Uptake of mannitol from the media by in vitro grown plants

Higher plants grown in vitro are very seldom fully autotrophic. Therefore, such cultures are usually supplied with exogenous sugars. However, at higher sugar concentration a decrease in dry matter accumulation is observed which can be explained by a decrease in osmotic potential of the medium. To test this explanation a series of experiments with mannitol, a sugar alcohol often used for simulation of osmotic stress, were performed with excised wheat embryos, rape seedlings and potato stem segments grown in vitro. As the presence of mannitol in the medium caused a significant decrease in dry matter accumulation, the content of mannitol in the shoot tissues was determined using HPLC analysis to estimate the uptake and transport of mannitol from roots to shoots. Mannitol contents up to 30% of dry weight in wheat and 20% in rape and potato shoots were found, indicating that mannitol is easily taken up by in vitro plants and transported to shoots. There were no large changes in the content of glucose, fructose and sucrose caused by the presence of mannitol in the tissues. These data show that mannitol can not be used as an inert osmoticum in in vitro studies.