Planta (Berl.) 71,257--267 (1966)

S T U D I E S ON I N D U C E D C H A N G E S I N G R O W T H P A T T E R N S AND P O L A R I T Y I N R O O T S OF

V I C I A F A B A L. t~. D. MAcL~oD * Botanisches Institut der Universit~t Tfibingen Received August 8, 1966

Summary. Roots of Vicia ]aba were treated with colchicine (0.025 %), or IAA (4.7 • 10--6M), or both, for 3 hours and fixed at various intervals over the following l l days. The axis of spindle orientation and the distribution of mitotic figures, lateral root primordia and xylem vessel elements was examined in the apical 10 mm of median longitudinal sections of these roots. No effect of IAA was found on the orientation of the spindle. However, evidence was obtained indicating that the systems controlling the polarity of cell division and cell expansion differ in some way. The number of lateral root primordia formed was greater in roots treated with IAA or colchicine than in control roots. These primordia were always initiated adjacent to a xylem vessel. Thus, no primordium was closer to the apex than the most apical xylem vessel, suggesting that an endogenous factor involved in primordia initiation is transported in the xylem. The primordia which develop after colchicine treatment grow out as lateral roots; this is in contrast with those which form after IAA treatment and which do not undergo elongation. These results, which it must be emphasized apply only to the apical 1 cm of treated roots, indicate that lateral root primordia become sensitive to IAA at a certain stage in their development. Exogenous IAA acts as an inhibitor. The new meristem, which forms in the primary root apex after colchicine treatmerit, contains both diploid and polyploid cells, i.e. it was formed from cells that were unaffected and from cells that were affected by eolchicine. Following colchieine treatment the size of the meristem shrinks and this can be prevented by treatment with IAA. This and other evidence presented here, suggests that IAA is a factor involved in the control of the size of the apical meristem in normal roots. Introduction I n a n g i o s p e r m r o o t apices, t h e s t r u c t u r e of which has been r e v i e w e d by CLowEs (1959), th e p a t t e r n of cell division in t h e apical initial cells is of g reat i m p o r t a n c e , since it appears to d e t e r m i n e the shape of t h e r o o t and t h e positions of t h e different tissues. There is a definite relationship b e t w e e n t h e o r i e n t a t i o n of t h e m i t o t i c figure, especially at telophase, a n d t h e direction of g r o w t h in gourds (SINNOTT, 1944) and this relationship also seems to be generally t r u e in t h e a n g i o s p e r m r o o t apex. Thus, t h e p o l a r i t y of r o o t g r o w t h is initially * Present address: Department of Biology Western Reserve University, Cleveland, Ohio.

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•. I). MAeLEOD

determined by the plane of cell division, and hence by the orientation of the telophase figure and, later, by the plane of cell elongation. Since BURSTg6M (1942) found that, under the influence of exogenous IAA (~-indole-3-acetic acid), the axis of cell division of some wheat root cells changed from a tangential to a radial plane, it is possible that IAA is involved in determining the orientation of the mitotic apparatus. In addition to its effects on the mitotic cycle (DAvIDsoN and MAcLEOD, 1966), and its effect on the orientation of the mitotic spindle (BugsTR6~, 1942), IAA affects differentiation and the polarity of cell expansion (BvgsT~6M, 1942; CARLTOn, 1943; MOHR, 1956; B~>~IxG, 1958; HUGH~S and STREET, 1960). IAA occurs naturally in plants (BENNET-CLARK and KEFFOBD, 1953; LEOPOLD, 1955; AUDUS, 1959). Evidence from irradiadiation experiments (G~AY and SC~OLES, 1951; GRAY and BOAG, unpublished, quoted by HOWARD and PELt, 1953; GoRDon, 1956) and the work of PILET (1951) has led to the suggestion that IAA is synthesized in the root apex (DAVIDSON, 1960). Colchicine also affects mitotic cycles and root growth (DAvIDSON, MAOLEon and TAYLOR, 1965 ; DAVIDSON and MAcLEoD, 1966). Colehicine affects the root in such a way that, a change in the polarity of cell expansion occurs, indicating a possible effect on the growth factors controlling cell elongation in the root. Such changes could account for various abnormalities seen after colchicine treatment, e.g. reduction of root growth (LEvant, 1938; HAW~ES, 1942" DAVIDSON, 1961, 1965) or aberrant patterns of xylem formation (DAvIDso~, 1963). Support for the hypothesis that colchicine changes the level of auxinlike growth factors in roots comes from the observations that IAA stimulates the growth of eolchicine inhibited roots (DAvIDSON, MACLEOD and TAYLOr, 1965) and reverses the effect of colchicine in stimulating mitosis (MAcL~oD, 1966; DAWDSO~ and MAcLEoD, 1966; DAVIDso~, MAcLEoD and O'RIoRDAN, 1966). I n view of the importance, in root growth, of the pattern of spindle orientation and since eolchicine and IAA affect spindle orientation or function it was decided to determine i) the pattern of spindle formation in normal roots and in roots treated with eolehicine or IAA or both; ii) whether colehieine and IAA showed any interaction in producing their effects; iii) the duration of the recovery period which treated roots pass through before normal cell division and growth are re-established; iv) the effects of treatment on meristem size and the location of mitotic figures. The results to be reported here indicate that exogenous IAA, in the concentration used, has no effect on the polarity of cell division, but it does affect the numbers and distribution of dividing cells. Other results to be reported here concern the site of xylem differentiation and the

