effect of irradiation on adult nuclei in plants
TRANSCRIPT
Genetica 28 (1956): 143-164
EFFECT OF IRRADIATION ON ADULT NUCLEI IN PLANTS
by
ARUN IKUMAR SHARMA and RAMENDRA K. MUKt!ERJI
Cytogenetics Laboratory Botany Department Calcutta University 35, Ballygunge Circular Road Calcutta-19, India
(Received/or publication40clobe~ zz, z955)
CONTENTS
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Materials, Methods, and Observations . . . . . . . . . . . . . . . . 144 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . ! 58 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
INTRODUCTION
Within the last few years considerable data has been accumulated
on irradiation effects on chromosomes. Though the chromosomes are
affected in all the divisional and intermitotic states, the manifestation
of the effects become different depending on the stage irradiated
(MULLER, 1954). This is specially because in some, restitution of ends
are favoured due to certain factors, whereas in o~hers there are a
number of factors which stand against such restitution and, therefore,
considerable structural rearrangements result. But all these researches have mainly been centered round on normal undifferentiated cells.
I t is worthy of note that as far as differentiated cells in plants are
concerned, data on this aspect is significantly lacking. It has been
emphasized recently, specially by one school of thought (HusKINS,
1947) that the non-meristematic differentiated nuclei undergo
endomitosis and thus lie in a highly polyploid state. Experimental attempts to prove the validity of the concept have also been met with success (HuSKINS and STEINITZ, 1948b; D'AMATO, 1950 ; SHaRMA and
143
144 ARUN KUMAR SHARMA AND RAMENDRA K. MUKHERJI
SEN, 1954). AS the effects of X-rays bring about a number of inter- esting issues, it was thought that irradiation on such nuclei might yield data interesting from a cytological standpoint.
Bulbs of Allium cepa, as noted in this Laboratory, consists of both normal and giant polyploid nuclei (differentiated) at the basal region destined to contribute to basal part of the roots. Obviously such onion bulbs were hoped to provide good experimental material for a study
on the effects of irradiation on diffe~'entiated nuclei, if treatment be carried out at this stage. Furthermore, a number of chemicals have recently been shown to induce division in differentiated nuclei. I t was planned that as attempts to grow the irradiated bulbs in these solutions might induce division in the differentiated nuclei, the mani- festations of X-ray effects on their chromosomes would thus be re- vealed.
With these considerations, the present investigation, involving
the study of effects of irradiation on non-meristematic polyploid nu- clei, following the growth of the irradiated roots in solutions of known division inducing property, was undertaken.
MATERIALS AND METHODS
In these treatments dry and healthy bulbs of onion were taken as experimental materials.
The bulbs without any root tip were taken in two groups, and were subjected to X-rays of dosages 250 r and 1000 r respectively. During irradiation, the bulbs were all placed upside down with their lower
s ides facing the direction of rays. Bulbs of different treatments were properly labelled immediately after exposure to avoid confusion. Tile bulbs of both treatments were placed in three kinds of solution, viz., Nucleic acid (.01%) solution, a mixture of equal proportions of Lae- vulose (.2%), Ammonium phosphate (.02%) and Uracil (1%), and the Laevulose sugar alone, contained in glass tubes ( 3 " • i"). Treated bulbs of both dosages were placed in Knop's solution and taken as the control, All these bulbs along with the tubes were kept in cold temperature (about 18 ~ C).
At intervals of every twenty-four hours from the time of irradiation new roots were taken, fixed in Aesculine solution for an hour in cold, heated in Orcein hydrochloric acid mixture (2% Aceto orcein and
E F F E C T OF IRRADIATION ON ADULT NUCLEI IN PLANTS [ 4 5
normM N.HC1 in the proportion of 9 parts : I part), and finally
mounted on clear glass-slides in 1% Aceto orcein solution and smeared with necessary pressure to have a thorough and uniform spreading of the tissue. Immediately after mounting, the prepared slides were sealed with melted paraffin wax. After preparation of the slides, necessary readings were taken under the microscope. The bulbs were denuded of roots every day, so that observations could be taken of new roots in consecutive periods. In this way, observations were made of root tips fixed one hundred and sixty-eight hours after irradiation.
