An improved method for the measurement of cell wall invertase activity in sugarcane tissue

Extraction and assay methods were developed for the determination of both soluble and cell wall invertase activity in sugarcane (Saccharum sp.) from minimal (0.5 g) tissue. Cell wall invertase (CWI) was measured using a pellet mix procedure and the pH optima ranged between pH 3.2 and 3.6. The pH optima for the soluble invertases were 4.5 and 7.3 for soluble acid (SAI) and neutral (NI) invertase, respectively. At low pH, acid hydrolysis of sucrose was observed and its spurious effect on measured enzyme activity was removed by the inclusion of additional controls run in parallel, which lacked crude plant extract. Invertase activity was examined in sugarcane tissues of varying ages. In leaves and stem, the SAI activity was greatly reduced in mature tissue extracts. Similarly, the CWI activity was reduced in older leaves. In contrast, a less marked drop in NI activity was observed in extracts from old leaves and activity from stem extracts remained constant irrespective of tissue age. The role of SAI has been linked to growth and differentiation and these observations suggest that CWI may also be intrinsically involved in these processes. NI appears to have a housekeeping role in maintaining hexose concentrations within the cytosol.