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Studies on the Distribution of BChromosomes in Different PlantParts of Trigonella Foenum-Graecum L.S. S. Raghuvanshia & Manjula Pant (neè Upreti)a

a Cytogenetics and Plant Breeding Laboratory, BotanyDepartment, Lucknow University, Lucknow, IndiaPublished online: 30 Jan 2014.

To cite this article: S. S. Raghuvanshi & Manjula Pant (neè Upreti) (1980) Studieson the Distribution of B Chromosomes in Different Plant Parts of Trigonella Foenum-Graecum L., Caryologia: International Journal of Cytology, Cytosystematics andCytogenetics, 33:2, 215-225, DOI: 10.1080/00087114.1980.10796833

To link to this article: http://dx.doi.org/10.1080/00087114.1980.10796833

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STUDIES ON THE DISTRIBUTION OF B CHROMOSOMES IN DIFFERENT PLANT PARTS

OF TRIGONELLA FOENUM-GRAECUM L.

S. S. RAGHUVANSHI and MANJULA PANT (nee UPRETI)

Cytogenetics and Plant Breeding Laboratory, Botany Department, Lucknow University, Lucknow, India

Received: 30'• July 1979

INTRODUCTION

One of the principal characteristics of the B chromosomes is their numerical variability between different tissues in the same individual and between cells in the same tissue. They are mechanically less efficient, succumbing to loss through anaphase lagging and mitotic non disjunction. The latter event leads to numerical variation within the individual and may be associated with a net gain or loss of Bs, depending on the stage of development at which it occurs and the way in which the dividing cells are subsequently distributed. Surveys in Poa alpina (Mi.iNTZING and NYGREN 1955) Poa timoleontis (NYGREN 1957), Haplopappus spinulosus (LI and JACKSON 1961), Xanthisma taxanum (BERGER and WITKUS et al. 1955), Crepis capillaris (RuTISHAUSER 1963 ), Regnellidium diphyllum, a pte­ridophyte (JosHI and RAGHUVANSHI 1973) indicate that B chromosomes frequently show numerical variability. There exists nevertheless, many different cases in which the number of Bs is remarkably constant in a single individual, as for example in Agrostis, Alopecurus, Anthoxanthum, Briza, Dactylis, Festuca, Holcus, Phleum, Secale etc.

The present work is an attempt to study the distribution of Bs in the various tissues of Trigonella foenum-graecum plants. B chromosomes smaller than the normal complement have already been reported in this species (RAGHUVANSHI and JosHI 1964) but the B chromosomes dealt herewith are indistinguishable from chromosomes of normal complement (RAGHUVANSHI and UPRETI 1977).

Caryologia, 33: 215-225, 1980

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216 RAGHUVANSHI and PANT

MATERIALS AND l\IETHODS

Seeds were germinated in petridishes. After two or three days primary root tips were cut and fixed and the remaining seeds were sown in saw dust. At two cotyledonary stage, the secondary roots were cut and finally seedlings were trans­planted in soil for further growth so that it was possible to study the chromosomal pattern in cells of root, shoot, leaf, petal and PMCs of the same plant.

Root tip tissues were pretreated in .04% aesculine at 15°C for 2 hours. Shoot tip, leaf tip and petal tip tissues were pretreated in .002 M oxyquinoline at 12°C for one hour. After pre-treatment all the material was thoroughly washed and then fixed in 1: .3 acetic alcohol. After 48 hours it was followed by hydrolysis in 1N HCl at 60°C for 20 minutes. Thorough washing was done and the tissues were kept in iron alum solution for one hour. Then stained in haematoxylin for 3 to 4 hours and squashed in 45% acetic acid.

For meiotic preparations young flower buds of individual plants were fixed separately in acetic alcohol ( 1: 3) fortified with iron. PMCs were observed after staining in aceto-carmine. Appropriate stages were studied and the photographs were obtained from temporary preparations. Later on the slides were made permanent by ethanol butanol schedule.

