Growth and Tropic Responses of Excised Avena Coleoptiles in Culture

Abstract

Excised coleoptiles, 3 mm. and 5 mm. long, were grown aseptically on 1-1.5% agar, agar with sucrose, and agar with sucrose and mineral nutrients; 3-indole acetic acid was supplied in certain exps. 3-mm. coleoptiles did not reach the length attained by 5 mm. coleoptiles. However, the former showed a far greater percentage increase in length than the latter, in spite of the relatively lower hormone content in the tip of the 3-mm. coleoptiles at the time of excision. Addition of sucrose and mineral nutrients had a markedly beneficial effect on growth of coleoptiles in culture. In liquid culture medium, low concs. of sucrose gave better results than high, although high concs. prolonged the growth period somewhat. 3-indole acetic acid added to the culture medium retarded growth in proportion to the cone. used. Decapitated excised coleoptiles capped with agar blocks containing 3-indole acetic acid showed significant length increases over the controls. The capacity of excised coleoptiles to respond to geo- and phototropic stimuli fell to approx. 20% of that of the controls 10-14 hours after excision; hormone conc. in 2 the coleoptile tips fell only to 55-65% of that of the controls. Growth of coleoptiles in agar culture (at 20-22[degree] C, and with suitable nutrition) continued for a period of 8 days or more, although growth hormone could not be detected in the tips of the coleoptiles more than 48 hrs. after excision.