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Changes in Mitotic Indices in Roots of Vicia faba L. II. Long-Term Effects of Colchicine and IAA

R. D. MacLeod and D. Davidson
The New Phytologist
Vol. 65, No. 4 (Oct., 1966), pp. 532-546
Published by: Wiley on behalf of the New Phytologist Trust
Stable URL: http://www.jstor.org/stable/2430124
Page Count: 15
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Changes in Mitotic Indices in Roots of Vicia faba L. II. Long-Term Effects of Colchicine and IAA
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Abstract

Roots of Vicia faba were treated with IAA (6.26 x 10-4 M) for 3 hours and fixed immediately or 5, 11 or 23 hours later. Mitotic indices (MI) fell in these treated roots; the decrease was apparent at 5 hours and was significant at 11 and 23 hours, indicating that IAA was inhibiting some interphase processes. Other V. faba roots were treated with colchicine (0.025%) or IAA (4.7 x 10-4 M) or they were given successive treatments with colchicine or IAA and fixed up to 201 hours later. (a) In roots treated with colchicine, the MI rose for the first 24 hours and then fell to values below 1, where it remained for several days. (b) In roots treated with IAA, a fall in MI was observed within the first 2 days but it eventually returned to normal. This recovery of normal levels of mitotic activity was dependent upon the age of the roots at the time of treatment, the youngest roots died after treatment with IAA while older roots recovered completely. (c) Roots treated with IAA 24 hours after treatment with colchicine showed a decrease in MI in the following 24 hours similar to that found in roots treated only with colchicine. However, the MI of these roots subsequently rose to values that were not significantly different from those of the controls, i.e. there is an IAA induced stimulation of mitotic activity. Polyploid cells are found in division following treatment with colchicine. Changes in the frequencies of polyploid metaphases occur if roots are also treated with IAA, suggesting, as we have seen above, that IAA affects the duration of mitotic cycles. These results provide further evidence that a decrease in the endogenous levels of auxins occurs in roots treated with colchicine and this decrease can be partially restored by exogenous auxin. It is suggested that the changes in levels of mitotic activity in treated meristems is due, at least in part, to the colchicine induced fall in endogenous auxins.

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