Photoperiodic and Genetic Control of Carbon Partitioning in Peas and Its Relationship to Apical Senescence 1

Apical senescence but not flower initiation is delayed by short days (SD) compared to long days (LD) in pea plants (Pisum sativum L.) of genotype E Sn Hr. We recently reported that delay of senescence correlated with slower reproductive development, suggesting that fruits are weaker sinks for assimilates under delayed senescence conditions. Thus, we have examined assimilate partitioning in peas to determine if genotype and photoperiod regulate relative sink strength. Assimilate diversion by developing fruit has been implicated in senescence induction. A greater percentage of leaf-exported 14C was transported to fruits and a smaller percentage to the apical bud of G2 peas (genotype E S.4 Hr) in LD than in SD. Relatively more of the 14C delivered to the apical bud of G2 peas was transported to flower buds than to young leaves in LD as compared to SD. There was no striking photoperiodic difference in carbon partitioning in genetic lines without the Sn Hr allele combination. The Sn Hr allele combination and photoperiod may regulate the relative strength of reproductive and vegetative sinks. Photoperiodic differences in sink strength early in reproduction suggest that these genes regulate sink strength by affecting the physiology of the whole plant. High vegetative sink strength in SD may maintain assimilate supply to the apical bud, delaying senes-