Phenolic metabolism, growth, and UV-B tolerance in phenylalanine ammonia-lyase-inhibited red cabbage seedlings

Red cabbage seedlings were grown with or without the phenylalanine ammonia-lyase (PAL) inhibitor, 2-amino-indan-2-phosphonic acid (AIP), at concentrations ranging from 0.5 to 50 mu M. The I-50 for anthocyanin accumulation was <0.1 mu M, with >99% inhibition at 10 mu M, but levels of sinapic acid esters were essentially unchanged by AIP. When grown with 50 mu M AIP, fresh and dry weights were increased slightly over controls, total chlorophylls were unchanged, and microscopic examination revealed no apparent effect of AIP on plant architecture. This suggests no toxic effect of AIP in red cabbage seedlings at levels highly effective in inhibiting PAL. At 50 mu M AIP, the cotyledon area was slightly increased but hypocotyls were significantly reduced in length, perhaps the result of enhanced blue light sensitivity in the absence of anthocyanins. Negative phloroglucinol reactions in AIP-grown plants are consistent with AIP inhibition of lignification. Plants grown with 50 mu M AIP were about twice as sensitive as control plant to UV-B damage of photosystem II, suggesting that phenylpropanoids carried over from the seed, as well as flavonoids, serve as UV screens in young red cabbage seedlings. (C) 1998 Elsevier Science Ltd. All rights reserved.