Limited Growth and Abnormalities in Excised Corn Root Tips

Abstract

The growth of excised corn (Zea mays) root tips under sterile conditions in a mineral nutrient solution containing Ca nitrate, MgSO4, K dihydrogen phosphate, FeCl3 and dextrose is limited. Many of the roots become abnormal. The substitution of levulose, cane sugar, xylose or maltose for dextrose was of no benefit; in fact the growth with xylose and maltose was very poor. The amount of growth varied somewhat with the brand of dextrose used, even when the dextrose was of high purity. Reducing the acidity of the solution, increasing its salt concn., substituting ferric tartrate or ferric citrate for FeCl3, the addition of quantitative (ashless) filter paper, absorbent cotton, CuSO4, thallium nitrate, gluta-thione or vitamin B to the medium were not found beneficial. Pfeffer''s solution, Uspenski''s solution and the solution used by White for the cultivation of excised tomato roots were no more effective than the soln. used by the writers. Growth was improved by addition of Difco agar, water extracts of agar, qualitative filter paper, water extracts of qualitative filter paper, soluble starch, autolyzed yeast, dried brewer''s yeast or a mixture of salts of Mn, B, and Zn. The best results were secured by addition of qualitative filter paper to the medium. Exposure of excised root tips originally 1 cm. long for 24 or 48 hrs. on the surface of moist qualitative filter paper or on the surface of a semi-solid agar medium was almost as beneficial on the later growth of the root tips as the addition of the filter paper or agar to the medium. Increased aeration of the root tips in the liquid medium increased the growth and delayed the development of abnormalities but the results were not as favorable as those secured by the addition of agar or filter paper to the medium. The maximum growth of individual excised corn root tips originally 1 mm. long was 612 cm. (0.9 cm. per 24 hrs.); of root tips 2 mm. long, 85.0 cm. (1.4 cm. per 24 hrs.) ; of root tips 10 mm. long, 98.2 (2.4 cm. per 24 hrs.).