Histo-cytological study of apices of coffee (Coffea racemosa and C. sessiliflora) in vitro plantlets during their cryopreservation using the encapsulation-dehydration technique

Les apex de microboutures #in vitro de #Coffea racemosa et #C. sessiliflora supportent la congélation dans l'azote liquide en utilisant la technique d'encapsulation-déshydratation. Une accumulation intense d'amidon est notée après une nuit de culture des apex sur le milieu standard. Les apex de #C. sessiliflora nécessitent 3 à 10 jours de préculture dans un milieu liquide contenant 0,75 M de saccharose, tandis que ceux de #C. racemosa$nécessitent une augmentation progressive de la concentration en saccharose de 0,5 à 1 M. Après la période de déshydratation, les cellules de certains apex sont très endommagées, présentant des granules osmophiles sur la surface du plasmalemme. Pour d'autres apex, les cellules sont moins endommagées, montrant des vésicules d'exocytose à la périphérie de la membrane plasmatique. Après congélation, des taux de survie de 27 à 37$ et #C. sessiliflora$ respectivement. Deux modes de croissance sont observés : développement direct du primordium foliaire ou callogenèse. (Résumé d'auteur

Beneficial effect of post-thawing osmoconditioning on the recovery of cryopreserved coffee (Coffea arabica L.) seeds

Osmoconditioning - controlled rehydration of seeds in a solution with low osmotic potential - has been shown to reinvigorate aged seeds. The present work aimed at investigating the effect of osmoconditioning on the germination of cryopreserved seeds of #Coffea arabica$, whose viability and vigour are drastically affected by cryopreservation. For cryopreservation, seeds were desiccated to 0.21 g H2O/g dw, cooled at 1°C/min to -50°C, then immersed rapidly in liquid nitrogen. After rapid rewarming, seeds were osmoconditioned for 1 to 6 weeks using solutions with osmotic potentials between -1 and -4 MPa. The time to produce half of the final percentage of normal seedlings, T50, was about three fold lower with osmoconditioned seeds than with non-osmoconditioned seeds (12-14 d vs 36 d). Moreover, after a 6-week osmoconditioning treatment with solutions with osmotic potential of -1 and -1.25 MPa, the percentage of seedlings recovered from cryopreserved seeds was 64-74%, against 13-16% only for cryopreserved seeds which were not osmoconditioned. (Résumé d'auteur

Beneficial effect of post-thawing osmoconditioning on the recovery of cryopreserved coffee (Coffea arabica L.) seeds

Osmoconditioning - controlled rehydration of seeds in a solution with low osmotic potential - has been shown to reinvigorate aged seeds. The present work aimed at investigating the effect of osmoconditioning on the germination of cryopreserved seeds of #Coffea arabica$, whose viability and vigour are drastically affected by cryopreservation. For cryopreservation, seeds were desiccated to 0.21 g H2O/g dw, cooled at 1°C/min to -50°C, then immersed rapidly in liquid nitrogen. After rapid rewarming, seeds were osmoconditioned for 1 to 6 weeks using solutions with osmotic potentials between -1 and -4 MPa. The time to produce half of the final percentage of normal seedlings, T50, was about three fold lower with osmoconditioned seeds than with non-osmoconditioned seeds (12-14 d vs 36 d). Moreover, after a 6-week osmoconditioning treatment with solutions with osmotic potential of -1 and -1.25 MPa, the percentage of seedlings recovered from cryopreserved seeds was 64-74%, against 13-16% only for cryopreserved seeds which were not osmoconditioned. (Résumé d'auteur

Evolution of sex chromosomes prior to speciation in the dioecious Phoenix species

International audienceUnderstanding the driving forces and molecular processes underlying dioecy and sex chromosome evolution, leading from hermaphroditism to the occurrence of male and female individuals, is of considerable interest in fundamental and applied research. The genus Phoenix, belonging to the Arecaceae family, consists uniquely of dioecious species. Phylogenetic data suggest that the genus Phoenix has diverged from a hermaphroditic ancestor which is also shared with its closest relatives. We have investigated the cessation of recombination in the sex-determination region within the genus Phoenix as a whole by extending the analysis of P. dactylifera SSR sex-related loci to eight other species within the genus. Phylogenetic analysis of a date palm sex-linked PdMYB1 gene in these species has revealed that sex-linked alleles have not clustered in a species-dependent way but rather in X and Y-allele clusters. Our data show that sex chromosomes evolved from a common autosomal origin before the diversification of the extant dioecious species