Relationship of Acid Invertase Activities to Sugar Content in Sugarcane Internodes during Ripening and after Harvest
2008
Lontom, W. | Kosittrakun, M. | Lingle, S.E.
It has been hypothesized that soluble acid invertase (SAI) and insoluble (cell wall) acid invertase (CWI) influence sucrose accumulation in sugarcane during ripening, and also sucrose breakdown after harvest. The activities of SAI and CWI were determined in selected immature and mature internodes during ripening and during postharvest storage at 18°C in two Louisiana sugarcane cultivars, HoCP 96-540 and L 97-128 grown in Louisiana, USA in 2004. SAI and sugars were extracted from each internode in extraction buffer (100 mM Na-Hepes (pH 7.5), 5 mM Na-EDTA, 10 mM MgCl2, 0.05% Triton X-100 and 5 mM DTT). CWI was solubilized from cell wall residue in the same buffer with the addition of 1 M NaCl. Sucrose, glucose and fructose were quantified by high pressure ion chromatography with pulsed amperometric detection. Total sugar content was calculated as the sum of the molar concentrations of sucrose, glucose and fructose. During ripening, the activity of SAI was highest in the youngest internode. It decreased with internode age. In contrast, the activity of CWI increased as the internode became older. Sucrose content during ripening was negatively correlated with SAI activity in both cultivars (r = -0.449** and -0.503** in HoCP 96-540 and L 97-128, respectively) as was the sucrose-to-total sugar ratio (r = -0.548** and -0.581**). After harvest, the activity of SAI in the immature internode increased with time in storage whereas that of CWI decreased in both immature and mature internodes. There was also a negative correlation between SAI activity and sucrose content (r = -0.426** and -0.493**) and the sucrose-to-total sugar ratio (r = -0.507** and -0.439**) during storage. The data from this study support the hypothesis that acid invertases play key roles in determining sucrose concentration during ripening and after harvest in sugarcane internodes.
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