JUIZ DE FORA-MG, BRAZIL

Universidade Federal de Juiz de Fora

VICOSA-MG, BRAZIL

Universidade Federal de Vicosa

 Image analysis as a tool for chromosome deficiency identification in maize --Viccini, LF, de Carvalho, CR Seeds originating from irradiated pollen (maize test-line L-869 of Federal University of Viçosa) were germinated in Petri dishes with a film of distilled water in the dark at 28-29 C. Root tips ranging from 0.5 to 1.0 cm in length were pre-treated with 0.02% colchicine solution for 2h30min. Slides were prepared by the air drying technique with enzymatic maceration.

Image analysis was performed on Macintosh computer using the public domain NHI-Image SXM 1.61 software (Rasband, 1997). Chromosome images were captured by a video camera coupled to the microscope-computer system so as to generate 256 gray value density profile plots.

Chromosome measurements were obtained by the difference of chromosomal area density and that of the background, with the selection tool of the software (profile plot line�width 12) being used. The plot pixel value of relative density was calibrated to the range of 0 (white) to 255 (black). The background picture was set to 0 gray value and the chromosome length spatial was perfomed in micrometers (Carvalho and Saraiva, 1997).

Five metaphases presenting deficiency in chromosome 6 were randomly chosen for analysis (Figure 1). When comparing the chromosome-6 arm length average values, it is observed that the measure of both short arms is about the same, while the long arm difference is 0.67 mm, corresponding approximately to 26% the size of a normal long arm (Table 1).

Normal and deficiency chromosome graphs were overlapped to evidence the alteration (Figure 2). The overlapping of the density graphics of each chromosome of the first homologue pair represented in Figure 1 shows a 0.90 mm chromosome II deficiency. Thus, making it possible to evaluate deficiency length, by considering the difference between chromosome density and that of the background.

It is verified that the image analysis by means of computational resources is a useful tool in studies of this nature.

Table 1. Measurements (mm) of deficient and normal chromosome 6 originated from five metaphases.
 
 
Chromosome 6
 
Deficient
Normal
 
Arm
  
Arm
  
  Short* Long Length Short* Long Length
  1.35 1.88 3.23 1.42 2.78 4.20
  1.53 1.87 3.40 1.59 2.44 4.03
  1.65 1.93 3.58 1.59 2.44 4.03
  1.63 1.99 3.62 1.65 2.73 4.38
  1.59 1.92 3.51 1.48 2.56 4.04
Average 1.55 1.92 3.47 1.55 2.59 4.14

* satellite out.
 
 

Figure 1. Five pairs of chromosome 6 in root tips of germinating seeds derived from g-irradiated pollen grains (72 Gy). The chromosomes (left) present a deficiency in the long arm. Bar=5 mm.

Figure 2. Graph showing density overlap of chromosome 6 pairs. The dark gray area corresponds to gray value of the normal chromosome and the clear gray area of the deficient chromosome.
 
 

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