What determines carbon partitioning between competing sinks?

Area of Science:

• Plant Physiology
• Biophysics
• Photosynthate Allocation

Background:

• Carbohydrate sinks in plants are characterized by their ability to attract photosynthate and their priority for supply.
• Sink strength, traditionally defined as carbohydrate flow rate, is influenced by supply, competing sinks, and transport pathway resistance.
• This indicates sink strength is a property of the entire plant system, not an isolated sink characteristic.

Purpose of the Study:

• To critically evaluate the definition and utility of "sink strength" in plant physiology.
• To explore an alternative model for understanding plant carbohydrate source-sink relationships.
• To review the efficacy of a revised model in mimicking observed plant carbohydrate dynamics.

Main Methods:

• Review of existing literature on plant carbohydrate transport and source-sink relationships.
• Analysis of a simple phloem flow model incorporating Münch's hypothesis and saturable unloading.
• Comparison of model outputs with observed plant source-sink behaviors.

Main Results:

• The traditional definition of sink strength as a flow rate is shown to be an invalid descriptor of a sink alone.
• A simple model based on Münch's ideas with saturable unloading effectively mimics key aspects of plant source-sink relations.
• This model generates a set of valid sink descriptors and explains sink priority.

Conclusions:

• The concept of sink strength requires re-evaluation as it is a systemic, not a sink-specific, property.
• A revised model of phloem flow provides a more accurate framework for understanding carbohydrate allocation in plants.
• This model offers valuable insights into sink prioritization and plant resource distribution.