|Johnson, Jane - UNIVERSITY OF MINNESOTA|
|Allan, Deborah - UNIVERSITY OF MINNESOTA|
|Weiblen, George - UNIVERSITY OF MINNESOTA|
Submitted to: Plant Physiology
Publication Type: Abstract Only
Publication Acceptance Date: June 4, 1995
Publication Date: N/A
Technical Abstract: White lupin, Lupinus albus L. when subjected to phosphate (P) stress develops proteoid or cluster root morphology. These densely clustered, short lateral roots are the site of organic acid excretion and are known to be effective in dissolving mineral P, thus increasing P availability. Phosphorus stress modifies carbon metabolism of proteoid roots to facilitate citrate excretion. Whole plant labelling of shoots or roots wit 14C was used to assess the relative contribution of shoot- and root- derived carbon to excreted citrate. Roots of P-stressed plants exuded about 25 times more acid stable 14C than P-sufficient plants, primarily in citrate and malate. When P-stressed roots were labelled, 64 % of the label was found in the root exudates; however, when P-stressed shoots were labelled only 36% of the label was found in root exudates. The rate of carbon fixation in roots was about 4 fold greater in P-stressed plants as compared to sufficient plants. CO2 fixed by roots contributes about 27 % o the carbon exuded from P-stressed plants. Evidence from the whole plant labelling experiment suggests that citrate exudation by proteoid roots is directly related to non-autotrophic CO2 fixation.