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comparison of transport rates 5000 nmol mgprotem ' min'

75 nmol mgproiem"' min'

greatly different, namely 70 times faster in vacuoles from suspension cells compared to those from internodal storage cells (Tab.l).

According to todays knowledge, sucrose concentration in the storage cells is mainly controled by two factors, the safe compartmentation of sucrose into the vacuoles, and the presence of vacuolar acid invertase (schematically represented in Fig.8). When the transfer of sucrose through the tonoplast is high, as is the case in sugarcane suspension cells, sucrose is subject to degradation by vacuolar and by cytosolic invertases. The concentration will stay low therefore. If, however, the transfer rate of sucrose through the tonoplast is low as in internodal storage cells, sucrose, which succeeded to reach the vacuolar compartment, will stay safe there if acid invertase activity is low. The low transfer rate through the tonoplast may of course increase the probability for cytosolic sucrose to be hydrolysed by cytosolic invertase, but since the cytosol is also the place of sucrose synthesis, a steady level of sucrose will be maintained.

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