OBSERVATION

The chromosome number of non carrier plant of this selection has been found to be 2n = 16 confirming the earlier reports for this species (DARLINGTON and WYLIE 1955; MoORE 1973; RAGHUVANSHI and JOSHI 1965). The carrier plants however, have 2n = 16 + 2B where the two chromosomes are extra and indistinguishable from chromosomes of normal complement. Their meiotic behaviour was carefully followed at different stages. The carrier plants have two types of PMCs, one having normal complement of eight bivalents (Fig. 1) and the other with nine bivalents (Fig. 2). These studies have clearly demonstrated that whenever present in a PMC, the B chromosomes are two in number (Fig. 2). They are euchromatic and regularly pair to form bivalent which orients itself with other bivalents at metaphase plates. This bivalent undergoes normal separation at subsequent stages. Ultimately one B chromosome is included in each of the four telophasic nuclei. As the behaviour of these B chromosomes is normal, it is expected that they will be passed on to pollen grains.

Since there is no phenotypic marker, meiosis was analysed first of all to identify the carrier plants before undertaking somatic study. For the present study fifteen plants having 2B chromosomes in PMCs ranging from 10 to 30.7% were selected. Like PMCs, in somatic cells also 0 or 2B chromosomes were seen (Figs. 3, 4, 5, 6, 7, 8). Normal cells had

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Fig. 1. - Normal PMC with 8 bivalents. Fig. 2. - Carrier PMC with 8 + 1B bivalent. Figs. 3, 5, 7. Normal root, leaf and shoot tip cells respectively with 2n = 16. Figs. 4, 6, 8. - Carrier root, leaf and shoot tip cells respectively with 2n = 16 + 2B.

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218 RAGHUVANSHI and PANT

16 chromosomes and the carrier cells showed 18 chromosomes. The two extra chromosomes are B chromosomes, apparently indistinguishable from other somatic chromosomes. It is apparent from Table-1 that in some plants all parts could not be studied due to lack of sufficient material.

Root tip cells of 13 plants were studied and B chromosomes were present in all the plants. Sufficient number of cells have been analysed to ensure accurate frequency of B chromosomes in different plant parts.

10

5

2 3 4 5 6 PLANT

_PMC ....... SHOOT TIP CEUS ----LEAF Tl P CEU.S ---ROOT Tl P CELLS

7891011 NUMBER

12 13 14 15

Fig. 9. - Distribution pattern of B chromosomes in the various plant parts arranged according to increasing order of B frequency in the PMCs from plant no. 1 to 15.

There is a remarkable variation in frequency of carrier cells in roots in different plants ranging from 12.5% to 34.7% . Shoot tip study in fourteen plants showed the presence of 2B chromosomes in 10.7 to 35.7% carrier cells. Leaf tip cells of all the fifteen plants could be successfully analysed and the cells were either normal type or had 2B chromosomes in 12.5 to 32% cells. Petal tip study was most difficult because dividing cells were rather rare. Despite best of efforts, division could be found in only two plants and in these also sufficient number of cells could not be studied. B chromosomes, however, were present in both the plants and their frequency varied from 7.5 to 11%.

In Fig. 9 the plants are arranged according to increasing frequency of carrier PMCs from 10% to 3 2% . It is to be noted that up to plants possessing more or less 20% carrier PMCs the distribution frequency in their other parts is more or less constantly higher. Beyond this, the

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Tab

le 1

Pla

nt w

ise

data

for

dis

trib

utio

n o

f B

Chr

omos

omes

in

PM

Cs,

pe

tal

tip,

sh

oot

tip,

le

af

tip

and

root

ti

p ce

lls.

PM

C

Pet

al

Sho

ot

Lea

f R

oot

Ave

rage

.....

e-0

"' "'

"' "'

"' c:

...

....

....

r:Q

t"''"C

r:Q

]~~

r:Q

]~13

r:Q

....

r:Q

... c:

... Jl

'"

0

N

N

N

N

~=ii

N

::I ..

E~

8..!!1

~ ..o

:::::l

...

B'

-a

:E-5

8

.... _

"'.

..C::

8 ...

. _

..!!l...c

:: 8

.... _

"'.

..C::

8"'

;a

"'...c:

: U

'"C

U

'"O

U'"O

....

C:::i

:i~ ~

:::::l

...

-...

:::::l

......

:i~

::I

:::::l

...

..... ..

..

........

