DNA content and heterochromatin in the genus Zea --C. Tito, L. Poggio and C. A. Naranjo New data about the 2C nuclear DNA content in seven taxa of the genus Zea are reported in the present work. The measurements were made by microdensitometry of Feulgen stained root tip telophase cells. The technique was done according to Poggio and Hunziker (J. Hered. 77:43-48, 1986). The results are summarized in Table 1 in which are included part of our previous data (Tito, Poggio and Naranjo, MNL 62:74-75, 1988).

Table 1. DNA content, C-band number and interval from germination to flowering.

An analysis of variance and comparisons between means using Scheffe's method on the overall data revealed significant differences between species of Zea and between lines and varieties of Z. mays ssp. mays. Lines or varieties with significant differences in total DNA content are indicated in Table 1.

Rayburn, Price, Smith and Gold (Amer. J. Bot. 72:1610-1617, 1985) and Laurie and Bennett (Heredity 55:307-313, 1985) have shown that there is a significant positive correlation between C band number, percent C band heterochromatin and genome size. The same correlation was observed in the accessions studied. Correspondence between the amount of C banded material in metaphase and in interphase nuclei has been observed as in other genera (Fig. 1).

Figure 1. C-banding. A, C and E mitotic metaphases. B, D and F interphases (chromocenters). A and B = Z. m. ssp. mays line 104; C and D = Z. m. ssp. mays line 129; E and F = Z. luxurians. The scale represents 10 um, all with the same enlargement.

The E and Z lines let us analyze an interesting phenomenon. Mazoti (Mendeliana 8:45-52, 1987) established that the knobs of Z line increase their size and DNA content in the presence of one plasmon of Z. mays ssp. mexicana (this combination is named E line). The total content is higher in the mentioned E line (Table 1). Although the C band numbers in mitotic interphase nuclei are the same in both lines, the C+ chromocenters are bigger in E line. Whether the results are due to an exceptional nucleus-cytoplasmic system or because of a more generalized phenomenon is still unknown.

The annual Z. luxurians has higher DNA content and C heterochromatic bands in comparison with other 2n=20 members of the genus (Table 1, Fig. 1). Similar results were obtained by Laurie and Bennett (ibid.).

Moreover, the results shown in Table 1 indicate a positive correlation between total DNA content and the interval from germination to flowering.


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