Scrapings from the basal region of bulb before irradiation were also observed and found to ~contain both giant- differentiated polyploid- nuclei and the normal nuclei in the resting state. After irradiation, therefore, following this method, the consecutive observations at different intervals could be made on the activity of the differentiated nuclei in addition to normal irradiated ones in the above-mentioned state.
O~SERVAXlONS
The observations made are tabulated below : (For lack of space, the following abbreviations have been used in the table: P- Polyploid;
Pr- Prophase; A- Anaphase; IV[- Metaphase; Redn.- Reduction; B- Bridge; Lag- Lagging; F- Fragment). The percentage of only po- lyploids and total abnormals out of total number of dividing cells have been counted and the approxinate figures given.
Genet ica XXV~I2 i0
146 ARUN KUMAR SHARMA AND RAMENDRA K. MUKHERJI
TABLE I .
I2o hours 1)
Tota l Divn . ~ells cells A b n o r m a l i t y
80
72
82
80
78
92
74
105
68
731
10
6
10
10
12
16
7
20
6
97
1 Redn., 1 Diplo., 2 M F
I P. Metaphase
2 Diplo., 1 A F B
2 A F B
2 Diplo.
2 P . Pr., I P M
1 M F
3 Pr . F, 1 M F, 1 Redn.
1 Diplo.
22
Abnormal - 22%
Poly. - 4%
~44 hours
40
44
46
72
62
64
40
55 75
105
95
42
64 60
49
913
0
2
4
5
6
8
9
7 I0
4
6
10
10 8
10
99 Abnormal -
Poly. -
Normal prophase
Do.
2 M 3 P r .
1P . P r . , 2 M , 1 A B
I A B, 7 Pr.
I P. Pr.
1 M F B 1 A B , 1 M F
l A B l A B
Normal cells
I A B , 1 M F Normal ceils
Do.
1I% 2%
1) Resu l t s of i r rad ia t ion a t a dosage of 250r, followed by g rowth in nucleic acid solut ion for different periods. As no divis ion of polyploid cells up to 96 hour s
af ter i r radia t ion has been obta ined, the i r resu l t s have no t been t abu la t ed .
EFFECT OF IRRADIATION ON ADULT NUCLEI IN PLANTS 147
TABLE I. (contd.) x68 hours
Total Divn. cells cells Abnormal i ty
44 24
37
47
36
50
54
37
329
0 1
2
3
3
5
7
5
27
Normal anaphase
Normal telophase
2 Meta., 1 Telo.
Ear ly prophase
l A B
1 M F
1 A F B , t P F
Abnorma l - 15~o
Polyploid - 0
TABLE II . Results o/irradiation at a dosage o/250 r/ollowed by growth in mixture/or different periods
24 hours
No division.
48 hours
Total Divn. ceils cells Abnormal i ty
72
60
40
62
57
59 64
84
71
62
50 78
60
819
8
7
0
11
4
6
5
15
10
6
5 13
5
95
2 P r . F.
1 Diplo., 2 P. Pr.
5 P r . F.
I P. Pr.
1 P. Pr.
I Diplo.
1 Diplo., 2 P. Pr.
1 M . F .
2 M . F .
1 Diplo. 1 P r . F .
1 Diplo.
Abnorma l - 20%
Poly. - 6%
148 ARUN KUMAR SHARMA AND RAMENDRA K. MUKHERJI
TABLE II . (contd.)
7 2 hours
Total Divn. cells cells Abnormality
64
70
55
52
31
50
82
68
96
60
628
10
t0
12
8
5
10
15
7
15
10
102
1 P. Pr.
2 M . F .
3A. F. B.
3A. F . B .
1 M . F .
2 P . Pr.
2 M . F .
1 M . F .
1A. B., 1M. F.
2 P r . F.
Abnorma l - I9%
Poly. - 3%
96 hours
40
42
55
62
50
68
70
85
65
50
50 72
64
773
4
7
8
12
6
8 10
7
7
6
10 7
10
102
1 M . F .
1 A . F . B .
i A . F .
1 A . B , , 1M. F.,
i Diplo.
2 M . F .
1 P. Pr.
1 Diplo.
1 P r . F . 1 Diplo., 1 M. F.
1 M.F.
Abnormal - 14%
Poly. - 1%
E F F E C T O F I R R A D I A T I O N ON A D U L T N U C L E I IN P L A N T S 149
TAB~ II (contd.)
