Fracheboud Y, Luquez V, Björkén L, Sjödin A, Tuominen H, Jansson S
The control of autumn senescence in European aspen
Plant Physiology: 2009 149:1982-1991

The initiation, progression, and natural variation of autumnsenescence in European aspen (Populus tremula) was investigatedby monitoring chlorophyll degradation in (1) trees growing innatural stands and (2) cloned trees growing in a greenhouseunder various light regimes. The main trigger for the initiationof autumn senescence in aspen is the shortening photoperiod,but there was a large degree of variation in the onset of senescence,both within local populations and among trees originating fromdifferent populations, where it correlated with the latitudeof their respective origins. The variation for onset of senescencewith a population was much larger than the variation of budset. Once started, autumn senescence was accelerated by lowtemperature and longer nights, and clones that started to senescencelate had a faster senescence. Bud set and autumn senescenceappeared to be under the control of two independent criticalphotoperiods, but senescence could not be initiated until acertain time after bud set, suggesting that bud set and growtharrest are important for the trees to acquire competence torespond to the photoperiodic trigger to undergo autumn senescence.A timetable of events related to bud set and autumn senescenceis presented.

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