Citrate exudation and proton release by phosphorus-deficient Lupinus albus as affected by fusicoccin and vanadate

摘要

White lupin (Lupinus albus L. cv. Kiev) plants were grown in nutrient solution at 0, 1, 25, 250 μM P for 36 d to examine carboxylate exudation and H~+ release from roots in response to fusicoccin and vanadate application and to assess relationship between carboxylate exudation and H~+ release. Root exudates were collected in the nutrient solution containing K, Ca, Mg, B, and vanadate or fusicoccin. The results showed that lupin crops tended to develop cluster root regardless of P supply before 12 days after treatment (DAT), but cluster root formation was significantly inhibited by high P supply with time. The application of 1 μM P induced more cluster roots compared with the 0 μM P treatment after 21 DAT. In contrast, cluster root formation was significantly inhibited by P supply of 25 or 250 μM P. The low-P supply induced higher citrate exudation and proton release. Acidification was also evident at 25 and 250 μM P though citrate exudation was not detected. Proton release mainly occurred in active normal or cluster roots, indicating higher spatial heterogeneity within root system. Proton release decreased with increased application of vanadate, and was significantly inhibited at over 100 μM vanadate. Citrate exudation showed a similar pattern to vanadate, but an increased exudation was observed at 500 μM vanadate. Localised supply of 100 μM vanadate to single cluster root inhibited proton release, but there was still a higher citrate exudation. Fusicoccin enhanced significantly the proton release and citrate exudation in comparison to control. The results suggest that non-synchronous processes may be involved in the release of proton and exudation of citrate under P deficiency, but citrate exudation is highly associated with activity of ATPase. Proton release is mainly caused by excess cation uptake by the roots of plants.