Arrest of chlorophyll accumulation prior to anthocyanin formation in Euphorbia pulcherrima

Euphorbia pulcherrima Klotz plants exposed to short days (11 h light/13 h d ark) for a period of eight weeks, developed flowers and a red canopy consis ting of bracts and few true leaves. Plants maintained for three weeks under short day conditions, failed to produce flower primordia or a red canopy i n the following 5 weeks in continuous light. Between the 4th and 5th short day week, the youngest leaves began to accumulate anthocyanin and turned re d while the apical meristems differentiated into flower primordia. Chloroph yll accumulation ceased at the onset of anthocyanin synthesis and the prote in content per unit leaf area declined, mRNA for glutamyl-tRNA(Glu) synthet ase (EC 6.1.1.17) and glutamyl-tRNA(Glu) reductase also declined during thi s period. Western blot analysis revealed a loss of glutamyl-tRNA(Glu) reduc tase, glutamate 1-semialdehyde (EC 5.4.3.8) and the Mg-chelatase subunits, Olive and CH42, in the last 2 to 4 weeks of the photoperiod. (C) Elsevier, Paris.