Studies of Hormone-directed Transport in Decapitated Stolons of Saxifraga Sarmentosa

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Auxin-directed transport of 14C-assimilates from subtending leaves has been studied in decapitated stolons of Saxifraga sarmentosa , treated at the distal end with dilute solutions (5 x 10~5 m) of indol-3-ylacetic acid (IAA). Mature, non-growing stolons are completely unresponsive but, in young growing stolons, IAA treatment augments accumulation of 14C in the distal 6 cm by nearly four times. Gibberellic acid (10~4 m) and kinetin (2 x 10~4 m) have similar but much smaller effects, but they do not synergize IAA action. The auxin-transport inhibitors N-l-naphthylphthalamic acid (NPA) and 2-chloro-3-hydroxyfluorene9-carboxylic acid (Morphactin) applied alone to the distal decapitated end, also augment 14C accumulation but when applied to IAA-treated stolons, either with IAA or on an intermediate, more proximal zone, have no marked effect on IAA-directed transport. On the other hand, 2,3,5-tri-iodobenzoic acid (TIBA) in similar experiments, induced no accumulation by itself, completely inhibited IAA action when applied with it but slightly promoted IAA-induced accumulation when applied in an intermediate more proximal ring. In the latter case it inhibited 14C movement from stele to cortex in that ring and when applied distally with IAA greatly inhibited the incorporation of translocated 14C into ethanol-insoluble material at the distal end. The protein-synthesis inhibitors puromycin (2 x 10~4 m) and cycloheximide (10 mg l1) and the RNAtranscription inhibitor actinomycin-D (15 mg l1) all inhibited completely the IAA-directed transport when applied with IAA at the distal end; they were virtually without effect when applied on an intermediate, more proximal region of the stolon. Dilute sucrose solutions (2 x 103 m) applied with IAA eliminated the IAA-directed transport, but strong solutions of mannitol (0-3 m) reduced but did not eliminate it. From these results and those previously published on the transport of 3H-IAA under comparable conditions, it was concluded that IAA-directed transport of 14C assimilates in Saxifraga sarmentosa stolon is due entirely to a metabolite sink, induced locally by IAA treatment. It is suggested that this sink is partly created by the induced extension growth or processes associated with it, and partly by an augmented sequestration of 14C translocates in the treated tissue.