Ws. Jia et al., METABOLISM OF XYLEM-DELIVERED ABA IN RELATION TO ABA FLUX AND CONCENTRATION IN LEAVES OF MAIZE AND COMMELINA-COMMUNIS, Journal of Experimental Botany, 47(301), 1996, pp. 1085-1091
When detached maize leaves were fed with an ABA solution via the xylem
, the relationship between the relative stomatal inhibition and ABA co
ncentrations was similar under different humidity conditions, but the
relationship between such inhibition and ABA flux was different accord
ing to changes of humidity. To understand whether such stomatal behavi
our was related to the way through which xylem-delivered ABA was metab
olized, detached leaves of maize and Commelina were fed with tritium-l
abelled (H-3)-ABA at concentrations similar to that found in xylem of
droughted plants and it was found that xylem-delivered ABA was metabol
ized rapidly in both species, The half-life of ABA metabolism, calcula
ted from the time-related ABA disappearance curve, was 42 and 64 min f
or maize and Commelina, respectively. The very short half-life suggest
s that there is a large capacity in leaves to metabolize xylem-deliver
ed ABA and that metabolism is a major factor in the control of ABA acc
umulation in leaves, When ABA was fed at different fluxes, either thro
ugh changing the feeding concentrations or through manipulating the ra
tes of leaf transpiration (i.e. the volume flux), ABA was metabolized
at rates that were proportional to the amount that was delivered, The
absolute rate of ABA metabolism was, therefore, linearly related to th
e amount of ABA that had arrived. It was found that xylem-delivered AB
A reached the epidermis of Commelina, and was metabolized at the same
pattern as that in mesophyll tissues, i.e. at a similar half-life and
at rates constantly related to the amount that was delivered, The role
of the rapid ABA metabolism was discussed in the context of stomatal
control by either concentration or flux of xylem-carried ABA.