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formation of lateral root primordia in the apical 1O,0O0 ~ of both treated and control roots. Materials and Methods B e a n s were g e r m i n a t e d as p r e v i o u s l y d e s c r i b e d (DAvzDSO~ a n d MACL]~o9,

1966). Roots were treated for three hours with 4.7 • 10-s l~f IAA or 0.025% colchicine or both, according to the scheme laid out in Figltre 1. A 10-s 1V[IAA solution was used because this concentration of IAA has been previously shown to stimulate the growth of colchicine treated roots (DAvIDSOIr MAC LEOD and TAYLOR, 1965)

~z7

.j Fig. 1. Schedule of treatments given to roots of V.faba. A 4.7 • 10-8 ]~i solution of IAA; B 0.025% solution of colehicine; C solution containing 4.7 x 10-8 M IAA and 0.025 % colehicine; D controls, grown in the culture medium a n d a 0.025 % colchicine s o l u t i o n w a s u s e d b e c a u s e t h i s c o n c e n t r a t i o n of colchicine h a s b e e n g e n e r a l l y u s e d to s t u d y m i t o t i c effects. O n e d a y i n t e r v a l s s e p a r a t e d e a c h t r e a t m e n t . P r i m a r y r o o t s were fixed in acetic alcohol (1/3 v/v) a t t h e s t a r t of t h e e x p e r i m e n t a n d a f t e r 27 h o u r s a n d 54 h o u r s a n d 4, 7, 9 a n d 11 d a y s . T h e r o o t s were t h e n e m b e d d e d in w a x a n d a n 8 ~ thick, 10 m m long m e d i a n l o n g i t u d i n a l s e c t i o n w a s m a d e f r o m e a c h of five p r i m a r y roots, g i v i n g a t o t a l of five sections for e a c h t r e a t m e n t a t e v e r y f i x a t i o n . T h e s e c t i o n were s t a i n e d w i t h h a e m a l u m (after Mayer) a n d p e r m a n e n t p r e p a r a t i o n s were m a d e . T h e b o u n d a r y b e t w e e n t h e r o o t cap a n d t h e r o o t apical m e r i s t e m w a s u s e d as a b a s e line for all m e a s u r e m e n t s m a d e .

Results

1. Polarity o/ spindle /ormation The numbers of cells in metaphase, anaphase and telophase and the orientation of these division figures with respect to the longitudinal axis of the root were recorded. I n the control roots most (79.1% ) of the mitotic figures seen in rectaphase, anaphase and telophase were oriented in a plane parallel to the longitudinal axis of the root. I n some metaphases, the axis of spindle orientation could not be determined with certainty; however, it seems probable t h a t m o s t will later divide in a plane parallel to the longitudinal axis of the root since t h a t is the axis of 95 % of anaphases and telophases. 18a Planta (Berl.), Bd. 71

