Impact of COVID-19 on 2020 transplant activity and waiting lists in France✰,✰✰.

The COVID-19 pandemic strongly affected organ procurement and transplantation in France, despite the intense efforts of all participants in this domain. In 2020, the identification and procurement of deceased donors fell by 12% and 21% respectively, compared with the mean of the preceding 2 years. Similarly, the number of new registrations on the national waiting list declined by 12% and the number of transplants by 24%. The 3-month cumulative incidence of death or drop out for worsening condition of patients awaiting a liver transplant was significantly greater in 2020 compared to the previous 2 years. Continuous monitoring at the national level of early post-transplant outcomes showed no deterioration for any organ in 2020. At the end of 2020, less than 1% of transplant candidates and less than 1% of graft recipients - of any organ - had died of COVID-19.

[Effects of repeated in vitro bud formation on somatic variation ability on a chlorophyll mutant of Nicotiana tabacum var. Samsun]. / Effets de cycles successifs de neoformation de bourgeons in vitro sur l'aptitude a la variation somatique chez un mutant chlorophyllien de Nicotiana tabacum var. Samsun.

A homozygous tl/tl chlorophyll mutant of Nicotiana tabacum var. Samsun shows spontaneous somatic variations on its leaves. These variations are either single (dark or light) or twinned (dark and light). In vitro culture of variation-free leaf fragments, on a particular medium, directly yields neoformed buds. These buds are placed on a medium for root formation, so that neoformed plants are obtained from which a new cycle of bud neoformation can be started. In this way, one obtains several sets of plants of the same somatic origin but which differ from each other by one or more neoformation cycles. At each cycle, the somatic variation ability is characterized on the basis of four criteria: (1) numbers and proportions of dark, light and twinned variations, (2) distribution of dark variations according to their sizes, (3) distribution of variations according to the foliar level, and (4) sexual transmission of each character. As early as at the second neoformation cycle, one observes a significant increase of variability among the numbers of variations and shifts in size distributions. The increase of variability is more striking after the third cycle; particularly, plants obtained in this manner have acquired, on the average, the ability to vary earlier in the development of the foliar initium. This property is expressed through the enlargement of the mean size of the variations. In each case, the observed variability is somatically maintained through cuttings. This, together with the fact that the observed shifts in frequency distributions as well as the changes in numbers of variations are sexually transmitted after the third neoformation cycle, definitely means that genetic changes have occurred. Consequently, it seems that from one neoformation cycle to another, in vitro culture of leaf fragments has cumulative effects which, beyond a particular threshold, are sexually transmitted. The only character, among four, not to be affected by in vitro culture is the distribution of somatic variations according to the foliar level. Thus, it seems that this character is strictly controlled by changes in physiological conditions which occur during the plant growth; in particular, the transition of the shoot apex from vegetative to flowering state. The effects of in vitro culture on the ability to somatically vary are discussed on the basis of four hypotheses: (1) modification in number of chromosomes (polyploidy, aneuploidy); (2) modification in chromosome structure (translocation); (3) selection of a particular kind of cells and (4) cumulative alteration of genetic information either by mutation or by disturbance in cell regulation process.

[Biotechnology using modified microorganisms]. / Biotechnologies par germes modifiés.

Few microorganisms, as compare to their high diversity, are used for human needs. They can produce molecules of interest, process fermentation, protect crops, treat wastes or clean environment. Molecular technics and genetic engineering are new tools offer to geneticists which breed microorganisms for years. Using them, it is now possible, theoretically, to introduce any gene in any organism. Some examples are given concerning genetic modifications in yeasts and lactic acid bacteria to optimize agrofood processes and to improve nutritive and flavour characteristics of fermented products like bread, beer, wine, cheese, meat, vegetable juices... In spite of scientific and industrial interest of the new technologies, limiting factors can explain that genetically modified microorganisms are not routinely used in agrofood yet. First, risks assessment on human health and environment are still in debate, but their is a consensus, within the scientific community, to consider that new characteristics of improved microorganisms are more important than the technics used for their construction. Second, regulations turn out to impose constraints susceptible to discourage technological innovations. At least, the public perception about the new technologies appears, actually, as the major factor to limit their development.

Cell frequencies of green somatic-variations in the tl chlorophyll mutant of Nicotiana tabacum var 'Samsun'.

