The objective of our study was to investigate the response of Sangiovese vines (one of the most diffused cultivar in Italy) to different solar UV regimes in open air and how plants grown without UVB and total UV react when exposed to full light conditions. Material and Method. Two years old grapevine plants were grown in 10 l pots under greenhouses covered with Teflon, transparent both to UV and visible wavelengths (Control), Mylar, transparent to wavelengths above 312 nm (-UVB) and LEE 226, transparent to wavelengths above 400 nm (-UVB/-UVA). Plant were fertilized and maintained in well watered conditions. Meteorological parameters, outside and inside greenhouses, were monitored and periodically spectral measurements in the range 290 to 800 nm were performed outside and inside each greenhouse to check spectral transparency of filters and PAR irradiance. Before bud break 20 plants were positioned both under Lee and Mylar filters while 10 plants were placed under Teflon. On July 9th 10 plants from Lee and 10 from Mylar were moved under Teflon in order to stimulate possible physiological reactions to the new environment. Leaf discs from the fully expanded 9th leaf from the bottom were taken and used for extraction of UV-B absorbing compounds in a mixture of HCl:methanol:water; absorption spectra were determined with a UV-visible spectrophotometer and absorbance was referred to both unit leaf area and unit of fresh and dry weight. Moreover epidermal flavonoids content, expressed in terms of FLAV-Index, was estimated using a non destructive approach by means of a Multiplex portable fluorimetric device. The photosynthetic properties were analyzed by the fluorescence of the chlorophyll a during the season: direct fluorescence parameters (JIP-test) were measured in different aged-leaves. Photosynthetic pigments were extracted from 5 leaf discs (1 cm2) per leaf with DMF and the absorbance of extracted solutions was read at 647, 664 and 480 nm with a DU spectrophotometer after 48 h of extraction at 4 °C. Results. Mean daily temperature differences measured under the three greenhouses were lower than 0.6°C.Temperature and humidity difference between outside and inside greenhouses not excided 2°C and 8% respectively. On July 9th, after 14 weeks of treatment, the 9th leaf of the control showed the UV-B absorbing compounds content statistically higher than both -UVB and -UVB/-UVA as confirmed also by FLAV-I data. The maximum quantum yield efficiency in the dark-adapted state (Fv/Fm) in plants -UVB was minor than in others light conditions. This difference was significant in younger leaves. On July 24th leaves of -UV-B moved under Teflon greenhouse increased their Fv/Fm reaching the control while -UVA/-UVB plants didn’t show any significant change. UV-absorbing compounds measured on mature leaves both with destructive and non destructive method showed only a partial recover compared with control which remained anyway significantly higher. After 15 days mature leaves previously exposed to -UVB and -UVA/-UVB appeared unable to react to the new radiative regime increasing their content of UV-B absorbing compounds up to reach the level of leaves grown under full light; even several weeks later, on September 10th, these differences were still present. UV-B absorbing compounds estimated by means of the FLAV-I on younger leaves showed a different behaviour: on July 24th leaves of plants exposed to -UVB and -UVA/-UVB treatment was significantly lower than control but plants that were moved under Teflon greenhouse showed a partial recover relative to control whose level was reached finally on September 10th.
