Ku. Tennakoon et Js. Pate, EFFECTS OF PARASITISM BY A MISTLETOE ON THE STRUCTURE AND FUNCTIONINGOF BRANCHES OF ITS HOST, Plant, cell and environment, 19(5), 1996, pp. 517-528
Infestation of Acacia acuminata by the xylem-tapping mistletoe Amyema
preissii invariably results in inhibition of growth, defoliation and e
ventual death of host branch parts distal to the mistletoe, Branch sec
tional areas proximal (P) and distal (D) to mistletoes are used to cla
ssify stages of parasitism, with P:D area ratios of 5-6 invariably ass
ociated with distal branch senescence, As monopolization of the branch
proceeds, mistletoe leaf area increases in parallel with declining ho
st foliage area, and the specific hydraulic conductivity of distal hos
t wood declines sharply relative to that of proximal wood, Mineral com
position and concentrations of nitrogenous solutes in xylem sap are at
no stage appreciably different from those of proximal mood, After the
demise of the distal branch parts, the transectional area of the host
branch stump increases linearly with increasing mistletoe leaf area,
the branch area supporting a unit of mistletoe leaf area always being
about 3 times greater than that supporting a unit of host foliage area
on unparasitized branches, This differential, compounded with high tr
anspiration rates and selective uptake of host xylem solutes by the ha
ustorium, fosters substantial mineral enrichment of the mistletoe rela
tive to its host, The study provides a background for future investiga
tion of possible cellular mechanisms continuously driving structural a
nd functional changes in favour of the mistletoe.