Wednesday, November 15, 2006

The Activities of Acid Invertases in HoCP 96-540 and L 97-128 Sugarcane During Ripening and After Harvest.

Watanachai Lontom1, Manit Kosittrakun1, and Sarah Lingle2. (1) Applied Taxonomic Research Center, Department of Biology, Faculty of Science, Khon Kaen University, Khon Kaen, 40002, Thailand, (2) USDA-ARS, 1100 Robert E. Lee Blvd, New Orleans, LA 70124

It has been hypothesized that soluble acid invertase (SAI) and insoluble (cell wall) acid invertase (CWI) influence sucrose accumulation in sugarcane (Saccharum spp. hybrids) during ripening, and also sucrose breakdown after harvest. We determined the activities of SAI and CWI in selected immature and mature internodes during ripening and during storage at 18ºC after harvest in two Louisiana sugarcane cultivars, HoCP 96-540 and L 97-128 grown in Louisiana, USA in 2004. The soluble invertases 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, 5 mM DTT). Cell wall invertase was extracted from cell wall residue in the same buffer with the addition of 1 M NaCl. Sucrose, glucose and fructose were determined by high pressure ion chromatography with pulsed amperometric detection. Total sugar 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, and decreased with internode age. CWI increased with internode age. Sucrose content during ripening was negatively correlated with SAI activity in both cultivars (r=-0.449** and -0.503** in HoCP96-540 and L97-128, 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 storage time 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.