Effect of Translocation-Hindering Procedures on Source Leaf Photosynthesis in Cucumber

Abstract

Three treatments which altered translocation rate were applied to cucumber plants: Girdling of source leaf petiole; removal of all aerial sinks; removal of all source leaves except one. Two different effects were observed, one short-term (during the initial 6 h), and one long-term (detected after several days). The short-term effect was observed exclusively in girdled leaves and involved a reduction in 14CO2 fixation rate paralleled by an increase in stomatal resistance. The effects were maximal after 3 h with subsequent recovery. Stomatal closure apparently resulted from the 5-10% water deficit temporarily detected in girdled leaves which probably induced the observed temporary increases in abscisic acid content. Kinetin counteracted the effects of girdling. The long-term effect was detected 3 days after girdling and 3-5 days after sink manipulation. An increase or decrease in 14CO2 fixation rate was observed when the sink-source ratio was increased or decreased, respectively, accompanied by a respective decrease or increase in starch content. Changes in the relative amount of 14CO2 incorporated into various photosynthetic products were also observed. Stomatal closure was not involved, and the decrease in CO2 fixation was not counteracted by kinetin.