Studying Phloem Loading with EDTA-Facilitated Phloem Exudate Collection and Analysis

Abstract

Sugars that are produced by photosynthesis in the leaves are transported in the phloem to heterotrophic sink tissues like roots, fruit, or flowers. Since sugars inside the highly specialized cells of the phloem move by bulk flow, it is the loading and unloading of sugars that determines the rates of allocation between organs. Here, a method is described for the relative quantification of sugars that are loaded into the phloem in leaves. It is based on EDTA-facilitated phloem exudate collection and, therefore, requires control experiments to exclude measurement artifacts. It can be applied to a wide range of plant species, including dicots, monocots, and trees.

Keywords: Carbohydrate allocation; EDTA-facilitated exudation; Phloem; Phloem loading; Sucrose transport.