Polyclonal antibodies were raised against either whole plasma membrane of sugar beet (Beta vulgaris L.) leaves or against the 42 kDa region polypeptides of the plasma membrane. The effect of these antibodies on the uptake of sucrose, 3-O-methyl glucose and α-aminoisobutyric acid by broad bean (Vicia faba L.) leaf protoplasts was tested. The anti-plasma membrane serum did not affect the uptake of these solutes, while the anti-42 kDa serum markedly and selectively inhibited the uptake of sucrose without effect on the absorption of hexoses or of amino acids. Sucrose is very poorly metabolized before or after its penetration into the cells, and the inhibition of uptake cannot be explained in terms of side-effects on invertase or glucan synthase activities. The data provide functional evidence confirming the previous hypothesis (Gallet, O., Lemoine, R., Larsson, C. and Delrot, S. (1989) Biochim. Biophys. Acta 978, 56-64) that the 42 kDa polypeptide is a component of the sucrose uptake system of plant plasma membrane. The immunoglobulins purified from the serum were unable to inhibit sucrose uptake, suggesting that the activity of the antibody subclass responsible for inhibition was lost during purification or that an additional component of the serum is necessary to observe this inhibition. © 1989.
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