Effects of salicylic acid on sugar and amino acid uptake

Ageing of sugar beet (Beta vulgaris L.) leaf discs induces a large stimulation of sugar and amino acid uptake, This may result from an hormonal imbalance, The effects of various hormones added during the ageing period were studied on sugar and amino acid uptake, Salicylic acid (SA) inhibited both valine and sucrose uptake in a concentration-dependent manner from 10 mu M to 200 mu M. This inhibition was specific for SA: various mono-and di-substituted analogues of benzoic acid did not significantly affect uptake, except for 2,4-dichlorobenzoic acid. SA inhibited the active component of uptake, and the inhibition was reversible upon its removal. SA did not affect the amounts of transcripts encoding the sucrose transporter and the amounts of the sucrose transporter protein, SA decreased medium acidification due to the activity of the 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 affect the uptake of sugars and amino acids by indirect inhibition of the plasma membrane H+-ATPase energizing this process.