:it;~

....-:i

t;~

........

zt; ~

..,.

_ .....

... r:a

&

u~

u~

u~

u~

0~

u~

1 60

6(

10

%)

--

50

8(16

%

) 48

6(

12.5

%)

12.8

%

2 46

5(

10.9

%)

-31

6(

19.4

%)

39

7(17

.9%

) 53

13

(24.

5%)

18.2

%

3 51

6(

11.8

%)

6 0(

0%)

28

3(10

.7%

) 34

5(

14.7

%)

60

12(2

0 %

) 11

.4%

4

48

6(12

.5%

) 9

1(11

.1%

) 25

6(

24

%)

28

5(17

.9%

) 26

5(

19.2

%)

16.9

%

5 93

14

(15.

1%)

14

1(7.

1)

36

7(19

.4%

) 42

7(

16.7

%)

-14

.6%

6

41

7(17

.1%

) -

22

6(27

.3%

) 42

13

(31.

0%)

31

7(22

.6%

) 24

.5%

7

39

7(17

.9%

) -

46

10(2

1.7%

) 24

6(

25

%)

38

9(23

.7%

) 22

.1%

8

37

7(18

.9%

) ·-

38

9(23

.7%

) 33

9(

27.3

%)

-23

.3%

9

65

13(2

0 %

) -

44

12(2

7.3%

) 41

11

(26.

8%)

16

3(18

.8%

\ 23

.2%

10

24

5(

20.8

%)

-35

5(

14.3

%

39

6(15

.4%

) 51

11

(21.

6%)

18

%

11

27

6(22

.2%

) -

42

9(21

.4%

) 32

4(

12.5

%)

36

6(16

.7%

) 18

.2%

12

26

6(

23.1

%)

-42

15

(35.

7%)

27

6(22

.2%

) 24

5(

20.8

%)

25.5

%

13

42

10(2

3.8%

) -

29

7(24

.1%

) 34

8(

23.5

%)

25

5(20

%

) 22

.9%

14

28

8(

28.6

%)

-32

11

(34.

4%)

42

11(2

6.2%

) 28

7(

25

%)

28.5

%

15

52

16(3

0.8%

) -

30

8(26

.7%

) 25

8(

32%

) 23

8(

34.8

%)

31.1

%

Tot

al

679

122

29

2 48

0 11

4 53

2 11

4 45

9 97

nu

mbe

r of

ce

lls

--

Tot

al

18.8

9 ±

1.

613

6.08

±

3.

250

23.5

8 ±

1.

810

21.6

7 +

1.609

21

.51 +

1.494

m

ean

valu

es

per

orga

n

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220 RAGHUVANSHI and PANT

situation changes, the frequency in root tip and leaf tip becomes lower but the shoot tip carrier cells maintain the higher position though initially after 20% carrier PMC plants there is a dip (plant no. 10). In the last plant, having 32% carrier PMCs, the pattern becomes just reverse. Here the B frequency in root tip cells and leaf tip cells show higher frequency while the shoot tip B frequency becomes lower. The over all pattern of B chromosome distribution in various plant parts of carriers is random.

PMC SHOOT TIP

PLANT

LEAF TIP

PART

Fig. 10. - Average pattern of B chromosomes per organ.

ROOT TIP

There is no generalized picture to correlate them. But the interesting point to be noted is that the total mean values of carrier cells per organ in PMCs, shoot tips, leaf tips and root tips of all the fifteen plants studied do not show a significant difference, that is they are almost same. This has been statistically proved in Table-2.

The average values of B frequency per plant in various parts is given in Table 1. It can be noted that the plants having lower B frequency in

TABLE 2

Test of significance for the differences among tissues of the mean frequencies of B-carrying cells (t-values and lowest P-values are presented; dF = 25-28).

Shoot Tissue

Leaf Root

P> P> P>

PMC 1.93 0.05 1.22 0.2 1.19 0.2 Shoot 0.79 0.1 0.88 0.3 Leaf 0.07 0.9

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B-CHROMOSOMES IN TRIGONELLA 221

the PMCs have lower average values (plant no. 1, 2, 3) as compared to the plants having higher B frequency in the PMCs (plant no. 14 and 15), although it does not have a well defined pattern through out the series.

