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Title: Relationship of acid invertase activities to sugar content in sugarcane internodes during ripening and after harvest

item Lingle, Sarah

Submitted to: Thai Journal of Agricultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2008
Publication Date: 12/31/2008
Citation: Lontom, W., Kosittrakun, M., Lingle, S.E. 2008. Relationship of acid invertase activities to sugar content in sugarcane internodes during ripening and after harvest. Thai Journal of Agricultural Science. 41(3-4):143-151.

Interpretive Summary: Sugar, mostly sucrose, accumulates in sugarcane stalks as the crop develops. In the fall, the concentration of sucrose goes up, a process called ripening. After harvest, sucrose may be lost if the stalks are not immediately processed at the factory. This study was done to determine the role two enzymes, soluble acid invertase, and cell wall acid invertase, play in sucrose accumulation during ripening or loss after harvest. We found that during ripening and during storage after harvest, sucrose content tended to be lower in stalk sections with higher activity of soluble acid invertase. In one of the varieties tested, sucrose content was higher in sections with higher cell wall acid invertase activity during ripening. After harvest, sucrose content in both varieties was higher in sections with higher cell wall acid invertase activity. There was also evidence of continued sucrose synthesis within some of stalk sections after harvest, which offset any loss there may have been. These results suggest that targeting one or both of these enzymes for alteration by selection or genetic engineering may result in a higher sucrose concentration at harvest.

Technical Abstract: 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 postharvest deterioration. The activities of SAI and CWI were determined in selected immature and mature internodes during ripening and during postharvest storage at 18 degree Celsius 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 and CWI was solubilized from cell wall residue. Sucrose, glucose, and fructose were quantified by high pressure ion chromatography with pulsed amperometric detection and 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. During ripening, SAI activity was negatively correlated with sucrose content in HoCP 96-540 (r = -0.449**) and L 97-128 (-0.503**), and with the sucrose: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:total sugar ratio (r = -0.507** and -0.439**) during storage in HoCP 96-540 and L 97-128, respectively. 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.