Interphase nuclei, karyotypes and nuclear DNA amounts in five species of Oenocarpus (Arecaceae)

The genus Oenocarpus Martius, 1823 (Arecaceae) includes five species commonly used in Amazonia, especially for their fruits. Little is known about the cytogenetic characteristics and DNA amounts of these species, except for O.bataua (Martius, 1823). This study characterized and compared the types of interphase nuclei, the chromosome sets, and estimated the nuclear DNA amounts of Oenocarpusbacaba (Martius, 1823), O.bataua, O.distichus (Martius, 1823), O.mapora (H. Karsten, 1857) and O.minor (Martius, 1823). Standard cytogenetic analyses and estimates of the nuclear DNA amount by flow cytometry were carried out. These are the first reports of chromosome numbers and DNA amounts, except for O.bataua, as is the description of the chromatin distribution in interphase nuclei and karyotype for all species. All species presented 2n = 36, confirming the previous report for O.bataua. Differences between karyotype formulas and the positioning of secondary constrictions were observed. There were no significant differences for the nuclear DNA amounts among species. The constancy in chromosome number and variations in karyotype formulas suggest the occurrence of chromosome rearrangement as an important mechanism in Oenocarpus speciation.

Polybia occidentalis and Polybia fastidiosa venom: a cytogenotoxic approach of effects on human and vegetal cells

The venoms of wasps are a complex mixture of biologically active compounds, such as low molecular mass compounds, peptides, and proteins. The aim of the study was to evaluate the action of wasp venoms, Polybia occidentalis and Polybia fastidiosa, on the DNA of human leukocytes and on the cell cycle and genetic material of the plant model Lactuca sativa L. (lettuce). The cultured leukocytes were treated with the venoms and then evaluated by the comet assay. On another assay, seeds were exposed to a venom solution; the emitted roots were collected and the occurrence of cell cycle alterations (CCAs) and DNA fragmentation were evaluated by agarose gel electrophoresis and TUNEL assay. The results demonstrated that the venom of both wasps induces several CCAs and reduces the mitotic index (MI) on treated cells. They induced damage on human leukocytes DNA. High frequencies of fragments were observed in cells exposed to P. occidentalis venom, while those exposed to P. fastidiosa showed a high frequency of non-oriented chromosome. Both venoms induced the occurrence of various condensed nuclei (CN). This alteration is an excellent cytological mark to cell death (CD). Additionally, CD was evidenced by positive signals in TUNEL assay, by DNA fragmentation in agarose gel electrophoresis with vegetal cells, and by DNA fragmentation of the human leukocytes evaluated. Furthermore, human leukocytes exposed to the venom of P. fastidiosa had high rate of damage. The data demonstrate that both vegetal and human cells are adequate to evaluate the genotoxicity induced by venoms.

Effects of long exposure to spent potliner on seeds, root tips, and meristematic cells of Allium cepa L

Spent potliner (SPL) is a solid waste generated in the aluminum mining and processing industry. It is sometimes dumped into the environment and leach in contact with water, thereupon affecting living beings, which are likely to be exposed to the waste for long periods. Considering this, we aimed to evaluate the effects of extended exposure to SPL through bioassays using Allium cepa as plant model system. Seeds of A. cepa were either directly exposed to SPL (continuous exposure) or first germinated in water and then exposed to SPL (discontinuous exposure). The germination rate was determined from 24 to 192 h of exposure. The maximum effects of SPL on germination were observed after 96 h in both exposure approaches. For the parameter root elongation, the discontinuous treatment was more efficient in demonstrating differences among the applied SPL concentrations (60% of reduction). Microscopic analysis was carried out in root tip cells discontinuously exposed to SPL for 96 h. A mitodepressive effect was observed (above 50%), as well as increased rate of chromosome abnormalities (up to 100-fold) and induction of cell death. The consequences of exposure to SPL for longer periods are discussed.

