Citrate transport into barley mesophyll vacuoles — comparison with malate-uptake activity

✍ Scribed by Doris Rentsch; Enrico Martinoia

• Book ID: 104659880
• Publisher: Springer-Verlag
• Year: 1991
• Tongue: English
• Weight: 624 KB
• Volume: 184
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00197903

✦ Synopsis

Citrate uptake into barley (Hordeum vulgare L.) mesophyll vacuoles was found to be saturable with a Km of about 200 p.M. Uptake appears to occur via the citrate 3-form, as indicated by concentration-dependent uptake studies at different pHs. Free citrate and not the Mg-citrate complex was taken up by the vacuoles, even though slow transport of the Mg complex could not be excluded. Citrate transport into vacuoles was competitively inhibited by malate (Ki=0.68 mM). Various organic acids and protein-modifying agents affected the uptake of malate and citrate to a similar extent. These results indicate that both organic acids cross the tonoplast by means of the same carrier. Accumulation of citrate was ATP-dependent and could be inhibited by ionophores. Bovine serum albumin strongly stimulated citrate uptake, but other proteins tested did not show a similar stimulatory effect.