220 hours
No Division
s44 hours
Total Divn. cells cells Abnormality
44
62
42
45
50
52
60
6O
65
74
34
81
80
749
8
12
6
6
10
10
9
7
5
12
4
7
10
106
2 M . F .
1Pr . F.
1 P r . F .
1 A . B .
1 M . F .
1 M . F .
1 P r . F .
I M . F .
A b n o r m a l - 9% Poly. - 0%
~68 hours
80
67
43
53
50
55
70
70
62
73
94
717
I5
10
10
11
3
7
10
9
6
6
13
100
I A. B., 2M. F.
4 M . F .
t A. F. , 3 P. Pr.
4M. F., 1P . Pr.
1 M . F .
2 M . F .
2 M . F .
1 Redn.
1M. F. , 1 A . B .
A b n o r m a l - 24~/o Poly. - 1
150 ARUN KUMAR SHARMA AND RAMENDRA K. MUKHERJI
TABLE I I I . Results o/irradiation at a dosage o/250 "r /ollowed by growth in Lavulose /or di//erent periods.
24 hours
Total Divn. Abnormali ty
cells cells
58
35
60 65
50
59 78
405
t2
3
20 25
15
23
35
133
2 Diplo. i Diplo.
2 Pr. F.
3 Pr. F.
2 M.F. 1 Diplo., 1 M.F.
1P. Pr. F.
13 Abnormal i ty- 9.7% Poly. - .7%
48 hours
No division
72 hours
No division
96 hours
60 51
52
48
211
10 3
7
9
34
1A. F., 1A. B.
1M.F .
1 P. Pr. 1 M. F., 1 Diplo.
6 Abnormal i ty- 18% Poly. - 3%
EFFECT OF IRRADIATION ON ADULT NUCLEI IN PLANTS 151
TABLE n I (contd.) I20 hours
Total Divn. cells cells Abnormal i ty
95
88 70
56 60
90 104
60
623
15
15 10
5
8
16
20
10
99
t M . F .
1M.F.
2 A . F .
1 Diplo. 1 P r . F .
4Pr . F.
4Pr . F.
2M. F., 1A. F. B.
17 Abnormal i ty- 17%
Poly. - 0%
z44 hours
58
30
50
45
40
228
5
3 6
5
4
23
Normal metaphase Normal Prophase
Do.
2 M . F .
1 A . F .
Abnormal i ty- 12%
Poly. - 0%
152 ARUN KUMAR SHARMA AND IRAMENDRA K. MUKHERJI
TABLE I I I (contd.) z68 hours
Total Divn. cells cells Abnormality
43
50
48
46
40
45
60
58
50
60
95
70
46
81
55
60
907
5
4
4
2
2
5
7
7
4
6
10
10
7
6
7
11
97
I Diplo.
4 Normal anaphase
4 Normal metaphase
1 M . F .
1 P r . F .
1A. lag., 1M. F.
1 M . F . , 1A. B.
1 Diplo. 1M. F., 2 P. Pr.
1 A . F .
I A . B .
I Diplo.
1 A . B .
16 Abnormal i ty - 16%
Poly. - 2%
TABLE IV. Results o/irradiation at a dosage o/I000 r/ollowed by growth in Nucleic acid solution/or different periods.
24 hours
Total Divn. Abnormality cells cells
48
52 50 52
212
7
12 10
12
41
1 P . F .
2 M . F . 1 P . F .
I P . F .
8
Abnormal i ty - Poly.
i2.1% 0
EFFECT OF IRRADIATION ON ADULT NUCLEI IN PLANTS 153
TABLE IV (contd.)
48 hours
Total Divn. cells cells Abnormality
2 M . F . 52
65
72
46
235
12
0
0
0
12 m
2
A b n o r m a l i t y - 16%
Poly. - 0
7 2 hours
20
37
87
100
55
68
70
70
65
62
634
0
2
I6
20
10
14
!2
10
I0
8
100
1 M . F .
3 M . F .
I A. B. and F.
1 P . F .
2 M . F .
1P. Pr.
A b n o r m a l i t y - 9% Poly. - 0
9 6 hours
68
70
56
60
55
72
381
8
10
10
9
8
12
57
I A. F . B . , 1M. F.
