Quantifying the Capacity of Phloem Loading in Leaf Disks with [¹⁴C]Sucrose

Area of Science:

• Plant physiology
• Plant molecular biology
• Plant biochemistry

Background:

• Phloem loading and transport are vital for plant survival, enabling communication between source and sink organs.
• Understanding carbon partitioning is key to optimizing plant growth and yield.
• Previous methods for assessing carbon transport had limitations.

Purpose of the Study:

• To present a reliable protocol for assessing sucrose loading into the phloem of mature leaves.
• To provide a method that can be combined with other protocols for a comprehensive analysis of whole-plant carbon partitioning.
• To minimize ambiguities in carbon transport studies.

Main Methods:

• *Arabidopsis* leaf disks were used to measure the relative rates of sucrose loading into the phloem.
• Leaf disks were infiltrated with buffered solutions containing radiolabeled sucrose ([¹⁴C]Suc).
• Sucrose uptake was visualized using autoradiography and quantified via scintillation counting.

Main Results:

• The protocol quantifies the relative rates of sucrose loading into the phloem vascular system.
• Results are expressed as disintegration per minute per unit of leaf disk fresh weight or area.
• This method is suitable for use with *Arabidopsis* and can be combined with other protocols.

Conclusions:

• This protocol provides a reliable method for assessing phloem loading in mature leaves.
• Combining this with other carbon transport and unloading protocols offers a comprehensive view of plant carbon partitioning.
• The study contributes to a more accurate understanding of physiological processes in plants.