Viçosa, Brazil
Universidade Federal de Viçosa
Cytogenetic mapping of sister chromatid
exchange points in maize
--Borges, CMO , Carvalho, CR
In order to map the sister chromatid exchange
(SCE) points in maize, image analysis resources by computational methods
(Rasband. NIH-image 1.60 anonymous ftp from zippy.nimh.ninh.gov) were used
in association with cytogenetic techniques. Maize seeds from the test line
from Universidade Federal de Viçosa were germinated and the roots
treated with a 100 µM 5-bromo-2`-deoxyuridine solution for 22 hours
and then with a 0.02% colchicine solution for 2 to 3 hours, both done in
the dark at 28 C. The roots were fixed in a methanol:acetic acid (3:1)
solution and slides were prepared by the air-drying technique after enzymatic
maceration (Carvalho, Saraiva. Heredity, 70:515-519,1993). The preparations
were stained with Hoechst 33258 for 10 minutes, irradiated with a UV-254
nm light for 5 to 15 minutes and stained with a 2% Giemsa solution, for
10 minutes (Perry, Wolff. Nature, 251,156,1974). Images of chromosome figures
were captured directly from the microscope by means of a video camera coupled
to a computer and digitized with an image analysis software. To generate
256 gray value density profile plots, chromosome images were calibrated
to the range of 0 (white) to 255 (black) and spatial calibration from chromosome
length was performed in micrometers. This methodology permitted the identification
of the SCE points with enough resolution to measure the relative and absolute
positions of the exchanged segments (Fig. 1). These results were used to
elaborate the maps of the positive and negative regions of the SCEs.
Figure
1. The plot pixel value of 256 gray scale of sister chromatid exchanges
in maize chromosomes (numbers: 6, 9, 1 and 3). The background picture was
set to a 0 gray value and chromosome length in micrometers. C = centromere.
Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.
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