METABOLIC REDUCTION OF PHENYLPROPANOID COMPOUNDS IN PRIMARY LEAVES OFRYE (SECALE-CEREALE L) LEADS TO INCREASED UV-B SENSITIVITY OF PHOTOSYNTHESIS

In the epidermal layers of rye primary leaves two flavone glycosides a nd several hydroxycinnamoyl esters are localized, whereas the mesophyl l contains two flavone glucuronides and two anthocyanins. The concentr ations of all these potential UV-B protective phenylpropanoid compound s could be reduced by application of 2-aminoindan-2-phosphonic acid (A IP), an efficient inhibitor of phenylalanine ammonia-lyase (EC 4.1.3.5 ). Photosystem II in the primary leaves of seven-days-old plants, grow n in the presence of 20 mu M AIP up to an age of 80 h, was more severe ly affected by UV-B than in control plants with the normal concentrati on of phenylpropanoid compounds. Damage of photosystem II in vivo was estimated by measuring the chlorophyll a fluorescence (parameter F-v/F -m) of PS II. The results indicate an essential role of phenylpropanoi d compounds as UV-B protectants in rye primary leaves.