Assessing Rates of Long-distance Carbon Transport in by Collecting Phloem Exudations into EDTA Solutions after Photosynthetic Labeling with [C]CO.

Phloem loading and transport of photoassimilate from photoautotrophic source leaves to heterotrophic sink organs are essential physiological processes that help the disparate organs of a plant function as a single, unified organism. We present three protocols we routinely use in combination with each other to assess (1) the relative rates of sucrose (Suc) loading into the phloem vascular system of mature leaves ( Yadav , 2017a ), (2) the relative rates of carbon loading and transport through the phloem (this protocol), and (3) the relative rates of carbon unloading into heterotrophic sink organs, specifically roots, after long-distance transport ( Yadav , 2017b ), We propose that conducting all three protocols on experimental and control plants provides a reliable comparison of whole-plant carbon partitioning, and minimizes ambiguities associated with a single protocol conducted in isolation ( Dasgupta , 2014 ; Khadilkar , 2016 ). In this protocol, [C]CO is photoassimilated in source leaves and phloem loading and transport of photoassimilate is quantified by collecting phloem exudates into an EDTA solution followed by scintillation counting.