2 Diplo.
2 P r . F.
1 Pr. Polyploid
2 P . Pr.
9
A b n o r m a l i t y - I5.7%
Poly. - 5%
154 ARUN KUMAR SHARMA AND RAMENDRA K. MUKHER]I
TABLE IV. (contd.) 120 hours
Total Divn. cells cells Abnormality
45 60 75
180
10
12
7
29
2 Pr. F. I M. F., 1Pr. F. 1 A . F . B . , 1M. F.
6 Abnormal i ty- 20.6%
Poly. - 0
z44 hours
28 17
20
30
24
119
0 0
1
0 1
2
Early prophase
Anaphase
Abnormal i ty- 0
Poly. - 0
z68 hours
63
61
40
62 60
286
2
10 7
10 0
29
Normal prophase
Normal metaphase Normal anaphase
Normal telophase
~bnormali ty- 0
Poly. - 0
EFFECT OF IRRADIATION ON ADULT NUCLEI IN PLANTS ] 5 5
TABLE V. Results o/irradiation at dosage o] ~ooo r/ollowed by growth in mixture/or di//erent periods
2 4 h o u r s
Total Divn. cells cells Abnormality
51
50
60
60
48
50
62
10
I0
15
10
12
7
8
73
2 Pr. F., 1 Diplo,
t M . F ,
2M, F.
1A, F,
I A . F .
3 Pr. F.
2 Diplo.
13
Abnorma l i t y - 17,8%
Poly. - 0
48 hours
62 60
60
56
46
8
5
9
8
5
27
2 P r . F.
1 P r . F .
2 Diplo., i M. F.
1 P r . F .
7
Abnorm a l i t y , 28%
Poly. - 0
72 hours
60
58
72 42
50 45
55
64 80
95
11
10 12
5
8
8
13
ll I0
12
100
2 P r . F,
2 A . F .
1A. F., 1M, F.
1 M . F .
I M . F .
3 Pr. F.
2A. F , B ,
1M. F., 2 Pr, F. 2M. F., I A. F. B
3A . F, B,
22 Abnorma l i t y - 22%
Poly. - 0
156 ARUN KUMAR SHARMA AND RAMENDRA K. MUKHERJI
TABLE V. (contd.)
9 6 hours
Total Divn. cells cells Abnormality
60
55
9
8
17
2 M . F .
1 M . F .
3
A b n o r m a ] i t y -
Poly.
17.6%
0
120 hotffs
55
60
60
62
10
12
8
10
40
2 P r . F.
I M . F .
I P r . F .
1A. F. B., 2 P. F.
7
A b n o r m a l i t y - 17.5~
Poly. - 0
I44 hours
43
44
31
39
50
62
75
4
3
2
4
5
6
10
34
I A . B .
1 A . B .
1 A . B .
2 A. B., 1 N . F .
2 A . B., N. F.
I Diplo.
10
A b n o r m a l i t y - 29%
Poly. - 0
z68 hours
t~oot Not Obtained.
E F F E C T OF I R R A D I A T I O N ON A D U L T N U C L E I IN PLANTS 157
TABLE VI. Results o/ irradiation at a dosage o/ zooo r /ollowed by
growth in Laevulose solution/or di//erent periods
2 4 hours
Total Divn. Abnormality cells cells
No Division
48 hours
25
40
30
1
5
4
I0
i P r . F .
I Pr. F. and Erosion
1 Ear ly prophase, Erosion
3
Abnorma l i t y - 30%
72 hours No Division
96 hours No Division
I20 hours
95
90
70
78
60
22
I5
10
20
10
77
4 P r . F.
2 M. F., I Pr. F.
2 A. F., 1 Diplo.
1P. Pr. F.
2 M . F .
13
Abnormal i ty - 16.5%
Poly. - 1
z44 hours
26 21
28
18
24
2
X
3
2
2
9
1 P. Pr.
X
Ear ly Prophase
2 Ear ly Prophase 1 P. Pr.
2 Abnormal i ty - 17%
Poly. - 9%
158 ARUN KUMAR AND SHARMA AND RAMENDRA K. MUKHERJ[
TABLE VI (contd.) I68 hours
Total Divn. cells cells Abnormality
22 19 12 15
DISCUSSION
That X-rays can affect the structure and behaviour of chromo- somes o f nuclei is well known. The manifestations of their effect are diverse and in addition to gene mutation, chromosomal abnormahties caused by irradiation need no further introduction. That X-rays can influence cell constituents and their behaviour at different stages of their cycle have also been well illustrated in a number of books and papers (LEA, 1946; KAUFMANN, 1954 etc.).
