Photomorphogenic effects of UVB and UVA radiation on leaves of six Mediterranean sclerophyllous woody species subjected to two different watering regimes at the seedling stage

We aimed to investigate the effects of UV radiation and drought on the leaf morphology and anatomy of six native Mediterranean species with different degrees of sclerophylly (Phillyrea angustifolia, Pistacia lentiscus, Daphne gnidium, Ilex aquifolium, Laurus nobilis, Rosa sempervirens). One-year-old seedlings of these species were grown in a glasshouse under three different UV conditions: UVB plus UVA radiation (UVBA), UVA radiation (UVA) and without UV radiation (UV0), and under two watering regimes (low- and well-watered). We observed a significant reduction in leaf area and thickness in response to drier conditions in all the species. The combination of UVB and UVA radiation resulted in leaves with a higher leaf mass area (LMA) and thickness, basically as a consequence of an increase in the thickness of the palisade parenchyma. UVA radiation specifically affected the adaxial epidermal cells, which were thicker and longer than those grown without UV. However, when UV radiation effects were analysed within each watering treatment, well-watered plants showed a higher sensitivity to UV whilst UV did not affect significantly the leaf parameters measured in low-watered plants. Lastly, the more sclerophyllous plants were the least sensitive to UV radiation which suggests that leaf sclerophylly would influence the UV plant response.

► UVB and UVA treated leaves showed higher leaf mass area and thickness basically due to thicker palisade parenchyma.
► UVA radiation specifically affected the adaxial epidermal cells, which were thicker and longer than those grown without UV.
► Leaf morpho-anatomical traits of well-watered plants showed a higher sensitivity to UV than those of low-watered plants.
► The more sclerophyllous the leaves were, the more insensitive they were to UV radiation or drought.