Developmental stage is an important factor that determines the antioxidant responses of young and old grapevine leaves under UV irradiation in a green-house.
The impact of UV irradiation was studied on photosynthesis, photosystem II photochemical
yields and antioxidant responses using green-house grown grapevine (Vitis vinifera L. cv. Chardonnay)
leaves. Supplemental UV irradiation (290-400 nm) was centred in the UV-B region, and corresponded
to 8.95 kJ m-2 d-1 global (280-400 nm) or 8.04 kJ m-2 d-1 UV-B (280-315 nm) biologically effective
dose. UV irradiation was applied daily and its effects were evaluated after 4-days. Younger (1-3 weeksold)
leaves (YL) and older (4-6 weeks-old) leaves (OL) were affected differently, UV irradiation
decreased their photochemical yields to 78% and 56%, respectively. Unlike OL, YL responded by an
increase in UV-B absorbing pigment, anthocyanin and total phenolics contents. UV irradiation
increased total antioxidant capacities in YL but not in OL. YL were also different in their ability to
increase speciıic hydroxyl radical and singlet oxygen neutralizing capacities in response to the
supplemental UV irradiation, which is reported here for the ıirst time. Our results suggest that the
ability of maintaining photosynthesis under supplemental UV is not necessarily determined by base
levels of antioxidants but rather by their inducibilities in response to the irradiation and emphasise the
importance of comparing leaves of the same age in UV studies. Correlations between various
antioxidant capacities, pigment contents and photosynthesis parameters were also examined.
However, no single element of the defence system can be picked up as decisive factor of sensitivity to
UV