Compartmentation of solutes and water in developing sugarcane stalk tissue

Previous studies have suggested that the apoplast solution of sugarcane stalk tissue contains high concentrations of sucrose, but the accuracy of these reports has been questioned because sucrose leakage from damaged cells may have influenced the results. In this study, the solute potential of the apoplast and symplast of the second (immature), tenth, twentieth, thirtieth, and fortieth internodes of field-grown sugarcane (Saccharum spp. hybrid) stalk tissue was determined by two independent methods. Solute potential of the apoplast was measured either directly by osmometry from solution collected by centrifugation, or inferred from the initial water potential of fully hydrated tissue determined by thermocouple psychrometry before the tissue was progressively dehydrated for generation of water potential isotherms. Both methods produced nearly identical values ranging from −0.6 to −1.8 megapascals for immature and mature tissue, respectively. The solute potential of the symplast determined by either method ranged from −1.0 to approximately −2.2 megapascals for immature and mature internodes, respectively. Solute quantitation by HPLC agreed with concentrations inferred from osmometry. Washing thirtieth internode tissue in deionized water increased pressure potential from 0.29 to 1.96 megapascals. The apoplast of mature sugarcane stalk tissue is a significant storage compartment for sucrose containing as much as 25% of the total tissue water volume and as much as 21% of the stored sucrose.