Through mutagenesis, deficiencies, and deficient trisomics it was possible to determine the cytological location of four closely linked genes of chromosome VI in petunia (An2, Rt, Dg1, and An1). An2 lies at the distal end of the short arm, whereas Rt, Dg1, and An1 are located on the long arm. In addition, mutagenesis experiments revealed a high sensitivity to radiation or tolerance for deficiency of the short arm, in contrast with the apparent stability of the long arm. Key works: petunia, trisomy, telotrisomy, gene location, genetic mapping, cytological mapping, mutagenesis, deletion.

Ribosomal DNA polymorphisms were studied in 6 lines of Petunia hybrida using EcoRI, BamHI, HindIII, KpnI, Sad or XhoI. Each line carries several unit types, and 13 types were found in lines, which was not expected. We characterized the unit types and we determined the number of loci. Two kinds of unit types carrying no or several HindIII sites were revealed. The longest EcoRI and BamHI fragments in St43 correspond to a 11.4 kb unit type. Moreover, a 2.6 kb EcoRI fragment cannot be mapped in the 11.4 kb unit. It was found to be equivalent to the 2.45 kb EcoRI fragment carrying the 25 S rRNA coding sequence. Consequently, it was mapped in another unit 11.7 kb long. In Tlh1 the corresponding EcoRI and BamHI fragments enabled us to construct 8.8, 9.2 and 10.8 kb segments. These fragments are therefore considered to be part of the 11.4 kb unit length. Other lines display combinations of these length units. The inheritance of polymorphic fragments of lines (St43 and Tlh1) for 50 individuals of the 2 possible backcrosses [(St43 x Tlh1) x St43] and [(St43 x Tlh1) x Tlh1] indicated at least 2 loci. The presence in Sk176 of 6.2, 5.7 and 5.4 EcoRI fragments suggested 3 loci. The haploid plants obtained from the hybrid (St43 x Tlh1) display 1 individual carrying the 3 unit types present in the hybrid which proves the presence of 3 rDNA loci in Tlh1. Moreover, the segregation in the backcrosses corresponds to only 2 loci in St43. It carries a nulli-allele. Evidence for such hypotheses were obtained by in situ hybridization with a biotinylated probe. The Tlh1 and Tlh7 dihaploid lines display more unit types and, consequently, more polymorphisms than other lines.

The progress of the knowledge of genetics and cytogenetics of Petunia and the applications of in vitro culture techniques and molecular biology to the species result in an important biological model. Particularly, the presence of numerous genic markers allow to use the haploid genomes of pollen as basis for experiments (mutagenesis, preservation techniques) as well as the result of a normal or abnormal functioning of meiosis. The radioresistance of Petunia pollen after gamma rays treatments allowed various applications. Mature pollen irradiated with middle doses (about 100 Gy) keeps a nearly normal fertilizing ability but carries numerous point or chromosomal mutations; only the point mutations are transmitted through the gametophytes of the next generation; gametophytes with deletions are lethal. These results suggest that the complete haploid genomes is necessary for the normal functioning of the Petunia pollen. The use of very strong doses on pollen (up to 1000 Gy) associated with in vitro culture of ovules, allow the production of gynogenetic haploid plants and even, in some cases, of asymetric hybrids carrying chromosome fragments from irradiated pollen (Raquin, 1985). Abnormalities in the course of male gametogenesis have been observed and used in Petunia:- nonreduction phenomena, often under genetic control, yield normal pollen from haploid sporophytes (a mitotic process taking place instead of meiosis) or diploid pollen from normal diploid plants. In the first case, one can obtain a homozygous diploid line directly by selfing a haploid plant and in the second case triploids or tetraploids;- nondisjunction phenomena produce gametes with 8 chromosomes, instead of 7, among which pollen presents a competitive disadvantage. Numerous cases of certation (pollen competition) are observed when genetic markers are available and segregate in hybrid progenies when it is used as a male parent. The poor competitivity of pollen often reveals a deficiency, even very small: it is particularly the case of gametes with reversion after the transposition of a movable element.

The ovaries of two different Petunia species: Petunia hybrida (hort) and Petunia parodii (Steere) were irradiated with τ-ray doses ranging from 50 to 1,000 Gy before pollination. Seed setting occurred after 4 days preculture on a non-sterile medium. Ovaries transformed into fruits were then cultivated aseptically with the following results: (1) τ-ray doses ranging from 200 to 1,000 Gy led to the development of two types of plants: haploids 2n=x=7 and overdiploids 2n>2x=14. (2) The androgenetic origin of haploids was ascertained by using genetic markers. The origin of overdiploids is discussed. (3) Androgenetic haploids contained the chloroplasts of the irradiated female parent. No visible change of cp DNA patterns was observed after irradiation. (4) The four possible androgenetic events were successfully obtained between the two Petunia species: hybrida haploids with hybrida or parodii cytoplasm, and parodii haploids with parodii or hybrida cytoplasm.

