The Localization in Cultured Carrot Cells of Factors that Induce their Growth

Abstract

Various previously recognized parts of the complex of growth factors present in the liquid endosperm of the coconut or in immature fruits of Aesculus woerlitzensis were generally tritiated. The labeled growth factors were applied singly to culture media which contained balanced requirements that had caused carrot explants to proliferate and grow in accordance with combinations of growth factors supplied. By the usc of electron microscopy and autoradiography, the radioactivity from each source was detected in the cells and its density and distribution, in the form of developed grains over different cellular compartments and organelles, was determined. The tabulated data relate to four labeled sources as observed over seven cellular compartments under six experimental treatments. Electron micrographs also show how the radioactivity from the various sources related to organization of the cells. The distribution of radioactivity within the cells varied with the source. Both 3H-myo-inositol and the tritiated growth factors from Aesculus (3H-AF1Aesc) with which it interacts (as in so-called Growth Promoting System I) contributed radioactivity, preferentially, to cell walls and sites of their formation in culturcd carrot cells. Both 3H-IAA and 3H-zatin (as in so-called Growth Promoting System II) contributed their radioactivity preferentially to the nucleoli of the cultured cells. Some other conspicuous distributions of radioactivity (e.g. from 3H-AF1Aesc to plastids and from 3H-IAA to the interstitial substance, i.e. middle lamella, where enlarging cells separate) involved these tritiated moieties without regard to their counterparts in Growth Promoting Systems I and II, respectively. The problems raised by such multiple effects due to different growth factors acting singly and in combinations at different cell sites are both recognized and discussed.