Anna Maria Tagliasacchi

The mitotic cycle in root apical meristems ofAllium porrum L. is controlled by the endomycorrhizal fungusGlomus sp. strain E3

SummaryThe mitotic cycle in root apical meristems of mycorrhizal and non-mycorrhizal plants ofAllium porrum L.+Glomus sp., strain E3, has been examined by3H-TdR labelling. Significant slowing down of the mitotic cycle in the mycorrhizas through an extension of G1, S and metaphase was observed, while G2 was drastically reduced. Lengthening of the cycle was proportional to increasing infection. The ways in which the fungus could influence cell division are discussed.

Different structure of polytene chromosomes ofPhaseolus coccineus suspensors during early embryogenesis: 1. Nucleolus organizing chromosome pairs S1 and S2

SummaryThe pattern of DNA puffs in two pairs of polytene chromosomes (S1 and S2, both involved in nucleolar organization) is described in the suspensor ofPhaseolus coccineus during the heart-like and early cotyledon stages of embryo development. Collected data show that: 1. a structural variability indicating differential DNA replication of bands bearing ribosomal cistrons occurs in the two chromosome pairs and within the same chromosome; 2. within chromosome S1, a positive correlation is found between extra replication (amplification) of band p 13 and under-replication of band p 12; 3. within chromosome S2, bands q 21 and q 22 often evidence a simultaneous DNA amplification; 4. a negative correlation is observed between amplification of band p 13 of chromosome S1 and amplification of bands q 21 and q 22 of chromosome S2; 5. within chromosome S2, no correlation is detectable between amplification of bands p 11 and q 11 and amplification of bands q 21 and q 22.

Arsenic-induced morphogenic response in roots of arsenic hyperaccumulator fern Pteris vittata

On the assumption that arsenic induces stress morphogenetic responses involved in As tolerance and hyperaccumulation in the Pteris vittata fern, we analyzed the root system of young sporophytes grown in 250, 334, and 500 μM As for five days and for 14 days. Anatomical and histological analyses were performed in plants grown for five days to evaluate the number, position, length and differentiation pattern of root hairs. AgNOR staining, employed to study nucleolus behavior in root apices, showed that arsenic influences nucleolar activity (evaluated by nucleolus size, number and absorbance) in the root meristem. In plants treated with 250 and 334 μM As an acropetal shift of root hair development and an increase in hair length and density were observed, linked to an ectopic pattern of differentiation. The opposite trend was recorded in plants treated with 500 μM As. It is worth noting the presence of living border-like cells, not yet observed in ferns, and their increase following As treatments. Analysis and vitality of border-like cells were surveyed after 14 days of treatments. In conclusion As treatments elicited a stress-induced morphogenic response which, by modifying the differentiation pattern, number and length of root hairs, modulating nucleolar activity and interacting with the rhizosphere by inducing border-like cell production, may adjust the rate of root uptake and its metabolic activity.

Root apical meristems ofAllium porrum L. as affected by arbuscular mycorrhizae and phosphorus

SummaryArbuscular mycorrhizal (AM) fungi significantly improve plant growth in soils with low phosphorus availability and cause many changes in root morphology, similar to those produced by increased P nutrition, mainly depending on root apex size and activity. The aim of this work was to discriminate between the morphogenetic role of AM fungi and P in leek (Allium porrum L.) by feeding mycorrhizal and nonmycorrhizal plants with two nutrient solutions containing 3.2 or 96 μM P and examining specific parameters related to adventitious root apices (apex size, mitotic cycle, and RNA synthesis). The results showed that AM fungi blocked meristem activity as indicated by the higher percentages of inactive apices and metaphases in the apical meristem of mycorrhizal plants, whereas the high P supply lengthened the mitotic cycle without blocking the apices, resulting in steady, slow root growth. The possible involvement of abscisic acid in the regulation of root apex activity is discussed.

Functional heterogeneity, during early embryogenesis, ofPhaseolus coccineus ribosomal cistrons in polytene chromosomes of embryo suspensor

SummaryIn the giant cells of thePhaseolus coccineus embryo suspensor the number of nucleoli is not constant during early embryogenesis. Over the same period the number and the type of chromosomes involved in the nucleolar organization also vary. Moreover, the percentage of DNA and RNA puffs organized by ribosomal cistron (rc) bearing regions changes. When single chromosome regions bearingrc are taken into account, it is seen that only the cistrons of some bands are engaged in the RNA puffing activity (nucleolus organization). These bands are generally undermethylated. The reported results show: 1. a functional heterogeneity amongrc carried by different nucleolus organizing chromosomes; 2. a functional heterogeneity amongrc carried by a single chromosome region; 3. a temporal correlation between undermethylation and transcription ofrc.

Distribution of 5-methylcytosine-rich regions in the polytene chromosomes of Phaseolus coccineus embryo suspensor as shown by the immunoperoxidase technique

5-Methylcytosine (5-mC) has been visualized in polytene chromosomes of Phaseolus coccineus, scarlet bean using specific antibodies to 5-mC and the immunoperoxidase technique. The results obtained indicate that most heterochromatic regions are methylated, even though the frequency of methylation is highly variable and sometimes low. A preferential binding of anti-5-mC to centromeric heterochromatic blocks was observed. Comparison between anti-5-mC binding and the results of hybridization with highly repetitive DNA and satellite DNA shows, moreover, that centrometric heterochromatic regions hybridize in particular with both DNAs. This finding is consistent with the fact that repetitive DNA and satellite DNA are methylated to a considerably greater extent than main band DNA, in line with many data to be found in the literature. The binding pattern of anti-5-mC that we observed also suggests that methylation does not occur in all classes of repetitive DNA. The high variability of band methylation frequency is discussed in relation to a possible characteristic DNA composition of the band.

