PHOTOPERIOD EFFECT ON BUD BURST IN PRUNUS IS PHASE-DEPENDENT - SIGNIFICANCE FOR EARLY PHOTOSYNTHETIC DEVELOPMENT

A 16-h photoperiod stimulated bud burst in mature rooted cuttings of P runus avium cv. Stella, but not in selfed Stella seedlings. However, i n a 12-h photoperiod, bud burst occurred earlier in the seedlings than in the mature cuttings. In the 12-h photoperiod, production of polype ptides involved in carbon dioxide fixation and photosynthetic electron transport was higher in seedlings than in mature cuttings, whereas in the 16-h photoperiod, shoot development and polypeptide production we re similar in seedlings and mature cuttings. In both photoperiods, the amount of large subunit of ribulose-1,5-bisphosphate carboxylase/oxyg enase that was associated with thylakoid membranes in young leaves was higher in seedlings than in mature cuttings. Transcript levels of rbc L mRNA were influenced by photoperiod in mature cuttings but not in se edlings. In seedlings, early bud burst and development of the light ha rvesting apparatus would be an advantage at the start of the growing s eason, before the mature tree canopy reduces irradiances near the wood land floor.