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A small number (3.2%) of metaphase, anaphase and telophase figures were oriented in a plane at right angles to the longitudinal axis of the root; i.e. radial divisions. These were in the apical 3270 V of the root. The plane of division of a small number of anaphase and telophase figures (1.3To) could not be determined with certainty. I t is probable t h a t most of these figures were dividing in a plane at right angles to both the longitudinM root axis and the plane at which the sections were cut; i.e. tangential divisions. Most of the division figures recorded in the control roots were in the apical 2070 ~, the m a x i m u m number occurring between 0 and 1270 from the meristem apex (Table). Outside the apical meristem, cell division gradually became cor~fined to the pericycle and adjacent cells. Table. Distribution o/metaphase, anaphase and telophase division ]igures on a percentage basis, and total number o/such ]igures, in the apical 2070 ~ o/ both treated and control primary roots o] Vicia labs. The apex o] the root was taken as the point o] the ~unction between the root cap and the meristem, t~oots were treated/or 3 hours with either 0.025% colehicine, 4.7 • 10-6 M I A A , or a solution containing 0.025% eolchicine and d.7 • 10-e M I A A at the beginning o/the experiment, and/ixed along with control roots, 54 hours alter the experiment began Distance from apex in

Treatment

Control

Colchieine

Colchicine and IAA

IAA

0--470 --870 --1270 --1670 --2070 Total cells

19.4 24.8 27.7 16.4 11.5 262

48.7 28.9 14.5 7.2 0.7 152

22.5 35.8 23.7 12.7 5.2 173

29.2 37.2 18.2 12.4 2.9 137

The results obtained from studies of the plane of cell division and the distribution of mitotic figures in the I A A treated roots are very similar to those obtained for the control roots. However, the majority of figures oriented to divide at right angles to the longitudinal axis of the root, appear to be, in general, 450 ~ closer to the apex in the IAA treated roots t h a n in the control roots. I n the colchicine treated roots anaphase and telophase figures were absent 24 hours after colchicine treatment. They re-appeared at 51 hours, however, and were present in all subsequent fixations. These figures were oriented as in the controls. There were m a n y e-metaphase figures 24 hours after treatment and, as expected in c-metaphases, the figures showed no orientation. After a further 27 hours a few metaphase figures were oriented relatively normally, and remained so for the duration of the experiment. 1No figures showed a radial orientation for the initial

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51 hours after treatment but subsequently such figures were observed; they were localized predominantly in the apical 470 ~ of the root and in the lateral root primordia and lateral roots, which had developed since treatment. Twenty-four hours after colchicine treatment, most of the division figures were in the apical 2070 ~ of the root, and in the apical 870 ~ at all subsequent times (Table 1). Thus we see t h a t the region in which cell division occurs is smaller following treatment with colchicine; it seem,s significant t h a t this contraction in the size of the active meristem should occur in a period in which it has already been shown that there is a marked reduction in MI (DAvIDSON, MACLEOD and O'RIORDAN, 1966; MAcL]soD and DAVIDSON, 1966). Following treatment with eolchicine and subsequently IAA, most (75.6%) of the anaphase and telophase figures and some (21.5%) of the metaphase figures were oriented parallel to the longitudinal axis of the root. A small number of metaphase figures were unoriented for the initial 72 hours after t r e a t m e n t with IAA, but the number of such unoriented cells found was far less than t h a t found after treatment with colchicine alone. These results indicate t h a t roots treated with eolchicine recover their normal polarity if they are subsequently treated with IAA, and are related to the I A A induced reversal of the mitotic inhibition found after colchicine treatment (MAcLEoD and DAVIDSON,1966). Unlike the roots treated with eolchicine alone, roots treated with a solution containing colchicine and I A A showed anaphase and telophase figures 24 hours after treatment. Such figures were predominantly (62.2%) oriented with respec~ to the longitudinal axis of the root. Three days later and in subsequent fixations m a n y (41.4%) of the metaphase figures were oriented parallel to the longitudinal axis of the root, and 16.4% were oriented radially. Of the spindles t h a t were oriented to produce a radial division most were in the apical 870 ~ of the root. I n roots fixed 8 or more days after treatment, 70 % of the figures oriented radially outside the apical 870 ~ were associated with primordia formation. No contraction of the apical meristem followed treatment with colchicine and I A A at the same time (Table).

2. Xylem Though the point at which differentiated xylem vessel elements were first seen in the controls varied greatly in different roots, none were seen in the apical 5,000 ~. The same was true initially for the roots treated only with IAA. However, in 8 day fixations of the I A A treated roots, xylem vessel elements were seen at 6470 ~ from the apex, and, b y 10 days, between 2070 ~0 and 2870 [~ from the apex, i.e. differentiation of xylem 18"

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vessels was occurring closer to the apex in I A A treated roots than in controls. Differentiated xylem vessel elements were generally seen between 2070 ~ and 3270 ~ from the apex of the colchicine treated roots, but 11 days after treatment, they were found between 870 ~ and 1270 from the apex. Similarly, eight days after treatment with colchicine followed b y IAA, vessel elements were seen between 470 ~ and 870 ~t from the apex in roots which had not yet begun to regenerate. I n regenerated roots, however, they were seen between 4070 ~ and 4470 ~ from the apex. Following treatment with colchicine and I A A at the same time, differentiated xylem vessel elements were found between 3270 ~ and 3670 ~ from the apex 2 days after treatment and between 870 ~ and 1270 ~ from the apex, 5 days later.