Attention in recent years has been focussed by certain schools on a particular aspect of nuclear nature, i.e., of the differentiated cells. Since the introduction by HUSKINS and others (1947, 1948a, 1948b) of his concept of endomitotically dividing polyploid nuclei of differen- tiated region, at least an understanding of the process of differentiation has been made possible. The concept even now cannot be considered as a well established one though the validity of the suggestion is being more and more appreciated with tile gradual accumulation of data in this aspect. I t has been repeatedly emphasized in a number of publications from this Laboratory (SI~A~MA and SEN, 1954; SHAR- MA and ]3HATTACHARYYA, 1954; SHARMA and MOOKERJEA, 1955) that polyploid nuclei of the differentiated cells can be induced to divide through treatment in a number of chemicals. I t is claimed that such induction brings about definite evidences of the dynamic nature of the differentiated cells whose activity in natural conditions is main-
tained through endomitosis. The present series of experiments have dealt with the effect of
irradiation on these polyploid differentiated nuclei. In the healthy bulbs without roots, which were subjected to irradiation, it may
EFFECT OF IRRADIATION ON ADULT NUCLEI IN PLANTS 159
reasonably be claimed that the flat stem region, which was irradiated, consisted of cells of different ages. Some of the cells constituting this region with potential growing capacity were absolutely young and destined to represent the future meristematic members. Others in the same region already were differentiated, and attained the giant size. Their activity no doubt remained fully checked as expected in the dried condition of the bulb. By irradiation, therefore, the influence of the latter could be exerted not only on the potentially meristematic
ones, but also on those which remained in the same region, but because of their ages were differentiated in nature.
I t may be emphasized at the same time that their existence at the time of irradiation has also been clearly brought out. The main evi- dence is provided by the fact that in cases where even after twenty- four hours of irradiation no division could be obtained in the tissue destined to give rise to roots, the giant nuclei, i.e., the so-called dif- ferentiated ones, were also detected in the resting stage. Furthermore, scrapings from the base of the bulbs before irradiation revealed both normal and giant nuclei, both in resting condition. This is possibly a direct proof that such giant nuclei were also in existence there even at the onset. These giant nuclei are in no case, therefore, to be considered as post-irradiation products. With the just emergence of the roots, these normally constitute their basal portion, a process, facilitated by their increase in cellular volume and consequent entrance into the root base.
I t is also to be pointed out that while taking the observations, new roots were taken every day, the bulbs being made devoid of any roots at the end of each observation. It may further be noted that while taking the data, the exact tip portion was discarded and the entire basal portion, about a centimeter in length adjoining the base of the bulb, was taken. No doubt a large number of dividing diploid cells were obtained at the region towards the tip, but the basal portion was found to be consisting of cells most of which were provided with giant polyploid nuclei. Induction of division in these nuclei was the purpose of investigation and as the table shows, it has been success- fully done in a number of cases.
I t is quite natural that complete chromosome reproduction ieading to subsequent separation is a process which is controlled to a large extent by the nucleic acid supply in the nucleus. In the differentiated
160 A R U N K U M A R S H A R M A AND R A M E N D R A K. M U K H E R J I
nuclei, which divide endomitotically, it has been assumed in the previous dissertations that there is possibly a proportionately less synthesis of nucleic acid. This is responsible for the apparently abnor- mal state of the nucleus which is comparable to the polytenic set up. If that be the case, it was thought that a supply of nucleic acid from outside might meet up this deficiency and induce division in them. Attempts were, therefore, given for culture of roots in Nucleic acid medium and to some extent induction was obtained (Sharma and Sen, 1954). The frequency of induced division was not found to be very high, possibly accountable to the difficulty in penetration of the highly polymerised nucleic acid molecules. Further attempts (SI~ARMA and MOOI~ERJEA, t955) were then given with different types of sugar, base and phosphate as wetl as :with mixtures not only to have an induction of division, but at the same time to get an approximate understanding regarding the particular moiety in which they were deficient. Best induction was obtained following Laevulose treatment showing thereby that possibly the main deficiency of such giant nuclei lies in the absence of sugars. Needless to mention, a mixture of the three, base, sugar and phosphate at a particular proportion was found to be capable of initiating division.
