LIGHT-ENTRAINED AND TEMPERATURE-ENTRAINED CIRCADIAN REGULATION OF ACTIVITY AND MESSENGER-RNA ACCUMULATION OF 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID OXIDASE IN STELLARIA-LONGIPES

Stem and leaf tissues of Stellaria longipes Goldie (prairie ecotype) e xhibit circadian rhythmicity in the activity and mRNA abundance for 1- aminocyclopropane-1-carboxylic acid oxidase (EC 1.4.3). The steady-sta te mRNA levels and enzymatic activity levels fluctuated with a period of approximately 24 h and reached their maxima by the middle of the li ght phase and minima by the middle of the dark phase. The oscillations showed damping under constant light, constant dark and constant tempe rature conditions, indicating that the rhythm is entrained by an exter nal signal. The results indicate that light/dark cycles have greater e ntraining effects than temperature cycles. A 15-min red light pulse, b ut not a blue light pulse, could reset rhythm in continuous darkness, suggesting the possible role of a red-light signal transduction pathwa y in the circadian regulation of 1-aminocyclopropane-1-carboxylic acid oxidase.