EFFECTS OF SALICYLIC-ACID ON SUGAR AND AMINO-ACID-UPTAKE

Ageing of sugar beet (Beta vulgaris L.) leaf discs induces a large sti mulation of sugar and amino acid uptake, This may result from an hormo nal imbalance, The effects of various hormones added during the ageing period were studied on sugar and amino acid uptake, Salicylic acid (S A) inhibited both valine and sucrose uptake in a concentration-depende nt manner from 10 mu M to 200 mu M. This inhibition was specific for S A: various mono-and di-substituted analogues of benzoic acid did not s ignificantly affect uptake, except for 2,4-dichlorobenzoic acid. SA in hibited the active component of uptake, and the inhibition was reversi ble upon its removal. SA did not affect the amounts of transcripts enc oding the sucrose transporter and the amounts of the sucrose transport er protein, SA decreased medium acidification due to the activity of t he plasma membrane H+-ATPase, without affecting the amounts of ATPase transcripts and ATPase protein, SA significantly decreased the energy charge of the tissues during ageing. It is suggested that SA may affec t the uptake of sugars and amino acids by indirect inhibition of the p lasma membrane H+-ATPase energizing this process.