3. Primordia No lateral root primordia or emerged lateral roots were found in the apical 10,000 f~ of the control roots. However, lateral root primordia were found in this part of the root after all treatments and emerged lateral roots were found following some of the treatments. Lateral root primordia were found in I A A treated roots fixed on days 10 and 11, but dividing cells were found only in the primordia t h a t occurred at a distance of 5670 ~ or more, from the root apex. The distance between the primary root apex and the nearest lateral root has not been changed to any marked extent from the control value. Lateral root primordia were first seen 4 days after treatment with colchicine and were found in all of the roots from subsequent fixations. These primordia were mainly in the c-tumour though some were found more basally in the root. All these primordia contained polyploid cells. Small lateral roots were seen above the c-tumour seven and eleven days after treatment and they were morphologically normal. No polyploid cells were seen in their apical meristems but such cells did occur basally in these roots. This suggests t h a t polyploid cells were present in the young primordinm but were lost as root growth took place. Following treatment with colchicine and subsequently with IAA, lateral root primordia were found. These primordia developed from the perieycle cells and they contained polyploid cells, as did the few lateral roots which developed after treatment. Some of the lateral root primordia contained no dividing cells. I n the roots treated with colchicine and I A A at the same time and, in some eases, with IAA 24 hours after the first treatment ended, lateral root primordia first appeared two days after treatment began. Such primordia were also found in most of the roots examined in later fixations.

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I n general, dividing cells were seen in these primordia after this time. Lateral roots were growing from roots treated with colchicine and IAA, after nine days. Polyploid cells were present in all of these primordia and lateral roots. Discussion

1. Polarity The distinct cell patterns found in roots (see CLOWES, 1961) suggests that cell expansion and division are controlled not by a single growth factor but by a combination of extrinsic and intrinsic factors, including chemical and mechanical factors. In cell expansion and in cell division, the common problem is to define the mechanism t h a t determines polarity - - in mitotic cells, the polarity of spindle orientation, and in growing cells the axis of elongation. IAA disturbs the polarity of cell expansion (LEvA~, 1939; CAnLTO~, 1943) and cell division (BuRsTtC6M, 1942; MoH~, 1956). BUI~STROM (1942) noted that in wheat roots, IAA changed the plane of division of some cells from a tangential to a radial plane. I n his experiments, and those of MoH~ (1956), the result of disturbing the polarity of cell division was the production of disorganized tissue. I n roots of V./aba treated with 4.7 • 10 -G M IAA alone, no effect on the polarity of cell division or the pattern or organization of cells in the root apex was seen. Thus, there is no evidence from these results t h a t IAA affects spindle orientation in V. /aba roots. After colchicine treatment, root elongation stops and tumours form in the zone of root elongation (L]~vA~, 1938; HAWKES, 1942). Eventually the roots regenerate (L~vA~, 1938; WITKUS and B~I~GEI~, 1950; DAVIDSO~, 1961, 1965; DAVlDSO~, MAcL~oD and TAYLOI~, 1965). I n the present experiments root regeneration was slow and did not begin until about eleven days after t r e a t m e n t with colchicine. Though these roots were not growing, mitosis was taking place and the orientation of the spindles was normal; cell elongation and spindle polarity must therefore be controlled by systems which differ in some way. I t has been found that the change in the polarity of cell expansion induced b y colchicine can be modified by I A A (DUHAlVIET, 1945; O'Rio~nA~, 1965). However, no evidence has been obtained indicating an effect of IAA on the polarity of the spindle in colchicine treated roots.