With this data from the results of previous works at hand, the present investigation was planned to study the extent of damage caused in the differentiated cells as manifested in their division following treatment in the mixture, Nucleic acid and Laevulose solution respectively of established induction property. I t was thought that irradiation experiments on these non-meristematic cells and their subsequent growth in these different solutions would give an idea of the changes undergone by the differentiated nuclei.
Root tips irradiated at a dosage of 250r and then grown in different division inducing solutions reveal a number of interesting features worth consideration. I t has already been pointed out that Laevulose solution has been found to be highly effective in inducing division in differentiated cells. But it may be recorded from the data that, with Laevulose solution, the division in polyploid ceils has been found to be occurring at a very negligible frequency even after one hundred and sixty-eight hours of keeping in Laevulose solution. While grown in Nucleic acid solution, induction after one hundred and twenty hours has to some extent been obtained, but there too the frequency -
E F F E C T OF IRRADIATION ON ADULT NUCLEI IN PLANTS 161
gradually falls with increasing period. It seems that with Nucleic acid, the same difficulty of penetration of polymerised nucleic acid molecule is there. That is why with continued accumulation through one hundred and twenty hours there is induction of division in poly- ploid cells to a certain extent.
But possibly their further accumulation may lead to toxicity resulting into the fall in this induction frequency. Though apparently it seems fallacious to assume toxicity through an essential chemical like Nucleic acid, but because this induced penetration to a large amount may cause a disbalance in the polyploid cells, the suggestion does not seem to be very unlikely. While in previous works, induction in polyploid cells was found to be high through sugars like Laevulose, etc. it was suggested that the normal polytenic condition of the dif- ferentiated nuclei is due to a deficiency in Nucleic acid synthesis mainly brought about through a decreased supply of sugar. Because of meeting up the sugar deficiency through artificial application, division in them could be induced.
In the present report, induction could not be so effectively brought about through Laevulose solution. It may be suggested that irradiation induces certain metabolic changes causing the deficiency in certain other chemicals in the polyploid nuclei in addition to the normal deficiency in sugar. That is why even with Laevulose division could not be induced in them.
The data on root growth in mixture solution shows that induction could easily be obtained at a quite high frequency (6~o) in even forty-
eight hours. With gradual increase in the period of treatment there is a fall in frequency. This high frequency of induction itself indicates that the mixture can meet up the deficiency in polyploid nuclei - a deficiency which could not be satisfied in Laevulose solution alone. This seems to be the reason of increased frequency of division in mixture than in Laevulose solution. Obviously, it may also be inferred that irradiation causes certain blockade in the metabolism of Phos- phate and/or base- a blockade which is normally not present in the polyploid nuclei. So in normal cases Laevulose alone can induce division whereas in irradiated polyploid nuclei, the induction of di- vision requires a supply of sugars, phosphates as well as bases. The gradual fall in frequency with increase in the period of mixture treat- ment may be assumed to be due to some toxic effect caused by a
G e n e t i c a X X V I I I 11
162 ARUN KUMAR SHARMA AND RAMENDRA K. MUKHERJI
continued accumulation of the constituents. Investigations are further necessary to find out whether a disbalance in both Phosphate and base metabolism is involved in polyploid cells following irradiation or only one of them. This is a fundamental issue which is yet to be settled.
With 1000 r irradiation, however, the damage is so heavy that division in significant percentage in polyploid nuclei could not be induced in any of them.
The present series o/investigation reveal at the same time that even at a dosage o/~ooo r while the capacity o/division o/polyploid cells in a
particular medium is lost, the normal cells can undergo division/or a
considerable period. This is a [eature which is worth noting as it may indicate that the susceptibility o I the diHerentiated nuclei to irradiation are more than the meristematic ones. I t is, however, contrary to general expec- tations. An investigation in this direction is highly desirable. The be- havionr of differentiated nuclei in similar set of experiments conducted at different temperatures are desired to be carried out later.
Within the polyploid nuclei it may be noted that fragments have been recorded, which is however quite expected following irradiation treatment, Though the frequency of the fragments has been found to be more or less the same ill all tile polyploid nuclei at different hours of observation, the exact frequency data has not yet been taken. Once the accurate confirmatory data is obtained, it may be possible to suggest that as far as the polyploid nuclei are concerned, their suscep- tibility at different stage of the resting state is practically the same towards irradiation. Its implications are far reaching.
In addition to abnormalities involving po!yp!oid nuclei, aberrations in diploid cells have been recorded in the table. This is, however, quite expected in irradiation experiments.
