Table 3.

Substrate cycles in sugarcane immature (internode 3 and 4) and maturing (internode 6 and 7) internodes to evaluate sucrose cycling (flux into sucrose from 1-¹³C glucose and flux toward fructose from sucrose relative to pool size; mmol min⁻¹ mg⁻¹ protein) and triose phosphate:hexose-phosphate cycling (arbitrary units) after a 6 h incubation time (mmol min⁻¹ mg⁻¹ protein)

	Flux into fructose from sucrose	Flux from 1-13C glucose into sucrose	Triose-P to hexose-P recycling
WT
Internode 3 + 4	9.98 ± 0.85	100.43 ± 14.56	4.37 ± 0.70
Internode 6 + 7	13.40 ± 1.56	254.87 ± 13.22	1.52 ± 0.13
OPu506
Internode 3 + 4	90.12 ± 9.56	901.33 ± 88.99	0.90 ± 0.42
Internode 6 + 7	42.30 ± 5.67	456.11 ± 50.87	1.68 ± 1.28

Internodal discs were incubated in 50 mM [1-¹³C] glucose (99.9% enrichment) and 50 mM unlabeled fructose prior to sugar extractions and determination of label incorporation by NMR spectroscopy. The triose phosphate to hexose phosphate recycling (vT → H) was determined as described by Fernie et al. (2001) taking into account the relative rate of external glucose metabolised to phosphorylated cytosolic glucose (vHK) and the proportion of the cytosolic glucose pool drawn from exogenous labeled glucose (φ) as defined in Malone et al. (2006). Values are presented as mean ± SE of three individual plants per line; bold indicates a value that were determined by the t-test to be significantly different (P < 0.05) from the respective wildtype (WT) internode