Population genetic structure of three species in the genus Astrocaryum G. Mey. (Arecaceae)

We assessed the level and distribution of genetic diversity in three species of the economically important palm genus Astrocaryum located in Pará State, in northern Brazil. Samples were collected in three municipalities for Astrocaryum aculeatum: Belterra, Santarém, and Terra Santa; and in two municipalities for both A. murumuru: Belém and Santo Antônio do Tauá and A. paramaca: Belém and Ananindeua. Eight microsatellite loci amplified well and were used for genetic analysis. The mean number of alleles per locus for A. aculeatum, A. murumuru, and A. paramaca were 2.33, 2.38, and 2.06, respectively. Genetic diversity was similar for the three species, ranging from H_E = 0.222 in A. aculeatum to H_E = 0.254 in A. murumuru. Both F_ST and AMOVA showed that most of the genetic variation was found within populations for all three species, but high genetic differentiation among populations was found for A. aculeatum. Three loci were not in Hardy-Weinberg equilibrium, with populations of A. paramaca showing a tendency for the excess of heterozygotes (F_IS = -0.144). Gene flow was high for populations of A. paramaca (N_m = 19.35). Our results suggest that the genetic diversity within populations followed the genetic differentiation among populations due to high gene flow among the population. Greater geographic distances among the three collection sites for A. aculeatum likely hampered gene flow for this species.

Reliability of plant root comet assay in comparison with human leukocyte comet assay for assessment environmental genotoxic agents

Comet assay is an efficient test to detect genotoxic compounds based on observation of DNA damage. The aim of this work was to compare the results obtained from the comet assay in two different type of cells extracted from the root tips from Lactuca sativa L. and human blood. For this, Spent Pot Liner (SPL), and its components (aluminum and fluoride) were applied as toxic agents. SPL is a solid waste generated in industry from the aluminum mining and processing with known toxicity. Three concentrations of all tested solutions were applied and the damages observed were compared to negative and positive controls. It was observed an increase in the frequency of DNA damage for human leukocytes and plant cells, in all treatments. On human leukocytes, SPL induced the highest percentage of damage, with an average of 87.68%. For root tips cells of L. sativa the highest percentage of damage was detected for aluminum (93.89%). Considering the arbitrary units (AU), the average of nuclei with high levels of DNA fragmentation was significant for both cells type evaluated. The tested cells demonstrated equal effectiveness for detection of the genotoxicity induced by the SPL and its chemical components, aluminum and fluoride. Further, using a unique method, the comet assay, we proved that cells from root tips of Lactuca sativa represent a reliable model to detect DNA damage induced by genotoxic pollutants is in agreement of those observed in human leukocytes as model. So far, plant cells may be suggested as important system to assess the toxicological risk of environmental agents.

Cytotoxicity of Spent Pot Liner on Allium cepa root tip cells: A comparative analysis in meristematic cell type on toxicity bioassays

Spent Pot Liner (SPL) is a waste generated during the production of aluminum. It is comprised of a mixture of substances most of which, like cyanide, aluminum and fluoride, are toxic. Previous studies indicate the highly toxic nature of SPL. However studies using cells of the differentiation/elongation zone of the root meristem (referred as M2 cells in this study) after a proper recovery period in water were never considered. Using these cells could be useful to further understanding the toxicity mechanisms of SPL. A comparative approach between the effects on M2 cells and meristematic cells of the proximal meristem zone (referred as M1 cells in this study) could lead to understanding how DNA damage caused by SPL behaves on successive generations of cells. Allium cepa cells were exposed to 4 different concentrations of SPL (2.5, 5, 7.5 and 10gL(-1)) mixed with soil and diluted in a CaCl2 0.01M to simulate the ionic forces naturally encountered on the environment. A solution containing only soil diluted on CaCl2 0.01M was used as control. M1 and M2 cells were evaluated separately, taking into account four different parameters: (1) mitotic alterations (MA); (2) presence of condensed nuclei (CN); (3) mitotic index (MI); (4) presence of micronucleus (MCN). Significant differences were observed between M1 and M2 roots tip cells for these four parameters accessed. M1 cells was more prompt to reveal citogenotoxicity through the higher frequency of MA observed. Meanwhile, for M2 cells higher frequencies of MCN and CN was noticed, followed by a reduction of MI. Also, it was possible to detect significant differences between the tested treatments and the control on every case. These results indicate SPL toxic effects carries on to future cells generations. This emphasizes the need to properly manage this waste. Joint evaluation of cells from both M1 and M2 regions was proven valuable for the evaluation of a series of parameters on all toxicity tests.