DISCUSSION

The regular me10t1c behaviour, indistinguishable and euchromatic nature of B chromosomes suggest comparatively recent origin of these Bs from A chromosomes. Though morphologically these Bs have not undergone sufficient evolution to be distinguished from choromosomes of normal complement but obviously some genetical mechanism is under operation that does not permit any multivalent configurations. In Regnellidium diphyl­lum {JOSHI and RAGHUVANSHI 1973) and Impatiens balsamina (RAGHU­VANSHI and SING 1979) Bs indistinguishable from chromosomes of regular complement behave in same manner as in Trigonella foenum-graecum.

Study of distribution of B chromosome in different plant parts has been carried out only in few cases. In Sorghum purpureosaricum (DARLINGTON and THOMAS 1941) and Poa alpina (MuNTZING 1946) elimination of B chromosomes by lagging from somatic tissue was judged by root tip examination, yet maintained in cells that become the germ track was reported. BERGER, McMAHON and WITKUS (1955) reported similar cases in Xanthisma texanum. In Poa alp ina, HAKANSSON ( 1948) reported presence of B chromosome in all the primary roots but they were eliminated from adventitious roots. Detailed studies of distribution of Bs in different plant parts of Regnellidium diphyllum, a pteridophyte (JosHI and RAGHUVANSHI 197 3) revealed their presence in spore mother cells, root, shoot and leaves in varying frequency (12.3% in root tip cells, 18.6% in shoot tip cells, 8.7% in leaf tip cells and 9.7% in spore mother cells). In Ficus krishnae, a tree, presence of Bs in adventitious roots and in sporogenous tissue has been reported from our laboratory (JosHI and RAGHUVANSHI 1970). Recently B chromosome distribution in various plant parts has been studied in detail in Impatiens balsamina (RAGHUVANSHI and SINGH 1979). They have reported their presence in PMCs, root, shoot, leaf and petal tip cells although frequency of carrier cells differed in the various parts. Meiotic cells have two Bs while the somatic cells have only one B in the carrier cells. Thus showing duplication of Bs in sporogenous tissue.

Present study has clearly revealed that the Bs are present in all parts of the plant though frequency of carrier cells is varying in different plants. Their total mean values per organ show that maximum frequency existed in cells of shoot tip followed by root tip, leaf tip and PMC. Though there is marked difference in the frequency of Bs in each plant part but when

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222 RAGHUVANSHI and PANT

total mean values per organ of all plants are statistically compared then no significant difference was found (Table 2). In the petal tip squashes very few cells could be screened. Although presence of Bs have been clearly demonstrated yet their low frequency in petals cannot be taken to be well established. In comparing the frequency of Bs in different plant parts, no clear cut generalization can be made. It is remarkable that plants having lower B frequency in the PMCs have somewhat lower frequency in all the plant parts, for example in plant number 1, ( PMC 10% ; leaf tip 16% ; and root tip 12.5% ). On the other hand plants having higher B frequency in the PMCs have more or less higher frequency in all the other parts of the plants, for example in plant number 15 (PMC 30.7%; shoot tip 26.6%; leaf tip 32%; root tip 34.7%). Although there is no well defined pattern in the sequence. Accessories in Pterotheca falconeri (MEHRA and MANN 1972) showed a fairly high degree of constancy in PMCs and somatic tissues (Root, shoot and anther wall) unlike Crepis conyzaefolia, Crepis pannonica (FROST and OsTERGREN 1959) Sorghum purpureosaricum (DAR­LINGTON and THOMAS 1941), Poa alpina (MUNTZING 1946, 1948, 1966), Xanthisma taxanum (BERGER, McMAHON and WITKUS 1955), Haplopappus gracilis (OsTERGREN and FROST 1962), Ranunculus acris and Phleum nodosum (FROST 1969a and 1969b) where difference in the number of accessories existed between certain somatic tissues and germ cells.

