A role of auxin in phloem regeneration in Coleus internodes

Abstract

The physiology of regenerative phloem formation in the number 5 internode of Coleus blumei Benth. was studied by estimating quantitatively its extent in plants or plant parts wounded so as to sever one or more of the existing phloem bundles and then allowed to regenerate for a short period (usually 5 days). Removal of all leaves and buds from plants resulted in a marked reduction (to approximately one-quarter of the value of the intact controls) in phloem regeneration. Primary leaf removal also resulted in some, though a smaller, reduction, as did the one other treatment—removal of all distal organs—which involved removal of young primary leaves. The other patterns of shoot organ removal tried—all buds removed and all proximal leaves and buds removed—had no effect on phloem regeneration. Indoleacetic acid (IAA) applied in aqueous solution (2 mg/l) to plants from which all leaves and buds had been removed completely substituted for them in phloem regeneration. Applied in lanolin paste (0.1% and 1%), it evoked more phloem regeneration than attached organs themselves. Sucrose (2%) applied alone or together with IAA in aqueous solution had no effect. IAA (0.1%) applied in lanolin to excised internodes increased phloem regeneration in these, but the anomalous appearance of some of the wound sieve tubes indicated that sugar or other material may have become limiting for full differentiation. A relationship between the number of phloem bundles cut in wounding and the extent of phloem regeneration was shown. This and other observations were interpreted as indicating the involvement in phloem regeneration of a substance or substances leaking from the cut phloem. Existing evidence is interpreted to mean that auxin is limiting for the cell divisions which immediately precede phloem differentiation and that some other factor, presently unknown, may be limiting for differentiation when auxin is in sufficient supply for cell division. However, present evidence neither implies nor excludes the possible participation of auxin in differentiation itself.