2. Primordia /ormation I A A (4.7 • 10 -6 M) stimulates lateral root primordia formation and these primordia formed closer to the primary root apex than in the controls. However, this was not true of lateral roots, indicating t h a t the primordia, which develop as a result of IAA treatment, do not grow as 18b

P l a n t a (Berl.), Bd. 71

264

R.D. MAcLnol) :

lateral roots. Similar results have been reported b y GoLDac~n (1959). He found that, though a 10-5 M solution of IAA promoted the formation, of lateral root primordia from the pericyele cells of isolated flax roots such primordia did not elongate to form lateral roots unless the roots were transferred to an IAA free medium. The lateral root primordia t h a t develop in the apical 10 m m of a root following treatment with colehicine or colchicine and I A A grow out as lateral roots. Thus, when exposed to cholchicine together with IAA, primordia are not inhibited by the IAA. However, treatment with IAA 24 hours after a colchicine plus I A A treatment again inhibits primordial development. I t appears, from these results, t h a t primordia become sensitive to IAA after a certain stage in their development and their growth is then inhibited. Similar results have been reported for growth of lateral roots of Vicia treated with colchieine and then IAA (DAvIDSON,MAcLEoD and TAYLOR, 1965). Some of the lateral roots formed by the colchicine treated roots grow from the e-tumour. These laterals and some of those originating outside the c-tumour contained polyploid cells; they must have developed, at least partly, from cells which were affected by the colchicine treatment. No estimates were made of the frequencies of polyploid cells, which can occur in high frequency in such roots (DAvIDSON,1961, 1965). I t can be seen t h a t differentiated xylem vessels occur closer to the apex in colchicine treated roots than in the controls. This differentiation in not prevented by IAA and even treatments with IAA alone lead to some xylem differentiation closer to the apex than in controls. However, it seems probable t h a t xylem differentiation occurs closer to the root apex in the colchicine treated roots than in the controls because colchieine treated roots have stopped growing and differentiation is a function of the age of the tissue. Lateral root primordium formation appears to be associated with vessel differentiation. This is a consequence of the fact t h a t primordia do not form closer to the primary root apex than differentiated xylem vessel elements in normal flax roots (GoLDACRE,1959). This suggests that it is some factor(s), transported in the xylem vessels, which is responsible for the initiation of these primordia. I t is difficult to explain these effects on the basis of changes in the level of one growth factor but it should be remembered t h a t any such change will also affect the balance between different growth factors in the root apex. Thus, the changes found in the root apical meristem following colchicine or colehieine and IAA treatments m a y be the result of an abnormal balance of growth factors in the root.

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3. Regeneration Order has been re-established in roots after treatment with eolchicine, or colchicine and IAA, once a linear arrangement of the cells in the root apex is seen. l~ows of polyp]old and diploid cells can then be seen. The new meristem consists of cells affected by the treatment, as well as cells which were not affected, i.e. m a y include cells of the old meristem and cells of the quiescent centre, which were not dividing at the time of treatment. We have previously suggested (DAvIDSON and MAcLEoD, 1966) that, following colehicine treatment, there is a decrease in the level of growth factors in roots and t h a t this decrease is responsible for the changes in MI, growth and patterns of differentiation that occur over a period of several days. On the basis of this hypothesis it would be expected that the responses of roots to eolehieine would be modified by exogenous sources of growth factors. This has been found to be so. IAA affects the changes in MI, both inhibiting the initial increase and facilitating recovery from the subsequent decrease (~)AVIDSONand )/[AcLEOD, 1966; ~/[AcLEOD and DAVIDSON~1966) and it stimulates the growth of roots previously inhibited by colehicine (DAvIDSON,I~r and TAYLOr, 1965). Furthermore, it appears t h a t IAA alters the pattern of lateral root initiation in colchicine treated roots and it also changes the size of the functional meristem. Mitoses continue to occur in colehicine treated roots of Vicia (DAVIDsoN, 1961) though their frequency is low for several days (DAVIDSON, MAcLEOD and O'RIORDAN, 1966; MAcLEoD and DAVIDSON, 1966). Though mitotic activity is maintained in some cells it is not maintained in all cells present at the time of treatment and the functional meristem appears to shrink. This contraction of the meristem can be prevented in part b y IAA. Thus, treatment with IAA one day after colchicine appears to maintain mitotic activity in some cells that would otherwise fail to divide (M_xcLEo~) and DAVIDSON,1966). The changes t h a t occur in meristems following treatment with colchicine are very similar to those that follow irradiation; mitosis is inhibited, the region of active meristematic activity contracts and root growth is inhibited (GnAY and SCI-IOLES, 1951). The re-establishment of meristematic activity is correlated with the onset of active mitotic activity in cells of the quiescent centre (CLowEs, 1959, 1961, 1963). X-rays are known to inhibit IAA synthesis (GoRDoN, 1956). This fact, together with the auxin gradient present in roots (PILET, 1951) and the high sensitivity of the apical meristem to X-rays, suggests that some synthesis of auxin-like growth factors occurs at the apex of the root. The parallels between the effects induced by colchicine and X-rays appear to lend support to the view t h a t colchieine disrupts the synthesis