Microsporogenesis analysis validates the use of artificially tetraploidized Brachiaria ruziziensis in breeding programs

The genus Brachiaria contains species that have great economic importance in the Brazilian agricultural sector, as they enable cattle ranching on acid and poor soils with species that are resistant to spittlebugs and form crop-livestock-forest integration systems. The genus mainly consists of tetraploid (2n = 4x = 36) and apomictic species such as B. decumbens and B. brizantha. Sexuality is found in diploid species (2n = 2x = 18) such as B. ruziziensis. Interspecific hybridization between species of interest is possible by the artificial tetraploidization of B. ruziziensis and the subsequent hybridization with genotypes of B. brizantha and B. decumbens. Therefore, tetraploidized plants have to have normal meiosis or low rates of irregularities, as well as produce viable pollen grains. The objective of this study was to compare meiosis and pollen grain viability and morphology in artificially tetraploidized B. ruziziensis with that of descendants generated from crossing and selfing. The frequency of meiotic abnormalities ranged from 4.43 to 11%, and pollen viability ranged from 61 to 85%. Abnormalities were detected from prophase I to the tetrad stage with a variable frequency between the genotypes. The meiotic behavior of the artificially tetraploidized plants was little affected, and the pollen viability of the genotypes was high. Regarding pollen grain ultrastructure, there were no variations or morphological changes in the different genotypes. The genotypes have meiotic stability and high pollen viability, and can be incorporated into Brachiaria breeding programs.

Implications of mitotic and meiotic irregularities in common beans (Phaseolus vulgaris L.)

The common bean has great social and economic importance in Brazil and is the subject of a high number of publications, especially in the fields of genetics and breeding. Breeding programs aim to increase grain yield; however, mitosis and meiosis represent under explored research areas that have a direct impact on grain yield. Therefore, the study of cell division could be another tool available to bean geneticists and breeders. The aim of this study was to investigate irregularities occurring during the cell cycle and meiosis in common bean. The common bean cultivar used was BRSMG Talismã, which owing to its high yield and grain quality is recommended for cultivation in Brazil. We classified the interphase nuclei, estimated the mitotic and meiotic index, grain pollen viability, and percentage of abnormalities in both processes. The mitotic index was 4.1%, the interphase nucleus was non-reticulated, and 19% of dividing somatic cells showed abnormal behavior. Meiosis also presented irregularities resulting in a meiotic index of 44.6%. Viability of pollen grains was 94.3%. These results indicate that the common bean cultivar BRSMG Talismã possesses repair mechanisms that compensate for changes by producing a large number of pollen grains. Another important strategy adopted by bean plants to ensure stability is the elimination of abnormal cells by apoptosis. As the common bean cultivar BRSMG Talismã is recommended for cultivation because of its good agronomic performance, it can be concluded that mitotic and meiotic irregularities have no negative influence on its grain quality and yield.

Karyotype and genome size in Euterpe Mart. (Arecaceae) species

Euterpe (Martius, 1823), a genus from Central and South America, has species with high economic importance in Brazil, because of their palm heart and fruits, known as açaí berries. Breeding programs have been conducted to increase yield and establish cultivation systems to replace the extraction of wild material. These programs need basic information about the genome of these species to better explore the available genetic variability. The aim of this study was to compare Euterpe edulis (Martius, 1824), Euterpe oleracea (Martius, 1824) and Euterpe precatoria (Martius, 1842), with regard to karyotype, type of interphase nucleus and nuclear DNA amount. Metaphase chromosomes and interphase nuclei from root tip meristematic cells were obtained by the squashing technique and solid stained for microscope analysis. The DNA amount was estimated by flow cytometry. There were previous reports on the chromosome number of Euterpe edulis and Euterpe oleracea, but chromosome morphology of these two species and the whole karyotype of Euterpe precatoria are reported for the first time. The species have 2n=36, a number considered as a pleisomorphic feature in Arecoideae since the modern species, according to floral morphology, have the lowest chromosome number (2n=28 and 2n=30). The three Euterpe species also have the same type of interphase nuclei, classified as semi-reticulate. The species differed on karyotypic formulas, on localization of secondary constriction and genome size. The data suggest that the main forces driving Euterpe karyotype evolution were structural rearrangements, such as inversions and translocations that alter chromosome morphology, and either deletion or amplification that led to changes in chromosome size.