Gamma-ray treatment and telotrisomic analysis were used for cytological mapping in petunia, which resulted in the genetic marking of both arms of the shorter median chromosome of the genome. An4, which is responsible for anthocyanin synthesis in part of the corolla and in the pollen, is located rather distally on the arm called α; both vs5, a mutation for virescent rosettes, and ph3, producing bluish hues of flower anthocyanins, are located on the other arm. The possibility of determining the order and physical distance of the genes with regard to the centromere is discussed. The sketch of a cytological map for chromosome VII revealed, as previously for chromosome VI, a strong inhibition of crossing-over between two genes located on both arms of the chromosome.Key words: petunia, telotrisomy, gene location, deletion.[Traduit par la revue]

Summary Effects of the herbicide EL-107 (N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl]-2,6-dimethoxy-benzamide) on the growth of dicotyledonous plants are described. The herbicide did not inhibit germination but reduced the growth of rape (Brassica napus L.) by half at 0.0057 mg l−1. The most characteristic symptom induced was a swelling of the apical regions, and histological observations of root tips of Polygonum persicaria and rape revealed a progressve disappearance of the meristematic zone, which was replaced by enlarged cells almost devoid of cytoplasm. Growth of cells of Acer pseudoplatanus L. and soybean (Glycine max L.) cultured in suspension was also inhibited by EL-107, which induced a characteristic change in the cell morphology to an enlarged, rounded shape. EL-107 apparently did not block cell division; at a high concentration it produced some inhibition of protein synthesis, but in Acer cells only. In both types of cell cultures it inhibited, to some extent, the incorporation of glucose into cell wall material. Resume Quelques effets de l'herbicide EL-107 sur la croissance et le metabolisme cellulaires Les effets de l'herbicide EL-107 (N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl]-2,6-dimethoxybenzamide) sur la croissance de dicotyledones sont decrits. L'herbicide n'inhibait pas la germination mais reduisait de moitie la croissance du colza (Brassica napus L.) pour une concentration de 0,0057 mg l−1. Le symptome le plus caracteristique etait un gonflement des regions apicales, et des observations histologiques d'extremites racinaires de Polygonum persicaria et de Brassica napus ont montre une disparition progressive de la zone meristematique, remplacee par une zone de cellules agrandies et presque vides de cytoplasme. La croissance de cellules d'Acer pseudoplatunus L. et de Glycine max L. cultivees en suspension, etait aussi inhibee par le EL-107, qui induisait une evolution caracteristique de la morphologie cellulaire vers une forme agrandie et arrondie. Le EL-107 ne bloquait apparemment par la division cellulaire. A forte concentration, il provoquait une inhibition de la synthese proteique, mais seulement chez les cellules d'Acer. Chez les deux types de cultures cellulaires, il s'est montre capable d'inhiber dans une certaine mesure l'incorporation de glucose dans la paroi cellulaire. Zusammenfassung Wirkungen des Herbizids EL-107 auf dus Zell-wachstum Es wird die Wirkung des Herbizids EL-107 auf das Wachstum zweikeimblattriger Pflanzen beschrieben. Die Keimung wurde nicht gehemmt, aber die ED50 fur das Wachstum von Brassica napus L. lag bei 0,0057 mg l−1. Das charakteristischste Symptom war die stauchung der Triebspitze, und die Wurzelspitzen von Polygonum persicaria L. und Brassica napus verloren ihr meristematisches Gewebe, das durch vergrosserte, fast cytoplasmalose Zellen ersetzt wurde. In Zellkulturen von Acer pseudoplatanus L. und Glycine max L. entwickelten sich vergrosserte, abgerundete Zellen. Die Zellteilung wurde offen-sichtlich nicht unterbunden. Bei hohen EL-107 Konzentrationen war die Proteinsynthese etwas gehemmt, jedoch nur bei Acer-Zellen. Die Einlagerung von Glukose in die Zellwande konnte in beiden Zellkulturen in geringem Umfang herabgesetzt sein.

The blind mutant of Petunia hybrida Hort. is characterized by a flower with a highly modified corolla: the much reduced or lacking corolla tube lamina is replaced by five supernumerary anthers, which produce scarce but fertile pollen. The ontogenic study of stamen and corolla formation shows the existence of three separate morphogenetic patterns corresponding to the development of undifferentiated appendages, the formation of pollen sacs or floral appendages, and the final intercalary growth (filament and corolla tube elongation), respectively. A first interpretative scheme of the floral morphogenesis is proposed and discussed.

The genes An2, Rt and An1 are located in chromosome VI and closely linked. Pollination of the triple recessive line W127 (an2an2rtrtan1) with irradiated pollen of the triple dominant line M1 (An2An2RtRtAn1An1) led to the recovery of at least 3.3% induced an2 recessives. Karyotype analysis and genetic data showed that these mutants all contained a deletion on the short arm of chromosome VI, ranging from “non-detectable” (a non-transmissable mutant, showing no visible deletion) to the complete short arm. It is concluded that An2 is located distally in the short arm, Rt and An1 in the long arm of chromosome VI. Deleted chromosomes are not transmitted to the next generation, neither through the male nor through the female; transmission of the dominant markers in the long arm of chromosome VI is possible after completion of the chromosome by crossing-over. There is a relationship between the length of the deletion in the short arm and the recombination frequency between the markers (Rt and An1) in the long arm: recombination increases with increasing length of the deletion. After completion of the chromosme by crossing-over, the normal recombination frequency is restored.