Effects of salicylic acid on sugar and amino acid uptake

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of organic compounds such as hexoses, sucrose and amino acids (Sakr et al., 1993). Uptake rates of these nutrients Ageing of sugar beet (Beta vulgaris L.) leaf discs depends on the activity of their respective H+-cotransinduces a large stimulation of sugar and amino acid porters and on the plasmalemma ATPase which energizes uptake. This may result from an hormonal imbalance. this transport. Stimulation of sucrose uptake by ageing The effects of various hormones added during the results from an increased activity of the plasma membrane ageing period were studied on sugar and amino acid H+-ATPase energizing the sucrose transporter, whereas uptake. Salicylic acid (SA) inhibited both valine and stimulation of hexose and valine uptake involves both an sucrose uptake in a concentration-dependent manner increased activity of the ATPase and of the corresponding from 10 mM to 200 mM. This inhibition was specific for hexose and amino acid transporter (Noubhani et al., SA: various mono- and di-substituted analogues of 1996; Sakr et al., 1997). benzoic acid did not significantly affect uptake, except The eVects induced by ageing may result from excision for 2,4-dichlorobenzoic acid. SA inhibited the active of leaf tissues, removal of the lower epidermis and cutting component of uptake, and the inhibition was reversible of discs which provokes wounding responses in the tissues upon its removal. SA did not affect the amounts of and may aVect the hormonal balance. Volatile methyl transcripts encoding the sucrose transporter and the jasmonate can be released from plant tissues, especially amounts of the sucrose transporter protein. SA if wounded (Albrecht et al., 1993); the levels of aminodecreased medium acidification due to the activity of 1-cyclopropane carboxylic acid synthase transcripts level the plasma membrane H+-ATPase, without affecting increase largely between 1 h and 4 h after wounding in the amounts of ATPase transcripts and ATPase protein. sliced tomato fruit (Li et al., 1992), and it is well known SA significantly decreased the energy charge of the that auxins and cytokinins are involved in the formation tissues during ageing. It is suggested that SA may of wound-induced callus. Therefore, the increase of nutriaffect the uptake of sugars and amino acids by indirect ent uptake which develops with ageing may be aVected inhibition of the plasma membrane H+-ATPase ener- by hormones. This hypothesis was tested in sugar beet gizing this process. leaf discs using several phytohormones or hormone-like substances.