The most important finding of the present investigation is invariable presence of only 2B chromosomes in all carrier cells of root, shoot, leaf, petal and PMCs of same plant although there is variation in the frequency of carrier cells. There is some genetic mechanism which is controlling the fixed number of 2Bs, both in shoot system and in root system. It is not doubtful that two Bs in PMCs are homologous pair because they show regular pairing, chiasma formation and normal segregation during meiosis. Only one B goes to the pollen grain so the question naturally arises about the nature of mechanism that ensures duplication of B chromosomes and at what stage it occurs. Total studies including all plant parts are based on 2179 cells out of which 449 cells had two B chromosomes. The shoot which is really the germ track has two B chromosomes. It is suspected that doubling in number of Bs takes place somewhere during zygote development or pollen mitosis. Many B systems have accumulation me­chanisms whereby the parental frequency of B chromosome is boosted before transmission to the next generation and these operate before or during or even after meiosis. Clearly such enhanced transmission can be an important factor in maintaining a B chromosome polymorphism (VosA 1962). In rye there is peculiar ability of the accessory chromosome to undergo non disjunction at first mitosis in the pollen grain. By this process

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B-CHROMOSOMES IN TRIGONELLA 223

both chromatids pass to the generative pole and in the offspring the number of accessory chromosomes will therefore be about twice as high as expected (MuNTZING 1954 ). OsTERGREN ( 1947) found the same mecha­nism in the pollen mitosis of a species of Anthoxanthum. One of the remarkable aspects of present material is absolute constancy in number of B chromosomes in all carriers.

Most species with accessory chromosome show a regular behaviour of the accessories in somatic mitosis and consequently the number of accessories present at meiosis is the same as the number present in root tips. In Zea mays (DARLINGTON and UPCOTT 1941) and Poa trivialis (BosEMARK 19.57) there is certain degree of somatic variation in number which has been thought to be due to weakness in the centromere of acces­sories. NYGREN (1957) has observed somatic elimination of 2 accessory chromosomes in Poa timoleontis. The single plant examined had 14 chromo­somes in the root tips and eight bivalents at meiosis. In Trigonella foenum­graecum there is no such elimination and different vegetative parts and PMCs show presence of 2B chromosomes. There are reports to indicate a premeiotic boosting mechanism to increase the number of B chromosomes in the PMCs in the species of Crepis pannonica (FROST 1960; RuTISHAUSER and RoTHLISBERGER 1966). Plant with one, two and three Bs in root and somatic tissues of immature flower head always show two, four and six Bs respectively in their pollen mother cells.

Concluding the studies these Bs appear to be newly derived from A complement but sufficiently evolved to suppress multivalent formation. Some genetic mechanism ensures presence of 2Bs in carrier meiotic and somatic cells. This ensures their regular transmission to successive progenies. Further evolution of these Bs may change their present nature. They are present in all the plant parts. The range of carrier cells from 10 to 34% indicate that 34% is the maximum tolerance limit in the present material. But interesting point to be noted is that despite variation in frequency of carrier cells in different tissues and different plants when total mean value of individual organ of all the plants is taken then no statistically significant difference was found.

REFERENCES

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BosEMARK N. 0., 1957b. - Further studies on accessory chromosomes in grasses. Hereditas, 43: 236-297.

DARLINGTON C. D. and THOMAS P. T., 1941. - Morbid mitosis and the activity of inert chromosomes in Sorghum. Proc. Roy. Soc. London B., 130: 127-150.

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224 RAGHUVANSHI and PANT

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B-CHROMOSOMES IN TRI&ONELLA 225

SUMMARY

A new strain of Trigonella foenum-graecum has B-chromosomes indistinguishable from chromosomes of regular complement. Study of carrier plants revealed that both somatic and meiotic carrier cells have 213 chromosomes. In PMCs the 2B chromosomes pair to form a bivalent that behaves normally during meiosis. The carrier cells of root, shoot, leaf and petal tips show 18 chromosomes besides 16 chromosomes in non carrier cells. Genetic mechanism ensuring 2Bs in the carrier cells is discussed. Their regular meiotic behaviour, indistinguishable and euchromatic nature, indicate comparatively recent origin. It has been found that the plants having lower B frequency in the PMCs have lower average values of its various parts and vise versa. There is a random distribution of chromosomes in the various plant parts but the interesting point to note is that the total mean values of carrier cells in PMCs, shoot tips, leaf tips and root tips of all carrier plants is almost the same.

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