Ribosomal DNA in diploid and polyploid Setaria (Poaceae) species: number and distribution

Setaria Beauvois, 1812 is a genus of economically important forage species, including Setaria italica (Linnaeus, 1753) Beauvois, 1812 and Setaria viridis (Linnaeus, 1753) Beauvois, 1812, closely related species and considered as model systems for studies of C4 plants. However, complications and uncertainties related to taxonomy of other species of the genus are frequent due to the existence of numerous synonyms for the same species or multiple species with the same name, and overlapping of morphological characteristics. Cytogenetic studies in Setaria can be useful for taxonomic and evolutionary studies as well as for applications in breeding. Thus, this study is aimed at locating 45S and 5S rDNA sites through fluorescent in situ hybridization (FISH) in Setaria italica, Setaria viridis and Setaria sphacelata (Schumacher, 1827) Stapf, Hubbard, Moss, 1929 cultivars (cvs.) Narok and Nandi. Setaria italica and Setaria viridis have 18 chromosomes with karyotype formulas 6m + 3sm and 9m, respectively. The location of 45S and 5S rDNA for these species was in different chromosome pairs among the evaluated species. Setaria viridis presented a more symmetrical karyotype, strengthening the ancestral relationship with Setaria italica. Setaria sphacelata cvs. Narok and Nandi have 36 chromosomes, and karyotype formulas 11m+7sm and 16m+2sm, respectively. The 45S rDNA signals for both cultivars were also observed in distinct chromosome pairs; however chromosomes bearing 5S rDNA are conserved. Karyotypic variations found among the studied species are evidence of chromosomal rearrangements.

Variation of karyotype and nuclear DNA content among four species of Plectranthus L' Héritier, 1788 (Lamiaceae) from Brazil

Plectranthus is a genus which includes species of ornamental and medicinal potential. It faces taxonomic problems due to aggregating species previously belonging to the genus Coleus, a fact that has contributed to the existence of various synonymies. The species Plectranthus amboinicus, Plectranthus barbatus, Plectranthus grandis and Plectranthus neochilus are included in this context. Some authors consider Plectranthus barbatus and Plectranthus grandis as synonyms. The present work was carried out with the aim of comparing plants of the above-mentioned species, originating from different localities in Brazil, with regards to chromosome number and karyotypic morphology, correlated to the nuclear DNA content. There was no variation in chromosome number among plants of the same species. Plectranthus amboinicus was the only species to exhibit 2n=34, whereas the others had 2n=30. No karyotypic differences were found among the plants of each species, except for Plectranthus barbatus. The plants of the Plectranthus species revealed little coincidence between chromosome pairs. The nuclear DNA content allowed grouping Plectranthus amboinicus and Plectranthus neochilus, with the highest mean values, and Plectranthus grandis and Plectranthus barbatus with the lowest ones. Differences in DNA amount among the plants were identified only for Plectranthus barbatus. These results allow the inference that the populations of Plectranthus amboinicus and Plectranthus neochilus present coincident karyotypes among their plants, and Plectranthus grandis is probably a synonym of Plectranthus barbatus.

