Carbon Economy and Translocation of 14C in Leaflets of the Seventh Leaf of Tomato During Leaf Expansion

Abstract

The growth pattern (leaf expansion, carbon metabolite accumulation) and the assimilation and translocation of leaf assimilate in the leaflets of the seventh leaf of tomato were examined on six occasions during a period of 35 days beginning 10 days after the leaf was first visible. Leaf expansion progressed basipetally within the leaf. The primary partitioning of the currently-fixed 14C and the 24 h incorporation of both self-fixed and imported 14C were closely related to the degree of leaf expansion. Therefore, leaflets of up to half final size within the same leaf, were markedly different in physiological function. Maximum import of 14C-leaf assimilate from the six basal leaves into the seventh leaf was recorded at 15 per cent expansion. The terminal and top-pair of leaflets reached one quarter full size first and exported 14C leaf assimilate to the basal-pair of leaflets and to the rest of the plant when the seventh leaf, as a whole, was only one tenth expanded. The transition from import to export in a given leaflet was gradual and overlapping. During the early part of leaflet expansion, more imported 14C-leaf assimilate was used for protein synthesis than for the synthesis of sugars and starch. Meanwhile, the capacity for sucrose synthesis from the self-fixed carbon increased significantly preceding the onset of export. Each leaflet resembles a whole leaf in functional development.