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of g r o w t h f a c t o r s . N o r e s u l t t h a t has b e e n r e p o r t e d so far c o n t r a d i c t s t h e h y p o t h e s i s t h a t eo]chicine l e a d s t o c h a n g e s in t h e l e v e l of g r o w t h f a c t o r s in roots. N o s u g g e s t i o n c a n be m a d e a t p r e s e n t c o n c e r n i n g t h e m e c h a n i s m b y w h i c h colchieine affects a u x i n s y n t h e s i s . F u r t h e r e x p e r i m e n t a l a n a l y s i s of r o o t s t r e a t e d w i t h colchieine a n d a u x i n s s h o u l d p r o v i d e crucial e v i d e n c e for t h e bases of n o r m a l a n d a b n o r m a l g r o w t h . References

Aw)vs, L. J.: Plant growth substances. London: Hill 1959. B~C~T-CLARK, T.A., and N. P. K~F~OaD: Chromatography of the growth substance in plant extracts. Nature (Lond.) 171, 645--647 (1953). B i ~ I ~ G , E. : Polarit~t und in~quale Teilung des pflanzlichen Protoplasten. Protoplasmatologia 8, 1--86 (1958). BURST~5~, H. : The influence of heteroauxin on cell growth and root development. Ann. Agr. Coll. Swed. 1O, 209--240 (1942). CArLTOn, W. M. : Histological and cytological responses of roots to growth-regulating substances. Bot. Gaz. 105, 268--281 (1943). CLowns, F. A. L.: Reorganisation of root apices after irradiation. Ann. Bot. (Lond.), N.S. 23, 205--210 (1959). - - Apical meristems. Oxford: Blackwell 1961. - - X-irradiation of root meristems. Ann. Bot. (Lond.), N.S. 27, 343--352 (1963). :DAu D. : Meristem initial cells in irradiated roots of Vicia ]aba. Ann. Bot. (Lond.), N.S. 24, 287--295 (1960). - - Mechanisms of reorganization and cell repopulation in meristems in roots of Vicia ]aba following irradiation and colchicine. Chromosoma (Berl.) 12, 484-504 (1961). - - Patterns of differentiation in Vicia roots (Abstr.) Trans. bot. Soc. Edinb. 39, 437 (1963). - - A differential response to colchicine of meristems of roots of Vicia/aba. Ann. Bot. (Lond.), N.S. 29, 253--264 (1965). - - , and R. D. MAcL]~oD : Changes in mitotic indices in roots of Vicia ]aba. I. Antagonistic effects of colchicine and IAA. Chromosoma (Berl.) 18, 421--437 (1966). , and M. O'RIOaDAN: Changes in mitotic index induced by colchicine. Nature (Lond.) (in press) (1966). , and J. E. TAYLOr: An IAA induced stimulation of growth of roots inhibited by colchieine. New Phytologist 64, 393--397 (1965). DU]tA~]~T, L.: Recherches sur l'action de l'h6t6ro-auxine et de la croissance de racine isol6es de Lupinus albus. Rev. Cytol. et Cytophysiol. v6g6t. 8, 35--78

(]945). GOLDACRV., P. L. : Potentiation of lateral root induction by root initials flax roots. Austr. J. biol. Sci. 12, 388--394 (]959). GORDOn, S.A.: Mechanism of phytohormone damage. Peaceful uses energy. United Nations Publication, Geneva. 283--291 (1956). GI~AY, L . H . , and M. E. ScnoLEs: The effect of ionizing radiation on bean root viii. Growth rate studies and histological analyses. Brit. 24, 82, 176, 228, 285, 348 (1951). HAWKES, J. G. : Some effects of the drug colchicine on cell division. J. 11--22 (1942).

in isolated of atomic the broad J. Radiol. Genet. 44,

I am grateful to S.R.C. and to N.A.T.O. for the award of a scholarship.

Induced Changes in Growth Patterns and Polarity in Roots

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Studies on induced changes in growth patterns and polarity in roots of Vicia faba L.

Roots of Vicia faba were treated with colchicine (0.025%), or IAA (4.7×10(-6) M), or both, for 3 hours and fixed at various intervals over the followi...
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