Genomic homeology between Pennisetum purpureum and Pennisetum glaucum (Poaceae)

The genus Pennisetum (Richard, 1805) includes two economically important tropical forage plants: Pennisetum purpureum (Schumacher, 1827) (elephant grass), with 2n = 4x = 28 chromosomes and genomes A'A'BB, and Pennisetum glaucum (Linnaeus, 1753) (pearl millet), with 2n = 2x = 14 chromosomes and genomes AA. The genetic proximity between them allows hybrids to be obtained (2n = 3x = 21) that yield forage of higher quality in relation to the parents. The study of genomic relationships provides subsidies for the knowledge about phylogenetic relations and evolution, and is useful in breeding programs seeking gene introgression. Concerning elephant grass and pearl millet, the homeology between the genomes A and A', and between these and the genome B, has been reported by conventional cytogenetic techniques. The objective of the present study was to demonstrate the degree of homeology between these genomes by means of genomic in situ hybridization (GISH). The results confirmed the homeology between the genomes A of pearl millet and A'B of elephant grass, and showed that there are differences in the distribution and proportion of homologous regions after hybridization. Discussion regarding the evolutionary origin of P. purpureum and P. glaucum was also included.

Cytotoxic and phytotoxic effects of the main chemical components of spent pot-liner: a comparative approach

Spent pot-liner (SPL) is a hazardous solid waste produced by the aluminum industry. Although its composition may vary, fluoride and cyanide salts as well as aluminum are predominant components. A seed-germination and root-elongation test was performed with Lactuca sativa seeds as a test system. SPL induced decrease of seed germination rate and root elongation. The concentration of 26.5g/L SPL was established from a regression curve as the IC50 (inhibition concentration 50%). Through chemical analyses, the concentrations of fluoride, cyanide and aluminum in SPL solutions of 26.5g/L (IC50), 39.75g/L (1.5IC50) and 13.25g/L (0.5IC50) were determined. Further, a cell-cycle test was conducted with root tips of L. sativa exposed to these same SPL solutions. All test chemicals presented toxic effects on meristematic cells of L. sativa. Aluminum was identified as the SPL component mainly responsible for reduction of the mitotic index. Chromosomal alterations resulted from the interactions among the three main chemical components of SPL, without a clear predominantly responsible agent. Induction of condensed nuclei was mainly due to effects of aluminum and fluoride, and may serve as an indicator of induced cell death.

Cytotoxic and phytotoxic effects of the main chemical components of spent pot-liner: a comparative approach

Spent pot-liner (SPL) is a hazardous solid waste produced by the aluminum industry. Although its composition may vary, fluoride and cyanide salts as well as aluminum are predominant components. A seed-germination and root-elongation test was performed with Lactuca sativa seeds as a test system. SPL induced decrease of seed germination rate and root elongation. The concentration of 26.5g/L SPL was established from a regression curve as the IC50 (inhibition concentration 50%). Through chemical analyses, the concentrations of fluoride, cyanide and aluminum in SPL solutions of 26.5g/L (IC50), 39.75g/L (1.5IC50) and 13.25g/L (0.5IC50) were determined. Further, a cell-cycle test was conducted with root tips of L. sativa exposed to these same SPL solutions. All test chemicals presented toxic effects on meristematic cells of L. sativa. Aluminum was identified as the SPL component mainly responsible for reduction of the mitotic index. Chromosomal alterations resulted from the interactions among the three main chemical components of SPL, without a clear predominantly responsible agent. Induction of condensed nuclei was mainly due to effects of aluminum and fluoride, and may serve as an indicator of induced cell death.

Effects of Spent Pot Liner on mitotic activity and nuclear DNA content in meristematic cells of Allium cepa

Industrial waste usually contains complex mixtures of mutagenic chemicals. Spent Pot Liner (SPL) is a complex solid waste from the aluminum industry, which is composed of organics, fluoride salts, inorganic cyanides, metals, and sodium. Due to the toxicity of these compounds, this study sought to use cytogenetics and flow cytometry to assess the effects of SPL on cell cycle parameters and DNA content in meristematic cells of Allium cepa. Three concentrations of leachates from SPL-soil mixtures were used for the study: 0, 10, and 25%. Roots were collected and analyzed after 4, 8, 12, 24, and 36 h of exposure to the above SPL leachates. The results showed an overall mitodepressive effect accompanied by an increased percentage of condensed nuclei and genomic instability as evidenced by the presence of cellular/chromosomal abnormalities. Terminal deoxynucleotidyl transferase dUTP nick end labeling revealed nuclei with fragmented DNA, a marker of programmed cell death. This study also addressed the question of reversibility of the effects of SPL and found that 36 h of exposure to 25% SPL seemed to be the point at which the effects on the induction of apoptosis became irreversible.

