Non-Invasive Monitoring of Sucrose Mobilization from Culm Storage Parenchyma by Magnetic Resonance Spectroscopy

Abstract

Because sucrose stored in mature stalks (in excess of 40% of stalk dry weight) can be wholly mobilized to supply carbon for the growth of heterotrophic tissues, we propose that sucrose mobilization requires a net sink-to-source transition that acts in toto within sett internode storage parenchyma. Based on our data we propose that mobilization of sucrose from culm storage parenchyma requires minimal investment of metabolic resources, and that the mechanism of sucrose mobilization is metabolically neutral. By magnetic resonance spectroscopy and phloem-specific tracer dyes, strong evidence was found that sucrose is mobilized from sett storage parenchyma via phloem to the growing shoot tissue. An analysis of the enzyme activities involved in sucrose metabolism and glycolysis suggested that sucrose synthase activity is downregulated due to the effects of sucrose mobilization. Overall, metabolism in storage parenchyma shifts from futile cycling to a more quiescent state during sucrose mobilization.