Patterns of Assimilate Distribution and Source—sink Relationships in the Young Reproductive Tomato Plant (Lycopersicon esculentum Mill.)

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Abstract
Patterns of distribution of 14C were determined in 47-day-old tomato plants (Lycopersicon esculentum Mill.) 24 h after the application of [14C]sucrose to individual source leaves from leaves 1–10 (leaf 1 being the first leaf produced above the cotyledons). The first inflorescence of these plants was between the ‘buds visible’ and the ‘first anthesis’ stages of development. The predominant sink organs in these plants were the root system, the stem, the developing first inflorescence and the shoot ‘apex’ (all tissues above node 10). The contribution made by individual source leaves to the assimilate reaching these organs depended upon the vertical position of the leaf on the main-stem axis and upon its position with respect to the phyllotactic arrangement of the leaves about this axis. The root system received assimilate principally from leaf 5 and higher leaves, and the stem apex from the four lowest leaves. The developing first inflorescence received assimilates mainly from leaves in the two orthostichies adjacent to the radial position of the inflorescence on the vertical axis of the plant; these included leaves which were major contributors of 14C to the root system (leaves 6 and 8) and to the shoot apex (leaves 1 and 3). This pattern of distribution of assimilate may explain why root-restriction treatments and removal of young leaves at the shoot apex can reduce the extent of flower bud abortion in the first inflorescence under conditions of reduced photoassimilate availability.