Application of Comet assay to assess the effects of white bean meal on DNA of human lymphocytes

This study was conducted to evaluate the potential induction of genotoxic effects of white bean flour using the Comet assay. The test was conducted with human lymphocytes present in whole blood immediately after collection, by incubation with white bean flour in three concentrations (3.92, 9.52 and 18.18 mg/mL) at 37 ºC for 4 h followed by preparation of slides. Samples were considered positive (above 20% damage) when the damage observed to cellular DNA was higher than the negative control. No genotoxic potential was found at the doses tested. However, it would be premature to suggest absence of risk to human health of DNA damage since the exposure of cells to the extract was restricted to four hours rather than a whole cell cycle. Additionally, further information on toxicology should be obtained in future studies.

Genotoxicity of SPL (spent pot lining) as measured by Tradescantia bioassays

Spent Pot Liner (SPL) is a solid waste product generated in the process of aluminum production. Tradescantia micronuclei (Trad-MN) and stamen hair mutation (Trad-SHM) bioassays are very useful tests to assess genotoxicity of environmental pollutants. In the present study, we intended to investigate the genotoxicity of this waste with Tradescantia bioassays using leachates of SPL simulating the natural leachability of SPL in soil. The formation of micronuclei (MN) was found to be concentration dependent. MN frequency enhanced significantly with SPL treatment. In addition, SPL also appeared to increase the percentage of dyads and triads. Trad-SHM assay showed that SPL increases pink mutation events as SPL concentration increases. These results demonstrated that SPL is a cytogenotoxic agent that affects different genetic end-points (induction of micronuclei and point mutations) even at low concentration (2% and 3%).

Spent Pot Liner (SPL) induced DNA damage and nuclear alterations in root tip cells of Allium cepa as a consequence of programmed cell death

There are various toxic effects of environmental pollutants, including apoptosis and carcinogenesis. Spent Pot Liner (SPL) is solid waste from the aluminum industry. It has a highly variable composition, including cyanide, fluoride, organics and metals. Preliminary characterizations of the effect of SPL on Allium cepa show the presence of condensed nuclei. Thus, the aim of this study was to analyze the toxic effect of SPL in A. cepa root meristem in the context of programmed cell death (PCD). A lot of specific features of this process such as DNA fragmentation, condensed chromatin, spherical nuclei and the formation of apoptotic-like bodies were observed in root meristem after SPL treatment. Root meristem treated with SPL 25% solution exhibited an alteration in antioxidant enzyme activities; a reduction in NCR as a consequence of high percentage of condensed nuclei; DNA fragmentation, detected by electrophoresis and TUNEL assay; cytoplasm vacuolization and also a disturbance in root morphology. These features are associated with programmed cell death (PCD) under abiotic stress. Therefore, these data show that SPL induces apoptosis-like PCD in root meristem cells of A. cepa.

The effect of cyanide compounds, fluorides, aluminum, and inorganic oxides present in spent pot liner on germination and root tip cells of Lactuca sativa

SPL (spent pot liner) is a solid waste produced by the aluminum industry. This waste has a highly variable composition, consisting of cyanides, fluorides, organics, and metals. The aim of this work was to study the effect of SPL on root tips of Lactuca sativa using current plant bioassays. We observed a decrease in the germination rate with increasing concentrations of SPL. In addition, SPL was found to reduce root growth, which is correlated with a decrease in the mitotic index. Nevertheless, we noticed a significant enhancement in the percentage of stickiness, c-metaphase, anaphase bridges, and laggard chromosomes in dividing cells and also an increase in the number of cells with condensed nuclei. Moreover, SPL was found to alter the root tip surface, resulting in a reduction in the amount of root hair. These results demonstrate that SPL is a toxic agent that leads to cell damage and disturbance.

