UV filtration and its impac on some biochemical parameters in Wheat

An UV-exclusion experiment was conducted on durum wheat plants (Triticum durum, var. Claudio) grown in pots. Plants were grown under three different radiative treatments under greenhouses covered with appropriate filters: Teflon transparent to the entire region of natural UV-visible sunlight (full solar spectrum, "Control"), polyester, transparent to wavelengths above 312 nm (UVB exclusion, "-UVB") and Lee transparent to wavelengths above 400 nm (UVB and UVA exclusion, "-UVB-UVA"). Comparing the micrometeorological conditions in the three tunnels, no significant differences were observed in either mean daily air temperature or relative humidity. Under each greenhouse, durum wheat was sown on February 29th 2012 in 9 pots of 32x32x30 cm (45 seeds/pot, subsequently thinned to 30 plants/pot). The pots have been irrigated regularly and fertilized. During plant growth some biochemical parameters were measured to assess the response of wheat to the different radiative conditions. Methanol extractable UV absorbing compounds and photosynthetic pigments measurements were performed on the last fully expanded leaves on April 6th and 24th and on May 21th. Concerning methanol extractable UV absorbing compounds (expressed in terms of absorbance for unit of leaf surface in cm2) the -UVB and -UVB-UVA showed significantly and statistically lower values than those of the Control for all the tested wavelengths (270, 300, 305, 330 and 350 nm) in the first two sampling date. On May 21th the absorbances of the -UVB-UVA treatment resulted statistically and significantly lower than those of the other treatments, but only at 270, 330 and 350 nm. Concerning photosynthetic pigments (expressed in terms of mg for unit of leaf surface in cm2) not statistically significant differences were observed, except for the sampling of May 21th (on the flag leaf) when the pigments in the Control resulted higher than in the others treatments. The nitrogen content (in % on dry weight) of leaves grown under UV exclusion resulted significantly decreased during all the developmental phases; no effect was observed on stem. Grain quality at harvest was significantly influenced by radiative regime: plants grown under UV exclusion showed a reduction in protein and dry gluten content (consequently without variation in the ratio dry gluten/protein), but at the same time a significant increase in gluten index which represent a criterion to define the gluten quality was observed. The results highlighted the role of UV radiations on wheat cultivated under Mediterranean conditions.