Different responses of Arbutus unedo and Vitis vinifera leaves to UV filtration and subsequent exposure to solar radiation

An UV-ex­clu­sion ex­per­i­ment was con­ducted on Mediter­ranean plant species grown in pots: the ever­green scle­ro­phyl­lous shrub Ar­bu­tus unedo and the de­cid­u­ous woody crop Vi­tis vinifera. Af­ter 130 days, of ex­clu­sion of UVB and both UVA and UVB ra­di­a­tions, dur­ing leaf un­fold­ing and de­vel­op­ment, the plants were ex­posed to the am­bi­ent so­lar ra­di­a­tion (about 80% of the whole so­lar spec­trum). The dif­fer­ent ra­dia­tive treat­ments were ob­tained with tun­nels, cov­ered with ap­pro­pri­ate fil­ters (cut­ting UV ra­di­a­tion), where the plants grown. The leaf UV ab­sorb­ing com­pounds were analysed, dur­ing the grow­ing sea­son, in both species, in plants un­der the dif­fer­ent ra­dia­tive regimes. The flavonols con­tent in leaf epi­der­mis was, also pe­ri­od­i­cally as­sessed, in both species, by means of a non-de­struc­tive op­ti­cal in­dex (the FLAV in­dex of the Mul­ti­plex sen­sor). Struc­tural char­ac­ter­is­tics and func­tion­al­ity of the pho­to­syn­thetic ap­pa­ra­tus of the plants were as­sessed by means of chloro­phyll a flu­o­res­cence mea­sure­ments. The UV-ex­clu­sion pro­voked a re­duc­tion of UVA-ab­sorb­ing com­pounds, mainly flavonols, in the leaves of both species. The re­sults ev­i­denced an in­crease of these com­pounds over time in plants pre­vi­ously grown un­der both UV-ex­clu­sion treat­ments, es­pe­cially in V. vinifera. Chloro­phyll a flu­o­res­cence analy­sis showed a de­lay in the de­vel­op­ment of the pho­to­syn­thetic ap­pa­ra­tus in V. vinifera leaves pre­vi­ously grown un­der to­tal UV ex­clu­sion (both UVA and UVB) and dam­age to the oxy­gen evolv­ing com­plex. No sig­nif­i­cant ef­fects of the UV treat­ments on the leaf pho­to­chem­i­cal prop­er­ties were de­tected in A. unedo. Over­all the re­sults high­lighted the rel­e­vance of UV ra­di­a­tion on the leaf phys­i­ol­ogy of the species con­sid­ered and its es­sen­tial role in the pho­to­mor­pho­gen­e­sis of pro­tec­tive sub­stances in the leaves.