Both turgor pressure and differences in membrane tension are capable of pro
viding an energy input into exocytosis, the process of fusion of Golgi vesi
cles with the cell membrane in plants. If is shown that the contribution of
turgor pressure is much larger than that of membrane tension, so that the
exocytotic process is not likely on thermodynamic grounds to be reversible
unless another source of energy is made available. However, recycling of me
mbrane material as flattened, empty vesicles is energetically possible and
is likely to be favoured when the magnitude of membrane tension in the cell
membrane is low. Thus the outward flows of membrane and cell wall material
are in principle linked to turgor, whereas membrane tension influences the
inward flow of membrane material.