Cytogenetic alterations induced by SPL (spent potliners) in meristematic cells of plant bioassays

Spent potliners (SPL) is solid waste generated by the aluminum industry during the manufacture of aluminum metal. Information on the cytotoxicity effect of SPL is necessary to facilitate understanding of their action on organisms and to subsidize environmentally correct solutions. Thus, the aim of the present investigation is to compare the effect of SPL on meristematic cells of Allium cepa and Zea mays and also to discuss the mechanisms of SPL cytotoxicity involved. A strong inhibition on root growth in higher SPL concentrations has been observed in both A. cepa and Z. mays. For cytogenetic analysis, the results showed a reduction of mitotic index and increase of different abnormalities as the SPL concentration increased. We observed bridges, chromosome fragments, stickiness, multipolar anaphase, later segregation and cell death. In general, it was possible to observe an increase of different abnormalities as the SPL concentration increased. It is obvious from the results of the present investigation that SPL is cytotoxic on meristematic cells of plant tests (A. cepa and Z. mays).

Karyotypic studies of Cratylia argentea (Desv.) O. Kuntze and C. mollis Mart. ex Benth. (Fabaceae - Papilionoideae)

Cratylia argentea and C. mollis (Fabaceae-Papilionoideae) are legume shrubs native to the Cerrado and Caatinga, respectively. Both species show great resistance to drought and high nutritive value, which makes them a valuable forage resource in tropical regions. Cytogenetic studies were carried out on accessions of C. argentea and C. mollis from Germplasm Banks of Embrapa Gado de Leite (Juiz de Fora, MG) and Embrapa Semi-Arido (Petrolina, PE), respectively. Root tips were treated with 3 mM 8-hydroxyquinoline and slides were made using the air-dry technique. Karyotype description for each accession took into account the following features: chromosome number; total length, relative length and arm ratio of each chromosome; haploid set length, and degree of asymmetry. Mitotic metaphases in both species showed 2n = 22 chromosomes, where this is the first report of diploid number for C. mollis. Chromosome length was also quite similar for the two species, ranging from 5.08 to 2.50 microm in C. argentea and 5.12 to 2.51 microm in C. mollis, with haploid sets of equal size, measuring 38.10 and 37.85 microm, respectively. However, they did not show the same karyotypic formula, which was 5 m + 4 sm + 2 st for C. argentea and 7 m + 2 sm + 2 st for C. mollis. This indicates the occurrence of rearrangements within chromosomes I and VI. Both karyotypes showed a tendency for asymmetry.

Effects of sorghum (sorghum bicolor L.) root exudates on the cell cycle of the bean plant (phaseolus vulgaris L.) root

Two experiments were conducted to test the allelopathic effect of sorghum (Sorghum bicolor L.) root exudates on bean (Phaseolus vulgaris L.) cell division. Research was conducted in the greenhouse of the Wistock Agricultural Research Institute of Minas Gerais State (EPAMIG) and in a laboratory of the Federal University of Lavras (UFLA). Sorghum variety BR-601 and bean variety Carioca MG were used. The exudate, called sorgoleone (SGL), was obtained by methylene chloride and acetic acid extraction from sorghum roots seven days after sowing on Petri dishes, and refrigerated until use. Solutions of 0.01, 0.05, 0.10, and 0.15 mM were prepared using Johanson solution as the SGL solvent. Seven-day-old bean seedlings grown in vermiculite in a greenhouse were transplanted to the solution. Seven days after transplantation, the beans did not show any sign of phytotoxicity; however, cytogenetic observations showed that SGL reduced the number of cells in prophase, metaphase, and anaphase stages. Colchicine effects were observed among cells in metaphase on the third and fifth days after treatments and varied with SGL concentrations. By the seventh day, the colchicine effects were inversely proportional to concentration, which varied from 34.3% for 0.01 mM to 6.6% for 0.15 mM. SGL acts as a mitotic inhibitor. It probably depolymerizes the microtubular proteins and induces the formation of colchicine metaphases causing polyploid nuclei. A largest period of SGL treatment also induced chromosome breaks and bridge formation in anaphase and telophase. Although SGL cannot be used as a herbicide for bean cultures, its allelochemical effects on other cultures are the factors that will define the use of sorghum as a natural herbicide.