Figure 8.
The difference in PMF (ΔPMF or ΔC) between SE/CCs and PPCs (ΔC = ΔΨm SE/CC − ΔΨm PPC) and the ratio (R) of theoretical substrate accumulation rates by SE/CCs versus PPCs in transport phloem of apoplasmically (□,▪) and symplasmically (○,•) phloem-loading species. R values were calculated from Nernst equation (Eq. 4). The open symbols represent the values for excised tissues, and the closed symbols those for intact plants. Photoassimilate retrieval by SE/CCs is presumed to be favored when R > 1, and photoassimilate accumulation by PPCs when R < 1. Inset, Magnification of the graph for R values <1.