The Relationship Between the Rates of Carbon Transport and of Photosynthesis in Tomato Leaves

The rate of carbon transport based on the carbon balance over a 6-h period from a mature tomato leaf was measured overa range of net photosynthetic rates from 0.1 to 4.9 mg C dm−2 h−1 under light flux densities from 4 to 140 W m−2. A proportional relationship was demonstrated between the rate of carbon transport and carbon fixation when the carbon fixation rate was higher than 2 mg C dm−2 h−1.Below a carbon fixation rate of 1 mg C dm−2 h−1, the rate of carbon export was maintained at 1 mg C dm−2 h−1 at the expense of the breakdown of starch. A highly significant correlation was observed between sucrose concentration and the rate of carbon transport. The sucrose concentration in the leaf appears to be the factor controlling carbon export.