Ku. Tennakoon et Js. Pate, XYLEM FLUXES OF FIXED N THROUGH NODULES OF THE LEGUME ACACIA-LITTOREAAND HAUSTORIA OF AN ASSOCIATED N-DEPENDENT ROOT HEMIPARASITE OLAX-PHYLLANTHI, Journal of Experimental Botany, 48(310), 1997, pp. 1061-1069
Nodulated 1-1.5-year-old plants of Acacia littorea grown in minus nitr
ogen culture were each partnered with a single seedling of the root he
miparasite Olax phyllanthi. Partitioning of fixed N between plant orga
ns of the host and parasite was studied for the period 4-8 months afte
r introducing the parasite. N fluxes through nodules of Acacia and xyl
em-tapping haustoria of Olax were compared using measured xylem flows
of fixed N and anatomical information for the two organs. N-2 fixation
during the study interval (635 mu g N g FW nodules(-1) d(-1)) corresp
onded to a xylem loading flux of 0.20 mu g N mm(-2) d(-1) across the s
ecretory membranes of the pericycle parenchyma of the nodule vascular
strands. A much higher flux of N (4891 mu g mm(2) d(-1)) exited throug
h xylem at the junction of nodule and root. The corresponding flux of
N from host xylem across absorptive membranes of the endophyte parench
yma of Olax haustorium was 1.15 mu g N mm(-2) d(-1), six times the loa
ding flux in nodules. The exit flux from haustorium to parasite rootle
t was 20.0 mu g N mm(-2) d(-1), 200-fold less than that passing throug
h xylem elements of the nodule. Fluxes of individual amino compounds i
n xylem of nodule and haustorium were assessed on a molar and N basis.
N flux values are related to data for transpiration and partitioning
of C and N of the association recorded in a companion paper.