A new heterochromatin banding pattern for maize root tip chromosomes was revealed by a modified HKG-(HCI-KOH-Giemsa) banding technique. Comparison of this pattern with that obtained by the C-banding technique showed that the two techniques stain different types of heterochromatin. The HKG-banding technique stains both centromeric and intercalary heterochromatin, whereas the C-banding technique reveals only knob heterochromatin. The presence of an 1-1KG intercalary band adjacent to the knob suggests a more complex constitution for the heterochromatic block of the knob.

The air drying technique, widely used in animal cytogenetics, was adapted for use with Zea mays L. chromosomes. Using a simple protocol without enzymatic maceration and avoiding the inconvenience of the squashing technique, good staining and C-banding were obtained from maize chromosome preparations.

(Nassar l978a,b,c,d, 1979(Nassar l978a,b,c,d, , 1985(Nassar l978a,b,c,d, , 1986. One of the most useful species for plant breeding is Manihot neusann Nassar. It is tolerant to low temperature, resistant to stem borers, highly resistant to bacterial diseases and has an evergreen habit (Nassar 1985). An interspecific hybrid between this species and cassava was obtained earlier (Nassar 1989

Root-Up maize chromosomes (2n= 20) were prepared by high-resoluUon procedures after ethidlum bromide/ colchlcine synchronization. Using HKG-banding (HCl-KOH-Glemsa), that shows both centromerlc and intercalary heterochromatin, the banding pattern of the elongated-chromosomes showed one to nine well-resolved dark bands. Differences of HKG-banding pattern of elongated and compacted chromosomes were performed by image analysis. Key words: Heterochromatin m High-resolution m HKG-banding m Image analysis ~ Maize chromosomesFrom a cytological viewpoint, two heterochromatin patterns have been revealed by banding procedures in maize root-tip chromosomes-the (1) knob heterochromatin and the (2) centromeric and intercalary heterochromatin. The first, was shown as a pronounced dark stained band by the C-banding technique (Carlson 1988), and the second, as distinct bands by HKG banding procedures (Carvalho and Saraiva 1993).According to Carvalho and Saraiva (1993), one to five HKG-bands were revealed in different chromosome sizes of the metaphasic set as well as in other phases of mitosis, suggesting differences of band numbers in relation to size and/or condensation of chromosomes.Improved technical achievements in banding chromosomes have added a new dimension to increasing band resolution. It is a well-documented fact that less condensed chromosomes display more bands. As a result, several methods to produce cytogenetic preparations with a large proportion of elongated chromosomes have been described, allowing greater accuracy in traditional karyo-type analysis on extended chromosomes in human and other vertebrates (Sumner 1990, Spowart 1994, Verma and Babu 1995.Little progress has been made in developing high-resolution banding procedures in plant. However, good elongated-chromosome preparations were obtained in celery (Murata and Orton 1984), Triticum (Zhu eta/. 1986), maize (Kakeda et a/. 1990) and Vicia faba (Belyayev 1993).

Bean (Phaseolus vulgaris) lines P.I. 207262 and AB 136, both resistant to delta and kappa races of Colletotrichum lindemuthianum, were crossed with Michelite, Dark Red Kidney, and Perry Marrow, susceptible to both races, and with Cornell 49-242, resistant to delta and susceptible to kappa. F1 and F2 reactions demonstrated that P.I. 207262 carries duplicate dominant genes for resistance to the delta race; AB 136 carries a dominant gene. These resistance genes are independent of the Are gene from Cornell 49-242. With respect to the kappa race, F1 and F2 data showed that the resistance controlled by P.I. 207262 and by AB 136 depends on a single dominant gene. Complementary factors were involved with AB 136 resistance to the delta race and with P.I. 207262 resistance to kappa.
As linhagens de feijão (Phaseolus vulgaris L.) P.I. 207262 e AB 136, ambas resistentes às raças delta e capa de Colletotrichum lindemuthianum (Sacc. & Magn.) Scrib., fungo causador da antracnose, foram cruzadas com Michelite, Dark Red Kidney e Perry Marrow, suscetíveis a ambas as raças, e com Cornell 49-242, resistente à delta e suscetível à capa. As reações das gerações F1 e F2 demonstraram que P.I. 207262 carrega dois genes dominantes de resistência à raça delta, qualquer um dos quais é capaz de conferir resistência; AB 136 carrega um gene dominante. Esses genes de resistência à raça delta são independentes do gene Are, proveniente do cv. Cornell 49-242. Com relação à raça capa, a resistência condicionada por P.I. 207262 e AB 136 depende de um gene dominante. Fatores complementares estão envolvidos com a resistência de AB 136 à raça delta e com a resistência de P.I. 207262 à raça capa

The identification of chemical substances which increase the efficiency of radiation is important to make easier the obtention of plants with structural chromosome aberrations which may be used in an alternative program for hybrid maize production. The present work was carried out to investigate the effect of the chemical substance metronidazole in maize seedlings submitted to gamma radiation. Several treatments were done, soaking the seeds in solutions with varied concentrations of the active substance combined with solution filtration and gamma radiation. On the third day of the experiment, germination percentage, root and stem lengths were evaluated. At a high concentration (1,250 mg/50 mL) metronidazole behaved as a radiosensibilizer in the presence of radiation. Even at a low concentration (250 mg/50 mL; 750 mg/50 mL) and in the absence of radiation, metronidazole behaved as toxic substance.
A identificação de substâncias químicas que aumentam a eficiência da radiação é importante para facilitar a obtenção de plantas portadoras de aberrações cromossômicas estruturais que possam ser usadas em um programa alternativo de produção de milho híbrido (Zea mays L.). Realizou-se o presente trabalho com o objetivo de investigar o efeito da substância química metronidazol na resposta de plântulas de milho à radiação gama. Diversos tratamentos foram feitos, embebendo as sementes em soluções com variadas concentrações da substância ativa, combinadas com filtragem e radiação gama. No terceiro dia do experimento, foram avaliados a porcentagem de germinação e os comprimentos das raízes e dos caules. Em alta concentração (1.250 mg/50 mL), o metronidazol, em presença de radiação, comportou-se como radiossensibilizador e, na sua ausência, como substância tóxica, mesmo em baixa concentração (250 mg/50 mL e 750 mg/50 mL)

O estudo dos fatores que afetam a eficiência da radiação é importante, pois facilita a obtenção de mutantes que possam servir como fonte de variabilidade em programas de melhoramento e de aberrações cromossômicas estruturais para estudos citogenéticos. O presente trabalho foi realizado com o objetivo de investigar a influência do teor de água na resposta de sementes de milho à radiação gama. Verificou-se, nos experimentos realizados, o efeito radiossensibilizador da água, uma vez que, nas sementes com maior teor de umidade, intensificaram-se os danos causados pela radiação. Verificou-se, também, que o aumento dos danos foi diretamente proporcional às doses de radiação.
The study of the factors that affect the radiation efficiency is important, because it makes easier to get mutants that may be used as source of variability on improvement programs or as structural chromossomic aberrations for cytogenetics studies. The main aim of this research was to investigate the influence of corn seed water content on gamma radiation response. As a rule, the damage caused by radiation was more evident on seeds with higher water content. Also, increased damages were observed with higher radiation doses

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