PHLOEM TRANSPORT AND CONJUGATION OF FOLIAR-APPLIED 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID IN COTTON (GOSSYPIUM-HIRSUTUM L)

The transport and metabolism of foliar-applied [2,3-C-14]1-aminocyclop ropane-1-carboxylic acid ([C-14]ACC) was investigated in 21-27 d old c otton plants (Gossypium hirsutum L.). The rapidity of export and patte rns of distribution of label in the shoot were consistent with translo cation in the phloem. When [C-14]ACC was applied to leaves at differen t positions on the plant, patterns of distribution of label correspond ed to those expected for the transport of photoassimilates from the sa me leaves. Label was consistently found in phloem exudates collected i n 20 mmol . dm(-3) EDTA from the cut petioles of leaves to which [C-14 ]ACC had been applied. [C-14]ACC was rapidly metabolised by leaves to a single labelled compound which was indistinguishable from N-malonyl- ACC (MACC) on the basis of its chromatographic mobility and acid hydro lysis to [C-14]ACC. MACC rapidly became the predominant radiolabelled compound in all organs to which transport occurred, but several lines of evidence indicated that MACC itself was not transported: (i) only [ C-14]ACC itself was found in EDTA exudates from labelled cotyledons; ( ii) export of label from attached leaves ceased when all the [C-14]ACC had been converted to the conjugate; and () no export of label occurr ed when purified [C-14]MACC was applied to leaves. It is concluded tha t whilst ACC is readily loaded into and transported by the phloem of c otton plants, its malonyl conjugate is not transported by this route.