IMPACT OF LOW-TEMPERATURE STRESS ON GENERAL PHENYLPROPANOID AND ANTHOCYANIN PATHWAYS - ENHANCEMENT OF TRANSCRIPT ABUNDANCE AND ANTHOCYANIN PIGMENTATION IN MAIZE SEEDLINGS

Changes in anthocyanin content and transcript abundance for genes whos e products function in general phenylpropanoid metabolism and the anth ocyanin pathway were monitored in maize (Zea mays L.) seedlings during short-term, low-temperature treatment. Anthocyanin and mRNA abundance in sheaths of maize seedlings increased with the severity and duratio n of cold. Anthocyanin accumulation was found in all tested lines that were genotypically capable of any anthocyanin production. Within 24 h of transferring 7-d maize (B37N) seedlings to 10 degrees C, phenylala nine ammonia-lyase (Pal) (EC 4.3.1.5)-homologous and chalcone synthase (C2) (EC 2.3.1.74) transcript levels increased at least 8- and 50-fol d, respectively, and 4-coumarate:CoA ligase (4Cl) (EC 6.2.1.12)-homolo gous and chalcone isomerase (Chi) (EC 5.5.1.6)-homologous transcripts increased at least 3-fold over levels in unstressed plants. Time-cours e studies showed that Pal (EC 4.3.1.5) and C2-transcript levels remain ed relatively constant for the first 12 h of cold stress, dramatically increased over the next 12 h, and declined to pretreatment levels wit hin 2 d of returning cold-stressed seedlings to ambient (25 degrees C) temperature. Transcripts 4Cl (EC 6.2.1.12) and Chi (EC 5.5.1.6) incre ased in abundance within 6 h of cold stress, exhibited no further incr ease over the next 36 h, and declined to pretreatment levels upon retu rning seedlings to 25 degrees C. Transcripts homologous to two regulat ory (R, C1) and three structural (A1, A2, and Bz2) anthocyanin genes i ncreased at least 7- to 10-fold during cold treatment, exhibiting simi lar kinetics of accumulation as for Pal (EC 4.3.1.5) and C2 transcript s. Transcripts encoded by Bz1, the anthocyanin structural gene for UDP :glucose-flavonol glucosyltransferase (EC 2.4.1.91), were relatively a bundant in control tissues and exhibited only a transient increase dur ing the cold period. Our studies suggest that the genes of the anthocy anin biosynthetic pathway can be considered cor (Cold-Regulation) gene s, and because this pathway is well defined, it is an excellent subjec t for characterizing plant molecular responses to low temperatures.