The chlorophyll deficient tl mutant of Nicotiana tabacum var 'Samsun' expresses green, clear and twin, green and clear somatic variations spontaneously on leaves at a low frequency. This character is maintained after both vegetative multiplication and sexual reproduction. However a very important phenotypic variability in the capacity for somatic variation appears in in vitro bud neoformations from leaf fragments of tl/tl homozygous plants. This variability is observed in the type of variations and the variation pattern, defined as the frequency and size of the variant areas.The present work was aimed at determining both the cell frequencies of the events which lead to the somatic variation and the preferential sequence of leaf initial development during which these frequencies are at a maximum. It was limited to plant populations with very different patterns for green variations, some having a high frequency of large variation, others having a high frequency of small variations. They were compared with a population of control plants having a low frequency.In the case of plants having a high frequency of large green variations, the events leading to somatic variation occurred between the twenty-first and the twelfth cell cycles preceding the end of the initial division phase, the maximum cell frequencies being in the seventeenth and sixteenth cycles. The maximum frequencies appeared extremely high, being on average about 10(-2). In plants with a high frequency of small green variations the event occurred between cell cycles nine and one, with mean frequencies of 10(-3) but without any clearly marked maximum. In the low frequency control plants the event also took place during the last ten cell cycles but with decreasing frequencies from 10(-4) to 10(-7).The frequency and the starting period of the cell events leading to somatic variation are closely dependent on the state of the cell. This is, on the one hand, strictly linked to the physiology of the plant and, on the other, closely correlated with the stage of differentiation, which may vary according to the genetic back ground of the leaf initial cells.The results are discussed in relation to comparable observations and the relevant interpretations made on other instability mutants.

Liposome-mediated transformation of tobacco mesophyll protoplasts by an Escherichia coli plasmid.

An Escherichia coli plasmid, pLGV23neo, carrying a kanamycin resistance gene expressed in plant cells, was encapsulated into negatively charged liposomes prepared by the reverse phase evaporation technique. These liposomes were induced to fuse with tobacco mesophyll protoplasts by polyethyleneglycol treatment. Kanamycin-resistant clones were reproducibly isolated from transfected cultures at an average frequency of 4 X 10(-5). Plants regenerated from these resistant colonies were confirmed to be transformed according to three criteria. Protoplasts isolated from their leaves were resistant to 100 micrograms/ml kanamycin. The enzyme aminoglycoside 3'-phosphotransferase II encoded by the plasmid pLGV23neo was detected in leaf extracts. Approximately 3-5 copies of the gene encoding for kanamycin resistance were inserted in the genome of at least one of the studied transformants. The restriction pattern of inserted DNA was best explained by assuming a tandem integration of the pPLGV23neo sequences, implying an homologous recombination event between these sequences during transformation. Kanamycin resistance was transmitted as a single dominant nuclear marker to the progeny of resistant plants after selfing or cross-pollination with the wild-type.

Cellular genetic study of a somatic instability in a tobacco mutant: in vitro isolation of valine-resistant spontaneous mutants.

A chlorophyll-deficient mutant line of tobacco (Nicotiana tabacum), named tl, displays spontaneously on leaves green, white, and twinned green/white somatic variations at high frequencies (10(-3) to 10(-2)). The frequency of cell events leading to the somatic variations has been shown to be closely dependent on the stage of differentiation of cells during plant development. The activity of transposable elements is suspected in the tl genotype, and a study of its mutagenic ability was performed by selecting in vitro new mutant cellular types. The cellular marker chosen was the resistance to toxic doses of valine conferred by a permeation deficiency. A reproducible method allowing efficient selection of valine-resistant mutant clones from haploid tobacco mesophyll protoplast-derived cells was used. In 10 out of 12 experiments, the frequency of spontaneous valine-resistant clones obtained with the wild-type control was null for cell populations tested to the 10(6). On the other hand, spontaneous valine-resistant clones were repeatedly isolated at variable and sometimes high frequencies (greater than 10(-3)) from cell populations of the tl type. Valine resistance of plants regenerated from these clones was transmitted to the progeny as a single monogenic mutation. These results indicate an increased mutagenic ability of the tl genotype, as compared to the wild-type line.