Sugar uptake and storage by sugarcane suspension cells at different temperatures and high sugar concentrations

Experiments with sugarcane cell suspensions were performed for two purposes : (a) To reveal the temperature dependence of sugar transport systems for i nterpretation of sugarcane growth at suboptimal temperatures; and (b) to te st whether different temperatures or high sugar concentrations elevate the intracellular sucrose level by shifting the sucrose cycle of synthesis and degradation. It was found that the hexose uptake systems (for glucose and fructose) of s uspension cells were strongly inhibited at low temperature (e.g. 15 degrees ), whereas high temperatures were much less harmful. The optimum temperatur e was 45 degrees. Hexose uptake was modulated by temperature and by develop ment during the batch culture growth period. Neither the presence of high c oncentrations of hexoses, sucrose or osmoticum (mannitol) nor the growth at low or high temperature did increase the intracellular sucrose concentrati on. The best effect was obtained at high sucrose concentration in the mediu m, when the cells were grown in chemostat culture, but still no sucrose acc umulation relative to the concentration in the medium occurred. Analysis of enzymes involved in sucrose metabolism showed that the correlation between internal sucrose and sucrose phosphate synthase minus acid invertase, a co rrelation that had been observed in sugarcane plants, did not exist in suga rcane suspension cells. Also, neutral invertase activity did not give any c orrelation to sucrose. it is speculated that the low sucrose level in suspe nsion cells and the absence of correlation to acid invertase is basically d ue to the low degree of vacuolization and the substantially faster sucrose transport at the tonoplast of suspension cells compared with internodal sto rage parenchyma cells.