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

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