SUMMARY
I. Dry bulbs of Allium cepa were exposed to X-rays of two dif- ferent dosages, viz. 250 r and 1000 r with a view to observe the effect of irradiation on the resting differentiated polyploid nuclei. The irra- diated bulbs were transferred to different media for growth, viz. Nucleic acid solution, a mixture of base, sugar and phosphate; and the Laevulose sugar alone. These solutions have been proved in earlier publications to be endowed with capacity of inducing division in poly- ploid nuclei. The observa.tiollS were continued upto one hundred and
EFFECT OF IRRADIATION ON ADULT NUCLEI IN PLANTS 168
sixty-eight hours of irradiation, at an interval of twenty-four hours
each, and every day new emerging roots were taken entirely for ob- servation with the basal portion intact. While taking the roots for observation, the layer of stem tissue adjoining the roots were also taken. I t is obvious that latter consisted of high number of adult nuclei, which was also observed in controls.
2. I t has been noted that the resting polyploid cells under the in- fluence of irradiation underwent such a tremendous change that neither Nucleic acid solution, nor Laevulose solution, which normally
induces division, could cause division significantly in them. The mixture t reatment on the other hand revealed considerable frequency of division
in polyploid nuclei in those which were irradiated at a dosage of 250 r: With 1000 r, however, the effect has been found to be very" drastic.
3. The implications of these findings have been discussed and it has
been suggested that irradiation causes a change in the normal synthe- sis of at least base and phosphate of Nucleic acid. A number of other abnormalities too have been recorded. I t has been claimed that the normal and differentiated nuclei differ in their susceptibility to irradiation.
REFERENCES
D'AMATO, F. 1950. Differenzione Is tologica Pe r Endopolyp lo id ia Nelle Rad ic i
D ; A l e u m lVIonocotiledoni. Caryologia, 3 : 11-26.
HUSKtNS, C. L. 1947. T h e subd iv i s ion of t he ch romosomes and the i r mul t ip l i -
ca t ion in non-d iv id ing t i s sues : Poss ible i n t e rp re t a t i ons in t e r m of gene
s t r uc tu r e & gene act ion. Amez. Nat., 8z: 401-434.
HUSKINS, C. L. and L. M. STENITZ 1948a. T he nuc leus in d i f fe rent ia t ion and
deve lopmen t . I. H e t e r o c h r o m a t i n bodies in energic nuclei of Rhoeo roots. J .
~ered., 39: 35-4&
- - & - - 1948b. T he nuc leus in d i f ferent ia t ion and deve lopment . II . I n -
duced mi tos i s in d i f fe ren t ia ted t i ssues of Rhoeo roots. J. Hered., 39 : 67-77. KAUFMANN, B. P. 1954. C h romosome aber ra t ion induced i n A n i m a l cells b y
Ioniz ing rad ia t ions . Radiation Biology, I : 627-711. LEA, D. E. 1946. Act ion of R a d i a t i o n on l iv ing ceils, Cambr idge U n i v e r s i t y Press .
MULLER, H. J. 1954. T h e m a n n e r of p roduc t ion of m u t a t i o n s by Rad ia t ion . Radiation Biology, I : 475-626.
SttARMA, A. K. a n d BIBHA BHATTACHARYYA 1954. V i t amins - the i r p r o p e r t y oi
i nduc ing divis ion in d i f ferent ia ted ce!ls. Abst., Proc. Ind. Sc. Congr., 149.
- - - a n d S. SEN 1954. I n d u c t i o n of division t h o u g h nucleic acid t r e a t m e n t . Caryologia, 6: 151-159.
- - ARCHANA MOOKERJiSA 1955. I n d u c t i o n of division- a s t u d y of t he causa l
fac tors involved. Bull. Bol. Soc., Beng., G. C. Bose Memorial Vol. (In press).
164 ARUN KUMAR SHARMA AND RAMENI)RA K. MUKHERJI
1
Fig. 4
IViicrophoto I IVficrophoto II
Figs. I to 4. Radiation effects on chromosomes of All{urn cep~ fo]lowing growth
in nucleic acid after irradiation at 250r showing polyploid metaphase, fragmen-
tation in anaphase, anaphase bridge and reductional grouping with fragments respectively.
Microphotos I & II. Photographs of Figs. 4 and 2 respectively.