Metabolie Reduction of Phenylpropanoid Compounds in Primary Leaves of Rye (Secale cereale L.) Leads to Increased UV-B Sensitivity of Photosynthesis

Rye Primary Leaf, Phenylalanine Ammonia-Lyase Inhibitor, 2-Aminoindan-2-phosphonic Acid, Photosystem II Damage, Ultraviolet-B In the epidermal layers of rye primary leaves two flavone glycosides and several hydroxycinnamoyl esters are localized, whereas the mesophyll contains two flavone glucuronides and two anthocyanins. The concentrations of all these potential UV-B protective phenylpropanoid compounds could be reduced by application of 2-aminoindan-2-phosphonic acid (AIP), an efficient inhibitor of phenylalanine ammonia-lyase (EC 4.1.3.5). Photosystem II in the primary leaves of seven-days-old plants, grown in the presence of 20 |̂ m AIP up to an age of 80 h, was more severely affected by UV-B than in control plants with the normal concentration of phenylpropanoid compounds. Damage of photosystem II in vivo was estimated by measuring the chlorophyll a fluorescence (parameter FJFm) of PS II. The results indicate an essential role of phenylpropanoid compounds as UV-B protectants in rye primary leaves.