Effect of Intact Lateral Shoot Leaves Just below the Fruit Truss on Photoassimilate Translocation to Tomato Fruit Using a Positron-emitting Tracer Imaging System

Abstract

The translocation of photoassimilate from intact tomato plant lateral shoot leaves and their rate of contribution to the soluble solid content of tomato fruit were investigated using ¹¹CO₂ and a positron-emitting tracer imaging system (PETIS). After ¹¹CO₂ application to the 4th leaf of the lateral shoots or to the leaf just below the fruit truss in the main shoots, ¹¹C translocation to the fruits began after about 40 min and 1 hour, respectively. The contribution of lateral shoot leaves to photoassimilate translocation to the fruits was based on the amount of ¹¹C translocated from the 7th, 8th, and 10–12th leaves of the main shoots and the 1st–4th leaves of the lateral shoots to the fruits. This contribution, expressed as a rate, of the 1st–4th leaves of the lateral shoots to photoassimilate translocation to the fruit was 44.6–80.1%. The photosynthetic rate of the 4th leaf of the lateral shoots was higher than that of the leaf just below the fruit truss. These results show that the lateral shoot leaves significantly contribute to the translocation of photoassimilate to fruits, and so leaving the lateral shoots may increase the soluble solid content of tomato fruit.