Related Experiment Video
Updated: Aug 8, 2026

Collection and Analysis of Arabidopsis Phloem Exudates Using the EDTA-facilitated Method
Published on: October 23, 2013
Evidence for Phloem loading from the apoplast: chemical modification of membrane sulfhydryl groups
1Central Research and Development Department, Experimental Station, E. I. du Pont de Nemours and Company, Wilmington, Delaware 19898.
Abstract:
The water-soluble, sulfhydryl-specific, chemical modifier p-chloromercuribenzenesulfonic acid reversibly inhibited the accumulation of exogenously supplied (14)C-sucrose into leaf discs of Beta vulgaris. P-Chloromercuribenzenesulfonic acid treatment did not inhibit photosynthesis or respiration or induce membrane leakage to sucrose, indicating that the site of inhibition was the plasmalemma. The active loading of sucrose and (14)CO(2)-derived assimilates into the phloem and their translocation from the source leaf were inhibited by the nonpermeant modifier. Several nonpermeant sulfhydryl group modifiers also inhibited sucrose accumulation into leaf discs while two amino-reactive reagents had no effect. The results indicate that sugars are actively accumulated into the phloem from the apoplast and that membrane sulfhydryl groups may be involved.
Related Concept Videos
Phloem and Sugar Transport
The Apoplast and Symplast
Short-distance Transport of Resources
Sulfur Assimilation
Protein Modifications in the RER
Broadly, these modifications can be categorized into four main categories — glycosylation, formation of disulfide bonds, assembly of protein subunits, and specific proteolytic cleavages like removal of signal sequences.
Protein Transport to the Thylakoids

