Changes induced in mitotic indices of roots of vicia faba L. by colchicine and IAA

Abstract

The effects of colchicine and IAA on roots of Vicia faba L. have been examined; changes were found mitotic index, polarity and differentiation. The following conclusions were reached: 1) IAA suppresses or delays some process(es) in the G2. S and probably also the G1 stages of interphase. IAA has no effect on mitosis, but because of its effects on interphase, causes a decrease in the MI. IAA does not appear to be a factor involved in spindle formation, and the time at which spindles reappear after colchicine treatment is not influenced by IAA. Colchicine blocks the anaphase separation of the chromatids. This is not due to a change in pH and it does not involve IAA. Because colchicine blocks the anaphase separation of the chromatids, restitution takes place and polyploid cells are seen in division one mitotic cycle later. The duration of metaphase is apparently increased after colchicine treatment. A result of colchicine induced metaphase delay is that the relative duration of metaphase is lengthened and a change occurs in the prophase: metaphase ratio in favour of metaphases, compared with the control values. This change in the prophase: metaphase ratio is reversed by IAA, many hours after treatment, to produce prophase: metaphase ratios similar to those of the control roots. IAA has this effect for at least two reasons; the relative duration of metaphase is shortened from the value found after treatment with colchicine, to a value similar to that of the controls and, the percentage of polyploid metaphases found after colchicine treatment is lowered by treatments with both IAA and colchicine. 4) Following colchicine treatment, changes occur in the MI; there is a significant increase 24 hours after treatment but after a further threa days the MI is less than 1. 5) Polarity of root growth is initially determined by the plane of cell division. In more basal regions of the root, it is determined by both the plane of cell division and that of cell expansion. Finally, it is determined by the plane of cell expansion along. 6) IAA induces lateral root primordia formation, but these fail to develop normally, however, unlike the primordia that appear in the apical 10 mm of roots treated with colchicine and which 'gram out as lateral roots. 7) The polarity of cell division is re-established in colchicine treated roots as soon as normal mitosis reappears. Thus, one aspect of root polarity returns to normal several days before cell elongation recommences. IAA does not affect the polarity of cell elongation or division in the concentration used. 8) The cessation of root growth after colchicine treatment is not due to the cessation of cell division, but to the altered polarity of cell division. 9) Differentiation of xylem vessel elements occurs closer to the apex in colchicine treated roots than in the controls. IAA does not prevent this differentiation. In roots treated only with IAA xylem elements are seen closer to the apex compared with the control roots. 10) All of the primordia that develop after colchicine or colchicine and IAA treatments do so, at least partly, from cells affected by the colchicine. This is also true of the new meristem which forms, after these treatments, in the root apex. The new apical meristem forms partly from the cells of the meristem which was present at the time of treatment and partly from the cells of the quiescent centre. 11) IAA does not induce polyploidy, nor does it induce polyploid cells present at the time of treatment to divide. 12) The response of roots to IAA treatment, with respect to MI, depends on the age of the root at the time of treatment.