Tissue discs as an experimental system for metabolic flux analysis in the sugarcane culm

Abstract

We have investigated the suitability of tissue discs as an experimental system to determine carbon fiux in sugarcane. Whilst the number of cells per tissue disc derived from young and older internodes differed largely, the protein content per cell of the discs was constant and is, therefore, most probably the best unit to accurately express metabolic flux. No significant changes in the glucose, fructose and sucrose pools within the tissue discs occurred during a 3h labelling period, which suggests that the uptake of sugars from the medium was adequate to balance the demand by the tissue. This also suggests that no major disturbances in the in vivo metabolism occurred. During a 3h labelling period the rate of 14CO2 release became linear, indicating that the system was approaching isotopic steady state between the external and internal glucose pool, and the respiratory processes involved in CO2 release. Despite this observation, the specific activity of the internal glucose pool was much lower than that of the external glucose pool. This is probably as a result of the intracellular compartmentation of glucose, with most of it present in a sub-cellular compartment making a small contribution in the provision of substrate for respiration.