CHANGING PATTERNS OF DISTRIBUTION OF PRODUCTS OF PHOTOSYNTHESIS IN TOMATO PLANT WITH RESPECT TO TIME AND TO AGE OF A LEAF

Two series of experiments were conducted with tomato plants grown in a glasshouse. In the first series the second leaf of a young plant was exposed to 14CO2 for periods up to a maximum of 4 h and the distribution of the 14C-products was determined either at intervals of 10 and 30 min, 1, 2, 3, 4, 5, 6, 12, and 24 h, or 1, 2, 3, 5, 7, 11, and 15 days after the 14CO2 was initially supplied. Seventeen per cent of the contained radioactive carbon was exported during the first day and a further 23 per cent during the following week. At the death of the leaf 44 per cent of the carbon originally fixed was present in the dead structure. There is evidence that the roots re-export a large proportion of the carbon products originally imported.In the second series the tenth leaf of a plant was supplied with 14CO2, and 24 h later the relative amounts of radioactivity were determined for every leaf, internode, and fruit truss and for the roots and shoot apex. The plants were selected so that leaf 10 was always immediately below truss 1. The experiment was performed seven times, each time at a different stage both in the life-cycle of the leaf and the development of the plant. There were differences in the total amounts of radioactivity found at the end of each experiment but these differences were not random. The pattern of distribution of the 14C exported by leaf 10 changed as the plant developed. The percentage of the 14C initially fixed which was exported by leaf 10 rose to a peak early in its life and then fell sharply but the distribution of 14C exported followed a different pattern. For a long period there was a heavy accumulation of 14C in the internode immediately below leaf 10 but later in development this was less evident and the proportions reaching the roots increased. The internode above leaf 10 never showed the same degree of accumulation. Truss I dominated the distribution patterns during the phase of its active growth. These results are discussed and a hypothesis to account for the changing patterns of distribution is presented. © 1969 OXFORD UNIVERSITY PRESS.