The Journal of Heredity 2001:92(4)
© 2001 The American Genetic Association 92:360-361
Brief Communication |
Banded Polytene Chromosomes in Developing Endosperm of Pearl Millet
From the Department of Botany, Andhra University, Waltair 530 003, India (Rajya Lakshmi, Nimmi, Raja Rao, and Narasinga Rao) and Oak Ridge Biotech (OrBit), 148 Brentwood Circle, Oliver Springs, Tennessee (Narayana).
Address correspondence to T. V. Rajya Lakshmi and N. R. Isola at the address above or e-mail: Rajyalakshmit{at}hotmail.com.
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionReferences |
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The occurrence of polyteny in the endosperm of field-grown plants as well as cultured endosperms of variety Vg272 of pearl millet (Pennisetum glaucum (L.) R.Br.) is recorded. There is a pronounced banded structure of these chromosomes similar to the ones observed in Dipteran salivary glands. Polyteny under physiologically controlled conditions also seems feasible in pearl millet.
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Introduction |
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Polytene chromosomes occur not only in the salivary glands of Diptera, but also in the storage tissues of certain angiosperm plants (reviewed by Nagl 1981). Polytene chromosomes were reported in the endosperm of cereals: wheat (Chojecki et al. 1986; Donovan 1979), rice (Ramachandran and Raghavan 1989), and maize (Kowles et al. 1990; Phillips et al. 1983). Nagl (1981) reviewed the occurrence, structure, function, and evolutionary aspects of plant polytene chromosomes. The somatic pairing and typical band and interband appearance of Dipteran polytene chromosomes usually is not observed in plants. They are normally granular in appearance and not paired (Nagl 1981). In this article we describe the occurrence of banded polytene chromosomes in the endosperm of pearl millet in vivo and in vitro conditions.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionReferences |
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Inflorescences were enclosed in waxed paper bags prior to the emergence of the styles. The bagged inflorescences were pollinated with pollen collected from sibs and samples were collected for both in vitro and in vivo analysis at different hours after pollination. The embryo sacs were dissected in 45% acetic acid and stained in 2% acetocarmine using standard cytological methods. Both nuclear and cellular endosperm were cultured in liquid N6 medium (Chu et al. 1975) containing 3.0 mg/L of 2,4-D and 10% sucrose pH 5.8 and the cultures were maintained at 28 ± 2°C with a 12 h light:12 h dark photoperiod.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionReferences |
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The endosperm of pearl millet is a polygonum type that begins in a free nuclear state and cell formation is complete by about 96 h after pollination. Cell division occurs at a very low frequency, with a mitotic index of 0.19%. The interphase cells are of two types: small cells containing a small nucleus and nucleolus, and large cells containing a prominently large nucleolus and chromatin threads. The latter are closer to the embryo and show banded polytene chromosomes by the seventh day after pollination. Band and interband regions are quite pronounced throughout the entire length of the chromosome (Figure 1a).
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perm nuclei of embryo sacs after 10 days of culture showing closely interwoven polyte
e chromosomes with thick disc-shaped bands (arrows) (x1000).When the cellular endosperm (4 days after pollination) was cultured in vitro no polytene chromosomes appeared, even after 25 days in culture. However, when the endosperm in the free nuclear stage (2 days after pollination) was cultured, about 5% of the embryo sacs showed large endosperm nuclei by about 10 days of culture and these nuclei contained polytene chromosomes (Figure 1b).
Nagl (1981) inferred that plants with smaller C values have a tendency to undergo endoreduplication and pearl millet with a C value of 2.5 pg (Kidd et al. 1987) is consistent with this correlation. While polytene chromosomes with no discernible banding patterns were reported in other cereals such as rice (Ramachandran and Raghavan 1989), wheat (Chojecki et al. 1986; Donovan 1979; Evers 1970), and corn (Kowles and Phillips 1985), clear banding patterns were observed in pearl millet endosperm nuclei both in vivo and in vitro. Banded polytene chromosomes were observed in Phaseolus (Nagl 1981) both in natural cultures as well as by induction with cold treatments. While the polytene chromosomes are restricted to one to three cells in the embryo suspensor cells of legumes, the developing endosperm of pearl millet consists of a large population of polytene nuclei, thus providing sufficient material for further studies such as understanding the mechanism of polyteny in plants and in situ hybridization mapping.
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Acknowledgments |
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The article is dedicated to late Prof. M. Krishna Rao our mentor and friend. We thank the Council of Scientific and Industrial Research for financial support (to T.V.R.L. and Ch.N.). This work was submitted for partial fulfillment of Ph.D. dissertation (Ch.N.) to Andhra University, Waltair, India.
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Footnotes |
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Corresponding Editor: Prem P. Jauhar
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References |
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Chojecki AJS, Bayliss MW, and Gale MD, 1986. Cell production and DNA accumulation in the wheat endosperm and their association with grain weight. Ann Bot 58:809–827.
Chu CC, Wang CC, Sun CS, Hsu CY, Yin KC, and Chu CY, 1975. Establishment of an efficient medium for anther culture of rice through comparative experiments on the nitrogen sources. Sci Sin 18:659–668.
Donovan GR, 1979. Relationship between grain nitrogen, non-protein nitrogen and nucleic acids during wheat grain development. Aust J Physiol 6:449–457.
Evers AD, 1970. Development of the endosperm of wheat. Ann Bot 34:547–555.
Kidd AD, Francis D, and Bennett MD 1987. Replicon size, mean rate of DNA replication and duration of cell cycle and its component phase in eight monocotyledonous species of contrasting DNA values. Ann Bot 59:603–609.
Kowles RV and Phillips RL, 1985. DNA amplification patterns in maize endosperm nuclei during kernel development. Proc Natl Acad Sci USA 82:7010–7014.
Kowles RV, Srienc F, and Phillips RL, 1990. Endoreduplication of nuclear DNA in the developing maize endosperm. Dev Genet 11:125–132.
Nagl W, 1981. Polytene chromosomes of plants. Int Rev Cytol 73:21–53.
Phillips RL, Wang AS, and Kowles RV, 1983. Molecular and developmental cytogenetics of gene multiplicity in maize. Stadler Genet Symp 15:105–118.
Ramachandran C and Raghavan V, 1989. Changes in nuclear DNA content of endosperm cells during grain development in rice (Oriza sativa). Ann Bot 64:459–468.
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