To increase the proportion of photosynthates exported from tomato leaves and to examine how far the subsequent distribution is linked with the activity of physiological sinks two types of procedures were used. In the first experiment the number of sources of photosynthates was reduced by removing leaves or excluding light from them and the growth of the fruit increased by applying growth regulators. By this means a 30-50 per cent increase in the export of radio-active photosynthates in the first 24 h from a test leaf exposed to 14CO2 was recorded. The enhanced activity of the sinks induced by growth regulators although increasing the amount of 14C material leaving a leaf did not increase the proportion of the exported fraction which entered the fruit. In contrast a reduction in the number of photosynthetic sources increased both the absolute and relative amounts entering the fruit from the treated leaf.In the second experiment grafts were made between potato and tomato in both directions. When the potato was the rootstock both tomato and potato leaves exposed to 14CO2 exported a higher proportion of the radioactive assimilates than when the tomato was the rootstock. Movement was greater from scion to root-stock than vice versa.The results are discussed in the context of fruit production by the tomato and the extent to which yield of fruit is determined by internal factors. © 1969 OXFORD UNIVERSITY PRESS.
