Chemical control of organ formation in root segments of Convolvulus cultured in vitro.

Plant parts x-ith a plasticity of n'orphogenetic respon se have l)rovi(le(l useful experimental material for stud( of the hol-rmionial control of organl formiiation. Of particular value are cases in which alternate org,an-formin-g l)otentials ca.n be attributed to the samiie cell or group) of cells. In the formationl of endogenous buds and(l lateral roots fromi Coiilzvolvds rz',ensizs roots, hoth types of organs originate fromii a smciall numiber of lericycle cells at sites opposite the protoxylem p)oles. Several y-ears acgo, Torrev ( 14) reported that a clone of roots of this species had been established from the ra(licle of a seedling germlinate(d in 1952. makiing l)ossil)le controlled inivestigations of the physiology of organi formation in conltinluous root cultures. The majority of physiological studies of bud an( root formationi in roots (leals with thickenedl root cuttings. Organ formationl in these cases is generally observed either in regionis surrouindinig old lateral root traces or fromii callus tisstue develop)ing at ctit ssurfaces. In either situtation organ formiiationl fromii root cuttinigs was found to be polar, with bud formaltion at the l)roximial4 end( ancl root formatioll or callus growtlh at the (listal end. Plant (9). workiiig With root cuttings of Crambe, \Varmike anld \VNarniike (17 ), with Tar-ax(aciwiii anid C(ichoriu,o cuttings. Emery (4), with Chamnacnci-ion cuttings, anid Lindnier (7), with Cochlcaria ctuttings, found(I that auxiii al)plication to the proximal end of the root cuttilngs resulted in inhibition of bud formiiation,l promotion of root formationi, aln(d sup)pression of the l)olaritv of organ formation. It was suggested that the polarity of organ formiiation intulltreate(l cuttinigs resultedI from (lifferelices in atixini conicenitrationi at the end(Is of the cuttinlgs. Lower auixini concenitrationls at the proximal end prlomoted bud formiationl anid hlighier conIcenitrationis at the distal end(l )romote(l root formationi. L owerinpg the auxinl level at the (listal ell(n should( then resuilt in 1)11(u formation at both ell(ls. Stouighltonl aiid(