Alteration of the Pattern of Distribution of Photosynthetic Products in the Tomato by Manipulation of the Plant

To increase the proportion of photosynthates exported from tomatoleaves and to examine how far the subsequent distribution islinked with the activity of physiological sinks two types ofprocedures were used. In the first experiment the number ofsources of photosynthates was reduced by removing leaves orexcluding light from them and the growth of the fruit increasedby applying growth regulators. By this means a 30–50 percent increase in the export of radio-active photosynthates inthe first 24 h from a test leaf exposed to ¹⁴CO₂ was recorded.The enhanced activity of the sinks induced by growth regulatorsalthough increasing the amount of ¹⁴C material leaving a leafdid not increase the proportion of the exported fraction whichentered the fruit. In contrast a reduction in the number ofphotosynthetic sources increased both the absolute and relativeamounts entering the fruit from the treated leaf. In the second experiment grafts were made between potato andtomato in both directions. When the potato was the rootstockboth tomato and potato leaves exposed to ¹⁴CO₂ exported a higherproportion of the radioactive assimilates than when the tomatowas the rootstock. Movement was greater from scion to root-stockthan vice versa. The results are discussed in the context of fruit productionby the tomato and the extent to which yield of fruit is determinedby internal factors.