The phenol content of plant extracts was estimated at 280 nm by deconvolution of UV-Vis spectra using a GA calibration curve whilst the radical activity was quantitated by EPR Spectroscopy at 77 Kelvin using the stable free radical DPPH • as a reference. Results: The radical activity ranged from 7 × 10 12 spins in O. vulgare L. to 2.2 × 10 13 spins in O. basilicum L. of DPPH • /g sample whilst the phenol content as GA ranged from 28.1 mg of GA/g sample in O. vulgare L. to 65.2 mg of GA/g sample in A. millefolium L. Moreover, EPR spectra showed that all samples contain stable radical signals with g-values 2.0046-49 and a line width of 3-5 Gauss. These are characteristic for π-type semiquinone radicals of GA compounds with the unpaired electron partially on the oxygen atom of the phenolic ring radicals. Conclusion: These significant differences between the UV-Vis and EPR measurements reveal that the stabilization of the radical fraction, type GA • in aromatic plants is a combined result of aromatic species and local effects; namely, phenolic groups and aromatic environment.

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