EFFECTS OF TEMPERATURE ON PHOTOSYNTHATE PARTITIONING IN ALFALFA

Abstract

This study was conducted to examine the effects of three temperature regimes (12/2 °C, 21/8 °C, and 34/25 °C day/night) on photosynthate partitioning in alfalfa (Medicago sativa L.). Plants were grown under greenhouse conditions for approximately 3 mo and then clipped back. When regrowth was at the bud stage, the plants were placed in growth chambers at the three temperatures, all having a photoperiod of 14 h. Two hours after the onset of the photoperiod of the second day, foliar application of 14 C-labelled urea was used to provide a source of 14 CO 2 for tracing the movement of photosynthate from the source leaf to other parts of the alfalfa plant. Plants were harvested 24 h later and each plant was subdivided into six portions. The plant parts included the source leaf, treated upper shoot, treated lower shoot, untreated shoot, crown and roots. The percent of 14 C exported of the total recovered radioactivity by the source leaf increased as temperature increased. As temperature increased, radioactivity recovery was increased in treated upper shoot, untreated shoots, and roots. The highest recovery of 14 C by the crown was at 21/8 °C. followed by those in 12/2 °C and 34/25 °C, respectively. Total 14 C recovered from the treated lower shoot was decreased as temperature increased.Key words: Relative specific activity (RSA), total plant radioactivity, translocation, 14 C, Medicago sativa L., alfalfa