Different structure of polytene chromosome ofPhaseolus coccineus suspensors during early embryogenesis 3. Chromosome pair VI

SummaryDifferent regions of polytene chromosomes pair VI have been characterized by: 1. morphological observations, 2. incorporation of3H-thymidine and3H-uridine, 3. cytophotometry of DNA and associated proteins, 4. hybridization with satellite DNA and highly repeated DNA sequences.The collected data indicate that DNA and RNA puffs are organized by heterochromatic segments. DNA puffs show often a clustered pattern of labeling by3H-thymidine and RNA puffs are always labeled by3H-uridine. Each heterochromatic segment is characterized by a definite ratio between DNA and associated fast-green stainable proteins. Satellite DNA binds mostly to heterochromatic blocks at centromere, highly repeated DNA sequences bind, with approximately the same frequency, to centromeric heterochromatin and to the main intercalary heterochromatic band. The telomeric portions of euchromatin seem to be also enriched in highly repeated DNA sequences.The results indicate that heterochromatic chromosome segments might be sites of intense localized DNA replication. The same chromosome regions are also engaged in an active transcription process. The response to hybridization suggests that heterochromatic blocks of chromosome pair VI are heterogeneous in nucleotide sequences.The present studies also indicate that DNA and RNA puffs organized by different chromosome sites are specific of particular steps of embryo differentiation.The observed metabolic aspects of the suspensorss polytene chromosomes are discussed in relation to the synthesis of growth regulators which is known to occur in the suspensor.

Ozone damage and tolerance in leaves of two poplar genotypes.

Abstract The effects induced by an acute ozone exposure were investigated in two poplar hybrids differen- tially O3 susceptible in terms of leaf injuries: Populus deltoides x maximowiczii, Eridano clone and Populus x euramericana, I-214 clone, the sensitive and the tolerant respectively. Both the leaf anatomy and the responses induced by ozone in the leaves were analysed, using a cyto-histochemical approach. Morphoanatomical characters, such as amphistomatous lamina, higher stomatal density and relaxed mesophyll cell packing (evaluated by the palisadeness coefficient), observed in the sensitive clone leaves, may favour a greater O3 uptake in the apoplast and increase the cumulative dose of pollutant per mesophyll cell, with respect to tolerant clone leaves. Mesophyll cells of sensitive plants were the main targets for O3. After an acute ozone treatment, the palisade parenchyma cells showed a decrease in chloroplast number and size, resulting best suited both to perceive the stress by O3 or reactive oxygen species and to activate several signal transduction pathways, in relation to their morphological, physiological and functional properties predisposing an efficient cell communication, signalling and stimuli sensing. The quick and well localized pattern of cell death induced by O3 in sensitive poplar leaves was accompanied by some hallmarks of programmed cell death: nuclear shrinkage, chromatin condensation and cell wall collapse.

Characterization and chromosomal localization of fast renaturing and satellite DNA sequences inPhaseolus coccineus

SummaryDNA was extracted from etiolated plantlets ofPhaseolus coccineus L. and studied by means of thermal denaturation and reassociation kinetics and CsCl analytical ultracentrifugation. A DNA fraction reassociating within an equivalent Cot of 1.15 × 10−1 (fast renaturing DNA sequences; FRS) was found to constitute 20.8% of the total DNA, 6.8% of which is composed of palindromic sequences. Analytical CsCl gradient ultracentrifugation showed a large heavier satellite banding at 1.702 g/ml (main peak 1.692g/ml); this DNA fraction was shown to consist of different components with buoyant densities of 1.696, 1.702, 1.706, and 1.714g/ml. FRS and the satellite fraction banding at 1.702 g/ml (SAT) were hybridizedin situ to the polytene chromosomes in the embryo suspensor cells after having been labeled by the nick translation method. FRS proved to be almost exclusively localized in the heterochromatic chromosome regions and several chromosome ends; SAT was found to be confined, as a rule, in the centromeric and pericentromeric heterochromatin. Different labeling patterns were detected over chromosome regions bearing 18S + 25S or 5 S ribosomal RNA cistrons and over corresponding regions of different chromosome pairs. These results are discussed for the light they may throw on certain aspects of the structure and organization at the chromosomal level of theP. coccineus genome.

Frequenza di cellule con « DNA puffs » nel sospensore di Phaseolus coccineus in momenti diversi dello sviluppo embrionale

Abstract Morphological aspects of Phaseolus coccineus suspensor cells at different periods of embryo development. — Embryo suspensor cells of Phaseolus coccineus have been analysed at different periods of seed and embryo development in field-grown plants and the frequency of cells involved in « DNA puffs » formation has been determined. The collected data show that: a) the relation between seed development and embryo development is not constant at different times in the season (from July to November); b) the frequency of cells showing « DNA puffs » is influenced by the above ratio. This fact seems to indicate that embryos of comparable developmental stages (as estimated by cotyledon length) show different metabolic patterns in relation to seed development and enviromental factors.