CUTTING, AGING AND EXPRESSION OF PLANT MEMBRANE TRANSPORTERS

The activity and the expression of sucrose, hexose and amino acid tran sporters were studied with fresh, cut or aged tissues and plasma membr ane vesicles (PMV) of mature sugar beet (Beta vulgaris L.) leaves. Cut ting and ageing both induced an increase of the transcripts coding for sucrose transporters and hexose transporters. No significant effect c ould be detected on the amino acid transporter transcripts with the pr obe used (aap1). A polyclonal serum directed against the Arabidopsis t haliana sucrose transporter (AtSUC1) reacted with a 42 kDa band of the sugar beet PMV, confirming previous biochemical identification of thi s band as a sucrose transporter. ELISA assays run with microsomal frac tions and PMV using the AtSUC1 sucrose transporter probe indicated tha t ageing, and to a lesser extent cutting, increased the amount of sucr ose transporter present in the plasma membrane. However, while cutting strongly stimulated proton-motive force driven uptake of sucrose in P MV, ageing only resulted in a slight stimulation. These data give evid ence for transcriptional, post transcriptional and post-translational controls of the activity of the sucrose transporter by mechanical trea tments. Proton-motive force driven uptake of 3-O-methylglucose and val ine in PMV was strongly stimulated in PMV from aged tissues, although previous data had shown that cutting did not affect theses processes. Therefore, the plant cells possess various levels of control mechanism s that allow them to regulate fluxes of the main assimilates across th e plasma membrane when their natural environment is directly or indire ctly altered. (C) 1997 Elsevier Science B.V.