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 s oluble and cell wall invertase activity in sugarcane (Saccharum sp.) from m inimal (0.5 g) tissue. Cell wall invertase (CWI) was measured using a pelle t mix procedure and the pH optima ranged between pH 3.2 and 3.6. The pH opt ima 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 remov ed by the inclusion of additional controls run in parallel, which lacked cr ude plant extract. Invertase activity was examined in sugarcane tissues of varying ages. In leaves and stem, the SAI activity was greatly reduced in m ature tissue extracts. Similarly, the CWI activity was reduced in older lea ves. In contrast, a less marked drop in NI activity was observed in extract s from old leaves and activity from stem extracts remained constant irrespe ctive of tissue age. The role of SAI has been linked to growth and differen tiation and these observations suggest that CWI may also be intrinsically i nvolved in these processes. NI appears to have a housekeeping role in maint aining hexose concentrations within the cytosol.